A lithium-sulfur battery electrode, its preparation method, and a lithium-sulfur battery

Abstract

This invention provides a lithium-sulfur battery electrode, its preparation method, and a lithium-sulfur battery. The lithium-sulfur battery electrode includes a current collector and a first active material layer disposed on at least one side of the current collector. A second active material layer is disposed on the side of the first active material layer away from the current collector. Both the first and second active material layers contain sulfur and carbon, with the sulfur content in the first active material layer being greater than that in the second active material layer. By increasing the sulfur content in the active material layer closer to the current collector and decreasing the sulfur content in the active material layer away from the current collector, this invention maintains the energy density of the lithium-sulfur battery while suppressing the shuttle effect caused by the dissolution of sulfur from the electrode surface into the electrolyte, thus mitigating self-discharge and capacity decay of the lithium-sulfur battery and improving the energy density, rate performance, and cycle stability of the lithium-sulfur battery electrode.

Description

Technical Field

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

[0002] Lithium-ion batteries have permeated all aspects of daily life, from power tools and digital devices to electric vehicles. However, their application also faces numerous challenges, such as range anxiety and energy density issues. Researchers are accelerating the development of new lithium-ion batteries, with lithium-sulfur batteries attracting particular attention due to their ultra-high volumetric energy density.

[0003] Lithium-sulfur batteries use sulfur as the positive electrode active material, which boasts advantages such as high energy density, non-toxicity, abundant electrode material sources, and low cost, making it an ideal next-generation energy storage device. However, lithium-sulfur batteries also face the problem that elemental sulfur or sulfides, the positive electrode active material, easily dissolve in the electrolyte and undergo a shuttle effect during battery charging and discharging, depositing on the positive electrode surface to form irreversible reaction products, leading to self-discharge and rapid capacity decay. To address this issue, researchers typically introduce highly conductive and high-volume carbon materials, such as microporous activated carbon materials, into the positive electrode to suppress or bind sulfur migration.

[0004] CN109346678A discloses a method for preparing a high-sulfur-loaded lithium-sulfur battery cathode. The method involves adding carbon materials and sulfur to water, mixing and then nano-ball milling, followed by drying, pulverizing, and melting to obtain a carbon-sulfur composite cathode material. A conductive agent, binder, and the carbon-sulfur composite cathode material are then added to water and mixed again, followed by nano-ball milling to obtain a slurry. The slurry is coated onto aluminum foil and dried to obtain the high-sulfur-loaded lithium-sulfur battery cathode. This method features low raw material costs, simple processes, and controllable operation. The presence of carbon effectively inhibits sulfur migration. CN110323447B discloses a lithium-sulfur battery cathode framework material and its preparation method. The lithium-sulfur battery cathode framework material in this patent is a hollow porous carbon material with a flower-like structure doped with Co and N. Co and N active sites are attached to the petals. This unique carbon structure can effectively adsorb polysulfides and inhibit the shuttle effect of polysulfides, thereby improving the rate performance and stability of the cathode material. CN109950472B provides a lithium-sulfur battery cathode material, which is formed by copolymerization of liquid sulfur formed by melting organic matter and sulfur powder. The material effectively fixes sulfur through chemical bonding, thereby improving the utilization rate of sulfur.

[0005] In existing technologies, carbon materials are typically added to lithium-sulfur battery electrodes to fix sulfur and suppress the shuttle effect of polysulfides. However, the introduction of carbon materials such as activated carbon further reduces the overall volumetric energy density and gravimetric energy density of lithium-sulfur batteries, thus reducing their application performance. Therefore, providing an electrode with high energy density and good cycle stability is of great significance for the research and development of lithium-sulfur batteries. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a lithium-sulfur battery electrode, its preparation method, and a lithium-sulfur battery. The lithium-sulfur battery electrode of the present invention has a first active material layer and a second active material layer with a sulfur content gradient distribution along the thickness direction. By increasing the sulfur content in the active material layer closer to the current collector and decreasing the sulfur content in the active material layer farther from the current collector, the energy density of the lithium-sulfur battery is maintained while suppressing the shuttle effect caused by the dissolution of sulfur from the electrode surface into the electrolyte, thus mitigating the self-discharge and capacity decay of the lithium-sulfur battery and improving the energy density, rate performance, and cycle stability of the lithium-sulfur battery electrode.

