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

Abstract

The invention discloses a lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization and a preparation method thereof, and relates to the technical field of lithium-sulfur battery preparation. Nitrogen-methyl pyrrolidone is used as an initiator, under the technical route of pre-freezing and low-temperature polymerization, the slow-release polymerization of ethyl cyanoacrylate is realized, and the obtained polymer poly (ethyl cyanoacrylate) (PECA-N) is used for preparing the lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization. The gel electrode prepared by the method can obviously improve the utilization rate of sulfur and the performance of the battery, greatly enhance the structural stability of the electrode, prolong the cycle life of the electrode, obviously slow down the shuttle effect, and solve the mechanical stability of the electrode and meet the functional design required by the lithium-sulfur battery from the design angle of the motor structure. And high performance and commercialization feasibility are both considered.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery preparation technology, specifically to a lithium-sulfur battery gel electrode based on PECA-N slow-release polymerization and its preparation method. Background Technology

[0002] The global energy structure is rapidly transitioning towards renewable energy, making the efficient storage of intermittent energy sources such as wind and solar power crucial. Lithium-sulfur batteries, due to their theoretical energy density (…),… ) and specific capacity ( Lithium-sulfur batteries far surpass traditional lithium-ion batteries, and with abundant, inexpensive, and environmentally friendly sulfur resources, they are considered one of the core candidates for next-generation large-scale energy storage technology. However, their commercialization process still faces three major bottlenecks: First, the active material sulfur and discharge products (such as Li2S) have extremely poor conductivity, leading to slow reaction kinetics and insufficient sulfur utilization. Second, the sulfur cathode undergoes significant volume expansion during charge and discharge. This volume change during the reaction process affects the internal structure of the electrode, causing contact failure between the active material and other cathode materials (conductive agents, binder networks, etc.) and current collectors. Macroscopically, this may manifest as cracks, powdering, and detachment of the electrode sheets, resulting in capacity decay and reduced cycle stability of the battery. Third, there is the troublesome "shuttle effect." Specifically, long-chain polysulfides (such as Li2S8 and Li2S6) generated during the discharge of lithium-sulfur batteries readily dissolve in the battery electrolyte and migrate towards the lithium metal anode, where they are reduced to short-chain polysulfides (such as Li2S4) on the anode surface, and then diffuse back to the cathode to be oxidized. In this cyclical process, the active material sulfur undergoes irreversible loss, while a lithium sulfide deposition layer forms on the surface of the negative electrode lithium metal, and this deposition layer is also insulating. The "shuttle effect" is currently the main cause of decreased battery coulombic efficiency and short cycle life. To overcome these bottlenecks, the scientific community has developed a variety of modification strategies, but existing technologies still have significant limitations, especially in the overall electrode structure design and functional synergistic regulation.

[0003] The cathode is the core site of electrochemical reactions in lithium-sulfur batteries, and its performance directly determines the overall performance of the battery. Existing cathode modification methods mainly fall into two categories: conductive / adsorption material composites, which combine sulfur with porous carbon (such as mesoporous carbon and carbon nanotubes) and metal compounds (such as TiO2, MnO2, and MoS2) to improve conductivity and polysulfide adsorption capacity. For example, Chinese patent CN110098375A discloses a method for modifying a sulfur cathode with a cyanopolymer. This method involves forming a cyanopolymer coating on the surface of the sulfur cathode using physical coating methods such as scraping and spin coating (ethyl cyanoacrylate is scraped onto the sulfur cathode, and a polycyanoacrylate coating is formed under the initiation of water in the air). The polar interaction between cyano groups and polysulfides is used to suppress the shuttle effect. However, this technology has the following key limitations: the coating has weak adhesion to the substrate, relying on physical coating for surface modification; the coating lacks chemical anchoring with the sulfur cathode active material and current collector, making it prone to peeling under long-term cyclic volume expansion, leading to polysulfide leakage and rapid capacity decay; the lack of a three-dimensional network results in poor volume expansion suppression; the coating is a two-dimensional planar structure, unable to construct a dynamic buffer space, making it difficult to alleviate electrode cracks caused by sulfur particle expansion; the polymer synthesis process is limited, using a conventional dissolution-coating method, resulting in a wide molecular weight distribution and disordered chain segment arrangement of the polymer, leading to low ionic conductivity of the coating and limiting sulfur utilization; and the function is singular, failing to synergistically address kinetic and mechanical stability, only suppressing shuttle through cyano chemical adsorption without considering the construction of ion transport channels, resulting in severe capacity decay at high rates.

