Lithium-sulfur battery positive electrode barrier layer and preparation method thereof

Abstract

The invention discloses a lithium-sulfur battery positive electrode barrier layer and a preparation method thereof, the barrier layer is a single-layer or multi-layer composite structure, and when the barrier layer is a single layer, the barrier layer is only composed of oxide particles and a conductive material in a mass ratio of 1: 1-20; when the positive electrode active layer is of a multi-layer composite structure, each sub-layer is composed of oxide particles and a conductive material with the mass ratio of 1: 1-20, and the mass ratio of the oxide particles to the conductive material in each sub-layer is increased in a gradient mode from near to far relative to the surface of the positive electrode active layer in the thickness direction. The barrier layer is arranged on the positive electrode of the lithium-sulfur battery, so that the problem of polysulfide shuttle effect in the lithium-sulfur battery can be effectively solved, and meanwhile, compared with a single carbon material barrier layer, the specific oxide and carbon material combination can provide more adsorption active sites and enhance the anchoring capability of capturing polysulfide; and the interaction between the polysulfide and the barrier layer is improved, and the lithium ion diffusion rate is accelerated, so that the lithium-sulfur battery has more excellent cycle performance and rate capability.

Description

Technical Field

[0001] The invention belongs to the field of lithium-sulfur secondary batteries, and in particular relates to a lithium-sulfur battery positive electrode barrier layer and a preparation method thereof. Background Art

[0002] With the development of society, it is becoming increasingly important to develop high energy density, safe and cheap electrochemical energy storage devices. Among them, lithium-ion batteries can provide higher energy density. However, the energy density of traditional lithium-ion battery cathode materials is close to the theoretical value and cannot meet the needs of future electric vehicles and smart grids. Lithium-sulfur (Li-S) batteries have a high theoretical energy density (2600Wh·kg -1 ) and high specific capacity (1675mAh·g -1 ) is considered a promising candidate for the next generation of energy storage devices. Although lithium-sulfur batteries have significant theoretical advantages, their practical application still faces many challenges, mainly including the low utilization rate of sulfur active substances, the shuttle effect of polysulfides and their deposition on the lithium negative electrode leading to severe capacity decay, and the large volume change of sulfur during charging and discharging leading to the crushing of electrode materials, etc. These problems seriously limit the actual electrochemical performance and stability of lithium-sulfur batteries.

[0003] In recent years, researchers have explored a variety of methods to inhibit the diffusion and shuttling of lithium polysulfide. Many studies have focused on combining sulfur with different types of host materials to improve the conductivity of the positive electrode and inhibit the shuttling of soluble polysulfide intermediates. For example, CN108232164B discloses a lithium-sulfur battery positive electrode material, including a host material and elemental sulfur loaded on the host material; the host material includes carbon nanotubes and transition metal sulfides composited on the carbon nanotubes, which adopts the strategy of adding transition metal sulfides to reduce the shuttle effect and add carbon nanotubes to prevent the collapse of the electrode structure.

[0004] CN114420926B discloses a positive electrode host material, wherein transition metal-doped SnS 2 The nanosheets are loaded on the carbon material, and then loaded with transition metal doped SnS 2 The carbon material of the nanosheet is phosphated, SnS 2 It has a good chemical adsorption effect. Phosphorus and transition metal doping can make SnS 2It has an excellent catalytic conversion effect on polysulfides. Using this material as a sulfur host material can ensure an excellent electron conduction path, accelerate the conversion of polysulfides, and reduce the loss of positive electrode sulfur, and finally show good cycle stability. However, this will result in a sulfur positive electrode with a low sulfur content and surface loading, resulting in the overall energy density of the battery being insufficient to meet actual needs. In addition, the complex nanostructure synthesis process has poor reproducibility, which poses challenges to large-scale production. Therefore, in addition to the internal modification of the positive electrode, optimizing and adjusting the external structure design has also become a new strategy to improve the performance of lithium-sulfur batteries. Among them, introducing a barrier layer between the separator and the sulfur positive electrode has been proven to be an effective strategy. The barrier layer with porous, conductive and flexible characteristics can act as a barrier to inhibit the shuttling of polysulfides, maintain cycle stability and good coulombic efficiency, and at the same time, the flexible structure of the intermediate layer helps to alleviate the volume change of the sulfur cathode and maintain the structural integrity of the electrode material. At present, most common barrier materials are carbon materials, including carbon cloth, carbon paper, carbon nanofiber membrane, graphene membrane, etc. These carbon materials have good conductivity and chemical stability, can capture soluble polysulfide to a certain extent and prevent the shuttle effect, and can also be used as an upper current collector to improve the utilization rate of active materials. However, due to the weak interaction of carbon materials, the adsorption capacity of polysulfide is limited, and a high degree of inhibition of the shuttle effect cannot be achieved. CN106450422A discloses a lithium-sulfur battery with a multi-protective layer structure, in which a barrier layer made of nitrogen-containing polymer / carbon composite is arranged between the sulfur positive electrode and the positive electrode side of the diaphragm, which can synergistically utilize the porosity of carbon materials and nitrogen elements to strengthen the adsorption of certain polysulfide ions, alleviate their diffusion to the negative electrode, and alleviate the shuttle effect; it can also be used as a reaction site to promote the further discharge of dissolved polysulfide ions, improve the utilization rate of sulfur, block the diffusion of polysulfide ions to the negative electrode, and alleviate the shuttle effect. CN104900830A discloses a lithium-sulfur battery using carbon fiber cloth as a barrier layer, which adds an activated carbon fiber cloth barrier layer between a conventional elemental sulfur positive electrode and a separator, thereby effectively preventing the shuttling of polysulfides in an electrolyte and the corrosion of polysulfides on a lithium negative electrode, and enabling discharge products to be more evenly deposited on the electrode surface, thereby improving the specific capacity and cycle life of the lithium-sulfur battery.

