A polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator and its preparation method and application

Abstract

The present invention provides a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator, as well as its preparation method and application. By designing the chemical composition and morphology of the lithium-sulfur battery separator, the present invention produces a lithium-sulfur battery separator with a three-dimensional composite fiber layer made from a mixture of Tencel fiber and glass fiber as a support layer and a polyacrylonitrile nanoporous carbon coating layer as a positive electrode modification layer. The lithium-sulfur battery prepared using this lithium-sulfur battery separator exhibits higher coulombic efficiency and cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator, a preparation method thereof, and an application thereof. Background Art

[0002] The energy foundation for global development remains the three major fossil fuels: coal, oil, and natural gas. However, these non-renewable energy sources are becoming increasingly depleted due to large-scale exploitation, leading to a serious energy crisis. Furthermore, the use of these fuels produces carbon dioxide and various harmful gases and particulate matter, contributing to global warming and a range of environmental pollution issues. To maintain sustainable development and preserve humanity's ecological home, the search for renewable, clean energy is urgent. Rechargeable chemical power systems with high energy density, environmental friendliness, low cost, and long cycle life hold promise for addressing these challenges.

[0003] Lithium-sulfur batteries (Li-S batteries) boast a high theoretical specific energy of 2600 Wh / kg, and their cathode sulfur is abundant, inexpensive, and environmentally friendly. However, challenges such as the poor conductivity of elemental sulfur (the active material) and its discharge end products, the "shuttle effect" caused by the dissolution and diffusion of polysulfide ions (intermediate discharge products) in the electrolyte, and volume expansion due to a decrease in discharge product density, result in low active material utilization and poor cycling performance, limiting their application. Li-S battery separators prevent direct contact between the positive and negative electrodes, which can cause electronic short circuits. They also maintain electrolyte connectivity between the positive and negative electrodes through pores within the separator, maintaining ion channels between the electrodes. While separators do not participate in the electrochemical reactions of batteries, they play a crucial role. Their structure and performance influence the battery's interface structure and internal resistance, thereby altering battery performance, including capacity, cycling performance, and safety and reliability. Therefore, separator materials with superior performance are crucial for improving the overall performance of batteries. Modification of the separator and interface design can, to a certain extent, address these issues and enhance the performance of Li-S batteries.

[0004] Most existing methods involve coating or composite modification of polyolefin films. For example, a Chinese patent discloses an aramid phase-transition coating separator. While this method inhibits polysulfide shuttle transport to some extent, the poor compatibility between the modified layer and the substrate makes it susceptible to detachment after prolonged immersion in the electrolyte, thus affecting the battery's cycle life. Furthermore, this coating or composite modification method cannot fundamentally address the polysulfide shuttle effect and therefore cannot significantly improve the coulombic efficiency and cycling stability of lithium-sulfur batteries. Summary of the Invention

[0005] In order to solve the problem that the coulombic efficiency and cycle stability of lithium-sulfur batteries in the above-mentioned prior art still need to be improved, the present invention designs the chemical composition and morphology structure of the lithium-sulfur battery separator, and provides a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator that can effectively inhibit the polysulfide effect and prevent the growth of lithium dendrites, thereby improving the coulombic efficiency and cycle stability of lithium-sulfur batteries.

[0006] Another object of the present invention is to provide a method for preparing the polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator.

[0007] Another object of the present invention is to provide an application of the polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator in the preparation of lithium-sulfur batteries.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator comprises a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure.

[0010] The present invention designs the chemical composition and morphological structure of a lithium-sulfur battery separator to prepare a lithium-sulfur battery separator having a composite fiber layer obtained by mixing tencel fiber and glass fiber and having a three-dimensional structure as a support layer, and a polyacrylonitrile nanoporous carbon coating layer as a modified layer close to the positive electrode surface of the separator. The lithium-sulfur battery prepared using the lithium-sulfur battery separator has higher coulombic efficiency and cycle stability.

