Aqueous polyurethane resin and porphyrin-based lithium-sulfur battery electrode binder prepared using the same

Abstract

The application provides a kind of water-based polyurethane resin and the electrode binder of porphyrin-based lithium-sulfur battery prepared using it, specifically relates to a kind of high molecular water-based polyurethane resin with carboxyl in molecular chain and its preparation method, is by polymeric dihydric alcohol, 2,2-dihydroxy methyl propionic acid, N-methyl diethanolamine and diisocyanate as raw material is prepared by condensation polymerization reaction isocyanate end-capped prepolymer solution, then sequentially by salt formation neutralizes carboxyl, emulsification, chain extension is prepared;Using the water-based polyurethane resin and porphyrin / metalloporphyrin in situ crosslinking preparation has the electrocatalytic performance lithium-sulfur battery electrode water-based binder, and the sulfur electrode preparation method based on the lithium-sulfur battery electrode water-based binder.The lithium-sulfur battery electrode water-based binder has higher initial discharge capacity, higher capacity retention rate and lower charge-discharge voltage polarization than commercial electrode binder, provides new ideas and schemes for developing high-performance lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery binder technology, specifically to an aqueous polyurethane resin and a porphyrin-based lithium-sulfur battery electrode binder prepared therefrom. More specifically, it relates to a high-molecular-weight aqueous polyurethane resin with carboxyl groups in its molecular chain and its preparation method, and to an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared by in-situ crosslinking of this aqueous polyurethane resin with porphyrin / metalloporphyrin. Background Technology

[0002] In 1800, Alessandro Volta first proposed the working principle of a battery and demonstrated a device capable of generating a continuous current. Since then, battery technology has continuously developed and progressed. Lead-acid, nickel-metal hydride, and nickel-cadmium batteries have reached near-limits in their development, while lithium-ion battery technology has received widespread attention and made significant progress in recent years, becoming an irreplaceable product in the field of electrochemical energy storage since its commercialization. Lithium-ion batteries (LIBs) have ultra-long lifespans and high energy densities, and are currently widely used in electronic products and electric vehicles. Compared to ordinary primary batteries, they also have advantages such as higher operating voltage, wider operating temperature range, stable discharge, and lower self-discharge rate. In recent years, my country's lithium-ion battery industry has also achieved rapid growth, accounting for more than 70% of global production capacity. However, due to the rapid development of electric vehicles, the energy sector, and the electronic equipment industry in recent years, the energy density of lithium-ion batteries has approached its theoretical limit, making further breakthroughs difficult. Therefore, lithium batteries with higher specific capacity and higher energy density have become the research focus of many researchers.

[0003] Among numerous novel lithium-ion batteries, lithium-sulfur batteries are one of the most widely discussed candidates. Lithium-sulfur batteries typically use elemental lithium as the negative electrode, a composite material of elemental sulfur, conductive agents, and binders as the positive electrode, a porous polymer as the separator, and an electrolyte to conduct lithium ions for energy conversion. Due to its advantages such as high energy density, low cost, environmental friendliness, and wide availability, lithium-sulfur batteries are considered one of the next-generation commercial lithium-ion battery options. However, the "shuttle effect" of lithium polysulfides, the volume expansion of the positive electrode, and the low conductivity of the active material during cycling can all lead to a decline in the capacity of lithium-sulfur batteries, affecting their cycle stability and even causing battery failure.

[0004] Electrode binders play a crucial role in positive electrode materials, suppressing the diffusion of lithium polysulfides to the negative electrode while maintaining structural stability. A good electrode binder needs to maintain contact between the active material and the conductive agent, preserve the positive electrode structure, stabilize the electrode material on the current collector, and maintain good mechanical strength while dispersing in the solvent. Compared to conventional lithium-ion batteries, lithium-sulfur batteries undergo a phase transition during charge and discharge, thus requiring the electrode binder to have a certain affinity for lithium polysulfides. Furthermore, due to the volume expansion of the positive electrode during discharge, the binder needs excellent mechanical properties to withstand these volume changes.

[0005] While commercially available electrode binders such as polyvinylidene fluoride (PVDF) exhibit good electrochemical stability, they only provide basic bonding. The volume changes of sulfur after multiple cycles can lead to cracks in the electrode structure, causing electrode failure. Furthermore, the binding force between PVDF and lithium polysulfides is weak, making it difficult to suppress the "shuttle effect" of lithium polysulfides, resulting in unsatisfactory cycling performance. Using PVDF as a binder also requires the use of toxic and flammable N-methylpyrrolidone (NMP) as a solvent, which poses a certain degree of environmental damage. Summary of the Invention

[0006] To address the problems identified in the prior art, this invention provides an aqueous polyurethane resin and a porphyrin-based lithium-sulfur battery electrode binder prepared therefrom. The first objective is to provide a high-molecular-weight aqueous polyurethane resin with carboxyl groups in its molecular chain and its preparation method. The second objective is to prepare an aqueous lithium-sulfur battery electrode binder with electrocatalytic properties by in-situ crosslinking this aqueous polyurethane resin with porphyrin / metalloporphyrin. This aqueous lithium-sulfur battery electrode binder exhibits higher initial discharge capacity, higher capacity retention, and lower charge / discharge voltage polarization compared to commercial electrode binders, providing a novel approach and solution for developing high-performance lithium-sulfur batteries.