[0004] To suppress polysulfide shuttle, electrolyte and separator modification has become an auxiliary method, but it also has inherent drawbacks: In electrolyte modification, although solid electrolytes (such as polymer electrolytes and sulfide electrolytes) can block polysulfide diffusion, their room temperature ionic conductivity is much lower than that of liquid electrolytes, resulting in poor battery rate performance. In separator modification, coating the surface of commercial separators with carbon materials or metal compounds can delay polysulfide diffusion, but the increased coating thickness leads to an increase in battery internal resistance, and the interfacial bonding between the coating and the separator substrate is weak, making it easy to detach during cycling and unable to function stably for a long time.

[0005] It is evident that current research largely focuses on the local optimization of individual components, with insufficient attention paid to the overall structural design of the electrode. As the "skeleton" of electrochemical reactions, the electrode architecture's mechanical stability determines the structural integrity during battery cycling, while its functional design influences the migration and transformation of polysulfides. The synergistic regulation of these two aspects is crucial for improving the overall performance of lithium-sulfur batteries. However, current technology suffers from two major gaps: First, the lack of synergistic integration between mechanical support and chemical adsorption. Existing electrodes cannot simultaneously provide dynamic buffering (to accommodate volume expansion) and polar adsorption (to suppress shuttle), leading to the detachment of active materials from the conductive network and polysulfide leakage during cycling. Second, insufficient construction of ion transport channels and three-dimensional networks. Traditional electrodes rely on linear polymer binders (such as PVDF), which only provide physical bonding and fail to form continuous ion transport channels, resulting in low sulfur utilization and poor rate performance. This piecemeal optimization approach makes it difficult for lithium-sulfur batteries to overcome the "high sulfur loading - high cycle stability - high rate performance" paradox, severely hindering their transformation from laboratory research to industrial applications.

[0006] To address the aforementioned shortcomings of existing technologies, this invention proposes a gel electrode solution based on the slow-release polymerization of ethyl cyanoacrylate. By designing a three-dimensional gel network that combines dynamic mechanical support and chemical regulation capabilities, synergistic optimization is achieved in improving sulfur utilization, buffering volume expansion, and anchoring polysulfides. This breakthrough in electrode structure overcomes existing technological bottlenecks and provides a novel solution for the commercial application of lithium-sulfur batteries. Summary of the Invention

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

[0008] The technical solution adopted in this invention is as follows: A method for preparing 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 100~500 RPM and keep the reaction environment refrigerated, slowly add pre-frozen ethyl cyanoacrylate, and after the addition is completed, adjust the stirring speed to 500~1000 RPM 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.

[0009] More preferably, in step (2), the volume ratio of ethyl cyanoacrylate monomer to N-methylpyrrolidone is 1:6.

[0010] The polymer PECA-N obtained by the above-described preparation method is PECA-N.

[0011] A lithium-sulfur battery gel electrode 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 polymer PECA-N is prepared by the method described above. The mass ratio of the sulfur / carbon mixture, conductive carbon black, and polymer PECA-N is 6~8:1~3:1~31.

[0012] The method for preparing the gel electrode 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.

[0013] Further, the preparation process of the sulfur / carbon mixture in step (1) is as follows: first, mix nano sulfur and conductive carbon black in a mass ratio of 3:1, and then melt the sulfur at 155℃~165℃ for 6 h to obtain the sulfur / carbon mixture.

[0014] Further, in step (3), a coating machine is used to apply the positive electrode slurry onto the current collector with a scraper with a thickness of 50 to 1000 micrometers.

[0015] Furthermore, the diameter of the positive electrode obtained by cutting in step (3) is 13 mm.

[0016] Further, 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.