[0007] In this invention, "high sulfur content" means that sulfur accounts for more than 70% of the total mass of the active material electrode.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a lithium-sulfur battery electrode, the lithium-sulfur battery electrode comprising a current collector and a first active material layer disposed on at least one side surface of the current collector, wherein a second active material layer is disposed on the side surface of the first active material layer away from the current collector.

[0010] Both the first active material layer and the second active material layer contain sulfur and carbon, with the sulfur content in the first active material layer being greater than that in the second active material layer.

[0011] The lithium-sulfur battery electrode of the present invention has a first active material layer and a second active material layer sequentially disposed on the surface of the current collector. The sulfur content in the first active material layer closer to the current collector is higher than that in the second active material layer farther away from the current collector. This electrode structure, which has a low sulfur content coating at the interface between the electrode and the separator and a gradient distribution of sulfur content, can reduce the shuttle effect caused by the dissolution of active sulfur into the electrolyte on the surface of the lithium-sulfur battery electrode while ensuring the energy density of the lithium-sulfur battery. This reduces the self-discharge and capacity decay of the lithium-sulfur battery and improves the energy density, rate performance and cycle stability of the lithium-sulfur battery electrode.

[0012] It should be noted that the sulfur content in the first active material layer is greater than the sulfur content in the second active material layer, meaning that the mass ratio of sulfur in the first active material layer to the mass ratio of sulfur in the second active material layer is greater than the mass ratio of sulfur in the second active material layer to the mass ratio of sulfur in the second active material layer.

[0013] Preferably, based on the mass of the first active material layer as 100%, the sulfur content in the first active material layer is 75% to 94%, for example, it can be 75%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or 94%, etc.

[0014] Preferably, based on the mass of the second active material layer as 100%, the sulfur content in the second active material layer is 10-90%, for example, it can be 10%, 15%, 20%, 30%, 40%, 50%, 55%, 60%, 70%, 75%, 80%, 85% or 90%, etc., preferably 55-75%.

[0015] It should be noted that the content of each substance in the first active material layer and / or the second active material layer in this invention refers to the content when coating one side. When both sides of the current collector are coated, the content of each substance in the first active material layer and / or the second active material layer on one side of the current collector can be the same as that on the other side, that is, the active material layers on both sides of the current collector are completely symmetrically distributed, or they can be different, as long as each layer meets its own preferred content range.

[0016] In this invention, by further optimizing the sulfur content in the first and second active material layers and improving the gradient structure, the rate performance and cycle performance of the lithium-sulfur battery are further improved while ensuring the energy density of the lithium-sulfur battery, making it more suitable for application in high-sulfur lithium-sulfur batteries.

[0017] Preferably, the thickness of the first active material layer is 130-150 μm, for example, it can be 130 μm, 132 μm, 134 μm, 136 μm, 138 μm, 140 μm, 142 μm, 144 μm, 146 μm, 148 μm or 150 μm.

[0018] Preferably, the thickness of the second active material layer is 30 to 50 μm, for example, it can be 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm, 42 μm, 44 μm, 46 μm, 48 μm or 50 μm.

[0019] The present invention rationally designs the thickness of the first active material layer and the second active material layer, and combines them with a specific gradient sulfur content structure and a specific sulfur content to meet more application scenarios. It suppresses the shuttle effect, slows down the self-discharge and capacity decay of lithium-sulfur batteries, and balances energy density, rate performance and cycle performance, thereby further improving the overall electrochemical performance of lithium-sulfur batteries.