[0007] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0008] In one aspect, the present invention provides a waterborne polyurethane resin with carboxyl groups in its molecular chain, the chemical structural formula of which is as follows:

[0009]

[0010] In the formula, n = 1 to 100, and R1 has the following structure:

[0011]

[0012] R2 can be any of the following structures:

[0013]

[0014] R3 can be any of the following structures, where m = 10 to 200:

[0015]

[0016] In the above chemical structural formula, “…” indicates the position where the chemical bond is connected.

[0017] On the other hand, the present invention also provides a method for preparing the above-mentioned waterborne polyurethane resin with carboxyl groups in its molecular chain. This method involves preparing an isocyanate-terminated prepolymer through a condensation polymerization reaction using polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine, and diisocyanate as raw materials. The prepolymer is then subjected to salt formation to neutralize the carboxyl groups, emulsification, and chain extension to obtain the waterborne polyurethane resin with carboxyl groups in its molecular chain. It should be noted that those skilled in the art can derive the specific preparation steps based on the raw material selection and reaction sequence shown above, and in particular, can balance the raw materials according to common knowledge in the art based on the specific chemical structural formulas described above. Therefore, the technical solutions provided below by the present invention do not imply the sole designation or limitation of the method for preparing the waterborne polyurethane resin with carboxyl groups in its molecular chain.

[0018] This invention also provides a method for preparing a waterborne polyurethane resin with carboxyl groups in its molecular chain, comprising the following steps:

[0019] A prepolymer with isocyanate-terminated structure was prepared by using polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate as raw materials, mixing them evenly and reacting them at a temperature of 30-100℃ for 0.5-12 hours. Then, the prepolymer was cooled to 0-80℃, the carboxyl groups were neutralized to form a salt, and after emulsification, the chain was extended using a water-soluble diamine as a chain extender to obtain a high molecular weight waterborne polyurethane resin with carboxyl groups in the molecular chain.

[0020] In this document, the polymeric diol is a polymer obtained by polymerizing monomers having two hydroxyl groups, such as any one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran ether glycol, with a molecular weight range of 600 to 10,000. Those skilled in the art can directly select commercially available conventional chemical raw material grade raw materials.

[0021] In one technical solution, the polymeric diol is used as a flexible segment of waterborne polyurethane, preferably polyethylene glycol with a molecular weight of about 1000.

[0022] In this paper, 2,2-dimethylolpropionic acid is an alkyl compound with propionic acid branches and two hydroxyl groups. It is introduced into the molecular chain through the reaction of hydroxyl groups and isocyanates, providing chemical sites for subsequent crosslinking. Commercially available conventional chemical raw materials are usually selected directly.

[0023] In this document, the diisocyanate is a compound having two isocyanate groups, such as any one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate. Those skilled in the art can directly select commercially available conventional chemical raw material grade raw materials.

[0024] In one of the technical solutions, the diisocyanate is preferably isophorone diisocyanate.

[0025] In this paper, the polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate are used as raw materials, and their specific proportions can be balanced according to the specific chemical structural formulas mentioned above, based on the ratio of isocyanate, hydroxyl and amino groups, according to the molar ratio required for the reaction.

[0026] To better illustrate the present invention and provide a reference technical solution, the molar ratio of the polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate is 1:(1-1.5):(1-1.5):(4-8).

[0027] In this document, the neutralization of carboxyl groups for salt formation refers to the neutralization of isocyanate-terminated prepolymers with carboxyl groups in their molecular chains into salts through a reaction between amino and carboxyl groups, thereby enhancing hydrophilicity and facilitating dispersion and emulsification. Those skilled in the art will understand that the specific method of neutralization of carboxyl groups for salt formation used in this invention is common knowledge in the field. For example, triethylamine (TEA) can be added for neutralization of carboxyl groups for salt formation, wherein the molar ratio of carboxyl groups to triethylamine in the isocyanate-terminated prepolymer is 1:(1-1.5). Under laboratory conditions, a molar ratio of 2,2-dimethylolpropionic acid to triethylamine of 1:(1-1.5) can be selected.

[0028] In this document, emulsification refers to uniformly dispersing a prepolymer that has undergone salt formation treatment in an immiscible liquid to form a prepolymer emulsion. Those skilled in the art should know that the specific emulsification method used in this invention is common knowledge in the field, such as uniformly dispersing and emulsifying in deionized water.

[0029] To better illustrate the present invention and provide a technical solution for reference, the emulsification specifically involves adding deionized water for uniform dispersion and emulsification, wherein the amount of deionized water added is 0.5 to 5 times the mass of the prepolymer after salt formation treatment.

[0030] In one of the technical solutions, the water-soluble diamine is selected from any one of ethylenediamine, propylenediamine, butanediamine, pentanediamine, and hexanediamine; the molar ratio of the chain extender to the diisocyanate is (0.5-1.5):1.

[0031] It should be noted that when using water-soluble diamines as chain extenders, the specific reaction conditions are based on the selected chain extender and should be carried out in accordance with common knowledge in the field or the relevant instructions for use of the chain extender.

[0032] To better illustrate the present invention and provide a technical solution for reference, when the water-soluble diamine is selected as ethylenediamine, ethylenediamine is added dropwise to the emulsified prepolymer emulsion and stirred and reacted at a temperature of 0-80°C for 1-10 hours.

[0033] In another aspect, the present invention also provides an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, prepared by in-situ crosslinking the above-mentioned aqueous polyurethane resin with porphyrin / metal porphyrin, mainly comprising the following steps:

[0034] The tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex and waterborne polyurethane resin were added to the reaction vessel at a mass ratio of 1:(1-20). A crosslinking agent was added, and the mixture was stirred thoroughly to obtain an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties.