[0005] The carbon-transition metal compound composites developed subsequently inherited the advantages of high conductivity of carbon materials, and polar transition metal compounds have stronger adsorption capacity for polysulfides. Xiao et al. developed graphene / TiO 2 The film is used as the middle layer of the lithium-sulfur battery, and its mass accounts for only 7.8wt% of the entire positive electrode. 2 The use of the film as an interlayer enables the sulfur cathode to still provide 1040 mAh g after 300 cycles at 0.5C. -1Reversible specific capacity. CN105280949A discloses a lithium-sulfur battery based on manganese dioxide / graphene as a positive electrode barrier layer, including a sulfur-containing positive electrode, a separator, an electrolyte, a metal lithium negative electrode and a nickel foam current collector; on the surface of the sulfur-containing positive electrode, a barrier layer is coated by an automatic coating machine, and the barrier layer is formed by coating the surface of the sulfur-containing active material positive electrode with a manganese dioxide / graphene composite. The battery introduces a manganese dioxide / graphene composite with good electrical conductivity, adsorption capacity and catalytic activity into the lithium-sulfur battery to improve the conductivity of the sulfur-containing positive electrode and limit the outward migration of polysulfides, thereby effectively alleviating the shuttle effect and improving the electrochemical performance of the battery. However, the preparation process of the composite material is relatively complicated, and the transition metal compound with poor conductivity will bring additional electronic and ionic resistance, making it difficult to reactivate the polysulfides captured in the interlayer, and in turn reduce the performance of the lithium-sulfur battery. Therefore, there is an urgent need to develop a carbon-metal compound composite barrier layer and its preparation technology that has a simple preparation process, is suitable for large-scale production, has low cost, stable structure, and has both high conductivity and high adsorption capacity, so as to realize the shuttle diffusion of polysulfides during the use of lithium-sulfur batteries, thereby improving the performance of lithium-sulfur batteries. Summary of the invention

[0006] In order to solve the defects in the prior art, the present invention provides a lithium-sulfur battery positive electrode barrier layer and a preparation method thereof. A barrier layer consisting only of oxide particles and conductive materials is arranged on the surface of the lithium-sulfur battery positive electrode, which can effectively solve the problem of polysulfide shuttle effect in lithium-sulfur batteries. At the same time, a specific oxide and carbon material combination can provide more adsorption active sites compared with a single carbon material barrier layer, enhance the anchoring ability of capturing polysulfides, and improve the interaction between polysulfides and the barrier layer, enhance the interface conversion of polysulfides, and effectively alleviate the shuttle effect of polysulfides. The oxide particles can not only adsorb polysulfides, but also accelerate the diffusion rate of lithium ions, and improve the diffusion of polysulfides on the oxide surface. At the same time, the presence of oxide particles can also produce more active surfaces, increase the contact area between the barrier layer and the electrolyte, and improve the infiltration of the electrolyte in the battery, so that the lithium-sulfur battery has better cycle performance and rate performance. At the same time, the barrier layer structure composed of multiple sublayers can make full use of the gradient difference formed by the oxide and the conductive material between each layer, improve the lithium ion transmission performance and the adsorption of polysulfides, improve the sulfur reaction kinetics to a certain extent, and greatly inhibit the polysulfide shuttle effect. At the same time, the specific barrier layer of the present application has better electron transmission performance and better mechanical strength than a single oxide layer, inhibits the expansion of the sulfur positive electrode, and improves the battery stability.

[0007] To achieve the above-mentioned purpose of the present invention, the present invention provides a positive electrode barrier layer for a lithium-sulfur battery, which is arranged on the surface of the positive electrode of the lithium-sulfur battery, between the positive electrode active layer and the separator; the positive electrode barrier layer is a single layer or a multi-layer composite structure, when the barrier layer is a single layer, the barrier layer is only composed of oxide particles and conductive materials; when the barrier layer is a multi-layer composite structure, each sublayer thereof is only composed of oxide particles and conductive materials. The barrier layer of the present invention uses only oxide particles and conductive materials, has better performance in inhibiting polysulfide shuttle, does not require the use of binders or other supporting layers, and improves the specific energy of the battery cell to a certain extent.