[0020] Preferably, based on the total mass of the first active material layer and the second active material layer being 100%, the total sulfur content in the first active material layer and the second active material layer is 70% to 90%, for example, it can be 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, or 90%, etc.

[0021] The lithium-sulfur battery electrode of the present invention is suitable for batteries with high sulfur content. It can also have good rate performance and cycle performance in batteries with sulfur content of 70-90%, and further improves the energy density of the battery by increasing the sulfur content.

[0022] As a preferred technical solution for the lithium-sulfur battery electrode sheet of the present invention, the first active material layer and / or the second active material layer further include a conductive agent and a binder.

[0023] Preferably, the conductive agent includes any one or a combination of at least two of multi-walled carbon nanotubes, single-walled carbon nanotubes, and conductive carbon black (SP). For example, it can be a combination of multi-walled carbon nanotubes and single-walled carbon nanotubes, a combination of single-walled carbon nanotubes and SP, a combination of multi-walled carbon nanotubes and SP, or a combination of multi-walled carbon nanotubes, single-walled carbon nanotubes, and SP, etc.

[0024] Preferably, the adhesive comprises carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR).

[0025] Preferably, the carbon comprises porous activated carbon.

[0026] Preferably, based on the mass of the first active coating, the total content of sulfur and carbon in the first active coating is 88-95%, for example, it can be 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95%, etc.

[0027] Preferably, based on the mass of the first active coating, the content of the conductive agent in the first active coating is 1-8%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, etc.

[0028] Preferably, based on the mass of the first active coating as 100%, the content of the binder in the first active coating is 1 to 4%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, etc.

[0029] As a preferred technical solution for the lithium-sulfur battery electrode sheet of the present invention, the total content of sulfur and carbon in the second active coating is 88-95% based on the mass of the second active coating being 100%, for example, it can be 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95%, etc.

[0030] Preferably, based on the mass of the second active coating, the content of the conductive agent in the second active coating is 1-8%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, etc.

[0031] Preferably, based on the mass of the second active coating, the content of the binder in the second active coating is 1 to 4%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, etc.

[0032] In this invention, the binder and conductive agent content in the first and second active material layers are optimized to further improve the synergistic effect of sulfur, carbon, conductive agent and binder in the lithium-sulfur battery electrode, thereby improving the energy density, rate performance and cycle stability of the lithium-sulfur battery electrode.

[0033] In a second aspect, the present invention provides a method for preparing a lithium-sulfur battery electrode according to the first aspect, the method comprising:

[0034] A first slurry and a second slurry are prepared separately. The first slurry is coated on at least one side of the current collector, and the second slurry is coated on the surface of the first slurry to obtain a lithium-sulfur battery electrode.

[0035] Both the first slurry and the second slurry contain sulfur and carbon, with the sulfur content in the first slurry being greater than that in the second slurry.

[0036] The preparation method of the present invention is simple and easy to implement, and the prepared lithium-sulfur battery electrode has a sulfur gradient distribution structure, and the electrode has high energy density, rate performance and cycle performance.

[0037] It should be noted that during the process of coating the surface of the first slurry with the second slurry, the first slurry can be dried first to form a first active material layer before coating the first slurry, or the second slurry can be coated directly after coating the first slurry and then dried together, or a double-layer coating machine can be used to coat the first slurry and the second slurry at the same time.

[0038] Preferably, the preparation process of the second slurry is the same as that of the first slurry.

[0039] As a preferred embodiment of the preparation method described in this invention, the first slurry and the second slurry further include a conductive agent, a binder, and a solvent.

[0040] Preferably, the solvent in the first slurry accounts for 40% to 60% of the total mass of the first slurry, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%, etc.

[0041] Preferably, the solvent in the second slurry accounts for 40% to 60% of the total mass of the second slurry, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, or 60%.