[0035] In this paper, tetra(4-carboxyphenyl)porphyrin (CAS: 14609-54-2) is a conventional commercially available chemical raw material and an important porphyrin compound. It can form porphyrin metal complexes with various metal ions. In this invention, when tetra(4-carboxyphenyl)porphyrin metal complexes are selected, compared with tetra(4-carboxyphenyl)porphyrin, porphyrin metal complexes have the advantages of strong adsorption of lithium polysulfides and catalytic conversion of lithium polysulfides.

[0036] In one technical solution, the tetra(4-carboxyphenyl)porphyrin metal complex is a metal complex formed by tetra(4-carboxyphenyl)porphyrin and any one of the following metal ions: iron ion, cobalt ion, nickel ion, and manganese ion; the tetra(4-carboxyphenyl)porphyrin metal complex is prepared by mixing tetra(4-carboxyphenyl)porphyrin with a metal salt and carrying out a metallization reaction.

[0037] To better illustrate the present invention and provide a reference technical solution, the preparation method of the tetra(4-carboxyphenyl)porphyrin metal complex specifically involves dissolving tetra(4-carboxyphenyl)porphyrin in an organic solvent, adding a metal salt, heating to 50–180°C and refluxing for 1–12 hours, and then sequentially undergoing precipitation, filtration, washing, and drying to obtain the tetra(4-carboxyphenyl)porphyrin metal complex; wherein the metal salt is selected from any one of ferric chloride, cobalt chloride, nickel chloride, and magnesium chloride, and the molar ratio of tetra(4-carboxyphenyl)porphyrin to the metal salt is 1:(1–1.5).

[0038] In the above technical solution, the crosslinking agent is a crosslinking agent commonly used in in-situ crosslinking reactions in this technical field. Those skilled in this technical field can select a suitable crosslinking agent according to actual needs, such as trimethylolpropane-tris[3-(2-methylaziridinyl)acrylate], and the molar ratio of aziridinyl group in the crosslinking agent to the carboxyl group in the waterborne polyurethane resin and the tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex is 1:(0.8~1.5).

[0039] In this document, the stirring refers to the stirring operation conventionally used in the art, including magnetic stirring or mechanical stirring. Those skilled in the art can choose a suitable stirring method according to the production scale or current process conditions. In one technical solution, the stirring can be carried out at a stirring rate of 100 to 800 rpm.

[0040] On another front, based on the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared above, in order to better illustrate the present invention and provide a reference application method, the present invention also provides a method for preparing a sulfur electrode based on the above-mentioned aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, comprising the following steps:

[0041] (1) Prepare the following raw materials by weight:

[0042] 50-90 parts of carbon-sulfur complex,

[0043] The electrodes use 3 to 20 parts of conductive carbon.

[0044] 5-30 parts of an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties;

[0045] (2) After the carbon-sulfur composite, conductive carbon for electrodes, and aqueous binder for lithium-sulfur batteries with electrocatalytic properties prepared in step (1) are thoroughly mixed and coated onto the surface of the electrode current collector, and then dried to obtain a sulfur electrode.

[0046] In step (1), the carbon-sulfur composite is a conventional component selection for the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain the carbon-sulfur composite based on the existing records of lithium-sulfur batteries.

[0047] To better illustrate the present invention and provide a technical solution for reference, the specific preparation method of the carbon-sulfur composite in step (1) is to ball-mill and mix sublimed sulfur and carbon nanotubes at a weight ratio of 7:3, transfer the mixture to a reaction vessel, and heat it at 155-160°C for 15-20 hours under inert gas protection to obtain the carbon-sulfur composite.

[0048] In step (1), the conductive carbon used for the electrode is a conventional component selected in the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain conductive carbon for the electrode based on the existing records of lithium-sulfur batteries.

[0049] To better illustrate the present invention and provide a technical solution for reference, the conductive carbon used for the electrode in step (1) is selected from at least one of conductive carbon black, graphene, and carbon nanotubes.

[0050] In step (2), the thorough mixing follows the general principles of common chemical knowledge. The components are mixed evenly by means of mechanical stirring, for example. Under laboratory conditions, mechanical mixing for 10 to 30 minutes is usually sufficient to achieve thorough mixing. Considering the industrial scale-up effect, in the actual conversion process, those skilled in the art can adopt a more suitable thorough mixing process according to the mixing of each component.

[0051] In this paper, the scraping process described in step (2) follows the general principles of common chemical knowledge. Those skilled in the art can directly refer to conventional dry electrode technology or conventional film formation methods suitable for preparing sulfur electrodes in literature reports.

[0052] In step (2), the electrode current collector is a conventional component selected from the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain the electrode current collector based on the existing records of lithium-sulfur batteries.

[0053] It should be noted that if the viscosity is not suitable before scraping in step (2), a small amount of solvent can be added.

[0054] The present invention has the following beneficial effects:

[0055] 1. The aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties provided by the present invention, when tested as a binder, has a large number of nitrogen-containing polar groups (pyrrole nitrogen, carbamate group, urea group and amine group, etc.) and metal ions that can adsorb lithium polysulfides, and can inhibit lithium polysulfide shuttle through adsorption.

[0056] 2. The aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties provided by this invention, when used as a binder, showed that the sulfur electrode prepared using it maintained a discharge specific capacity of 724 mAh g⁻¹ after 200 cycles at 1C. -1 It exhibits good cyclic stability.

[0057] 3. The aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties provided by this invention, when used as a binder, shows superior rate performance compared to conventional commercial battery binders used in the prior art when the resulting sulfur electrode is prepared. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the chemical structure of the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared in Example 3 of the present invention.