[0011] The composite fiber support layer contains Tencel fibers with high crystallinity and orientation. The glass fibers are mixed and formed using an oblique mesh forming technique, allowing the Tencel fibers and glass fibers to entangle together, forming a high-strength, three-dimensional porous structure that further improves the dimensional stability of the separator. This three-dimensional porous structure has a richer pore structure and a large specific surface area, resulting in the composite fiber support layer having excellent liquid absorption and retention properties. The synergistic effect of the high strength and large specific surface area of ​​the fibers in the composite fiber support layer not only effectively mitigates the volume change of lithium-sulfur batteries during charge and discharge, but also suppresses the self-discharge phenomenon of lithium-sulfur batteries, resulting in higher rate performance and improved cycling stability for the resulting battery.

[0012] In the polyacrylonitrile nanoporous carbon coating, 1) after carbonization, a large number of micropores (pore size <2nm) are formed in the polyacrylonitrile fibers, with a narrow pore size distribution range, and most of the micropores are directly connected to the outer surface, which improves the reaction activity in the lithium-sulfur battery. At the same time, the carbonized polyacrylonitrile fibers also have a smaller diameter (approximately 100nm to 6μm), which gives them low mass transfer resistance and rapid adsorption power, effectively promoting the transfer efficiency of electrolyte and lithium ions, accelerating lithium ion transmission during charge and discharge, and improving the battery's rate performance. 2) In addition to carbon, polyacrylonitrile nanoporous carbon also contains a small amount of heteroatoms such as N and O. The presence of heteroatoms increases the surface polarity, further improving its adsorption performance for polysulfides and their reuse, further inhibiting the shuttling effect of polysulfides, and improving the battery's cycle stability. 3) In addition, polyacrylonitrile nanoporous carbon is resistant to strong acids, strong bases, and highly polar solvents, has good affinity with electrolytes, and has good conductivity, further improving the battery's cycle life.

[0013] Through the specific combination of the membrane composition and structure, the synergistic effect between the polyacrylonitrile nanoporous carbon coating layer and the composite fiber support layer further inhibits the shuttle effect of polysulfides, the growth of lithium dendrites and the volume change during charging and discharging of the lithium-sulfur battery. At the same time, the affinity between the membrane and the electrolyte is improved, the lithium ion transmission is accelerated, and the battery's rate performance and cycle stability can be significantly improved.

[0014] Preferably, the weight ratio of the tencel fibers to the glass fibers is 1:0.07 to 3. The ratio of the tencel fibers to the glass fibers will affect the pore distribution and porosity in the support layer.

[0015] In order to obtain a supporting layer with a richer and more uniform pore structure, preferably, the weight ratio of the Tencel fiber to the glass fiber is 1:0.09-1.4.

[0016] Preferably, in the composite fiber support layer, the average diameter of the Tencel fibers is 100 nm to 5 μm.

[0017] Preferably, in the composite fiber support layer, the average diameter of the glass fibers is 2 to 10 μm.

[0018] More preferably, in the composite fiber support layer, the average diameter of the glass fibers is 3 to 8 μm.

[0019] Preferably, the thickness of the lithium-sulfur battery separator is 25 to 50 μm.

[0020] More preferably, the thickness of the lithium-sulfur battery separator is 27 to 49 μm.

[0021] Preferably, the weight of the lithium-sulfur battery separator is 15 to 30 g / m2 .

[0022] More preferably, the weight of the lithium-sulfur battery separator is 15 to 25 g / m 2 .

[0023] Preferably, the thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.1-0.4.

[0024] More preferably, the thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.1-0.3.

[0025] More preferably, the thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:(0.2-0.26).

[0026] Preferably, in the lithium-sulfur battery separator, the average diameter of the composite fibers is 500 to 1000 nm.

[0027] More preferably, in the lithium-sulfur battery separator, the average diameter of the composite fibers is 800 nm.