[0008] Furthermore, the oxide particles are at least one of titanium dioxide, silicon dioxide, and molybdenum dioxide, or a combination of multiple thereof; and the conductive material is at least one of carbon nanotubes, carbon fibers, conductive carbon black, and Ketjen black, or a combination of multiple thereof.

[0009] Furthermore, when the positive electrode barrier layer is a single layer, the mass ratio of oxide particles to conductive material in the layer is 1:1 to 20, and preferably, the mass ratio of oxide particles to conductive material is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20; when the barrier layer is a multi-layer composite structure, the mass ratio of oxide particles to conductive material in each sublayer is 1:1 to 20, and the mass ratio of oxide particles to conductive material in each sublayer increases gradually from near to far relative to the surface of the positive electrode active layer in the thickness direction, that is, the sub-barrier layer closer to the positive electrode active material layer has a higher oxide particle content.

[0010] Furthermore, when the barrier layer is a composite structure consisting of two sublayers, the mass ratio of oxide particles to conductive materials in the first sublayer close to the positive electrode active layer is 1:10.5-20, and the mass ratio of oxide particles to conductive materials in the second sublayer away from the positive electrode active layer is 1:5-10.

[0011] Furthermore, when the barrier layer is a composite structure consisting of three sublayers, the mass ratio of oxide particles to conductive materials in each sublayer is 1:1 to 20, and the mass ratio of oxide particles to conductive materials in each sublayer increases gradually from near to far relative to the surface of the positive electrode active layer in the thickness direction.

[0012] Furthermore, when the barrier layer is a three-layer composite structure, the mass ratio of oxide particles to conductive materials in the first sublayer close to the positive electrode active layer is 1:20, the mass ratio of oxide particles to conductive materials in the second sublayer above the first sublayer and away from the positive electrode active layer is 1:17, and the mass ratio of oxide particles to conductive materials in the third sublayer above the second sublayer and away from the positive electrode active layer is 1:14.

[0013] Furthermore, when the barrier layer is a multi-layer composite structure, the types of oxide particles and conductive materials in each sublayer are the same. Compared with different types of oxide particles and conductive materials in each sublayer, the same composition makes it easier for each sublayer to have closer properties, which is beneficial to the preparation and acquisition of multi-layer structures and the formation of a more uniform property gradient change.

[0014] Furthermore, the thickness of the positive electrode barrier layer is 1 μm to 500 μm. When the positive electrode barrier layer is a multi-layer composite structure, the thickness of each sub-layer is the same.

[0015] Another object of the present invention is to provide a method for preparing a positive electrode barrier layer of a lithium-sulfur battery. The preparation method mainly comprises mixing oxide particles and conductive materials in different solvents in a certain proportion, filtering and freeze-drying to obtain a self-supporting barrier film. The barrier layer can be directly used in a lithium-sulfur battery after simple processing such as cutting and lamination. The barrier layer prepared by the preparation method of the present invention can be used as a barrier layer of the positive electrode of a lithium-sulfur battery, and can improve the cycle performance and kinetic performance of the lithium-sulfur battery. When the positive electrode barrier layer is a single layer, the following steps are included:

[0016] (1) dispersing a certain amount of oxide particles into solvent 1 and stirring thoroughly to obtain a suspension A;

[0017] (2) dispersing a certain amount of conductive material into solvent 2 and stirring thoroughly to obtain suspension B;

[0018] (3) Add suspension B drop by drop into suspension A, stir and mix evenly to obtain a precursor solution for the barrier layer;

[0019] (4) filtering the barrier layer precursor solution, placing the filtered membrane material in a freeze dryer, and freeze drying it at -70°C to -20°C for 24 to 48 hours to obtain a single-layer positive electrode barrier layer for a lithium-sulfur battery;

[0020] When the positive electrode barrier layer is a multi-layer composite structure, the method comprises the following steps:

[0021] (1) dispersing a certain amount of oxide particles into solvent 1 and stirring thoroughly to obtain a suspension A;

[0022] (2) dispersing a certain amount of conductive material into solvent 2 and stirring thoroughly to obtain suspension B;

[0023] (3) Dropping suspension B into suspension A drop by drop, stirring and mixing, to obtain a precursor solution of the first sub-layer of the barrier layer; repeating the above steps (1) to (3) to obtain precursor solutions of other sub-layers of the barrier layer;

[0024] (4) The first sub-layer precursor solution is filtered, and after the filtration is completed, the second sub-layer precursor solution is added for filtration, and each sub-layer precursor solution is added and filtered in turn according to the barrier layer structure. The membrane material after filtration is placed in a freeze dryer and freeze-dried at -70°C to -20°C for 24 to 48 hours to obtain a positive electrode barrier layer for a lithium-sulfur battery.

