A sulfur cathode with a layered reinforced concrete structure and its preparation and application

Abstract

The present invention belongs to the field of battery technology, and more specifically, relates to a sulfur positive electrode with a layered reinforced concrete structure, and its preparation and application. The sulfur positive electrode active material of the lithium-sulfur battery is mixed with a binder, a conductive agent and carbon fiber to form a slurry, which is coated on a current collector to obtain a sulfur positive electrode pole piece; the obtained sulfur positive electrode pole piece is freeze-dried and roll-pressed to obtain a sulfur positive electrode with a layered reinforced concrete structure. The present invention aims to effectively solve the current problems of low ion and electron conductivity, low active material utilization and poor cycle life inside thick electrodes; at the same time, the mechanical properties of the electrode are improved so that the electrode maintains structural integrity during the charge and discharge process. The sulfur electrode prepared by this method has high energy density and excellent cycle stability under practical conditions of lean solution and low lithium.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and more specifically, relates to a sulfur positive electrode with a layered reinforced concrete structure and a preparation and application thereof. Background Art

[0002] With the continuous depletion of fossil energy and the environmental pollution problems it brings, the use of new energy has occupied an increasingly large proportion in modern society. Among them, lithium batteries are undoubtedly the most eye-catching new energy technology since the 21st century. Although the application of lithium-ion batteries can be seen everywhere in our lives, the low specific capacity of lithium-ion batteries limits its further development. Therefore, people turn their attention to electrode materials with specific capacity to meet the needs of manufacturing advanced energy storage devices with high specific energy. Lithium-sulfur batteries are considered to be one of the most promising materials to break through the limitations of lithium-ion battery energy storage systems due to their high theoretical specific capacity (1675mAh / g), and are very suitable for positive electrode materials for high specific energy secondary batteries. Under the growing demand for high energy density and low-cost driving energy storage to meet electrical applications, the concept of thick electrodes has attracted increasing attention because their direct and universal design can be quickly applied to various battery technologies. Optimizing the electrode system structure area capacity and low active component ratio (such as metal current collector, polymer binder, conductive material) is considered to be a promising method to maximize the high-capacity electrode. In addition, through the positive electrode structure design of thick electrodes, lithium-sulfur batteries with high energy density are obtained.

[0003] However, the traditional electrode composition and manufacturing process have the following problems when preparing thick electrodes: (1) When using traditional processes to prepare electrodes, the electrode sheets are prone to cracking after drying; (2) During the charge and discharge process, traditional thick electrodes limit the conduction of ions and electrons, reduce the active utilization rate of the material, and thus greatly reduce the electrochemical performance; (3) Thick electrodes undergo large volume changes during the charge and discharge process, and poor mechanical properties cause the positive electrode structure to be destroyed; (4) Thick electrodes have poor electrochemical performance in practical lithium-sulfur batteries (poor solution and low lithium).

[0004] Therefore, developing a thick cathode strategy with high ionic and electronic conductivity is of great significance for achieving practical lithium-sulfur batteries with high energy density. Summary of the invention

[0005] In view of the defects of the prior art, the object of the present invention is to provide a thick electrode with a reinforced concrete structure having high ion and electron conductivity, and to enable it to obtain high energy density and stable cycle under practical conditions (poor liquid - E / S ≤ 5 and low lithium N / P ≤ 5).

[0006] To achieve the above object, the present invention provides a method for preparing a sulfur cathode having a layered reinforced concrete structure, comprising the following steps:

[0007] (1) mixing the sulfur positive electrode active material of the lithium-sulfur battery with a binder, a conductive agent, carbon fiber and a solvent to form a slurry, and coating the slurry on a current collector to obtain a sulfur positive electrode sheet;

[0008] (2) freeze-drying the sulfur cathode electrode obtained in step (1) and rolling it, wherein during the freeze-drying process, the solvent freezes quickly to form ice crystals, and the ice crystals directly sublimate to form a straight channel inside the electrode. The straight channel forms a layered structure inside the electrode, and carbon fibers are interspersed between the layered structures to play the role of steel bars, thereby obtaining a sulfur cathode with a layered reinforced concrete structure.

