A lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization and a preparation method thereof

Abstract

The application discloses a lithium-sulfur battery gel electrode based on PECA-N slow release polymerization and a preparation method thereof, relates to the technical field of lithium-sulfur battery preparation, and is characterized in that, in the technical route of pre-freezing and low-temperature polymerization, the slow release polymerization of ethyl cyanoacrylate is realized by taking nitrogen-methyl pyrrolidone as an initiator, and the obtained polymer polyethyl cyanoacrylate (PECA-N) is used to prepare a gel electrode, so that the utilization rate of sulfur and the performance of the battery can be obviously improved, the stability of the electrode structure and the cycle life are greatly enhanced, and the occurrence of the "shuttle effect" is obviously slowed down.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium-sulfur battery preparation, and particularly relates to a lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization and a preparation method thereof. BACKGROUND

[0002] The global energy structure is accelerating the transformation to renewable energy, and the efficient storage of intermittent energy sources such as wind and solar energy has become a key. Lithium-sulfur batteries are considered as one of the core candidates for the next generation of large-scale energy storage technology because of their theoretical energy density ( ) and specific capacity ( ) far exceeding those of traditional lithium-ion batteries, and the abundant sulfur raw material reserves, low cost and environmental friendliness. However, its commercialization process still faces three major bottlenecks: first, the active material sulfur and the discharge product (such as Li2S) have extremely poor electrical conductivity, which leads to slow reaction kinetics and insufficient sulfur utilization; second, the sulfur positive electrode will undergo significant volume expansion during charging and discharging, and the volume change in this reaction process will affect the internal structure of the electrode to change, leading to the loss of contact between the active material and other positive electrode materials (conductive agent, binder network, etc.), the current collector, and macroscopically, the electrode sheet may crack, powder and fall off, resulting in capacity attenuation and reduced cycle stability of the battery; third, the "shuttle effect" that plagues researchers. Specifically, during the discharge process of the lithium-sulfur battery, the long-chain polysulfide (such as Li2S8, Li2S6) generated is easily dissolved in the battery electrolyte and migrates to the lithium metal negative electrode, where it is reduced to short-chain polysulfide (such as Li2S4) on the negative electrode surface, and then diffuses back to the positive electrode to be oxidized. In this cycle, the active material sulfur will irreversibly lose, and a lithium sulfide deposition layer will form on the surface of the lithium metal negative electrode, and this deposition layer is also insulating. The "shuttle effect" is currently the cause of the decrease in battery coulomb efficiency and short cycle life. To break through these bottlenecks, the research community has developed various modification strategies, but the existing technologies still have significant limitations, especially in the overall structural design and functional synergistic regulation of the electrode.

[0003] The positive electrode is the core place of lithium-sulfur battery electrochemical reaction, and its performance directly determines the overall performance of the battery. The existing positive electrode modification methods are mainly divided into two categories: conductive / adsorption material composite, which is combined with porous carbon (such as mesoporous carbon, carbon nanotube), metal compound (such as TiO2, MnO2, MoS2) to improve the conductivity and polysulfide adsorption capacity. For example, Chinese patent CN110098375A discloses a method for modifying a sulfur positive electrode with a cyano polymer, which forms a cyano polymer coating (cyanoacrylate is scraped onto the sulfur positive electrode, and a poly cyanoacrylate coating is formed in the air under the initiation of water) on the surface of the sulfur positive electrode by physical coating such as scraping and spinning. The polar interaction between cyano and polysulfide is used to inhibit the shuttle effect. However, this technology has the following key limitations: the coating has weak adhesion to the substrate, relies on physical surface modification, and lacks chemical anchoring between the coating and the sulfur positive active material and current collector, which is prone to peeling under the action of long-term volume expansion, leading to polysulfide leakage and rapid capacity decay; the three-dimensional network is missing, the volume expansion suppression ability is poor, the coating is a two-dimensional planar structure, which cannot build a dynamic buffer space, and it is difficult to relieve the electrode cracks caused by sulfur particle expansion; the polymer synthesis process is limited, the conventional dissolution-coating method is used, the polymer molecular weight distribution is wide, and the chain segment arrangement is disordered, resulting in low coating ionic conductivity and limiting sulfur utilization; the function is single, and the dynamic and mechanical stability are not solved simultaneously, the shuttle is only inhibited by cyano chemical adsorption, and the ion transmission channel is not constructed, leading to serious capacity decay at high rate.