[0025] Furthermore, the solvents in steps (1) and (2) are independently selected from alcohol, deionized water, and ethylene glycol, and the compositions of solvent 1 and solvent 2 are different. The above arrangement can improve the dispersion effect of the precursor solution and the uniformity of the product of the filtration film. The mass concentration of the solid in the suspension A is 0.1 mg mL -1 ~20 mg mL -1 The mass concentration of solid in suspension B is 0.1 mg mL -1 ~20mg mL -1 The oxide particles are at least one or a combination of titanium dioxide, silicon dioxide, and molybdenum dioxide; the conductive material is at least one or a combination of carbon nanotubes, carbon fibers, conductive carbon black, and Ketjen black.

[0026] The mass ratio of oxide particles to conductive material in the positive electrode barrier layer is 1:1-20. Preferably, the mass ratio of oxide particles to conductive material is 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20. When the barrier layer is a multilayer composite structure, the mass ratio of oxide particles to conductive material in each sublayer is 1:1-20, and the mass ratio of oxide particles to conductive material in each sublayer increases gradually from near to far relative to the surface of the positive electrode active layer in the thickness direction, that is, the sub-barrier layer closer to the positive electrode active material layer has a higher oxide particle content.

[0027] Another object of the present invention is to provide a lithium-sulfur battery comprising a positive electrode barrier layer, wherein the positive electrode barrier layer is arranged on the positive electrode surface of the lithium-sulfur battery, between the positive electrode active layer and the diaphragm, and the positive electrode barrier layer precursor is filtered and freeze-dried to be in the form of a membrane sheet, which can be directly used for the positive electrode sheet of the lithium-sulfur battery after simple cutting. The capacity retention rate of a lithium-sulfur battery using a single-layer barrier layer is higher than 80% after 1000 charge and discharge cycles at a 1C rate. The capacity retention rate of a lithium-sulfur battery using a multi-layer composite structure barrier layer is higher than 87% after 1000 charge and discharge cycles at a 1C rate.

[0028] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0029] 1. The technical solution of the present invention is simple, and the problem of polysulfide shuttle effect in lithium-sulfur batteries can be effectively solved by simple structure and composition adjustment. The use of a specific oxide and carbon material combination as a barrier layer can provide more active sites, enhance the anchoring ability to capture polysulfides, and improve the interaction between polysulfides and the barrier layer, effectively alleviating the shuttle effect of polysulfides, and improving the capacity retention rate and cycle effect of lithium-sulfur batteries.

[0030] 2. The barrier layer of the present invention has good charge transfer and lithium ion diffusion rate, improves the infiltration of the electrolyte in the battery, and makes the lithium-sulfur battery have better cycle performance and rate performance. At the same time, the multi-layer composite barrier layer structure composed of multiple sub-layers can make full use of the gradient difference between the oxide and the conductive material between each layer, improve the lithium ion transmission performance and the adsorption of polysulfide, and improve the sulfur reaction kinetics. At the same time, the barrier layer of the present invention has better mechanical strength, which can alleviate the volume expansion of sulfur during the charging and discharging process to a certain extent, reduce the material pulverization and shedding phenomenon, and stabilize the pole piece.

[0031] 3. The preparation method of the present invention has a simple process, low raw material cost, and is convenient for large-scale production; the positive electrode barrier layer of the lithium-sulfur battery prepared by the present invention has good flexibility and fully adjustable size, and can be used for the assembly of lithium-sulfur batteries of various types and sizes, and has little effect on the overall thickness, weight and energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is an infrared test image of the barrier layer prepared in Example 1 of the present invention;

[0033] Figure 2 This is a scanning electron microscope (SEM) image of the barrier layer prepared in Example 1 of the present invention;

[0034] Figure 3 The EIS diagram of the lithium-sulfur button cell using the barrier layer in Example 1 of the present invention is shown in FIG.

[0035] Figure 4 This is the EIS diagram of the lithium-sulfur button cell in Comparative Example 2. DETAILED DESCRIPTION

[0036] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0037] It should be noted that the reference to "embodiment" in this document means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0039] The performance test of the lithium-sulfur battery in the present invention is carried out by assembling a 2032 lithium-sulfur button cell. Specifically, the prepared barrier layer is pressed and cut into a small disc with a diameter of 12 mm and placed on the positive electrode active material layer. Then, a commercial lithium sheet of the same size is used as the negative electrode, and the electrolyte is 1 mol lithium bistrifluoromethylsulfonyl imide (LiTFSI) and 0.1 mol / L lithium nitrate (LiNO 3 ) 1,3-dioxolane / ethylene glycol dimethyl ether (DOL / DME, volume ratio of 1:1) solution, Celgard 2400 as separator, assembled into 2032 button cells. The specific assembly method is: place the positive electrode containing the barrier layer into the positive electrode shell, add 100mL of electrolyte, put in the separator, then place the negative electrode on the separator, add the gasket spring and the negative electrode shell on the negative electrode in turn, and finally press the positive electrode shell and the negative electrode shell together under a pressure of 50MPa to obtain a 2032 button cell.