[0028] The preparation method of the polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator comprises the following steps:

[0029] S1. Preparation of composite fiber support layer

[0030] The Tencel fiber and glass fiber raw materials are sequentially processed by beating, oblique mesh papermaking, drying and calendering to obtain a composite fiber support layer;

[0031] S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer

[0032] S21. The polyacrylonitrile fiber raw material is activated after forming and carbonized at a high temperature of 300 to 850 ° C in an inert atmosphere, and then cooled to obtain polyacrylonitrile nanoporous carbon;

[0033] S22. Prepare the polyacrylonitrile nanoporous carbon obtained in S21 into a slurry and apply it to the surface of the composite fiber support layer obtained in S1. After drying, the polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator is obtained.

[0034] Preferably, the beating degree in step S1 is 70-96°SR. The purpose of beating is to fibrillate the Tencel fibers. Within the beating degree range of the present invention, the diameter of the Tencel fibers in the prepared composite fiber support layer can be ensured to reach 300nm-5um.

[0035] Preferably, the flow rate of the inclined mesh papermaking in step S1 is 100 to 300 m 3 / h; more preferably 100 to 200m 3 / h; more preferably 150m 3 / h.

[0036] Preferably, the drying in step S1. is performed at 100-140° C. until the moisture content of the aramid fiber is 1-5 wt %.

[0037] Preferably, the calendering temperature in step S1 is 180-200°C.

[0038] Preferably, the activation in step S21 is performed by immersion activation using a KOH solution. The purpose is to obtain a large number of microporous structures after carbonization of the polyacrylonitrile fiber. Before activation, the polyacrylonitrile needs to be pre-oxidized in a high-temperature oven at 250°C. The purpose of the pre-oxidation treatment is to convert the linear molecular structure of the polyacrylonitrile into a heat-resistant trapezoidal structure to meet the thermal stability requirements during the subsequent carbonization treatment. It is a key process to ensure that the fiber maintains stable performance and does not melt during the high-temperature heating process during carbonization.

[0039] Preferably, the inert atmosphere in step S21 is an atmosphere formed by one or more gases selected from nitrogen, argon or helium.

[0040] Preferably, the high-temperature carbonization in step S21 is carried out in two stages: first, the temperature is raised to 300-600°C at a rate of 2-8°C / min and maintained for 1-2 hours; then, the temperature is raised to 600-850°C at a rate of 5-10°C / min and maintained for 1-2 hours.

[0041] Preferably, the drying temperature in step S22 is 180-200°C.

[0042] The use of the above-mentioned polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator in the preparation of lithium-sulfur batteries is also within the protection scope of the present invention.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention designs the chemical composition and morphological structure of a lithium-sulfur battery separator to prepare a lithium-sulfur battery separator with a composite fiber layer obtained by mixing tencel fiber and glass fiber and having a three-dimensional structure as a support layer and a polyacrylonitrile nanoporous carbon coating layer as a positive electrode modification layer. The lithium-sulfur battery prepared using the lithium-sulfur battery separator has higher coulombic efficiency and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1This is a schematic structural diagram of a polyacrylonitrile multi-level porous carbon-modified composite fiber lithium-sulfur battery separator prepared in an embodiment of the present invention. In the figure, 1 is a composite fiber support layer, 2 is a polyacrylonitrile nanoporous carbon coating layer;

[0046] Figure 2 This is a SEM morphology image of the composite fiber support layer of the lithium-sulfur battery separator prepared in Example 1 of the present invention;

[0047] Figure 3 This is a SEM morphology image of the polyacrylonitrile nanoporous carbon coating layer of the lithium-sulfur battery separator prepared in Example 1 of the present invention;

[0048] Figure 4 This is a cross-sectional SEM morphology of the lithium-sulfur battery separator prepared in Example 1 of the present invention. In the figure, 1 is a composite fiber support layer, 2 is a polyacrylonitrile nanoporous carbon coating layer;

[0049] Figure 5 This is a schematic diagram of an inclined screen papermaking former, in which A represents a pulp distributor, B represents a rectifying area, C represents a substrate forming area, and D represents a supporting layer wet paper sheet after forming. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to specific examples and accompanying drawings, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0051] Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0052] Example 1

[0053] This example prepares a polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator (schematic diagram as shown in FIG Figure 1 shown),

[0054] It includes a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure;

[0055] The weight ratio of Tencel fiber to glass fiber is 1:3;

[0056] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.14.