[0009] like Figure 1 As shown, a slurry containing carbon fibers is coated on a positive electrode current collector, and a positive electrode having a layered reinforced concrete structure is obtained after freeze drying and roll pressing.

[0010] In a preferred embodiment, the sulfur cathode active material is Se x S y @pPAN,Te m S n @pPAN, S@pPAN, C / S composite material, wherein 0.02≤x≤0.15, y>0, and x+y=1; 0.01≤m≤0.15, n>0, and m+n=1; the mass percentage of the sulfur positive electrode active material in the slurry is more than 90%.

[0011] In the preferred embodiment, the binder is selected from sodium carboxymethyl cellulose, styrene-butadiene rubber, PVDF (polyvinylidene fluoride) and guar gum; the conductive agent is selected from Super P, Ketjen black and graphene oxide; the solvent is selected from deionized water and NMP (N-methylpyrrolidone). When a water-soluble binder is used, deionized water is used as a solvent to prepare the slurry; when a non-water-soluble binder such as PVDF is used, NMP is used as a solvent to form a liquid binder for preparing a fluid slurry. In order to ensure the mechanical strength and good conductivity of the pole piece, the mass percentage of carbon fiber in the slurry is 1wt.%-5wt.%; the length of the carbon fiber is millimeter-level, preferably 1-10mm, and the diameter is micrometer-level, preferably 5-10 microns. The length of the carbon fiber is in the millimeter level (1-10mm) to ensure long-range conductivity and improve mechanical properties, and the diameter is about 10μm to ensure uniform mixing. The solid content in the slurry is 30wt.%-40wt.%, to further ensure uniform mixing and viscosity of the slurry.

[0012] The sulfur cathode preparation method of the present invention is compatible and can prepare high-load thick electrodes and low-load thin electrodes. The thicker the thickness, the more difficult it is to maintain low tortuosity. In the preferred embodiment, the coating thickness of step (1) is 400-1200 μm. According to the purpose of the present invention, the coating thickness of step (1) is preferably in the range of 700 μm or more to prepare a cathode loading (the cathode loading refers to the total loading of the cathode including the cathode active material, carbon fiber, conductive agent and binder) of not less than 20 mg / cm 2 Experiments have shown that the coating without carbon fiber in the preparation of high-load thick electrodes will crack. The introduction of carbon fiber has a more obvious effect on the structure and electrochemical performance of the battery when preparing high-load electrodes.

[0013] In the preferred embodiment, the coating thickness in step (1) is 700-1200 μm; the coating thickness after roller pressing is 181-272 μm, and the positive electrode loading is 20-30 mg / cm 2 .

[0014] In the preferred embodiment, the freeze-drying in step (2) includes a freezing step and a sublimation drying step, and the freezing temperature ranges from -120°C to 0°C. In order to allow the thick electrode to quickly form a directional through hole without forming an ice-sandwich-like positive electrode structure due to too low a temperature, the freezing temperature is preferably in the range of -40°C to -90°C. The method is an ice template method, and the freezing time is 2h-24h. In order to ensure that the electrode has a good freezing effect and ensure the preparation efficiency, the freezing time is preferably 6h-12h. In the freeze-drying method, after the positive electrode is frozen, in order to obtain a directional through hole, the electrode needs to be sublimated and dried. Preferably, the sublimation drying is carried out under a vacuum degree of 0.1Pa to 10Pa, and the temperature during the vacuum drying process is not higher than -10°C.

[0015] In the preferred embodiment, in order to ensure the energy density of the battery and the electrochemical performance under the condition of lean solution, the prepared electrode sheet needs to be rolled. The rolling pressure in step (2) is 10-90 tons, and the compaction density of the obtained sulfur positive electrode with a layered reinforced concrete structure is 1-1.5 g / cm 3 between.