[0004] To inhibit polysulfide shuttle, electrolyte and separator modification become auxiliary means, but also have inherent defects: in electrolyte modification, although solid electrolyte (such as polymer electrolyte, sulfide electrolyte) can block polysulfide diffusion, the room temperature ionic conductivity is much lower than that of liquid electrolyte, resulting in poor battery rate performance. In the modification of the separator, the carbon material and metal compound coating are coated on the surface of the commercial separator, which can delay the diffusion of polysulfide, but the increase in coating thickness leads to the increase of battery internal resistance, and the interface adhesion between the coating and the separator substrate is weak, which is easy to fall off during the cycle process, and cannot play a long-term stable role.

[0005] It can be seen that the existing research focuses on the local optimization of a single component, and the attention to the overall structure design of the electrode is seriously insufficient. The electrode architecture as the "skeleton" of the electrochemical reaction, its mechanical stability determines the structural integrity in the battery cycle process, and the functional design affects the migration and conversion of polysulfides, the synergistic regulation of the two is the key to improve the comprehensive performance of lithium-sulfur battery. However, there are two major gaps in current technology: the lack of synergy between mechanical support and chemical adsorption, existing electrodes cannot provide dynamic buffering (to adapt to volume expansion) and polar adsorption (to inhibit shuttling) at the same time, leading to the separation of active materials and conductive network during the cycle process, and polysulfide leakage; the construction of ion transport channels and three-dimensional network is insufficient, traditional electrodes rely on linear polymer binders (such as PVDF), which only play a physical bonding role and do not form continuous ion transport channels, resulting in low sulfur utilization and poor rate performance. This "headache medicine head, foot pain medicine foot" optimization mode makes it difficult for lithium-sulfur batteries to break through the "high sulfur loading-high cycle stability-high rate performance" paradox, which seriously restricts their transformation from laboratory research to industrial application.

[0006] In view of the above defects of the prior art, the present application proposes a gel electrode scheme based on cyanacrylate slow-release polymerization. By designing a three-dimensional gel network with dynamic mechanical support and chemical regulation ability, the synergistic optimization of sulfur utilization rate improvement, volume expansion buffering and polysulfide anchoring is realized, which breaks through the bottleneck of existing technology from the perspective of electrode structure and provides a new solution for the commercial application of lithium-sulfur batteries. SUMMARY

[0007] The present application discloses a lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization and a preparation method thereof, to solve the technical problems of low sulfur utilization and poor rate performance existing in the prior art.

[0008] The technical scheme adopted by the present application is as follows:

[0009] A preparation method of a polymer PECA-N, comprising the following steps:

[0010] (1) Pre-freeze cyanacrylate monomer and initiator nitrogen-methyl pyrrolidone in an environment of-10℃~10℃;

[0011] (2) Under the refrigeration condition of-10℃~10℃, first put the nitrogen-methyl pyrrolidone into the stirring container, stir at a lower speed of 100~500 RPM and keep the reaction environment refrigerated, slowly add the pre-frozen cyanacrylate, after the addition is completed, adjust the stirring speed to 500~1000 RPM and keep for 30 seconds, and the polymer PECA-N can be obtained;

[0012] In step (2), the volume ratio of cyanacrylate monomer to nitrogen-methyl pyrrolidone is 1:1~30.

[0013] More preferably, the volume ratio of ethyl cyanoacrylate monomer to N-methyl pyrrolidone in step (2) is 1:6.