[0057] The lithium-sulfur battery separator is prepared according to a method comprising the following steps:

[0058] S1. Preparation of composite fiber support layer

[0059] 6g / m 2 A certain amount of Tencel fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.2 wt %. After being evenly dispersed, Tencel fiber pulp with a beating degree of 96° SR was obtained by beating. 18 g / m 2 A certain amount of glass fiber was diluted with a slurry pump to a fiber concentration of 0.02 wt%. The obtained composite fiber slurry was placed on an inclined wire papermaking machine (schematic diagram as shown in FIG. Figure 5 As shown), at 150m 3 / h flow rate after forming and dehydration to obtain wet paper sheet, dried at 130 ° C to obtain dry paper sheet (water content of 5wt%), and then hot calendered by metal rollers and elastic rollers at 200 ° C to obtain composite fiber support layer, wherein the composite fiber support layer has a thickness of 35μm and a basis weight of 24g / m 2 ;

[0060] S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer

[0061] S21. The polyacrylonitrile fiber raw material was pre-oxidized in a high-temperature oven at 250°C for 2 h, then immersed in a 0.2 g / mL KOH solution for 8 h, transferred to a tube furnace, and heated to 400°C at a rate of 8°C / min under nitrogen protection and held for 1 h. Then, the temperature was increased to 700°C at a rate of 5°C / min under nitrogen protection and held for 1 h. Finally, it was cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon.

[0062] S22. Take 9g of polyacrylonitrile nanoporous carbon and polyvinylidene fluoride (PVDF) in a ratio of 9:1 and mix them in an agate mortar. Then add an appropriate amount of N-methylpyrrolidone (NMP) to adjust the viscosity. After the addition is complete, grind quickly and evenly coat it on one side of the surface of the para-aramid fiber support layer obtained in S1. and dry it. The thickness of the dried polyacrylonitrile nanoporous carbon coating layer is 5μm and the weight is 1g / m 2 .

[0063] The thickness of the prepared lithium-sulfur battery separator is 40 μm and the weight is 25 g / m 2 It should be noted that, in the present invention, the quantitative determination is carried out using the TAPPI standard.

[0064] Example 2

[0065] This embodiment provides a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator, comprising a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure;

[0066] The weight ratio of Tencel fiber to glass fiber is 1:1.4;

[0067] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.17.

[0068] The lithium-sulfur battery separator is prepared according to a method comprising the following steps:

[0069] S1. Preparation of composite fiber support layer

[0070] 10g / m 2 A certain amount of Tencel fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.2 wt %. After being evenly dispersed, Tencel fiber was beaten to obtain a Tencel fibrillated fiber slurry with a beating degree of 96° SR. 14 g / m 2 The obtained composite fiber slurry is placed on an inclined wire papermaking machine (schematic diagram as shown in FIG Figure 5 As shown), at 100m 3 / h flow rate after forming and dehydration to obtain wet paper sheet, dried at 140 ° C to obtain dry paper sheet (water content of 1wt%), and then hot calendered by metal rollers and elastic rollers at 200 ° C to obtain composite fiber support layer, wherein the composite fiber support layer has a thickness of 30μm and a basis weight of 24g / m 2 ;

[0071] S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer

[0072] S21. The polyacrylonitrile fiber raw material was pre-oxidized in a high-temperature oven at 250°C for 2 h, then immersed in a 0.2 g / mL KOH solution for 8 h, transferred to a tube furnace, and carbonized according to the high-temperature carbonization heating program in Example 1. Finally, it was cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon;