[0016] According to another aspect of the present invention, a sulfur positive electrode having a layered reinforced concrete structure prepared by the preparation method is provided.

[0017] According to another aspect of the present invention, a lithium-sulfur battery is provided, wherein the positive electrode material thereof is the sulfur positive electrode.

[0018] In the preferred embodiment, in order to further improve the energy density, the obtained pole piece is assembled into a button cell under the conditions of low-lithium Li (1.5≤N / P≤5) ​​and lean electrolyte (1.5≤E / S≤5). The amount of electrolyte is controlled to make it 1.5≤E / S≤5μL / mg s -1 ; Control the amount of negative electrode so that 1.5≤N / P≤5;

[0019] In order to obtain an energy density of more than 350Wh / kg and balance high energy density and long cycle performance, the amount of electrolyte should be controlled to 2≤E / S≤3μL / mg s -1 ; Control the amount of negative electrode so that 2≤N / P≤3.

[0020] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0021] At present, the thick sulfur cathode (cathode loading greater than 5mg / cm 2 ) generally face great challenges: low ion and electron conduction, resulting in low active material utilization and poor cycle performance; during the cycle, the thick sulfur cathode produces a large volume expansion, which causes electrode damage and battery failure; when the cathode loading is greater than 5 mg / cm 2 When the thick electrode is formed, it is easy to crack and fall off. Compared with the prior art, the present invention adds carbon fiber when preparing the slurry. In a preferred embodiment, the percentage of the total mass of the positive electrode is 1-5%, which can effectively reduce the surface tension of the positive electrode slurry and improve the coating effect of the positive electrode slurry on the positive electrode collector; in addition, it can reduce the cracking and falling caused by the thick electrode formation process and the formation of a layered reinforced concrete structure. The electronic conductivity of the thick electrode material is greatly improved, the electronic channel inside the thick electrode is ensured, and the conduction of electrons is accelerated; at the same time, the carbon fiber plays the role of steel bars to avoid the destruction of the positive electrode structure due to the volume change of the positive electrode during the cycle of the lithium-sulfur battery, so that the positive electrode structure maintains integrity during the cycle, and the positive electrode structure can still be maintained even at a high compaction density.

[0022] The present invention obtains a thick electrode with a layered reinforced concrete structure by freeze drying. During freeze drying, the solvent freezes quickly to form ice crystals from top to bottom. After the ice is directly sublimated at low temperature, many straight-through channels from top to bottom (with the surface of the current collector as "bottom" and the surface of the slurry coating on the current collector as "top") are left. The channel forms a layered structure inside the slurry coating. In the preferred embodiment of the present invention, carbon fibers with millimeter length are selected, and the carbon fibers are dispersed in the slurry parallel to the current collector. After freeze drying to form a straight-through channel, the carbon fibers are interspersed between the layered structures, which is similar to forming a layered reinforced concrete structure, in which the carbon fibers play a role similar to "rebar". And the carbon fibers with micrometer diameter are selected to maintain certain mechanical properties, ensure the stability of the electrode, and ensure the electronic and ion conduction inside the thick electrode, thereby improving the rate performance and long cycle performance of the thick electrode ion battery. The thick electrode prepared by the traditional high-temperature heating method is too thick. The upper and lower layers are heated unevenly during the traditional high-temperature heating process. The upper layer evaporates first to form a dense electrode, and then the lower layer solvent evaporates again, breaking through the electrode to produce cracks. In addition, as the solvent evaporates, the binder slowly moves from a uniform state to the upper layer of the electrode. After drying, the electrode surface is covered with an electrolyte-impermeable adhesive. Many closed pores are usually formed inside the traditional thick sulfur positive electrode, while the layered reinforced concrete structure thick sulfur positive electrode of the present invention has a pipe-capillary pore structure, which is evenly distributed inside the electrode, so that the electrode still has good electrochemical performance under lean liquid conditions.