[0040] Example 1

[0041] A lithium-sulfur battery positive electrode barrier layer, the positive electrode barrier layer is a single-layer structure, and is composed of silicon dioxide particles and a conductive material in a mass ratio of 1:1. The preparation method is as follows: 10g of silicon dioxide is weighed and added to 1L of anhydrous ethanol, and ultrasonic stirring is performed to obtain a suspension A after the silicon dioxide is completely dispersed in the anhydrous ethanol;

[0042] (2) Weigh 5 g of carbon nanotubes and 5 g of carbon fibers and add them to 1 L of deionized water, stir them ultrasonically, and completely disperse them in the deionized water to obtain a suspension B;

[0043] (3) slowly dripping suspension B into suspension A and stirring thoroughly to obtain a barrier layer precursor solution;

[0044] (4) The barrier layer precursor solution is filtered, and the filtered membrane material is placed in a freeze dryer and freeze-dried at -70°C for 24 hours to obtain a 50 μm thick lithium-sulfur battery single-layer positive electrode barrier layer.

[0045] Example 2

[0046] A positive electrode barrier layer for a lithium-sulfur battery has a single-layer structure and is composed of titanium dioxide particles and a conductive material in a mass ratio of 1:20. The preparation method is as follows: 1g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A; 15g of carbon nanotubes and 5g of conductive carbon black are weighed and added to 1L of ethylene glycol, ultrasonically stirred, and completely dispersed in the ethylene glycol to obtain a suspension B; the suspension B is slowly dripped into the suspension A and fully stirred to obtain a barrier layer precursor solution; the barrier layer precursor solution is suction filtered, and the filtered membrane material is placed in a freeze dryer, and freeze-dried at -20°C for 48 hours to obtain a single-layer positive electrode barrier layer for a lithium-sulfur battery with a thickness of 300μm.

[0047] Example 3

[0048] A lithium-sulfur battery positive electrode barrier layer has a single-layer structure and is composed of titanium dioxide particles and a conductive material in a mass ratio of 1:15. The preparation method is as follows: 1g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A; 15g of carbon nanotubes are weighed and added to 1L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in the anhydrous ethanol to obtain a suspension B; the suspension B is slowly dripped into the suspension A and fully stirred to obtain a barrier layer precursor solution; the barrier layer precursor solution is filtered, and the filtered membrane material is placed in a freeze dryer, and freeze-dried at -50°C for 30 hours to obtain a lithium-sulfur battery single-layer positive electrode barrier layer with a thickness of 3μm.

[0049] Example 4

[0050] A positive electrode barrier layer for a lithium-sulfur battery, the positive electrode barrier layer being a composite structure of two sublayers, and the preparation method is as follows: weighing 1g of titanium dioxide and adding it to 1L of deionized water, ultrasonically stirring, and waiting for the titanium dioxide to be completely dispersed in the water to obtain a suspension A, weighing 20g of carbon nanotubes and adding them to 1L of anhydrous ethanol, ultrasonically stirring, and completely dispersing them in the anhydrous ethanol to obtain a suspension B, and slowly dripping the suspension B into the suspension A and fully stirring to obtain a first sublayer precursor solution; weighing 1.9g of titanium dioxide and adding it to 1L of deionized water, ultrasonically stirring, and waiting for the titanium dioxide to be completely dispersed in the water to obtain a suspension B; Titanium dioxide is completely dispersed in water to obtain suspension A1, 19.1 g of carbon nanotubes are weighed and added to 1 L of anhydrous ethanol, and ultrasonically stirred to completely disperse in anhydrous ethanol to obtain suspension B1, and suspension B1 is slowly dropped into suspension A1 and fully stirred to obtain a second sub-layer precursor solution; the first sub-layer precursor solution is filtered, and after the filtration is completed, the second sub-layer precursor solution is added for filtration, and the membrane material after filtration is placed in a freeze dryer, and freeze-dried at -60°C for 40 hours to obtain a 200 μm thick lithium-sulfur battery positive electrode barrier layer.

[0051] Example 5

[0052] A positive electrode barrier layer for a lithium-sulfur battery, the positive electrode barrier layer being a composite structure of three sublayers, and the preparation method thereof is as follows: 1 g of titanium dioxide is added to 1 L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A; 20 g of carbon nanotubes are added to 1 L of anhydrous ethanol, ultrasonically stirred, and the carbon nanotubes are completely dispersed in the anhydrous ethanol to obtain a suspension B; the suspension B is slowly dripped into the suspension A and fully stirred to obtain a first sublayer precursor solution; 1.17 g of titanium dioxide is added to 1 L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A1; 19.83 g of carbon nanotubes are added to 1 L of anhydrous ethanol, ultrasonically stirred, and the carbon nanotubes are completely dispersed in the anhydrous ethanol to obtain a suspension B1; and the suspension B1 is slowly dripped into the suspension A and fully stirred to obtain a first sublayer precursor solution. Slowly drip it into the suspension A1 and stir it thoroughly to obtain the second sub-layer precursor solution; weigh 1.4g of titanium dioxide and add it to 1L of deionized water, stir it ultrasonically, and wait until the titanium dioxide is completely dispersed in the water to obtain suspension A2, weigh 19.6g of carbon nanotubes and add them to 1L of anhydrous ethanol, stir it ultrasonically, and completely disperse them in anhydrous ethanol to obtain suspension B2, and slowly drip the suspension B2 into the suspension A2 and stir it thoroughly to obtain the third sub-layer precursor solution; filter the first sub-layer precursor solution, add the second sub-layer precursor solution after the filtration is completed, and then add the third sub-layer precursor solution for filtration after the filtration is completed. Place the membrane material after filtration in a freeze dryer and freeze-dry it at -60°C for 45h to obtain a 300μm thick lithium-sulfur battery positive electrode barrier layer.