[0017] A lithium-sulfur battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is a gel electrode as described above or prepared by the method for preparing a gel electrode as described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses N-methylpyrrolidone as an initiator to achieve the release polymerization of ethyl cyanoacrylate under a pre-freezing and low-temperature polymerization technical route. The resulting polymer, polyethyl cyanoacrylate (PECA-N), has advantages over traditional water-initiated polyethyl cyanoacrylate (PECA-W) in terms of good processability and high viscosity. With the help of an appropriate amount of N-methylpyrrolidone solvent, it can be directly mixed with sulfur / carbon mixtures and conductive carbon black to form a slurry. The preparation process of PECA-N is simple, and the degree of polymerization can be controlled at low temperatures, showing promising potential for widespread application.

[0019] 2. This invention utilizes PECA-N prepared by pre-freezing and low-temperature polymerization using nitrogen-methylpyrrolidone as an initiator to prepare a gel electrode, which can significantly improve the utilization rate of sulfur and the performance of the battery. The secondary gelation makes the prepared gel electrode form an ion-conducting three-dimensional network structure, providing an efficient ion transport channel for the active material sulfur, effectively improving the actual utilization rate of sulfur. The lithium-sulfur battery assembled with the gel electrode prepared by PECA-N has a 72% higher discharge specific capacity than the lithium-sulfur battery assembled with the electrode prepared by traditional PVDF after 150 charge-discharge cycles, which significantly solves the problem of insufficient power caused by slow reaction kinetics. 3. This invention utilizes PECA-N, prepared by pre-freezing and low-temperature polymerization using N-methylpyrrolidone as an initiator, to prepare a gel electrode that significantly enhances the stability of the electrode structure and cycle life. The adaptability and dynamic elastic deformation capability of the polymer PECA-N gel network can significantly adapt to the volume expansion of the lithium-sulfur battery cathode during charging and discharging compared to the traditional linear polymer PVDF. Through the multiple functions of the gel network, the active material is firmly fixed, preventing electrode pulverization and detachment. After 150 cycles, the battery electrode assembled with the gel electrode has a smooth morphology, while the PVDF electrode shows obvious cracks. At the same time, the cycle decay rate of the batteries assembled with the two can be consistent with the improvement of battery electrode stability by the gel network, significantly improving the battery life. 4. This invention utilizes PECA-N, prepared by pre-freezing and low-temperature polymerization using N-methylpyrrolidone as an initiator, to prepare a gel electrode that significantly mitigates the "shuttle effect." The dense network structure of the PECA-N polymer gel effectively confines some polysulfides, blocking their diffusion. Abundant polar functional groups, such as cyano groups, strongly chemisorb polysulfides through coordination. This synergistic effect of physical confinement and chemisorption restricts the polysulfides within the gel layer, effectively limiting the "shuttle effect." The coulombic efficiency of the battery remains consistently above 95%. 5. This invention utilizes PECA-N prepared by pre-freezing and low-temperature polymerization using nitrogen-methylpyrrolidone as an initiator to prepare a gel electrode. The gel electrode design, starting from the electrode structure, achieves synergistic performance and cost optimization. Compared with the relatively simple modification technology in current lithium-sulfur battery research, the novel lithium-sulfur battery gel electrode technology designed and prepared by this invention based on the ethyl cyanoacrylate slow-release polymerization method does not require complex cathode composite processes, expensive electrolyte additives, or separator layers. By starting from the design perspective of motor structure, it solves the problems of electrode mechanical stability and functional design that meets the requirements of lithium-sulfur batteries, thus taking into account both high performance and commercial feasibility. Attached Figure Description