[0014] The polymer PECA-N obtained by the preparation method of the polymer PECA-N.

[0015] A lithium-sulfur battery gel electrode, comprising a current collector and a positive electrode composite coated on the current collector, the positive electrode composite comprising a sulfur / carbon mixture, conductive carbon black, a polymer PECA-N and N-methyl pyrrolidone as a solvent, the polymer PECA-N being prepared by the preparation method of the polymer PECA-N, the mass ratio of the sulfur / carbon mixture, the conductive carbon black and the polymer PECA-N being 6-8:1-3:1-31.

[0016] The preparation method of the gel electrode, comprising the following steps:

[0017] (1) preparing a sulfur / carbon mixture;

[0018] (2) mixing the sulfur / carbon mixture, the conductive carbon black and the polymer PECA-N, adding N-methyl pyrrolidone as a solvent, and stirring uniformly to obtain a positive electrode slurry;

[0019] (3) coating the positive electrode slurry on a current collector, drying and cutting to obtain a positive electrode sheet;

[0020] (4) infiltrating the positive electrode sheet with an electrolyte, causing the positive electrode composite to undergo secondary gelation, thereby obtaining a lithium-sulfur battery gel electrode.

[0021] Further, the preparation process of the sulfur / carbon mixture in step (1) is as follows: first, mix nano-sulfur and conductive carbon black at a mass ratio of 3:1, then melt the sulfur at 155-165°C for 6 h to obtain the sulfur / carbon mixture.

[0022] Further, in step (3), a coating machine is used to coat the positive electrode slurry on the current collector with a doctor blade having a thickness of 50-1000 microns.

[0023] Further, the diameter of the positive electrode sheet obtained by cutting in step (3) is 13 mm.

[0024] Further, the electrolyte in step (4) comprises a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether at a volume ratio of 1:1, and the solvent also contains 1.0 M lithium bis(trifluoromethane)sulfonamide and 2% lithium nitrate by mass percentage.

[0025] A lithium-sulfur battery comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode being the above-mentioned gel electrode or being prepared by the above-mentioned preparation method of the gel electrode.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] 1、The present application uses nitrogen-methyl pyrrolidone as an initiator, realizes the release polymerization of ethyl cyanoacrylate in the pre-freezing and low-temperature polymerization technical route, and obtains the polymer polyethyl cyanoacrylate (PECA-N), which has the advantages of good processability and high viscosity compared with traditional water-initiated polyethyl cyanoacrylate (PECA-W), and can be directly mixed with sulfur / carbon mixture and conductive carbon black to form a slurry with the help of a proper amount of nitrogen-methyl pyrrolidone solvent; the PECA-N preparation process is simple, and the polymerization degree is controllable at low temperature, so it has a popular prospect.

[0028] 2、The present application uses PECA-N prepared by using nitrogen-methyl pyrrolidone as an initiator, pre-freezing and low-temperature polymerization to prepare a gel electrode, which can significantly improve the utilization rate of sulfur and the performance of the battery, and the secondary gelation enables the prepared gel electrode to form a three-dimensional network structure that can guide ions, providing an efficient ion transmission channel for the active material sulfur, effectively improving the actual use rate of sulfur, and the lithium-sulfur battery assembled by the gel electrode prepared from PECA-N has a discharge specific capacity improvement of 72% after 150 cycles of charging and discharging compared with the lithium-sulfur battery assembled by the electrode prepared from traditional PVDF, significantly solving the problem of insufficient power caused by slow reaction kinetics;