[0042] As a preferred embodiment of the preparation method described in this invention, the first slurry is prepared in the following manner:

[0043] The first composite material, conductive agent, binder and solvent are mixed and stirred to obtain a uniform first slurry.

[0044] In some embodiments, the solvent includes deionized water.

[0045] Preferably, the first composite material is prepared in the following manner:

[0046] Sulfur and porous activated carbon are mixed evenly and then treated at high temperature to obtain the first composite material.

[0047] Preferably, the mixing time is 10 to 120 minutes, for example, 10 minutes, 20 minutes, 40 minutes, 60 minutes, 80 minutes, 100 minutes, or 120 minutes.

[0048] Preferably, the high-temperature treatment temperature is 150-200℃, for example, it can be 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃.

[0049] Preferably, the high-temperature treatment is carried out in a nitrogen atmosphere.

[0050] Thirdly, the present invention provides a lithium-sulfur battery, wherein the positive electrode material of the lithium-sulfur battery adopts the lithium-sulfur battery electrode sheet as described in the first aspect.

[0051] The lithium-sulfur battery of the present invention combines high energy density, rate performance and cycle performance, and also has good electrochemical performance at ultra-high sulfur content (S content = 88%).

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The lithium-sulfur battery electrode of the present invention has a first active material layer and a second active material layer sequentially disposed on the surface of the current collector. The sulfur content in the first active material layer closer to the current collector is higher than that in the second active material layer farther away from the current collector. This electrode structure, which has a low sulfur content coating at the interface between the electrode and the separator and a gradient distribution of sulfur content, can reduce the shuttle effect caused by the dissolution of active sulfur into the electrolyte on the surface of the lithium-sulfur battery electrode while ensuring the energy density of the lithium-sulfur battery. This reduces the self-discharge and capacity decay of the lithium-sulfur battery and improves the energy density, rate performance and cycle stability of the lithium-sulfur battery electrode. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of a lithium-sulfur battery electrode in a specific embodiment of the present invention.

[0055] Wherein, 1-current collector; 2-first active material layer; 3-second active material layer. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] The specific embodiments of this invention provide a lithium-sulfur battery electrode, the structural schematic of which is shown in the figure below. Figure 1 As shown, the lithium-sulfur battery electrode includes a current collector 1 and a first active material layer 2 disposed on at least one side surface of the current collector 1, wherein a second active material layer 3 is disposed on the side surface of the first active material layer 2 away from the current collector 1.

[0058] Both the first active material layer 2 and the second active material layer 3 contain sulfur and carbon, and the sulfur content in the first active material layer 2 is greater than the sulfur content in the second active material layer 3.

[0059] In some embodiments, the sulfur content in the first active material layer 2 is 75-94% based on 100% of the mass of the first active material layer 2.

[0060] In some embodiments, the sulfur content in the second active material layer 3 is 10-90%, preferably 55-75%, based on 100% of the mass of the second active material layer 3.

[0061] In some embodiments, the thickness of the first active material layer 2 is 130–150 μm.

[0062] In some embodiments, the thickness of the second active material layer 3 is 30–50 μm.

[0063] In some embodiments, the total sulfur content in the first active material layer 2 and the second active material layer 3 is 70-90% based on the total mass of 100%.

[0064] In some embodiments, the first active material layer 2 and / or the second active material layer 3 further include a conductive agent and a binder.

[0065] In some embodiments, the conductive agent includes any one or a combination of at least two of multi-walled carbon nanotubes, single-walled carbon nanotubes, and SP.

[0066] In some embodiments, the adhesive comprises carboxymethyl cellulose and / or styrene-butadiene rubber.

[0067] In some embodiments, the carbon comprises porous activated carbon.

[0068] In some embodiments, the total sulfur and carbon content in the first active coating is 88-95% based on 100% by mass.

[0069] In some embodiments, the content of conductive agent in the first active coating is 1-8% based on the mass of the first active coating being 100%.