[0023] Based on the sulfur cathode preparation method of the present invention, a thick sulfur cathode with a layered concrete structure is obtained, the slurry coating thickness is greater than or equal to 700 microns, and the cathode loading is greater than 20 mg / cm 2 , which is actually an ultra-thick electrode. Experiments have shown that, unlike traditional thick sulfur electrodes, the thick electrode of the present invention can s -1 ) and low lithium (N / P = 2.7), the practical lithium-sulfur battery has excellent cycle stability (capacity remains above 80% after 140 cycles) and high energy density (close to 390Wh / kg). 2 ) and high compaction density (1.43 g / cm 3 ) still has good cycle performance. It still has a high specific capacity or active material utilization under the condition of a small amount of electrolyte. It may be because the sulfur positive electrode with a layered concrete structure prepared by the present invention has straight-through pores, does not form a closed dead volume, has good wettability to the electrode, and improves the utilization of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a flow chart of preparing a thick electrode with a reinforced concrete structure according to Example 1 of the present invention.

[0025] Figure 2 These are scanning electron microscope images of the thick electrode surface (left picture) and cross-section (right picture) of the layered reinforced concrete structure of Example 1 of the present invention.

[0026] Figure 3 The cycle performance diagram of the ultra-thick electrode with a layered reinforced concrete structure prepared in Example 1 of the present invention under lean solution and low lithium conditions and its comparison with the traditional thick electrode.

[0027] Figure 4 This is a cycle performance diagram of the ultra-thick electrode with a layered reinforced concrete structure prepared in Example 1 of the present invention at different loads and compaction densities, where content a is the specific capacity and content b is the surface capacity.

[0028] Figure 5 This is a cross-sectional view of the ultra-thick electrode with a layered reinforced concrete structure prepared in Example 1 of the present invention after cycling.

[0029] Figure 6 This is a cross-sectional morphology diagram of the ultra-thick electrode with a layered structure prepared in Comparative Example 1 of the present invention before and after cycling, with content a being before cycling and content b being after cycling.

[0030] Figure 7 This is a cycle performance diagram of the ultra-thick electrode with a layered structure prepared in Comparative Example 1 of the present invention.

[0031] Figure 8 The cross-sectional morphology of the ultra-thick electrode prepared in Comparative Example 2 of the present invention before and after battery cycling is shown, with the left picture showing before cycling and the right picture showing after cycling.

[0032] Fig. 9 This is a test diagram of the cycle performance of a battery made from the ultra-thick electrode prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] The object of the present invention is to provide a thick electrode of reinforced concrete structure with high ion and electron conductivity, and to obtain high energy density and stable cycle under practical conditions. The overall process setting of the method of adding a certain proportion of carbon fiber and freeze drying during mixing and the reaction parameter conditions of key steps (such as processing temperature, processing time, amount and size of carbon fiber, etc.) are improved and further optimized to ensure the successful synthesis of layered reinforced concrete structure thick electrodes. The present invention aims to effectively solve the problems of low ion and electron conductivity, low utilization rate of active materials and poor cycle life in the current thick electrodes; at the same time, improve the mechanical properties of the electrode so that the electrode maintains structural integrity during the charge and discharge process. In summary, the sulfur electrode prepared by this method has high energy density and excellent cycle stability under practical conditions of lean solution and low lithium.

[0035] The sulfur positive electrode active material Se used in the embodiment of the present invention x S y @pPAN and Te m S n @pPAN is to obtain Se x S y and Te m S n The composite is then compounded with polyacrylonitrile (PAN); S@pPAN is obtained by mixing polyacrylonitrile and sulfur powder in a certain proportion and then heat treating; C / S composite material is obtained by mixing carbon material (carbon nanotubes or bp2000, etc.) and sulfur powder in a certain proportion and then heat treating.