[0029] 3、The present application uses PECA-N prepared by using nitrogen-methyl pyrrolidone as an initiator, pre-freezing and low-temperature polymerization to prepare a gel electrode, which greatly enhances the stability of the electrode structure and the cycle life: the adaptive dynamic elastic deformation ability of the polymer PECA-N gel network can obviously adapt to the volume expansion of the lithium-sulfur battery positive electrode during the charging and discharging process compared with the traditional linear polymer PVDF, and the active material is firmly fixed through the multiple effects of the gel network, avoiding electrode pulverization and falling off, after 150 cycles, the battery pole piece assembled by the gel electrode has a smooth appearance, but the PVDF electrode has obvious cracks, and the cycle decay rate of the batteries assembled by the two can also be consistent with the improvement of the stability of the battery pole piece by the gel network, significantly improving the service life of the battery;

[0030] 4、The application utilizes PECA-N prepared by using nitrogen-methyl pyrrolidone as an initiator, pre-freezing and low-temperature polymerization, and the prepared gel electrode significantly slows down the occurrence of the "shuttle effect": the dense network structure of the gel network composed of the polymer PECA-N blocks the diffusion of part of the polysulfides from the perspective of physical confinement, and the rich polar functional groups such as cyano form strong chemical adsorption on the polysulfides, and the synergistic effect of the physical confinement and the chemical adsorption forms the limitation of the gel layer to the polysulfides, which firmly limits the polysulfides in the interior of the gel, and greatly limits the occurrence of the "shuttle effect". The coulombic efficiency of the battery is stably above 95%;

[0031] 5、The application utilizes PECA-N prepared by using nitrogen-methyl pyrrolidone as an initiator, pre-freezing and low-temperature polymerization, and the prepared gel electrode, from the perspective of the gel electrode structure, realizes the synergy of performance optimization and cost optimization, compared with the relatively single modification technology in the current lithium-sulfur battery research, the new type of lithium-sulfur battery gel electrode technology designed and prepared based on the cyanoacrylate slow-release polymerization method does not need complex positive electrode composite process, high-priced electrolyte additives or separator layers, and solves the mechanical stability of the electrode and the functional design meeting the demand of lithium-sulfur batteries from the perspective of the design of the motor structure, and both high performance and commercial feasibility are considered. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a physical picture of PECA-N (left) prepared in Example 1 and cyanoacrylate monomer (right) used;

[0033] Figure 2 It is a physical picture of PECA-W prepared in Example 1 using water as an initiator;

[0034] Figure 3 It is an infrared spectrum of the initiator nitrogen-methyl pyrrolidone, the raw material cyanoacrylate monomer and PECA-N and PECA-W;

[0035] Figure 4 It is an aluminum current collector coated with PECA-N after drying in Example 2;

[0036] Figure 5 It is a display process diagram of the secondary gelation experiment in Example 2;

[0037] Figure 6 It is a freeze SEM imaging diagram of the PECA-N gel electrode prepared in Example 3;

[0038] Figure 7 It is a result diagram of the electrode material made of PECA-N in Example 3 characterized by the synchrotron X-ray three-dimensional nanometer imaging technology;

[0039] Figure 8 Results of the synchrotron X-ray three-dimensional nanotomography characterization of the electrode material prepared in Example 3 using PVDF;

[0040] Figure 9 Graph of the discharge specific capacity vs. cycle number of two lithium-sulfur batteries prepared using the polymer PECA-N and the comparative sample PVDF at 0.5 C rate;

[0041] Figure 10 Graph of the charge-discharge curves of the lithium-sulfur battery prepared using the polymer PECA-N at 0.5 C rate at cycle 1 and cycle 150.

[0042] Figure 11 Graph of the charge-discharge curves of the lithium-sulfur battery prepared using the comparative sample PVDF at 0.5 C rate at cycle 1 and cycle 150. DETAILED DESCRIPTION

[0043] The advantages and various effects of the present application will be more clearly apparent from the following detailed description of the application in conjunction with the specific embodiments and examples. It should be understood by those skilled in the art that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present application.

[0044] Throughout this specification, unless otherwise specifically indicated otherwise, the terms used herein are understood in the ordinary sense as used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. In case of conflict, the present specification prevails.