[0070] In some embodiments, the binder content in the first active coating is 1 to 4% based on the mass of the first active coating being 100%.

[0071] In some embodiments, the total sulfur and carbon content in the second active coating is 88-95% based on 100% by mass.

[0072] In some embodiments, the content of conductive agent in the second active coating is 1-8% based on 100% by mass.

[0073] In some embodiments, the binder content in the second active coating is 1-4% based on 100% by mass.

[0074] The specific embodiments section of this invention also provides a method for preparing the above-mentioned lithium-sulfur battery electrode, the method comprising:

[0075] A first slurry and a second slurry are prepared respectively. The first slurry is coated on at least one side of the current collector 1, and the second slurry is coated on the surface of the first slurry to obtain a lithium-sulfur battery electrode.

[0076] Both the first slurry and the second slurry contain sulfur and carbon, with the sulfur content in the first slurry being greater than that in the second slurry.

[0077] In some embodiments, the first and second slurries further include a conductive agent, a binder, and a solvent.

[0078] In some embodiments, the solvent in the first slurry accounts for 40-60% of the total mass of the first slurry.

[0079] In some embodiments, the solvent in the second slurry accounts for 40-60% of the total mass of the second slurry.

[0080] Example 1

[0081] This embodiment provides a lithium-sulfur battery electrode, the structural schematic of which is shown below. Figure 1 As shown, the lithium-sulfur battery electrode includes an aluminum foil current collector 1 and a first active material layer 2 disposed on both sides of the current collector 1. A second active material layer 3 is disposed on the side of the first active material layer 2 away from the current collector 1. The thickness of the first active material layer 2 on one side is 160 μm, and the thickness of the second active material layer 3 on one side is 20 μm.

[0082] Based on the mass of the first active material layer 2 as 100%, the first active material layer 2 includes 90% elemental sulfur, 6% porous activated carbon, 3% conductive agent, and 1% binder; based on the mass of the second active material layer 3 as 100%, the second active material layer 3 includes 45% elemental sulfur, 48% porous activated carbon, 4% conductive agent, and 3% binder; based on the total mass of the first active material layer 2 and the second active material layer 3 as 100%, the total content of elemental sulfur in the first active material layer 2 and the second active material layer 3 is 85%.

[0083] This embodiment also provides a method for preparing the above-mentioned lithium-sulfur battery electrode, including:

[0084] (1) Mix elemental sulfur and porous activated carbon in a high-temperature tank according to the ratio for 50 min until uniform, and treat at 180°C for 60 min under nitrogen atmosphere to obtain the first composite material. The second composite material is prepared in the same way.

[0085] (2) The first composite material, conductive agent SP, binder SBR and deionized water are placed in a mixer and stirred for 100 min to obtain a uniform first slurry. The second slurry is prepared in the same way. The solid raw materials in the first slurry include 90% elemental sulfur, 6% porous activated carbon, 3% conductive agent and 1% binder, and also include 50% deionized water of the total mass of the first slurry. The solid raw materials in the second slurry include 45% elemental sulfur, 48% porous activated carbon, 4% conductive agent and 3% binder, and also include 50% deionized water of the total mass of the second slurry.

[0086] (3) Using a double-layer coating machine, the first slurry and the second slurry are coated on the surface of the aluminum foil of the current collector 1, wherein the first slurry is close to the surface of the current collector 1 and the second slurry is located on the surface of the first slurry. After completing the single-sided coating, the coating is repeated once to complete the double-sided coating and obtain the lithium-sulfur battery electrode.

[0087] Examples 2 to 11 and Comparative Example 1 are based on the steps of Example 1 with parameter changes. The specific parameters changed are shown in Table 1. Among them, sulfur content refers to the proportion of the mass of elemental sulfur in the first active material layer 2 to the total mass of the first active material layer 2, or the proportion of the mass of elemental sulfur in the second active material layer 3 to the total mass of the second active material layer 3; total sulfur refers to the proportion of the total mass of elemental sulfur in the first active material layer 2 and the second active material layer 3 to the total mass of the first active material layer 2 and the second active material layer 3. In each example, the part of the sulfur content that is increased or decreased is replaced by porous activated carbon, that is, the content of conductive agent and binder in the first active material layer 2 and the second active material layer 3 remains unchanged.