[0059] Figure 2 Figure (a) shows a comparison of the peeling force-displacement results of the sulfur electrode samples prepared in Example 7 and Comparative Example 1, and a photograph showing the results after the peeling experiment. Figure (b) shows a comparison of the peeling force-displacement results of the sulfur electrode samples prepared in Example 7 and Comparative Example 1 in the sulfur cathode peeling experiment; Figure (c) shows a photograph showing the results of the sulfur electrode samples prepared in Example 7 and Comparative Example 1 after the sulfur cathode peeling experiment.

[0060] Figure 3 Figure (a) shows a bar chart comparing the swelling rates of the sulfur electrode samples prepared in Example 7 and Comparative Example 1, and photographs after immersion. Figure (b) shows a photograph of the sulfur electrode samples prepared in Example 7 and Comparative Example 1 after immersion in 1 mL of LS-001 electrolyte for 12 hours.

[0061] Figure 4 The graph shows the comparison of the long-cycle performance of the batteries assembled from the sulfur electrode samples prepared in Examples 6-9 and Comparative Example 1 at 1C after 200 cycles.

[0062] Figure 5 The graph shows a comparison of the rate performance curves of the batteries assembled from the sulfur electrode samples prepared in Examples 6-9 and Comparative Example 1 of this invention.

[0063] Figure 6The image shows the GITT curves at 0.1C of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention.

[0064] Figure 7 The image shows a comparison of the EIS curves of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention.

[0065] Figure 8 The cyclic voltammetry curves are comparisons of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention.

[0066] Figure 9 These are photographs of the sulfur electrode and separator after 200 cycles at 1C in the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention. Specifically, Figure (a) shows the sulfur electrode after 200 cycles at 1C in the battery assembled from the sulfur electrode sample prepared in Example 7; Figure (b) shows the sulfur electrode after 200 cycles at 1C in the battery assembled from the sulfur electrode sample prepared in Comparative Example 1; Figure (c) shows the separator after 200 cycles at 1C in the battery assembled from the sulfur electrode sample prepared in Example 7; and Figure (d) shows the separator after 200 cycles at 1C in the battery assembled from the sulfur electrode sample prepared in Comparative Example 1. Detailed Implementation

[0067] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0068] In one aspect, the present invention provides a waterborne polyurethane resin with carboxyl groups in its molecular chain, the chemical structural formula of which is as follows:

[0069]

[0070] In the formula, n = 1 to 100, and R1 has the following structure:

[0071]

[0072] R2 can be any of the following structures:

[0073]

[0074] R3 can be any of the following structures, where m = 10 to 200:

[0075]

[0076] In the above chemical structural formula, “…” indicates the position where the chemical bond is connected.

[0077] On the other hand, the present invention also provides a method for preparing the above-mentioned waterborne polyurethane resin with carboxyl groups in its molecular chain. This method involves preparing an isocyanate-terminated prepolymer through a condensation polymerization reaction using polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine, and diisocyanate as raw materials. The prepolymer is then subjected to salt formation to neutralize the carboxyl groups, emulsification, and chain extension to obtain the waterborne polyurethane resin with carboxyl groups in its molecular chain. It should be noted that those skilled in the art can derive the specific preparation steps based on the raw material selection and reaction sequence shown above, and in particular, can balance the raw materials according to common knowledge in the art based on the specific chemical structural formulas described above. Therefore, the technical solutions provided below by the present invention do not imply the sole designation or limitation of the method for preparing the waterborne polyurethane resin with carboxyl groups in its molecular chain.

[0078] This invention also provides a method for preparing a waterborne polyurethane resin with carboxyl groups in its molecular chain, comprising the following steps:

[0079] A prepolymer with isocyanate-terminated structure was prepared by using polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate as raw materials, mixing them evenly and reacting them at a temperature of 30-100℃ for 0.5-12 hours. Then, the prepolymer was cooled to 0-80℃, the carboxyl groups were neutralized to form a salt, and after emulsification, the chain was extended using a water-soluble diamine as a chain extender to obtain a high molecular weight waterborne polyurethane resin with carboxyl groups in the molecular chain.

[0080] In this document, the polymeric diol is a polymer obtained by polymerizing monomers having two hydroxyl groups. In one embodiment, it includes, for example, any one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran ether diol, with a molecular weight range of 600 to 10,000. Those skilled in the art can directly select commercially available conventional chemical raw material grade raw materials.

[0081] In one embodiment, the polymeric diol is used as a flexible segment of waterborne polyurethane, preferably polyethylene glycol with a molecular weight of about 1000.

[0082] In this paper, 2,2-dimethylolpropionic acid is an alkyl compound with propionic acid branches and two hydroxyl groups. It is introduced into the molecular chain through the reaction of hydroxyl groups and isocyanates, providing chemical sites for subsequent crosslinking. Commercially available conventional chemical raw materials are usually selected directly.

[0083] In this document, the diisocyanate is a compound having two isocyanate groups, and in one embodiment, it includes, for example, any one of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate. Those skilled in the art can directly select commercially available conventional chemical raw material grade raw materials.

[0084] In one embodiment, the diisocyanate is preferably isophorone diisocyanate.

[0085] In this paper, the polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate are used as raw materials, and their specific proportions can be balanced according to the specific chemical structural formulas mentioned above, based on the ratio of isocyanate, hydroxyl and amino groups, according to the molar ratio required for the reaction.

[0086] To better illustrate the present invention and to provide an embodiment for reference, the molar ratio of the polymeric diol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine and diisocyanate is 1:(1-1.5):(1-1.5):(4-8).