[0020] Figure 1 The images show the physical samples of PECA-N (left) and the ethyl cyanoacrylate monomer used in Example 1 (right); Figure 2 The image shows a physical sample of PECA-W prepared using water as an initiator in Example 1. Figure 3 Infrared spectra of initiator N-methylpyrrolidone, raw material ethyl cyanoacrylate monomer and PECA-N, PECA-W; Figure 4 The aluminum current collector coated with PECA-N and dried in Example 2; Figure 5 This is a diagram illustrating the secondary gelation experiment in Example 2; Figure 6 This is a cryosurgery SEM image of the PECA-N gel electrode prepared in Example 3; Figure 7 The image shows the results of characterization of the electrode material made using PECA-N in Example 3 using synchrotron X-ray three-dimensional nanoimaging technology. Figure 8 The image shows the results of characterization of the electrode material made of PVDF in Example 3 using synchrotron X-ray three-dimensional nanoimaging technology. Figure 9 The discharge specific capacity versus cycle number plots for two lithium-sulfur batteries prepared using polymer PECA-N and control sample PVDF at 0.5 C rate; Figure 10 The first and 150th charge-discharge curves of a lithium-sulfur battery prepared using polymer PECA-N at a rate of 0.5 C are shown. Figure 11 The first and 150th charge-discharge curves of a lithium-sulfur battery prepared using the control sample PVDF at a 0.5 C rate are shown. Detailed Implementation

[0021] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0022] Throughout this specification, unless otherwise specified, the terminology used herein should be understood to have the meaning commonly 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 this invention pertains. In the event of any conflict, this specification shall prevail.

[0023] Unless otherwise specified, all raw materials, reagents, instruments and gel electrodes used in this invention can be purchased from the market or prepared by existing methods.

[0024] The present invention will be further illustrated below with specific experimental examples and comparative examples.

[0025] Example 1 This embodiment explores the polymerization process of ethyl cyanoacrylate.

[0026] First, PECA-N was prepared using ethyl cyanoacrylate as a monomer and N-methylpyrrolidone as an initiator: Ethyl cyanoacrylate and N-methylpyrrolidone were pre-frozen at 0°C. Under refrigeration, N-methylpyrrolidone was placed in a stirred container, stirred at 500 RPM while maintaining a refrigerated reaction environment. After the stirring speed stabilized, the pre-frozen ethyl cyanoacrylate was slowly added dropwise. After the addition was complete, the reaction container was tightly sealed, and the stirring speed was increased to 1000 RPM and maintained for 30 seconds to obtain the polymer PECA-N. A photograph of PECA-N and the ethyl cyanoacrylate monomer at room temperature is shown below. Figure 1 As shown in the figure (PECA-N was prepared from ethyl cyanoacrylate monomer and N-methylpyrrolidone in a volume ratio of 1:6), PECA-N is in a gel state at room temperature. The two materials with different volume ratios were mixed at different temperatures, and the resulting mixtures all yielded the desired gel state. Figure 1 The polymer PECA-N in the shown state was repeatedly tested and the target material was obtained in each test, which proves the high reproducibility of this polymerization method.

[0027] Meanwhile, we prepared PECA-W under the same conditions using ethyl cyanoacrylate as the monomer and water as the initiator. A physical image of PECA-W at room temperature is shown below. Figure 2As shown, PECA-W is a sheet-like solid at room temperature, rather than a gel, making it difficult to mix with nano-sulfur, conductive carbon black, and N-methylpyrrolidone to form a uniform slurry. The poor processability of PECA-W indicates that PECA-N and PECA-W have different physicochemical properties.

[0028] The obtained products PECA-N and PECA-W were subjected to infrared spectroscopy, and the results are as follows: Figure 3 As shown, the initiator N-methylpyrrolidone, ethyl cyanoacrylate monomer, and products PECA-N and PECA-W are compared. PECA-N and PECA-W both have values ​​of 2990, 1750, 1255, and 2250 cm⁻¹. -1 A spectral band of considerable intensity appeared nearby, while 3130 and 1665 cm⁻¹... -1 The disappearance of the peak indicates that, compared with water as an initiator, N-methylpyrrolidone also initiates the cleavage of the hydrocarbon double bond in the ethyl cyanoacrylate monomer, retaining the characteristic functional groups of the ester and cyano groups in the anionic polymerization reaction. This proves that N-methylpyrrolidone does indeed successfully initiate the polymerization reaction of ethyl cyanoacrylate. The difference in physicochemical properties between PECA-N and PECA-W may be because N-methylpyrrolidone participated in the polymerization process.