[0036] In the process of preparing the sulfur positive electrode of the present invention, when the total mass of carbon fiber is less than 1%, it is impossible to make the thick electrode construct a good layered reinforced concrete structure, improve the internal electronic conductivity of the electrode, and improve the mechanical stability of the thick electrode during the cycle; when the total mass of the carbon fiber is greater than 5%, the addition of too much carbon fiber may bring some negative effects, such as uneven mixing, and the cost is also significantly increased. As an improvement of the thick electrode of the present invention, it is preferred that the carbon fiber accounts for 1 to 5% of the total mass percentage of the positive electrode sheet. In addition, in the process of preparing the thick electrode of the present invention, it is preferred to use carbon fiber with a length of millimeters, which can achieve significant battery performance improvement of smaller-sized carbon materials (such as carbon nanotubes, etc.).

[0037] The following are specific embodiments:

[0038] Example 1

[0039] 1. Sulfur cathode active material Se 0.05 S 0.95 Preparation of @pPAN complex:

[0040] (1) Sulfur selenium (Se 0.05 S0.95 Preparation of the complex

[0041] Ethanol was used as solvent, and commercial selenium powder and sulfur powder were mixed evenly by wet ball milling, with the mass ratio of sulfur to selenium being 15:1. The obtained mixture was dried in an oven at 60°C for 6 hours. The mixture was then sealed in a 200mL autoclave, heat treated at 260°C for 12 hours, and then naturally cooled to room temperature to obtain sulfur selenium (Se 0.05 S 0.95 ) complex.

[0042] (2)Se 0.05 S 0.95 Preparation of @pPAN composite cathode materials

[0043] Polyacrylonitrile (PAN) and Se 0.05 S 0.95 The composite was mixed uniformly in a mass ratio of 3:1 and then heat treated at 300 °C for 2.5 h in a tube furnace under argon protection to obtain Se 0.05 S 0.95 @pPAN.

[0044] 2. Preparation of reinforced concrete pole pieces with different load layers

[0045] A certain amount of Se 0.05 S 0.95 @pPAN powder was ball-milled and then sieved. 0.05 S 0.95 @pPAN powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000; diameter: 8μm, length: 2mm), sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive, mixed with deionized water (solid content 40wt.%) in a ratio of 9:0.4:0.1:0.25:0.25, put into a Zhongyi disperser and mix well ( Figure 1 The obtained slurry was then evenly coated on carbon-coated aluminum foil at different coating thicknesses (700 μm, 800 μm, 900 μm, 1000 μm) to obtain different loadings (20.2 mg / cm 2 -30.4mg / cm 2 )(When coating 700 μm, it corresponds to 20.2 mg / cm 2 , when coated at 800μm, it corresponds to 23.1mg / cm 2 , when coated at 900μm, it corresponds to 26.5mg / cm 2 , corresponding to 30.4mg / cm when coating 1000μm 2) positive electrode. The electrode was placed in a freeze dryer at -84°C, frozen for 6 hours, and then dried at a pressure of 0.1 Pa for 12 hours. Finally, the dried electrode was taken out and left at room temperature for 3 hours, and then 20.2 mg / cm 2 The pole piece was rolled (the corresponding pressures were 10, 13, and 15 tons, respectively) to obtain different compaction densities (1.1 g / cm 3 -1.43g / cm 3 ) pole piece (where 10 tons of pressure corresponds to a compaction density of 1.35g / cm 3 , 13 tons of pressure corresponds to a compaction density of 1.1g / cm 3 , 15 tons of pressure corresponds to a compaction density of 1.43g / cm 3 .

[0046] Comparative Example 1

[0047] The other conditions were the same as those in Example 1, except that no carbon fiber was added to the slurry, the slurry coating thickness was 700 μm, and the pole piece loading was 20.2 mg / cm 2 .

[0048] Battery assembly and electrochemical performance testing:

[0049] The pole pieces prepared in Example 1 and Comparative Example 1 (including different loadings and compaction densities) were punched into discs with a diameter of 12 mm, and the battery was assembled in a glove box. The electrolyte selected was 0.66M LiFSI and 0.33M LiTFSI dissolved in DOL, DME and TTE (molar ratio of 0.2:1:3). 200μmLi (N / P=2.7) tablets and lean solution (2μL / mg s -1 ) and set aside for 12 hours to allow the electrolyte to fully penetrate. The assembled batteries were subjected to impedance tests, rate performance tests, and long cycle tests.