[0073] S22. 9 g of polyacrylonitrile nanoporous carbon and polyvinylidene fluoride (PVDF) were mixed in an agate mortar in a ratio of 9:1. An appropriate amount of N-methylpyrrolidone (NMP) was then added dropwise to adjust the viscosity. After the addition was complete, the mixture was quickly ground and evenly coated on one side of the surface of the para-aramid fiber support layer obtained in S1. and dried. The dried polyacrylonitrile nanoporous carbon coating had a thickness of 5 μm and a weight of 1 g / m 2 .

[0074] The thickness of the prepared lithium-sulfur battery separator is 35 μm and the weight is 25 g / m 2 .

[0075] Example 3

[0076] This embodiment provides a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator, comprising a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure;

[0077] The weight ratio of Tencel fiber to glass fiber is 1:1;

[0078] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.19.

[0079] The lithium-sulfur battery separator is prepared according to a method comprising the following steps:

[0080] S1. Preparation of composite fiber support layer

[0081] 12g / m 2 A certain amount of Tencel fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.2 wt %. After being evenly dispersed, Tencel fiber was beaten to obtain a Tencel fibrillated fiber slurry with a beating degree of 96° SR. 12 g / m 2 The obtained composite fiber slurry is placed on an inclined wire papermaking machine (schematic diagram as shown in FIG. Figure 5 As shown), at 200m 3 / h flow rate after forming and dehydration to obtain wet paper sheet, dried at 150 ° C to obtain dry paper sheet (water content of 5wt%), and then hot calendered by metal rollers and elastic rollers at 180 ° C to obtain composite fiber support layer, wherein the composite fiber support layer has a thickness of 26μm and a basis weight of 24g / m 2 ;

[0082] S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer

[0083] S21. The polyacrylonitrile fiber raw material was pre-oxidized in a high-temperature oven at 250°C for 2 h, then immersed in a 0.2 g / mL KOH solution for 8 h, transferred to a tube furnace, and carbonized according to the high-temperature carbonization heating program in Example 1. Finally, it was cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon;

[0084] S22. 9 g of polyacrylonitrile nanoporous carbon and polyvinylidene fluoride (PVDF) were mixed in an agate mortar in a ratio of 9:1. An appropriate amount of N-methylpyrrolidone (NMP) was then added dropwise to adjust the viscosity. After the addition was complete, the mixture was quickly ground and evenly coated on one side of the surface of the para-aramid fiber support layer obtained in S1. and dried. The dried polyacrylonitrile nanoporous carbon coating had a thickness of 5 μm and a weight of 1 g / m 2 .

[0085] The thickness of the prepared lithium-sulfur battery separator is 31 μm and the weight is 25 g / m 2 .

[0086] Example 4

[0087] This embodiment provides a polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator, comprising a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure;

[0088] The weight ratio of Tencel fiber to glass fiber is 1:0.09;

[0089] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.23.

[0090] The lithium-sulfur battery separator is prepared according to a method comprising the following steps:

[0091] S1. Preparation of composite fiber support layer

[0092] 22g / m 2 A certain amount of Tencel fiber was added with water in a fiber deflaking machine to a fiber concentration of 0.2 wt %. After being evenly dispersed, Tencel fiber was beaten to obtain a Tencel fibrillated fiber slurry with a beating degree of 96° SR. 2 g / m 2 The obtained composite fiber slurry is placed on an inclined wire papermaking machine (schematic diagram as shown in FIG. Figure 5 As shown), at 150m 3 / h flow rate after forming and dehydration to obtain wet paper sheet, dried at 140 ° C to obtain dry paper sheet (water content of 5wt%), and then hot calendered by metal rollers and elastic rollers at 200 ° C to obtain composite fiber support layer, wherein the composite fiber support layer has a thickness of 22μm and a basis weight of 24g / m 2 ;