[0053] Comparative Example 1

[0054] A lithium-sulfur battery positive electrode carbon nanotube barrier layer, the preparation method is as follows: weigh 5g of carbon nanotubes, add them into 500mL of deionized water, ultrasonically stir, and completely disperse them in the deionized water to obtain a suspension; filter the suspension, and place the filtered membrane material in a freeze dryer, freeze-dry at -70°C for 24h to obtain a 50μm thick positive electrode barrier layer.

[0055] Comparative Example 2

[0056] A lithium-sulfur battery positive electrode carbon nanotube barrier layer, the preparation method is as follows: weigh 5g of silicon dioxide particles, add them into 500mL of deionized water, ultrasonically stir, and completely disperse them in the deionized water to obtain a suspension; filter the suspension, and place the filtered membrane material in a freeze dryer, freeze-dry at -70°C for 24h to obtain a 50μm thick positive electrode barrier layer.

[0057] Comparative Example 3

[0058] A positive electrode barrier layer for a lithium-sulfur battery has a single-layer structure and is composed of titanium dioxide particles and a conductive material in a mass ratio of 2:1. The preparation method is as follows: 10 g of titanium dioxide and 5 g of carbon nanotubes are weighed and added to 1 L of deionized water in sequence, and ultrasonically stirred until uniformly dispersed to obtain a suspension; the suspension is filtered, and the filtered membrane material is placed in a freeze dryer, and freeze-dried at -60°C for 45 hours to obtain a single-layer positive electrode barrier layer for a lithium-sulfur battery with a thickness of 50 μm.

[0059] Comparative Example 4

[0060] A positive electrode barrier layer for a lithium-sulfur battery, the positive electrode barrier layer being a composite structure of two sublayers, and the preparation method is as follows: weighing 1g of titanium dioxide and adding it to 1L of deionized water, ultrasonically stirring, and waiting for the titanium dioxide to be completely dispersed in the water to obtain a suspension A, weighing 10g of carbon nanotubes and adding them to 1L of anhydrous ethanol, ultrasonically stirring, and completely dispersing them in the anhydrous ethanol to obtain a suspension B, and slowly dripping the suspension B into the suspension A and fully stirring to obtain a first sublayer precursor solution; weighing 1g of titanium dioxide and adding it to 1L of deionized water, ultrasonically stirring, and waiting for the titanium dioxide to be completely dispersed in the water to obtain a suspension B; Titanium dioxide is completely dispersed in water to obtain suspension A1, 15 g of carbon nanotubes are weighed and added to 1 L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in anhydrous ethanol to obtain suspension B1, and suspension B1 is slowly dripped into suspension A1 and fully stirred to obtain a second sub-layer precursor solution; the first sub-layer precursor solution is filtered, and after the filtration is completed, the second sub-layer precursor solution is added for filtration, and the membrane material after filtration is placed in a freeze dryer, and freeze-dried at -60°C for 40 hours to obtain a 200 μm thick lithium-sulfur battery positive electrode barrier layer.

[0061] Comparative Example 5

[0062] A positive electrode barrier layer for a lithium-sulfur battery, the positive electrode barrier layer being a composite structure of two sublayers, and the preparation method is as follows: 1g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and titanium dioxide is completely dispersed in the water to obtain a suspension A, 20g of carbon nanotubes are weighed and added to 1L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in the anhydrous ethanol to obtain a suspension B, the suspension B is slowly dripped into the suspension A and fully stirred to obtain a first sublayer precursor solution, the first sublayer precursor solution is filtered, and the membrane material after the filtration is placed in a freeze dryer, and freeze-dried at -60°C for 40h; 1.9g of titanium dioxide is weighed and added to 1L of deionized water, and the carbon nanotubes are completely dispersed in the water to obtain a suspension B, and the suspension B is slowly dripped into the suspension A and fully stirred to obtain a first sublayer precursor solution, and .... 1. The titanium dioxide is completely dispersed in water with ultrasonic stirring to obtain suspension A1; 19.1 g of carbon nanotubes are weighed and added to 1 L of anhydrous ethanol with ultrasonic stirring to completely disperse in anhydrous ethanol to obtain suspension B1; the suspension B1 is slowly dripped into the suspension A1 and fully stirred to obtain a second sub-layer precursor solution; the second sub-layer precursor solution is filtered, and the membrane material after filtration is placed in a freeze dryer and freeze-dried at -60°C for 40 h; the dried first sub-layer membrane material and the second sub-layer membrane material are stacked and cold-pressed to obtain a 200 μm thick lithium-sulfur battery positive electrode barrier layer.