[0029] Example 2 In this embodiment, a secondary gelation verification experiment was conducted on PECA-N prepared by reacting ethyl cyanoacrylate monomer and N-methylpyrrolidone at a volume ratio of 1:6. Using PECA-N prepared in Example 1 as the material, a 1000-micron-thickness layer was uniformly coated onto a blank aluminum current collector using a scraper. The PECA-N-coated aluminum current collector was then placed in a vacuum oven and dried for 12 hours. The actual image of the dried aluminum current collector is shown below. Figure 4 As shown, the aluminum current collector was then incised with a scalpel while maintaining the integrity of the dry PECA-N film. Next, it was immersed in an electrolyte solution for approximately 3 minutes. This electrolyte solution was a 1:1 volume ratio mixture of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (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. Figure 5 As shown, we can clearly observe the secondary gelation of the previously dry PECA-N film, exhibiting stretchability and gloss in the gel state. This embodiment successfully verifies that the polymer PECA-N can achieve secondary gelation.

[0030] Example 3 In this embodiment, PECA-N was prepared by mixing ethyl cyanoacrylate monomer and N-methylpyrrolidone in a volume ratio of 1:6, and its battery was assembled and its performance was investigated.

[0031] First, the gel electrode is prepared, as follows: (1) Preparation of sulfur / carbon mixture: Nano sulfur and conductive carbon black are mixed at a mass ratio of 3:1, and then sulfur is melted at 155℃~165℃ for 6 h to prepare sulfur / carbon mixture; (2) The sulfur / carbon mixture, conductive carbon black and PECA-N (ethyl cyanoacrylate monomer and nitrogen-methylpyrrolidone in a volume ratio of 1:6) prepared in Example 1 are mixed, nitrogen-methylpyrrolidone as a solvent is added, and the mixture is stirred evenly to obtain a positive electrode slurry. The mass ratio of the sulfur / carbon mixture, conductive carbon black and polymer PECA-N is 8:1:7. (3) The positive electrode slurry is coated onto the current collector using a coating machine with a scraper to a thickness of 50-1000 micrometers. After drying at room temperature for 1-24 hours, it is placed in a vacuum drying oven overnight. After drying, it is cut into positive electrode sheets with a diameter of 13 mm using a die-cutting machine. (4) The positive electrode sheet was immersed in an electrolyte solution, which was a 1:1 volume ratio mixture of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) containing 1.0 M bis(trifluoromethane)sulfonamide lithium (LiTFSI) and 2% lithium nitrate (LiNO3). This caused secondary gelation of the positive electrode composite material, thus obtaining a lithium-sulfur battery gel electrode. We performed cryogenic SEM characterization on the gel electrode, and the results are as follows: Figure 6 As shown, the electrode has a distinct three-dimensional morphology.

[0032] Then, the battery was assembled, using the lithium-sulfur battery gel electrode prepared above as the positive electrode and commercial lithium metal wafers as the negative electrode. A lithium-sulfur battery containing a positive electrode, a negative electrode, and an electrolyte was assembled in a Micron glove box, with the liquid-sulfur ratio controlled at 10 μL·mg. -1 The electrolyte is a 1:1 mixture of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) containing 1.0 M lithium bis(trifluoromethane)sulfonamide (LiTFSI) and 2% lithium nitrate (LiNO3).

[0033] Simultaneously, using the same electrode preparation method and under the same conditions, battery electrodes with the same raw material ratio and PVDF as the binder were prepared (i.e., PECA-N was replaced with PVDF). Before conducting electrochemical tests, we characterized the two electrode materials using synchrotron X-ray three-dimensional nanoimaging technology, and the results are as follows: Figures 7-8As shown, the electrode material prepared using PECA-N exhibits a more dense and uniform three-dimensional network structure (red structure in the figure), with sulfur (yellow part in the figure) also being evenly and dispersed. In contrast, the electrode material prepared using PVDF does not show ideal results; the electrode structure (green structure in the figure) exhibits localized stacking, and the distribution of sulfur (yellow part in the figure) shows significant agglomeration due to this stacking. The uniform and dense three-dimensional network structure resulting from PECA-N in the electrode slurry preparation provides better dispersion of the active material sulfur. This means that this electrode structure design provides more active sites for the performance of lithium-sulfur batteries, thereby improving the capacity, rate performance, and cycle life of lithium-sulfur batteries.