[0093] S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer

[0094] S21. The polyacrylonitrile fiber raw material was pre-oxidized in a high-temperature oven at 250°C for 2 h, then immersed in a 0.2 g / mL KOH solution for 8 h, transferred to a tube furnace, and carbonized according to the high-temperature carbonization heating program in Example 1. Finally, it was cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon;

[0095] S22. 9 g of polyacrylonitrile nanoporous carbon and polyvinylidene fluoride (PVDF) were mixed in an agate mortar in a ratio of 9:1. An appropriate amount of N-methylpyrrolidone (NMP) was then added dropwise to adjust the viscosity. After the addition was complete, the mixture was quickly ground and evenly coated on one side of the surface of the para-aramid fiber support layer obtained in S1. and dried. The dried polyacrylonitrile nanoporous carbon coating had a thickness of 5 μm and a weight of 1 g / m 2 .

[0096] The thickness of the prepared lithium-sulfur battery separator is 27 μm and the weight is 25 g / m 2 .

[0097] Example 5

[0098] The difference between this embodiment and embodiment 1 is that:

[0099] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.2.

[0100] In step S22, the coating thickness of the polyacrylonitrile nanoporous carbon is increased to control the amount of the added polyacrylonitrile nanoporous carbon coating layer to a thickness of 7 μm and a quantitative value of 1.5 g / m 2 .

[0101] The thickness of the prepared lithium-sulfur battery separator is 42 μm and the weight is 25.5 g / m 2 .

[0102] Example 6

[0103] The difference between this embodiment and embodiment 1 is that:

[0104] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.26.

[0105] In step S22, the coating thickness of the polyacrylonitrile nanoporous carbon is increased, and the thickness of the obtained polyacrylonitrile nanoporous carbon coating layer is 9 μm, and the quantitative value is 2 g / m 2 .

[0106] The thickness of the prepared lithium-sulfur battery separator is 44 μm and the weight is 26 g / m 2 .

[0107] Example 7

[0108] The difference between this embodiment and embodiment 1 is that:

[0109] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.34.

[0110] In step S22, the coating thickness of the polyacrylonitrile nanoporous carbon is increased, and the thickness of the obtained polyacrylonitrile nanoporous carbon coating layer is 12 μm, and the quantitative value is 2.5 g / m 2 .

[0111] The thickness of the prepared lithium-sulfur battery separator is 47 μm and the weight is 27.5 g / m 2 .

[0112] Example 8

[0113] The difference between this embodiment and embodiment 1 is that:

[0114] The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.4.

[0115] In step S22, the coating thickness of the polyacrylonitrile nanoporous carbon is increased, and the thickness of the obtained polyacrylonitrile nanoporous carbon coating layer is 14 μm, and the quantitative value is 3 g / m 2 .

[0116] The thickness of the prepared lithium-sulfur battery separator is 49 μm and the weight is 28 g / m 2 .

[0117] Example 9

[0118] The difference between this embodiment and embodiment 1 is that in step S1, the beating degree is 70°SR, the thickness of the obtained composite fiber support layer is 38 μm, and the basis weight is 24 g / m 2 .

[0119] The thickness of the prepared lithium-sulfur battery separator is 43 μm and the weight is 25 g / m 2 .

[0120] Example 10

[0121] The difference between this embodiment and Example 1 is that in step S21., the heating procedure for carbonization of polyacrylonitrile nanoporous carbon is as follows: the polyacrylonitrile fiber raw material is placed in a high-temperature oven at 250°C for pre-oxidation for 2 hours, then immersed in a 0.2 g / mL KOH solution for 8 hours, transferred to a tubular furnace, and heated to 400°C at a rate of 8°C / min under nitrogen protection and maintained for 1 hour, then heated to 600°C at a rate of 5°C / min under nitrogen protection and maintained for 1 hour, and finally cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon.