[0050] The obtained electrode and the electrode after long cycle were prepared into SEM samples, such as Figure 2 and 5 As shown, Figure 2 The above loading was observed to be 20.2 mg / cm 2 The morphology of the layered reinforced concrete structure electrode surface (left) and cross-section (right). The formation of the layered reinforced concrete structure can be observed after roller compaction, and carbon fibers are interspersed between the layers, indicating that this structure improves the mechanical properties of the electrode sheet. This structure can still be observed in the cross-section of the positive electrode after cycling, further indicating that this structure improves the mechanical properties of the electrode sheet ( Figure 5 ).

[0051] Figure 6In Comparative Example 1, no carbon fiber is added, and the loading capacity prepared is 20 mg / cm 2 The cross-sectional diagram of the positive electrode structure of the electrode before and after the cycle (content a is the electrode before the cycle, content b is the electrode after the cycle). It can be seen that the straight-through channel before the cycle no longer exists after the electrode is cycled, proving that carbon fiber has greatly improved the stability of the positive electrode structure. Figure 7 Comparative Example 1 does not add carbon fiber, and the thick electrode (20 mg / cm 2 ) cycle performance, it can be seen that although it has a good utilization rate of active materials, the capacity drops sharply after 83 cycles. Figure 6 From the electrode after the medium cycle, it can be seen that the electrochemical performance decreases due to the failure of the positive electrode structure. Therefore, it can be seen that carbon fiber is of great significance to the cycle life of thick electrode sheets.

[0052] Figure 3 The positive electrode loading prepared in Example 1 is 20.2 mg / cm 2 The cycle performance comparison diagram of the electrode sheet and the traditional thick electrode shows that compared with the traditional thick electrode, the layered reinforced concrete positive electrode of this embodiment has high ion and electron conductivity due to its special structure, so that the electrode has better active material utilization and stable cycle in the case of poor liquid and low lithium; In addition, Figure 4 , content a is the specific capacity, content b is the surface capacity, and by assembling the battery with positive electrodes of layered reinforced concrete structures of different compaction densities and loadings, it still has excellent electrochemical properties.

[0053] Comparative Example 2

[0054] The other conditions are the same as those in Example 1, except that the carbon fibers are replaced by carbon nanotubes, the carbon nanotubes have a size of (diameter: 20 nm, length: 30 μm), the slurry coating thickness is 700 μm, and the pole piece loading is 20 mg / cm 2 .

[0055] Figure 8 The positive electrode obtained in Comparative Example 2 is assembled into a battery according to the method of Example 1. The scanning electron microscope image of the electrode shows that (as shown in Figure 8 , it can be seen from the cross-sectional view before the cycle (left figure) that the thick electrode prepared by carbon nanotubes does not have the layered reinforced concrete structure proposed in the embodiment of the present invention. The reason may be that the length and diameter of the carbon nanotubes are too small to form such a special structure, and they can only play the role of a conductive agent. In addition, Figure 8 The SEM of the electrode after cycling (right picture) shows that the layered structure is destroyed, which may be the main reason for the decline in electrochemical performance. Fig. 9 This is the cycle performance diagram of the positive electrode test. It can be seen that the positive electrode loading of the comparative example is 20 mg / cm2 After 60 cycles of the thick electrode, the cycle performance decayed rapidly, and the performance was far inferior to the cycle performance of the thick electrode in Example 1.