[0063] Comparative Example 6

[0064] A positive electrode barrier layer for a lithium-sulfur battery, the positive electrode barrier layer being a composite structure of three sublayers, and the preparation method is as follows: 1.17g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A; 19.83g of carbon nanotubes are weighed and added to 1L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in the anhydrous ethanol to obtain a suspension B; the suspension B is slowly dripped into the suspension A and fully stirred to obtain a first sublayer precursor solution; 1g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and the titanium dioxide is completely dispersed in the water to obtain a suspension A1; 20g of carbon nanotubes are weighed and added to 1L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in the anhydrous ethanol to obtain a suspension B1; the suspension B1 is slowly dripped into suspension A1 and fully stirred to obtain a second sub-layer precursor solution; 1g of titanium dioxide is weighed and added to 1L of deionized water, ultrasonically stirred, and titanium dioxide is completely dispersed in the water to obtain suspension A2; 10g of carbon nanotubes are weighed and added to 1L of anhydrous ethanol, ultrasonically stirred, and completely dispersed in anhydrous ethanol to obtain suspension B2; suspension B2 is slowly dripped into suspension A2 and fully stirred to obtain a third sub-layer precursor solution; the first sub-layer precursor solution is filtered, and the second sub-layer precursor solution is added after the filtration is completed, and the third sub-layer precursor solution is added after the filtration is completed, and the membrane material after the filtration is placed in a freeze dryer, and freeze-dried at -60°C for 45h to obtain a 300μm thick lithium-sulfur battery positive electrode barrier layer.

[0065] Test results analysis

[0066] Figure 1 This is an infrared test image of the barrier layer prepared in Example 1. By comparing the infrared absorption peaks, it can be seen that the barrier layer prepared by the method of the present invention does not change the structure of the original material. Figure 2 This is a scanning electron microscope image of the barrier layer prepared in Example 1. It can be seen from the figure that the barrier layer is mainly woven by carbon nanotubes and carbon fibers, and the silicon dioxide particles are relatively evenly distributed inside and on the surface of the main structure woven by carbon nanotubes and carbon fibers. This can ensure that the barrier layer has a higher conductivity while maintaining higher lithium ion transmission and better polysulfide adsorption, thereby improving the stability of the lithium-sulfur battery.

[0067] Figure 3 and Figure 4 The electrochemical impedance spectroscopy test diagrams of the lithium-sulfur batteries prepared in Example 1 of the present invention and Comparative Example 2 are respectively shown. The kinetics of the complex sulfur redox reaction can be fundamentally reflected from the apparent electrochemical impedance. In the present invention, different batteries are cycled in a low-temperature environment, and in-situ electrochemical impedance spectroscopy (EIS) tests are performed at different discharge or charging depths under low temperature conditions to analyze the interface impedance. The interface impedance involves the resistance of the solid electrolyte interface layer (RSEI) and the charge transfer resistance (Rct). A smaller Rct can produce faster kinetics, which can accelerate the faster charge transfer process to achieve better rate performance. It can be seen from the above figure that the battery obtained in the embodiment of the present invention has a smaller charge transfer resistance, indicating that the kinetics of the conversion reaction of polysulfides is less hindered.

[0068] The button batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were tested on a blue light battery tester. The test method was a constant current charge and discharge test. The test current was 0.2 to 1C and the test temperature was room temperature. The test results are shown in Table 1:

[0069] Table 1 Lithium-sulfur battery performance test results

[0070]

[0071] It can be seen from the above test data that the positive electrode barrier layer of the lithium-sulfur battery prepared by the method of the present invention and the assembled button battery have higher discharge capacity and better cycle stability. From the comparison of the discharge specific capacity after 1000 cycles of the electrode at a 1C rate, it can be seen that the setting of the specific barrier layer of the present invention can significantly improve the cycle performance of the lithium-sulfur battery. This is because the presence of the barrier layer can prevent the dissolution and migration of polysulfides in the electrolyte, and can effectively prevent lithium polysulfide from migrating to the negative electrode and reacting with it, thereby helping to improve the cycle performance of the lithium-sulfur battery. The present invention also provides a high-performance lithium-sulfur battery barrier layer and a mass production solution for lithium-sulfur batteries. The positive electrode barrier layer has good flexibility and is fully adjustable in size. It can be used for the assembly of lithium-sulfur batteries of various types and sizes, and has little effect on the overall thickness, weight and energy density of the battery.