[0045] Unless otherwise specifically indicated otherwise, the various raw materials, reagents, instruments and gel electrodes used in the present application can be purchased on the market or can be prepared by existing methods.

[0046] The present application is further illustrated below in conjunction with the specific experimental examples and comparative examples.

[0047] Example 1

[0048] This example investigates the polymerization process of ethyl cyanoacrylate.

[0049] First, with ethyl cyanoacrylate as a monomer, and nitrogen-methyl pyrrolidone as an initiator, PECA-N was prepared: ethyl cyanoacrylate and nitrogen-methyl pyrrolidone were pre-frozen to a temperature of 0°C in an environment of 0°C, nitrogen-methyl pyrrolidone was placed in a stirring container under refrigeration, and the reaction environment was kept refrigerated using a stirring speed of 500 RPM. After the speed was stabilized, the pre-frozen ethyl cyanoacrylate was slowly added dropwise, the reaction container was tightly capped after the addition was completed, and the stirring speed was increased to 1000 RPM for 30 seconds to obtain the polymer PECA-N. The physical picture of PECA-N and ethyl cyanoacrylate monomers at room temperature is shown in Figure 1 As can be seen from the figure (PECA-N was prepared from ethyl cyanoacrylate monomer and nitrogen-methyl pyrrolidone at a volume ratio of 1:6), PECA-N is in a gel state at room temperature. Different volume ratios of the two materials were mixed at different temperatures, and the regulated polymers PECA-N were synthesized as shown in Figure 1 The repeated experiments all obtained the target substance, proving the high reproducibility of the polymerization method.

[0050] Meanwhile, PECA-W was prepared under the same conditions with ethyl cyanoacrylate as a monomer and water as an initiator, and the physical picture of PECA-W at room temperature is shown in Figure 2 As can be seen, PECA-W is a flaky solid substance at room temperature, rather than a gel state, and it is difficult to mix it with nano-sulfur, conductive carbon black, and nitrogen-methyl pyrrolidone to form a uniform slurry. PECA-W exhibits poor processability, indicating that PECA-N and PECA-W have different physicochemical properties.

[0051] The obtained products PECA-N and PECA-W were tested by infrared spectrum, and the results are shown in Figure 3 The initiator nitrogen-methyl pyrrolidone and ethyl cyanoacrylate monomer were compared with the products PECA-N and PECA-W, respectively. PECA-N and PECA-W both have certain intensity bands near 2990, 1750, 1255, and 2250 cm -1 , and the peaks of 3130 and 1665 cm -1 disappear, indicating that compared with water as an initiator, nitrogen-methyl pyrrolidone also initiates the rupture of the hydrocarbon double bond of ethyl cyanoacrylate monomer, retains the anionic polymerization of the characteristic functional groups of ester and cyano groups, proves that nitrogen-methyl pyrrolidone indeed initiates the successful polymerization of ethyl cyanoacrylate, and the difference in the physicochemical properties of PECA-N and PECA-W may be because nitrogen-methyl pyrrolidone participates in the polymerization process.

[0052] Example 2

[0053] Example 2 Figure 4 A second gelation verification test was performed on PECA-N prepared from ethyl cyanoacrylate monomer and N-methyl pyrrolidone in a volume ratio of 1:6. PECA-N prepared in Example 1 was used as the material, and a 1000-micron-thick doctor blade was used to uniformly coat the material on a blank aluminum current collector. The aluminum current collector coated with PECA-N was then placed in a vacuum oven for 12 h. After drying, the aluminum current collector was cut with a scalpel, and the intact PECA-N film was kept dry. The aluminum current collector was then placed in an electrolyte solution for about 3 min. The electrolyte solution was a 1:1 mixture of 1,3-dioxolane (DOL) and dimethoxyethane (DME) containing 1.0 M lithium bis(trifluoromethane)sulfonamide (LiTFSI) and 2% lithium nitrate (LiNO3). Then, the two ends of the aluminum current collector were lifted and slowly stretched. As shown in Figure 5 , the PECA-N film that was previously in a dry state was clearly observed to be secondarily gelled, and the gel exhibited stretchability and gloss in the gelled state. This example successfully verified that the polymer PECA-N can be secondarily gelled.