[0122] Example 11

[0123] The difference between this embodiment and Example 1 is that in step S21., the heating procedure for carbonization of polyacrylonitrile nanoporous carbon is as follows: the polyacrylonitrile fiber raw material is placed in a high-temperature oven at 250°C for pre-oxidation for 2 hours, then immersed in a 0.2 g / mL KOH solution for 8 hours, transferred to a tubular furnace, and heated to 400°C at a rate of 8°C / min under nitrogen protection and maintained for 1 hour, then heated to 800°C at a rate of 5°C / min under nitrogen protection and maintained for 1 hour, and finally cooled to room temperature (25-30°C) to obtain polyacrylonitrile nanoporous carbon.

[0124] Comparative Example 1

[0125] The difference between this embodiment and embodiment 1 is that in step S1, the inclined wire papermaking machine is replaced by a cylinder wire papermaking machine.

[0126] The thickness of the prepared lithium-sulfur battery separator is 41 μm and the weight is 25 g / m 2 .

[0127] Comparative Example 2

[0128] This comparative example provides a lithium-sulfur battery separator, which is different from Example 1 in that the separator is not coated with a polyacrylonitrile nanoporous carbon coating layer.

[0129] The thickness of the prepared lithium-sulfur battery separator is 35 μm and the weight is 24 g / m 2 .

[0130] Comparative Example 3

[0131] This comparative example provides a lithium-sulfur battery separator, which is different from Example 1 in that the "6g / m 2 Tencel fiber and 18g / m 2 Glass fiber" replaced with 24g / m 2 Tencel fiber.

[0132] The thickness of the prepared lithium-sulfur battery separator is 25 μm and the weight is 25 g / m 2 .

[0133] Comparative Example 4

[0134] This comparative example provides a lithium-sulfur battery separator, which is different from Example 1 in that the "6g / m 2 Tencel fiber and 18g / m 2 Glass fiber" replaced with 24g / m 2 Fiberglass.

[0135] The thickness of the prepared lithium-sulfur battery separator is 42 μm and the weight is 25 g / m 2 .

[0136] The structure and performance of the lithium-sulfur battery separators prepared in the above examples and comparative examples were tested. The specific test contents and results are as follows:

[0137] 1. Maximum pore size of the support layer: Use a PMI pore size analyzer to measure the pore size of the aramid fiber support layer;

[0138] 2. Tensile Strength of Support Layer The tensile strength of the para-aramid fiber support layers prepared in the Examples and Comparative Examples was tested in accordance with GB / T 3690-2017.

[0139] 3. Specific surface area of ​​the support layer: The specific surface area of ​​the fiber support layers prepared in the examples and comparative examples was measured using a Micromeritics ASAP 2460 instrument.

[0140] 2. Appearance morphology and pore structure of lithium-sulfur battery separator: Scanning electron microscopy (SEM) was used to test and analyze the appearance morphology and pore structure of each layer of lithium-sulfur battery separator. The test results are detailed in Figure 3 ;

[0141] 5. Electrochemical performance test:

[0142] The lithium-sulfur battery separators prepared in the examples and comparative examples were placed in a battery test cabinet to assemble lithium-sulfur batteries. Specifically, the specific capacity, coulombic efficiency, cycle life, and fast charge and discharge capability of the assembled batteries were tested. The specific test conditions were as follows:

[0143] This article uses a battery test cabinet to test the battery's specific capacity, coulombic efficiency, cycle life, and rapid charge and discharge capabilities. All assembled batteries are left for 6 hours before testing, and are charged and discharged using a constant current within a range of 1.7-2.6V.

[0144] The test results are detailed in Tables 2 and 3.