[0072] The above is a detailed introduction to a lithium-sulfur battery positive electrode barrier layer and its preparation method. The above content is a further detailed description of the present invention in combination with a specific preferred embodiment, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, its architecture can be flexible and can derive a series of products. Just making a few simple deductions or substitutions should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. A lithium-sulfur battery positive electrode barrier layer, characterized in that: The positive electrode barrier layer is arranged on the surface of the positive electrode of the lithium-sulfur battery, and is located between the positive electrode active layer and the diaphragm; the positive electrode barrier layer is a single-layer or multi-layer composite structure. When the barrier layer is a single-layer, the barrier layer is only composed of oxide particles and conductive materials; when the barrier layer is a multi-layer composite structure, each sublayer thereof is only composed of oxide particles and conductive materials.

2. The lithium-sulfur battery positive electrode barrier layer according to claim 1, characterized in that: The oxide particles are at least one of titanium dioxide, silicon dioxide, and molybdenum dioxide, or a combination of multiple thereof; the conductive material is at least one of carbon nanotubes, carbon fibers, conductive carbon black, and Ketjen black, or a combination of multiple thereof.

3. The lithium-sulfur battery positive electrode barrier layer according to claim 1, characterized in that: When the positive electrode barrier layer is a single layer, the mass ratio of oxide particles to conductive materials in the layer is 1:1 to 20; when the barrier layer is a multi-layer composite structure, the mass ratio of oxide particles to conductive materials in each sublayer is 1:1 to 20, and the mass ratio of oxide particles to conductive materials in each sublayer increases gradually from near to far relative to the surface of the positive electrode active layer in the thickness direction.

4. The lithium-sulfur battery positive electrode barrier layer according to claim 3, characterized in that: The barrier layer is a two-layer composite structure. The mass ratio of oxide particles to conductive materials in the first sublayer close to the positive electrode active layer is 1:10.5-20, and the mass ratio of oxide particles to conductive materials in the second sublayer away from the positive electrode active layer is 1:5-10.

5. The lithium-sulfur battery positive electrode barrier layer according to claim 3, characterized in that: The barrier layer is a three-layer composite structure, the mass ratio of oxide particles to conductive materials in each sublayer is 1:1-20, and the mass ratio of oxide particles to conductive materials in each sublayer increases gradually from near to far relative to the surface of the positive electrode active layer in the thickness direction.

6. The lithium-sulfur battery positive electrode barrier layer according to claim 5, characterized in that: The barrier layer is a three-layer composite structure. The mass ratio of oxide particles to conductive materials in the first sublayer close to the positive electrode active layer is 1:20, the mass ratio of oxide particles to conductive materials in the second sublayer above the first sublayer and away from the positive electrode active layer is 1:17, and the mass ratio of oxide particles to conductive materials in the third sublayer above the second sublayer and away from the positive electrode active layer is 1:

14.

7. The lithium-sulfur battery positive electrode barrier layer according to any one of claims 1 to 6, characterized in that: When the barrier layer is a multi-layer composite structure, the types of oxide particles and conductive materials in each sub-layer are the same.

8. The lithium-sulfur battery positive electrode barrier layer according to claim 1, characterized in that: The thickness of the positive electrode barrier layer is 1 μm to 500 μm. When the positive electrode barrier layer is a multi-layer composite structure, the thickness of each sub-layer is the same.

9. A method for preparing a positive electrode barrier layer for a lithium-sulfur battery according to any one of claims 1 to 6, characterized in that: When the positive electrode barrier layer is a single layer, the method comprises the following steps: (1) dispersing a certain amount of oxide particles into solvent 1 and stirring thoroughly to obtain a suspension A; (2) dispersing a certain amount of conductive material into solvent 2 and stirring thoroughly to obtain suspension B; (3) Add suspension B drop by drop into suspension A, stir and mix evenly to obtain a precursor solution for the barrier layer; (4) filtering the barrier layer precursor solution, placing the filtered membrane material in a freeze dryer, and freeze drying it at -70°C to -20°C for 24 to 48 hours to obtain a single-layer positive electrode barrier layer for a lithium-sulfur battery; When the positive electrode barrier layer is a multi-layer composite structure, the method comprises the following steps: (1) dispersing a certain amount of oxide particles into solvent 1 and stirring thoroughly to obtain a suspension A; (2) dispersing a certain amount of conductive material into solvent 2 and stirring thoroughly to obtain suspension B; (3) Dropping suspension B into suspension A drop by drop, stirring and mixing, to obtain a precursor solution of the first sub-layer of the barrier layer; repeating the above steps (1) to (3) to obtain precursor solutions of other sub-layers of the barrier layer; (4) The first sub-layer precursor solution is filtered, and after the filtration is completed, the second sub-layer precursor solution is added for filtration, and each sub-layer precursor solution is added and filtered in turn according to the barrier layer structure. The membrane material after filtration is placed in a freeze dryer and freeze-dried at -70°C to -20°C for 24 to 48 hours to obtain a positive electrode barrier layer for a lithium-sulfur battery.

10. A lithium-sulfur battery, characterized in that: The lithium-sulfur battery comprises the positive electrode barrier layer according to any one of claims 1 to 6, wherein the positive electrode barrier layer is arranged on the positive electrode surface of the lithium-sulfur battery and is located between the positive electrode active layer and the separator.

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