[0054] Example 3

[0055] In this example, a battery was assembled using PECA-N prepared from ethyl cyanoacrylate monomer and N-methyl pyrrolidone in a volume ratio of 1:6, and the performance of the battery was investigated.

[0056] First, a gel electrode was prepared as follows:

[0057] (1) A sulfur / carbon mixture was prepared by mixing nano-sulfur and conductive carbon black in a mass ratio of 3:1, and then melting the sulfur at 155-165 °C for 6 h to obtain the sulfur / carbon mixture;

[0058] (2) The sulfur / carbon mixture, conductive carbon black, and PECA-N prepared in Example 1 (ethyl cyanoacrylate monomer and N-methyl pyrrolidone were mixed in a volume ratio of 1:6, and N-methyl pyrrolidone was added as a solvent to obtain a positive electrode slurry. The mass ratio of the sulfur / carbon mixture, conductive carbon black, and polymer PECA-N was 8:1:7;

[0059] (3) A coating machine was used to coat the positive electrode slurry on a current collector with a doctor blade thickness of 50-1000 microns. After drying at room temperature for 1-24 h, the current collector was placed in a vacuum drying oven overnight. After drying, a sheet puncher was used to cut the positive electrode into a 13-mm-diameter electrode sheet;

[0060] (4) The positive electrode sheet is infiltrated with an electrolyte, which is a mixed solution of 1,3-dioxolane (DOL) and dimethoxyethane (DME) with a volume ratio of 1:1, containing 1.0 M lithium bis(trifluoromethane)sulfonamide (LiTFSI) and 2% lithium nitrate (LiNO3), so that the positive electrode composite material is secondarily gelled, and a lithium-sulfur battery gel electrode is obtained. We perform a frozen SEM characterization on the gel electrode, and the results are shown in FIG. 8. It can be seen that the electrode has a clear three-dimensional morphology. Figure 6

[0061] Then, a battery is assembled. The lithium-sulfur battery gel electrode prepared above is used as the positive electrode, and a commercial lithium metal round sheet is used as the negative electrode. A lithium-sulfur battery containing a positive electrode sheet, a negative electrode sheet, and an electrolyte is assembled in a Mikron glove box, and the liquid sulfur ratio is controlled at 10 μL·mg -1 The electrolyte is a mixed solution of 1,3-dioxolane (DOL) and dimethoxyethane (DME) with a volume ratio of 1:1, containing 1.0 M lithium bis(trifluoromethane)sulfonamide (LiTFSI) and 2% lithium nitrate (LiNO3).

[0062] At the same time, the same electrode preparation method is used to prepare a battery electrode sheet (i.e., PECA-N is replaced by PVDF) of the same raw material ratio under the same conditions. Before the electrochemical test, we use the synchrotron X-ray three-dimensional nanometer imaging technology to characterize the two kinds of electrode materials, and the results are shown in FIG. 9. The electrode material prepared using PECA-N presents a more dense and uniform three-dimensional network feature (red structure in the figure), and the distribution of sulfur (yellow part in the figure) is also uniform and dispersed. The electrode material prepared using PVDF presents an unsatisfactory result, and the electrode structure (green structure in the figure) appears local stacking, and the distribution of sulfur (yellow part in the figure) also obviously agglomerates with the stacking of the structure. The uniform and dense three-dimensional network structure brought by PECA-N in the preparation of the electrode slurry gives the active material sulfur better dispersibility, which means that this electrode structure design provides more active sites for the performance of the lithium-sulfur battery, thereby improving the capacity, rate performance, and cycle life of the lithium-sulfur battery. Figure 7~8