[0056] Example 2

[0057] A certain amount of Se 0.05 S 0.95 @pPAN powder (prepared in the same manner as in Example 1) was ball-milled, and the ball-milled powder was then sieved. 0.05 S 0.95 @pPAN powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000), sodium carboxymethyl cellulose and styrene butadiene rubber adhesive were put into deionized water (solid content 40wt.%) in a ratio of 9:0.25 / 0.25:0.25 / 0.25, and then mixed evenly in a Zhongyi disperser. The obtained slurry was then evenly coated on a carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2 The positive electrode sheet with a loading capacity of about 1000 μg / cm2 was placed in a freeze dryer at -84°C, frozen for 6 hours, and then dried at a pressure of 0.1 Pa for 12 hours. Finally, the dried electrode sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the electrode sheet. Other conditions were the same as those in Example 1.

[0058] Example 3

[0059] A certain amount of S@pPAN (polyacrylonitrile and sulfur powder are mixed in a mass ratio of 1:3 and heated at 350℃ for 3 hours) powder is ball-milled, and then the ball-milled powder is sieved. Then S@pPAN powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000), sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive are put into deionized water (solid content is 40wt.%) in a ratio of 9:0.4 / 0.1:0.25:0.25, and then mixed evenly in a Zhongyi disperser. Then the obtained slurry is evenly coated on the carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2 The positive electrode sheet with a loading capacity of about 1000 μg / cm2 was placed in a freeze dryer at -84°C, frozen for 6 hours, and then dried at a pressure of 0.1 Pa for 12 hours. Finally, the dried electrode sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the electrode sheet. Other conditions were the same as those in Example 1.

[0060] Example 4

[0061] A certain amount of C / S composite material (obtained by mixing carbon nanotubes and sulfur powder in a ratio of 1:3 and then heating at 300°C for 10 hours) powder was ball-milled, and then the ball-milled powder was sieved. Then, C / S composite material powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000), sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive were put into deionized water (solid content of 40wt.%) in a ratio of 9:0.4 / 0.1:0.25:0.25, and then mixed evenly in a Zhongyi disperser. Then, the obtained slurry was evenly coated on a carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2 The positive electrode sheet with a loading capacity of about 1000 μg / cm2 was placed in a freeze dryer at -84°C, frozen for 6 hours, and then dried at a pressure of 0.1 Pa for 12 hours. Finally, the dried electrode sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the electrode sheet. Other conditions were the same as those in Example 1.

[0062] Example 5

[0063] A certain amount of C / S composite powder was ball-milled, and then the ball-milled powder was sieved. Then, C / S composite powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000), sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive were put into deionized water (solid content was 40wt.%) in a ratio of 9:0.4 / 0.1:0.25:0.25, and then mixed evenly in a Zhongyi disperser. Then, the obtained slurry was evenly coated on a carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2 The positive electrode sheet with a loading capacity of about 100%. The sheet was placed in a freeze dryer at -84℃, frozen for 6 hours, and then dried at a pressure of 0.1Pa for 12 hours. Finally, the dried sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the sheet. Finally, in sufficient electrolyte (≥5μL / mg s -1 ) and low lithium (N / P≤2.7) when assembling the battery, and other conditions are the same as those in Example 1.

[0064] Example 6

[0065] A certain amount of C / S composite powder was ball-milled, and then the ball-milled powder was sieved. Then, C / S composite powder, ED600JD (KB), carbon fiber (purchased directly, model M40JB-6000), sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive were put into deionized water (solid content was 40wt.%) in a ratio of 9:0.4 / 0.1:0.25:0.25, and then mixed evenly in a Zhongyi disperser. Then, the obtained slurry was evenly coated on the carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2The positive electrode sheet with a loading capacity of about 200 μL was placed in a freeze dryer at -84°C, frozen for 6 hours, and then dried at a pressure of 0.1 Pa for 12 hours. Finally, the dried electrode sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the electrode sheet. Finally, in the lean solution (≤2μL / mg s -1 ) and sufficient lithium source (N / P≥5), and the other conditions are the same as in Example 1.