[0087] In this document, the neutralization of carboxyl groups for salt formation refers to the neutralization of isocyanate-terminated prepolymers with carboxyl groups in their molecular chains into salts through a reaction between amino and carboxyl groups, thereby enhancing hydrophilicity and facilitating dispersion and emulsification. Those skilled in the art will understand that the specific method of neutralization of carboxyl groups for salt formation used in this invention is common knowledge in the field. In one embodiment, for example, triethylamine (TEA) is added for neutralization of carboxyl groups for salt formation, wherein the molar ratio of carboxyl groups to triethylamine in the isocyanate-terminated prepolymer is 1:(1-1.5). Under laboratory conditions, the molar ratio of 2,2-dimethylolpropionic acid to triethylamine can be selected as 1:(1-1.5), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, or any range or point value between them.

[0088] In this document, emulsification refers to uniformly dispersing a prepolymer that has undergone salt formation treatment in an immiscible liquid to form a prepolymer emulsion. Those skilled in the art should know that the specific emulsification method used in this invention is common knowledge in the field, such as uniformly dispersing and emulsifying in deionized water.

[0089] To better illustrate the present invention and to provide a reference embodiment, the emulsification specifically involves adding deionized water for uniform dispersion and emulsification. The amount of deionized water added is 0.5 to 5 times the mass of the prepolymer after salt formation treatment, for example, 0.5 times, 0.6 times, 0.8 times, 1 time, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, or any range or point value between them.

[0090] In one embodiment, the water-soluble diamine is selected from any one of ethylenediamine, propylenediamine, butanediamine, pentanediamine, and hexanediamine; the molar ratio of the chain extender to the diisocyanate is (0.5 to 1.5):1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any range or point value between them.

[0091] It should be noted that when using water-soluble diamines as chain extenders, the specific reaction conditions are based on the selected chain extender and should be carried out in accordance with common knowledge in the field or the relevant instructions for use of the chain extender.

[0092] To better illustrate the present invention and provide an embodiment for reference, when the water-soluble diamine is selected as ethylenediamine, ethylenediamine is added dropwise to the emulsified prepolymer emulsion and stirred and reacted at a temperature of 0-80°C for 1-10 hours.

[0093] In another aspect, the present invention also provides an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, prepared by in-situ crosslinking the above-mentioned aqueous polyurethane resin with porphyrin / metal porphyrin, mainly comprising the following steps:

[0094] The tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex and waterborne polyurethane resin were added to the reaction vessel at a mass ratio of 1:(1-20). A crosslinking agent was added, and the mixture was stirred thoroughly to obtain an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties.

[0095] In this paper, tetra(4-carboxyphenyl)porphyrin (CAS: 14609-54-2) is a conventional commercially available chemical raw material and an important porphyrin compound. It can form porphyrin metal complexes with various metal ions. In this invention, when tetra(4-carboxyphenyl)porphyrin metal complexes are selected, compared with tetra(4-carboxyphenyl)porphyrin, porphyrin metal complexes have the advantages of strong adsorption of lithium polysulfides and catalytic conversion of lithium polysulfides.

[0096] In one embodiment, the tetra(4-carboxyphenyl)porphyrin metal complex is a metal complex formed by tetra(4-carboxyphenyl)porphyrin and any one of the following metal ions: iron ion, cobalt ion, nickel ion, and manganese ion; the tetra(4-carboxyphenyl)porphyrin metal complex is prepared by mixing tetra(4-carboxyphenyl)porphyrin with a metal salt and carrying out a metallization reaction.

[0097] To better illustrate the present invention and provide a reference embodiment, the method for preparing the tetra(4-carboxyphenyl)porphyrin metal complex specifically involves dissolving tetra(4-carboxyphenyl)porphyrin in an organic solvent, adding a metal salt, refluxing at 50–180°C for 1–12 hours, and then sequentially undergoing precipitation, filtration, washing, and drying to obtain the tetra(4-carboxyphenyl)porphyrin metal complex; wherein the metal salt is selected from any one of ferric chloride, cobalt chloride, nickel chloride, and magnesium chloride, and the molar ratio of tetra(4-carboxyphenyl)porphyrin to the metal salt is 1:(1–1.5), for example 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, or any range or point value between them.

[0098] In one embodiment, the mass ratio of the tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex to the aqueous polyurethane resin is 1:(1 to 20), for example 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20 or any range or point value between them.

[0099] In the above technical solution, the crosslinking agent is a crosslinking agent commonly used in in-situ crosslinking reactions in this technical field. Those skilled in the art can select a suitable crosslinking agent according to actual needs. In one embodiment, for example, trimethylolpropane-tris[3-(2-methylaziridinyl)acrylate] is preferred. The molar ratio of the aaziridinyl group in the crosslinking agent to the carboxyl group in the waterborne polyurethane resin and the tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex is 1:(0.8~1.5), for example, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5 or any range or point value between them.

[0100] In this document, the stirring refers to the stirring operation conventionally used in the art, including magnetic stirring or mechanical stirring. Those skilled in the art can choose a suitable stirring method according to the production scale or current process conditions. In one embodiment, the stirring can be carried out at a stirring rate of 100 to 800 rpm.

[0101] On another front, based on the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared above, in order to better illustrate the present invention and provide a reference application method, the present invention also provides a method for preparing a sulfur electrode based on the above-mentioned aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, comprising the following steps:

[0102] (1) Prepare the following raw materials by weight:

[0103] 50-90 parts of carbon-sulfur complex,

[0104] The electrodes use 3 to 20 parts of conductive carbon.