[0088] Table 1

[0089]

[0090] I. Assembly of Pouch Batteries

[0091] The lithium-sulfur battery electrodes from Examples 1-11 and Comparative Example 1 of this invention were baked, die-cut, and assembled with a separator and lithium-plated copper foil into a soft-pack battery. The electrolyte was a commonly used 1.0M LiTFSI and 0.1M LiNO3 (solvent: DME:DOL = 1:1 Vol%).

[0092] II. Performance Testing

[0093] The prepared pouch cells were tested for energy density, 5C rate discharge capacity retention, and 100-cycle capacity retention. The test results are shown in Table 2. The test conditions were as follows:

[0094] Energy density: The soft-pack battery was charged and discharged at a rate of 0.2C within a voltage range of 1.6 to 2.3V, and the discharge energy of the battery was recorded. Then, the volume was measured by the water displacement method to obtain the volume of the battery. The energy density was obtained by dividing the discharge energy by the volume.

[0095] 5C rate discharge capacity retention rate: Charge the battery at a 1C rate to 2.3V to obtain the charging capacity, then discharge the battery at a 5C rate to 1.6V to obtain the discharging capacity. Divide the discharging capacity by the charging capacity to obtain the 5C rate discharge capacity retention rate.

[0096] 100-cycle capacity retention: The battery is charged and discharged at a rate of 0.2C within a voltage range of 1.6 to 2.3V for 100 cycles. The discharge capacity of the battery in the first cycle and the discharge capacity in the 100th cycle are recorded. The 100-cycle capacity retention is obtained by dividing the discharge capacity in the 100th cycle by the discharge capacity in the first cycle.

[0097] Table 2

[0098]

[0099]

[0100] As can be seen from Examples 1-11 above, the lithium-sulfur battery electrode of the present invention has a first active material layer 2 and a second active material layer 3 with a sulfur content gradient distribution in the thickness direction. By increasing the sulfur content in the active material layer near the current collector 1 and decreasing the sulfur content in the active material layer away from the current collector 1, the energy density of the lithium-sulfur battery is guaranteed, while the shuttle effect caused by the dissolution of sulfur from the active material from the electrode surface into the electrolyte is suppressed, thus slowing down the self-discharge and capacity decay of the lithium-sulfur battery and improving the energy density, rate performance and cycle stability of the lithium-sulfur battery electrode.

[0101] A comparison of Examples 1-9 shows that the thickness of the first active material layer 2 and the second active material layer 3, as well as the sulfur content distribution in each layer, affect the energy density, rate performance, and cycle stability of the lithium-sulfur battery electrode. Compared to Example 3, in Example 7, the thickness of each layer remains unchanged, and the sulfur content in the second active material layer 3 also remains unchanged. However, the sulfur content in the first active material layer 2 is lower, which affects the cell's energy density. Although the rate performance and cycle performance of Example 7 are improved, its energy density is 60 Wh / L lower than that of Example 3. In Examples 8-9, the first active material layer 2 remains unchanged, but the sulfur content in the second active material layer 3 changes. In Example 8, the lower sulfur content improves electrical performance but reduces energy density. In Example 9, the higher sulfur content leads to a decrease in electrical performance. Therefore, Example 3 has better overall performance.