[0063] Then, lithium-sulfur batteries of the same negative electrode and electrolyte are assembled under the same conditions. The electrochemical tests are performed on the two batteries and compared, and the results are shown in FIG. 10. The initial specific capacity of the PECA-N battery can reach 1005 mAh·g -1 The capacity retention rate is 88% after 150 cycles. Compared with the PVDF battery prepared under the same conditions, the PECA-N battery has obvious advantages. Figure 9~11 ​​​

[0064] Finally, it is also important to note that the term "comprising" or "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or gel electrode that comprises a list of elements is not necessarily limited to those elements, but can include other elements not expressly listed or inherent to such process, method, article, or gel electrode. While the preferred embodiments of the application have been described, additional variants and modifications can be suggested to those skilled in the art in the light of the basic inventive concept. It is, therefore, intended that the appended claims be interpreted as including all such variants and modifications as fall within the true scope of the application.

[0065] The above embodiments only express the specific implementation of the present application, which is described in more detail and specifically, but it should not be understood as the limitation of the protection scope of the present application. It should be noted that for those skilled in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A lithium-sulfur battery gel electrode, characterized in that, The device includes a current collector and a positive electrode composite material coated on the current collector. The positive electrode composite material comprises a sulfur / carbon mixture, conductive carbon black, polymer PECA-N, and nitrogen-methylpyrrolidone as a solvent. The mass ratio of the sulfur / carbon mixture, conductive carbon black, and polymer PECA-N is 6~8:1~3:1~31. The preparation process of the polymer PECA-N includes the following steps: (1) Pre-freeze the ethyl cyanoacrylate monomer and the initiator N-methylpyrrolidone in an environment of -10℃ to 10℃; (2) Under the refrigeration conditions of -10℃ to 10℃, first put nitrogen-methylpyrrolidone into a stirring container, stir at a low speed of 100~500RPM and keep the reaction environment refrigerated, slowly add pre-frozen ethyl cyanoacrylate, and after the addition is completed, adjust the stirring speed to 500~1000RPM and keep it for 30 seconds to obtain polymer PECA-N; In step (2), the volume ratio of ethyl cyanoacrylate monomer to nitrogen-methylpyrrolidone is 1:1~30.

2. The lithium-sulfur battery gel electrode as described in claim 1, characterized in that, In step (2), the volume ratio of ethyl cyanoacrylate monomer to N-methylpyrrolidone is 1:

10.

3. The method for preparing a lithium-sulfur battery gel electrode as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of sulfur / carbon mixture; (2) The sulfur / carbon mixture, conductive carbon black and polymer PECA-N are mixed, and nitrogen-methylpyrrolidone is added as a solvent. The mixture is stirred evenly to obtain a positive electrode slurry. (3) The positive electrode slurry is coated onto the current collector, dried, and then cut to obtain a positive electrode sheet; (4) The positive electrode sheet is immersed in the electrolyte to cause the positive electrode composite material to undergo secondary gelation, thereby obtaining the lithium-sulfur battery gel electrode.

4. The preparation method according to claim 3, characterized in that, Step (1) The preparation process of sulfur / carbon mixture is as follows: first, mix nano sulfur and conductive carbon black at a mass ratio of 3:1, and then melt sulfur at 155℃~165℃ for 6 hours to prepare sulfur / carbon mixture.

5. The preparation method according to claim 3, characterized in that, In step (3), a coating machine is used to apply the positive electrode slurry to the current collector with a scraper with a thickness of 50 to 1000 micrometers.

6. The preparation method according to claim 3, characterized in that, The diameter of the positive electrode obtained by cutting in step (3) is 13 mm.

7. The preparation method according to claim 3, characterized in that, The electrolyte in step (4) comprises a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and the solvent also contains 1.0 M lithium bis(trifluoromethane)sulfonamide and 2% lithium nitrate by mass percentage.

8. A lithium-sulfur battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the gel electrode according to claim 1 or 2 or a gel electrode prepared by the preparation method according to any one of claims 3 to 7.

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