[0105] 5-30 parts of an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties;

[0106] (2) After the carbon-sulfur composite, conductive carbon for electrodes, and aqueous binder for lithium-sulfur batteries with electrocatalytic properties prepared in step (1) are thoroughly mixed and coated onto the surface of the electrode current collector, and then dried to obtain a sulfur electrode.

[0107] In step (1), the carbon-sulfur composite is a conventional component selection for the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain the carbon-sulfur composite based on the existing records of lithium-sulfur batteries.

[0108] To better illustrate the present invention and provide an embodiment for reference, the specific preparation method of the carbon-sulfur composite in step (1) is to ball-mill and mix sublimed sulfur and carbon nanotubes at a weight ratio of 7:3, transfer the mixture to a reaction vessel, and heat it at 155-160°C for 15-20 hours under inert gas protection to obtain the carbon-sulfur composite.

[0109] In step (1), the conductive carbon used for the electrode is a conventional component selected in the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain conductive carbon for the electrode based on the existing records of lithium-sulfur batteries.

[0110] To better illustrate the present invention and to provide an embodiment for reference, the conductive carbon used for the electrode in step (1) is selected from at least one of conductive carbon black, graphene, and carbon nanotubes.

[0111] In step (2), the thorough mixing follows the general principles of common chemical knowledge. The components are mixed evenly by means of mechanical stirring, for example. Under laboratory conditions, mechanical mixing for 10 to 30 minutes is usually sufficient to achieve thorough mixing. Considering the industrial scale-up effect, in the actual conversion process, those skilled in the art can adopt a more suitable thorough mixing process according to the mixing of each component.

[0112] In this paper, the scraping process described in step (2) follows the general principles of common chemical knowledge. Those skilled in the art can directly refer to conventional dry electrode technology or conventional film formation methods suitable for preparing sulfur electrodes in literature reports.

[0113] In step (2), the electrode current collector is a conventional component selected from the sulfur electrode of lithium-sulfur batteries in this technical field. Those skilled in the art can know how to select and obtain the electrode current collector based on the existing records of lithium-sulfur batteries.

[0114] It should be noted that if the viscosity is not suitable before scraping in step (2), a small amount of solvent can be added.

[0115] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0116] Example

[0117] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0118] 1. Raw materials

[0119] Polyethylene glycol (PEG, Mw = ~4000), 2,2-dimethylolpropionic acid (DMPA), N-methyldiethanolamine, isophorone diisocyanate (IPDI), triethylamine (TEA), ethylenediamine (EDA), hydrochloric acid (36.0%~38.0%), N,N-dimethylformamide (DMF) (≥99.5%), carbon disulfide (CS2), isopropanol (IPA), and N-methylpyrrolidone (NMP) (≥99.0%) were purchased from Chengdu Kelong Chemical Reagent Co., Ltd.

[0120] Tetra(4-carboxyphenyl)porphyrin (>98%), ferric chloride, cobalt chloride, manganese chloride, nickel chloride, and deuterated chloroform (99.8%) were purchased from Shanghai Titan Technology Co., Ltd. Aziridine crosslinking agent HD-100A was purchased from Ningxia Zhuoyu New Material Technology Co., Ltd. Multi-walled carbon nanotubes (MWCNTs) (>98%) were purchased from Shenzhen Suiheng Technology Co., Ltd. Single-layer graphene (battery grade) was purchased from Suzhou Carbon-Feng Graphene Technology Co., Ltd. Conductive carbon black Super P (battery grade) was purchased from TMEGO, Switzerland.

[0121] Polyvinylidene fluoride (PVDF) (battery grade) was purchased from Shanghai Lanbai Technology Co., Ltd. LS-001 electrolyte (battery grade) was purchased from Suzhou Duoduo Chemical Technology Co., Ltd. Lithium sulfide (≥99.9%) was purchased from Maclean's Biochemical Technology Co., Ltd. Polypropylene separator (battery grade) was purchased from Jiangxi Enbo New Materials Co., Ltd. Deionized water was used in all experiments. Unless otherwise specified, all reagents were analytical reagent (AR) grade and could be used without further purification.

[0122] 2. Testing Methods

[0123] 180° Peel Test: During sample preparation, the back side of the positive electrode sheet (24mm wide, 50mm long) prepared with different adhesives was first attached to a glass slide using double-sided adhesive, and then the front side was fixed to the adhesive tape. A dual-column benchtop testing machine (INS Tron General Material Testing Machine 5967, USA) was used at a constant tensile speed of 10mm / min. -1 Record the external load generated on the sample.

[0124] Constant current charge-discharge test: In this invention, the MIHW-200-160CH constant temperature test chamber from Shenzhen Xinwei Co., Ltd. was used to conduct constant current charge-discharge tests on the battery at different cycle periods and charge-discharge rates. The nominal specific capacity is 1675 mAh g. -1 The test voltage was 1.7V to 2.8V, and the temperature was 30℃. The scan rate was 0.033mV / s. -1 We assembled lithium-sulfur batteries based on different binders and tested them to investigate the effect of the prepared binders on the electrochemical performance of the sulfur cathode.

[0125] Constant-current intermittent titration (GITT) is a reaction kinetics testing technique that analyzes the relationship between potential and time. A complete GITT test consists of multiple "current step" units. Within each current step unit, the battery is charged (discharged) at a small current for a period of time, then the current is cut off and maintained for a period of time to allow ions to fully diffuse within the active material and reach equilibrium. By analyzing the relationship between changes in electrode potential and relaxation time, the diffusion coefficient of ions within the battery is calculated.