[0066] Example 7

[0067] A certain amount of C / S composite powder was ball-milled, and then the ball-milled powder was sieved. Then, C / S composite powder, ED600JD (KB), carbon fiber, sodium carboxymethyl cellulose and styrene-butadiene rubber adhesive were put into PVDF (solid content was 40wt.%) in a ratio of 9:0.4 / 0.1:0.25:0.25, and then mixed evenly in a Zhongyi disperser. Then, the obtained slurry was evenly coated on a carbon-coated aluminum foil at a thickness of 700μm to obtain 20mg / cm 2 The positive electrode sheet with a loading capacity of about 100%. The sheet was placed in a freeze dryer at -84℃, frozen for 6 hours, and then dried at a pressure of 0.1Pa for 12 hours. Finally, the dried sheet was taken out and left at room temperature for 3 hours, and then rolled to obtain the sheet. Finally, in sufficient electrolyte (≥5μL / mg s -1 ) and sufficient lithium source (N / P≥5), and the other conditions are the same as in Example 1.

[0068] By testing and comparing the thick electrodes prepared in Examples 2 to 7 under different electrolyte and lithium source conditions, it was found that the electrochemical performance obtained by preparing a layered reinforced concrete structure in different electrolytes is not much different, making this thick electrode conducive to application under practical conditions of lean solution and low lithium content, and can obtain higher energy density.

[0069] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a sulfur cathode having a layered reinforced concrete structure, characterized in that: The steps include: (1) The sulfur positive electrode active material of the lithium-sulfur battery is mixed with a binder, a conductive agent, carbon fiber and a solvent to form a slurry, which is coated on a current collector to obtain a sulfur positive electrode sheet; the mass percentage of the carbon fiber in the slurry is 1wt.%-5wt.%; the length of the carbon fiber is 1-10mm, the diameter is 5-10 μm; the coating thickness is 400-1200 μm; (2) freeze-drying the sulfur cathode electrode obtained in step (1) and rolling the coating to a thickness of 181-272 μm and a cathode loading of 20-30 mg / cm 2 ; In the freeze-drying process, the solvent freezes quickly to form ice crystals, and after the ice crystals directly sublimate, a straight channel is formed inside the electrode. The straight channel forms a layered structure inside the electrode, and carbon fibers are interspersed between the layered structures to act as steel bars, thereby obtaining a sulfur positive electrode with a layered reinforced concrete structure.

2. The preparation method according to claim 1, characterized in that The sulfur positive electrode active material is Se x S y @pPAN,Te m S n @pPAN, S@pPAN, and at least one of C / S composite materials, wherein 0.02≤x≤0.15, y>0, and x+y=1; 0.01≤m≤0.15, n>0, and m+n=1; and the mass percentage of the sulfur positive electrode active material in the slurry is greater than 90%.

3. The preparation method according to claim 1, characterized in that: The binder is selected from sodium carboxymethyl cellulose, styrene-butadiene rubber, PVDF and guar gum; the conductive agent is selected from Super P, Ketjen black and graphene oxide; and the solvent is selected from deionized water and NMP.

4. The preparation method according to claim 1, characterized in that: The solid content of the slurry is 30 wt.%-40 wt.%.

5. The preparation method according to claim 1, characterized in that: The freeze drying in step (2) includes a freezing step and a sublimation drying step, wherein the freezing temperature in the freezing step is in the range of -120 o C to 0 o C, the freezing time is 2 h-24 h; in the sublimation drying step, the vacuum degree is 0.1 Pa-10 Pa, and the temperature during the vacuum drying process is not higher than -10°C.

6. The sulfur positive electrode having a layered reinforced concrete structure prepared by the preparation method according to any one of claims 1 to 5.

7. A lithium-sulfur battery, characterized in that: The positive electrode material is the sulfur positive electrode as claimed in claim 6.

8. The lithium-sulfur battery according to claim 7, characterized in that: Control the amount of electrolyte so that 1.5≤E / S≤5 μL / mg s -1 ; Control the amount of negative electrode so that 1.5≤N / P≤5.

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