[0034] Then, lithium-sulfur batteries with the same negative electrode and electrolyte were assembled under the same conditions. Electrochemical tests were performed on the two batteries and compared. The results are as follows: Figures 9-11 As shown, under 0.5 C cycling, the PECA-N battery achieves an initial charge-discharge specific capacity of 1005 mAh·g. -1 The above results show a capacity retention rate of 88% after 150 cycles. This demonstrates a significant advantage over PVDF batteries prepared under the same conditions.

[0035] Finally, it should be noted that the terms "comprising," "including," or any other variations are intended to cover a non-exclusive inclusion, such that a process, demolding method, article, or gel electrode that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, demolding method, article, or gel electrode. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make further changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0036] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for the preparation of a polymer PECA-N, characterized in that, The method comprises the following steps: (1) Pre-freezing ethyl cyanoacrylate monomer and initiator N-methyl pyrrolidone in an environment of -10°C to 10°C; (2) Under the refrigeration condition of -10°C to 10°C, first put N-methyl pyrrolidone into a stirring container, stir at a low speed of 100-500 RPM and keep the reaction environment refrigerated, slowly drop the pre-frozen ethyl cyanoacrylate, after the dropping is completed, adjust the stirring speed to 500-1000 RPM and keep for 30 seconds, and then the polymer PECA-N can be obtained. In step (2), the volume ratio of ethyl cyanoacrylate monomer to N-methyl pyrrolidone is 1:1-30.

2. The production method according to claim 1, wherein In step (2), the volume ratio of ethyl cyanoacrylate monomer to N-methyl pyrrolidone is 1:

10.

3. The polymer PECA-N obtained by the preparation method of claim 1 or 2.

4. A lithium-sulfur battery gel electrode, characterized by, The positive electrode composite comprises a sulfur / carbon mixture, conductive carbon black, the polymer PECA-N prepared by the preparation method of claim 1 or 2, and N-methyl pyrrolidone as a solvent, and the mass ratio of the sulfur / carbon mixture, the conductive carbon black and the polymer PECA-N is 6-8:1-3:1-31.

5. The method for preparing a lithium-sulfur battery gel electrode as described in claim 4, characterized in that, The method comprises the following steps: (1) Preparing a sulfur / carbon mixture; (2) Mixing the sulfur / carbon mixture, conductive carbon black and the polymer PECA-N, adding N-methyl pyrrolidone as a solvent, and stirring uniformly to obtain a positive electrode slurry; (3) Coating the positive electrode slurry on a current collector, drying and cutting to obtain a positive electrode sheet; (4) Immersing the positive electrode sheet in an electrolyte, and causing the positive electrode composite to undergo secondary gelation, so that a lithium-sulfur battery gel electrode is obtained.

6. The method of making a lithium-sulfur battery gel electrode according to claim 5, wherein, In step (1), the preparation process of the sulfur / carbon mixture is as follows: first mix nano-sulfur and conductive carbon black at a mass ratio of 3:1, and then melt the sulfur at 155°C-165°C for 6 h to obtain the sulfur / carbon mixture.

7. The method for preparing a lithium-sulfur battery gel electrode as described in claim 5, characterized in that, In step (3), use a coating machine to coat the positive electrode slurry on the current collector with a doctor blade of 50-1000 microns in thickness.

8. The method of making a lithium-sulfur battery gel electrode of claim 5, wherein, The diameter of the positive electrode sheet obtained by cutting in step (3) is 13 mm.

9. The method of making a lithium-sulfur battery gel electrode of claim 5, wherein, In step (4), the electrolyte comprises a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether at a volume ratio of 1:1, and the solvent further dissolves 1.0 M lithium bis(trifluoromethane)sulfonamide and 2% lithium nitrate by mass percentage.

10. A lithium-sulfur battery, characterized by, The positive electrode is the gel electrode of claim 4 or prepared by the gel electrode preparation method of any one of claims 5-9.

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