[0126] Electrochemical Impedance Spectroscopy (EIS): The lithium-sulfur batteries were subjected to EIS testing using a CHI 600E electrochemical analyzer / workstation from Shanghai Chenhua Instruments Co., Ltd., to characterize electrode performance and electron transfer resistance. The test frequency range was 100 Hz to 0.01 Hz, and the amplitude was 10 mV.

[0127] Cyclic voltammetry: In this invention, a CHI 600E electrochemical analyzer / workstation from Shanghai Chenhua Instruments Co., Ltd. was used to perform cyclic voltammetry (CV) tests on lithium-sulfur batteries to characterize the redox reactions occurring at the electrodes and to explore their mechanisms. The scan rate was 0.1 mV / s. -1 .

[0128] Scanning Electron Microscopy (SEM) Testing: Scanning electron microscopy (SEM) uses a focused high-energy electron beam to scan the sample surface and analyzes the surface structure of the material by collecting the excited secondary electrons. In this invention, the sample was sputter-coated with gold and studied using a JEM-F200 field emission transmission electron microscope from NEC Corporation at an accelerating voltage of 5 kV.

[0129] Example 1

[0130] This embodiment prepares a waterborne polyurethane resin with carboxyl groups in its molecular chain. The specific preparation steps are as follows:

[0131] Polyethylene glycol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine, and isophorone diisocyanate were used as raw materials. After being mixed evenly, the mixture was reacted at 90°C for 5 hours to prepare an isocyanate-terminated prepolymer. The prepolymer was then cooled to 30°C, and triethylamine was added to neutralize the carboxyl groups and form a salt. After being added to deionized water and uniformly dispersed and emulsified, ethylenediamine was used as a chain extender. Ethylenediamine was added dropwise at 30°C and stirred for 1 hour to prepare a high molecular weight waterborne polyurethane resin with carboxyl groups in the molecular chain.

[0132] The molar ratio of polyethylene glycol, 2,2-dimethylolpropionic acid, N-methyldiethanolamine, isophorone diisocyanate triethylamine, and ethylenediamine is 1:1:1:6:1:3;

[0133] The amount of deionized water added is three times the mass of the prepolymer after salt formation treatment.

[0134] Example 2

[0135] This embodiment utilizes the waterborne polyurethane resin with carboxyl groups in its molecular chain prepared in Example 1, and crosslinks it with metalloporphyrin in situ to prepare a waterborne binder for lithium-sulfur battery electrodes with electrocatalytic properties. The main steps include:

[0136] Tetra(4-carboxyphenyl)porphyrin was dissolved in DMF, ferric chloride was added, and the mixture was heated to 150°C and refluxed for 6 hours. The mixture was then subjected to precipitation, filtration, washing, and drying to obtain a tetra(4-carboxyphenyl)porphyrin metal complex. The molar ratio of tetra(4-carboxyphenyl)porphyrin to ferric chloride was 1:1.

[0137] The tetra(4-carboxyphenyl)porphyrin metal complex and the aqueous polyurethane resin were added to the reaction vessel at a mass ratio of 1:1. Trimethylolpropane-tris[3-(2-methylacridinyl)acrylate] was added and stirred thoroughly to obtain an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, denoted as Fe-PWPU.

[0138] The molar ratio of the propidium group in the trimethylolpropane-tris[3-(2-methylacridinyl)acrylate] to the carboxyl group in the aqueous polyurethane resin and the tetra(4-carboxyphenyl)porphyrin metal complex is 1:1.

[0139] Example 3

[0140] Example 3 is a water-based binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared by replacing ferric chloride with manganese chloride according to the steps of Example 2. It is denoted as Mn-PWPU.

[0141] Example 4

[0142] Example 4 is an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared by replacing ferric chloride with cobalt chloride according to the steps of Example 2. It is denoted as Co-PWPU.

[0143] Example 5

[0144] Example 5 is an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared by replacing ferric chloride with nickel chloride, following the steps of Example 2. This binder is denoted as Ni-PWPU.

[0145] Example 6

[0146] This embodiment utilizes the aqueous binder with electrocatalytic properties for lithium-sulfur battery electrodes prepared in Example 2 to prepare the sulfur electrode used for testing, including the following steps:

[0147] (1) Prepare the following raw materials by weight:

[0148]

[0149]

[0150] The specific preparation method of the carbon-sulfur composite is to ball-mill and mix sublimed sulfur and carbon nanotubes at a weight ratio of 7:3, transfer the mixture to a reaction vessel, and heat it at 155°C for 15 hours under inert gas protection to obtain the carbon-sulfur composite.

[0151] (2) After thoroughly mixing the carbon-sulfur composite, conductive carbon black, graphene, and aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared in step (1), the mixture is coated onto the surface of aluminum foil with an active material loading of 1 mg / cm³. 2 The sulfur electrode was prepared and used as a sample after being dried at room temperature and under vacuum at 50°C. It is denoted as S@Fe-PWPU.

[0152] Example 7

[0153] Example 7 is a sample prepared by using the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties obtained in Example 3, following the steps of Example 6, to prepare the sulfur electrode used for testing, denoted as S@Mn-PWPU.

[0154] Example 8

[0155] Example 8 is a sample prepared by using the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties obtained in Example 4, following the steps of Example 6, to prepare the sulfur electrode used for testing, denoted as S@Co-PWPU.

[0156] Example 9

[0157] Example 9 is a sample prepared by using the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties obtained in Example 5, following the steps of Example 6, to prepare the sulfur electrode used for testing, denoted as S@Ni-PWPU.