[0145] Table 1 Test results of pore size of composite fiber support layer

[0146]

[0147] Table 2 Charge and discharge performance of lithium-sulfur batteries assembled with the lithium-sulfur battery separators prepared in Examples and Comparative Examples at 0.2C

[0148]

[0149] Table 3 Charge and discharge performance of lithium-sulfur batteries assembled with the lithium-sulfur battery separators prepared in Examples and Comparative Examples at 1C

[0150]

[0151] From the results in Tables 1 to 3, we can see that:

[0152] The results of Examples 1 to 4 show that as the content of Tencel fiber increases, the tensile strength of the composite fiber support layer increases, and the battery performance thereof increases first and then decreases.

[0153] The results of Example 1 and Examples 5 to 8 show that as the thickness of the polyacrylonitrile nanoporous carbon coating layer increases, the initial specific capacity and the volume retention rate both show a trend of first increasing and then decreasing.

[0154] The results of Examples 1 and 9 to 11 show that the beating degree and the carbonization temperature rise program have little effect on the performance.

[0155] The results of Example 1 and Comparative Example 1 show that the form of papermaking has a great influence on the structure and performance of the support layer. Among them, the oblique mesh papermaking forming technology is beneficial to enhancing the control of the structure and uniformity of the diaphragm, making the fibers evenly distributed and tightly combined, improving the dimensional stability of the diaphragm, and facilitating the stability of subsequent hot calendering and modification of the positive and negative electrode surfaces of the lithium-sulfur battery diaphragm.

[0156] The results of Example 1 and Comparative Examples 2 to 4 show that the performance of lithium-sulfur battery separators made of pure fibrillated Tencel fibers and glass fibers is poor, indicating that a separator with good performance can only be made through the synergistic effect between fibrillated Tencel fibers and glass fibers.

[0157] from Figure 2 and Figure 4 It can be seen that the fiber diameter of the composite fiber support layer is small (below 1 μm) and evenly dispersed, with a three-dimensional pore structure; Figure 3 It is a polyacrylonitrile nanoporous carbon coating.

[0158] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator, characterized in that: It includes a composite fiber support layer and a polyacrylonitrile nanoporous carbon coating layer; wherein the composite fiber support layer is prepared by oblique mesh papermaking of composite fibers obtained by mixing Tencel fibers and glass fibers, and has a three-dimensional pore structure; The preparation method of the polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator comprises the following steps: S1. Preparation of composite fiber support layer The Tencel fiber and glass fiber raw materials are sequentially processed by beating, oblique mesh papermaking, drying and calendering to obtain a composite fiber support layer; S2. Coating of Polyacrylonitrile Nanoporous Carbon Coating Layer S21. The polyacrylonitrile fiber raw material is activated after forming and carbonized at a high temperature of 300 to 850 ° C in an inert atmosphere, and then cooled to obtain polyacrylonitrile nanoporous carbon; S22. The polyacrylonitrile nanoporous carbon prepared in S21 was prepared into a slurry and coated on the surface of the composite fiber support layer obtained in S1, and dried to obtain the polyacrylonitrile nanoporous carbon-modified composite fiber-based lithium-sulfur battery separator; The weight ratio of Tencel fiber to glass fiber is 1:0.07-1.4; The thickness ratio of the composite fiber support layer to the polyacrylonitrile nanoporous carbon coating layer is 1:0.1-0.

34.

2. The polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to claim 1, characterized in that: The weight ratio of Tencel fiber to glass fiber is 1:0.09-1.

4.

3. The polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to claim 1, characterized in that: In the composite fiber support layer, the average diameter of the Tencel fibers is 100 nm to 5 μm.

4. The polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to claim 1, characterized in that: In the composite fiber support layer, the average diameter of the glass fibers is 3 to 8 μm.

5. The polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to claim 1, characterized in that: The thickness of the lithium-sulfur battery separator is 27 to 49 μm.

6. The polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to claim 1, characterized in that: The basis weight of the lithium-sulfur battery separator is 15 to 30 g / m 2 .

7. Use of the polyacrylonitrile nanoporous carbon modified composite fiber-based lithium-sulfur battery separator according to any one of claims 1 to 6 in the preparation of lithium-sulfur batteries.

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