[0102] Furthermore, through a comparison between Examples 1-6, it can be seen that Example 3, by using a specific sulfur content and specific thicknesses of the first active material layer 2 and the second active material layer 3, achieves the highest 5C rate discharge capacity retention rate and 100-cycle capacity retention rate under the premise that the total sulfur content remains unchanged and the battery energy density is the same, thus exhibiting the best overall electrochemical performance. In contrast, even if the sulfur content and the thickness of each layer are adjusted in Examples 1 and 6 to maintain the total sulfur content unchanged, although the battery energy density is the same as in Example 3, its rate performance and stability will decrease. Therefore, compared with Examples 1 and 6, Example 3 has the best overall electrochemical performance.

[0103] The comparison between Example 3 and Comparative Example 1 shows that Comparative Example 1 lacks a sulfur gradient structure and fails to further regulate the sulfur content and thickness of the two layers, thus failing to leverage the synergistic effect of the first active material layer 2 and the second active material layer 3. Even though the total amount of sulfur is exactly the same as in Example 3, its rate of return and cycle performance are significantly worse than those in Example 3.

[0104] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-sulfur battery pole piece, characterized by, The lithium-sulfur battery pole piece comprises a current collector and a first active material layer arranged on at least one side surface of the current collector, and a second active material layer arranged on the side surface away from the current collector; The first active material layer and the second active material layer each comprise sulfur and carbon, and the content of sulfur in the first active material layer is greater than that in the second active material layer. The content of sulfur in the first active material layer is 90-94% based on the mass of the first active material layer. The content of sulfur in the second active material layer is 60-75% based on the mass of the second active material layer. The thickness of the first active material layer is 130-150 μm, and the thickness of the second active material layer is 30-50 μm. The total content of sulfur in the first active material layer and the second active material layer is 85-90% based on the total mass of the first active material layer and the second active material layer.

2. The lithium-sulfur battery pole piece of claim 1, wherein, The first active material layer and / or the second active material layer further comprise a conductive agent and a binder.

3. The lithium-sulfur battery pole piece of claim 2, wherein, The conductive agent comprises any one or a combination of at least two of multi-walled carbon nanotubes, single-walled carbon nanotubes and SP.

4. The lithium-sulfur battery pole piece of claim 2, wherein, The binder comprises carboxymethyl cellulose and / or butadiene-styrene rubber.

5. The lithium-sulfur battery pole piece of claim 1, wherein, The carbon comprises porous active carbon.

6. The lithium-sulfur battery pole piece of claim 2, wherein, The content of the conductive agent in the first active material layer is 1-8% based on the mass of the first active material layer.

7. The lithium-sulfur battery pole piece of claim 2, wherein, The content of the binder in the first active material layer is 1-4% based on the mass of the first active material layer.

8. The lithium-sulfur battery pole piece of claim 1, wherein, The total content of sulfur and carbon in the second active material layer is 88-95% based on the mass of the second active material layer.

9. The lithium-sulfur battery pole piece of claim 2, wherein, The content of the conductive agent in the second active material layer is 1-8% based on the mass of the second active material layer.

10. The lithium-sulfur battery pole piece of claim 2, wherein, The content of the binder in the second active material layer is 1-4% based on the mass of the second active material layer.

11. The method of making a lithium-sulfur battery pole piece according to any one of claims 1-10, wherein, The preparation method comprises: Preparation of a first slurry and a second slurry respectively, coating the first slurry on at least one side surface of the current collector, and coating the second slurry on the surface of the first slurry to obtain a lithium-sulfur battery pole piece. The first slurry and the second slurry each comprise sulfur and carbon, and the content of sulfur in the first slurry is greater than that in the second slurry.

12. The method of claim 11, wherein, The first slurry and the second slurry further comprise a conductive agent, a binder and a solvent.

13. The preparation method according to claim 11, characterized in that, The mass of the solvent in the first slurry accounts for 40-60% of the total mass of the first slurry.

14. The method of claim 11, wherein, The mass of the solvent in the second slurry accounts for 40-60% of the total mass of the second slurry.

15. A lithium-sulfur battery, characterized by, The positive electrode material of the lithium-sulfur battery adopts the lithium-sulfur battery pole piece according to any one of claims 1-10.

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