[0158] Example 10

[0159] This embodiment utilizes the waterborne polyurethane resin with carboxyl groups in its molecular chain prepared in Example 1, and crosslinks it with porphyrin in situ to prepare a waterborne binder for lithium-sulfur battery electrodes with electrocatalytic properties. The main steps include:

[0160] Tetra(4-carboxyphenyl)porphyrin and aqueous polyurethane resin were added to a reaction vessel at a mass ratio of 1:1. Trimethylolpropane-tris[3-(2-methylacrylidine)acrylate] was added and stirred thoroughly to obtain an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, denoted as PWPU.

[0161] The molar ratio of the propidinyl group in the trimethylolpropane-tris[3-(2-methylacridinyl)acrylate] to the carboxyl group in the waterborne polyurethane resin and tetra(4-carboxyphenyl)porphyrin is 1:1.

[0162] Comparative Example 1

[0163] Comparative Example 1 describes the preparation of a control sulfur electrode for testing using a conventional commercial battery binder (PVDF), comprising the following steps:

[0164] (1) Prepare the following raw materials by weight:

[0165]

[0166] The specific preparation method of the carbon-sulfur composite is to ball-mill and mix sublimed sulfur and carbon nanotubes at a weight ratio of 7:3, transfer the mixture to a reaction vessel, and heat it at 155°C for 15 hours under inert gas protection to obtain the carbon-sulfur composite.

[0167] (2) After the carbon-sulfur composite, conductive carbon black, graphene and PVDF prepared in step (1) are thoroughly mixed, they are coated onto the surface of aluminum foil and dried at room temperature and 50°C under vacuum to obtain the sulfur electrode as a control sample, denoted as S@PVDF.

[0168] To test the sulfur electrodes prepared in Examples 6-9 and Comparative Example 1, the sulfur electrodes were used as positive electrodes to assemble lithium-sulfur batteries. The battery casing included a positive electrode casing and a negative electrode casing, both made of 316 stainless steel, and a polypropylene separator. Spring contacts and gaskets were placed sequentially in the negative electrode casing, followed by the placement of the lithium metal negative electrode and separator on the gasket. Commercial electrolyte was then injected into the separator, and the positive electrode was placed on top, sealing the casing. Specifically, a pressure-controlled electric button cell packaging machine was used to package the button half-cells.

[0169] 3. Test Results

[0170] Figure 1 This is a schematic diagram of the chemical structure of the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties prepared in Example 3 of the present invention.

[0171] Figure 2 The images show the test results of a 180° peel test on the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention. According to the images, the average peel force of S@Mn-PWPU is 4.78 N, which is significantly higher than that of S@PVDF (1.58 N). The morphology of the electrode after the peel process was characterized... Figure 2 (b) shows that Mn-PWPU can retain most of the active material on the current collector, with only a small portion detaching. This is mainly due to the three-dimensional structure of Mn-PWPU after in-situ cross-linking. The weaker adhesive properties of PVDF cause most of the active material to detach.

[0172] Figure 3After immersing the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention in 1 mL of LS-001 electrolyte for 12 hours, their swelling ratio was calculated based on the weight difference of the sulfur cathode before and after immersion. The swelling ratio of S@Mn-PWPU reached 195%, significantly higher than that of S@PVDF (123%), indicating that the electrode prepared using the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties has good electrolyte affinity. Figure 3 (b) It can be seen that S@Mn-PWPU did not exhibit peeling or detachment, demonstrating good solvent resistance and adhesion; while S@PVDF showed electrode detachment, indicating that it could not effectively bond the active material and current collector.

[0173] Figure 4 The 1C cycle performance of batteries assembled from the sulfur electrode samples prepared in Examples 6-9 and Comparative Example 1 of this invention was tested. The specific capacities of S@PVDF, S@Fe-PWPU, S@Co-PWPU, S@Ni-PWPU, and S@Mn-PWPU in the first cycle at 1C were 1293 mAh g. -1 1365mAh g -1 1396mAh g -1 1407mAh g -1 1344mAh g -1 The capacity after 200 cycles of stable constant current charge-discharge at 1C is 640 mAh g. -1 687mAh g -1 707mAh g -1 717mAh g -1 724mAh g -1 The capacity retention rates were 49.50%, 50.33%, 50.64%, 50.96%, and 53.87%, respectively. The average capacity loss per cycle was 0.35%, 0.34%, 0.34%, 0.34%, and 0.31%, respectively, and the coulombic efficiencies after 200 cycles were 97.35%, 96.52%, 97.67%, 97.59%, and 97.58%, respectively. However, the cycle decay rate of S@PVDF was higher, and due to its lower initial capacity, it was not significantly higher than that of sulfur electrodes prepared with other binders in the experiment. These results demonstrate that the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties provided by this invention exhibits excellent performance in sulfur cathodes, with high initial capacity and capacity retention. In contrast, electrodes based on PVDF binders suffer greater loss of active material, with a large amount of lithium polysulfides undergoing a "shuttle effect." Furthermore, the binder struggles to maintain electrode structural stability, leading to a significant decrease in specific capacity, resulting in reduced electrode cycle performance and even battery failure.

[0174] Figure 5The results show the rate performance of batteries assembled from the sulfur electrode samples prepared in Examples 6-9 and Comparative Example 1 of this invention. The aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties exhibits better rate performance than PVDF at different rates. At 0.2C and 5C, the discharge specific capacity of S@Mn-PWPU reached 1147.93 mAh g⁻¹. -1 and 274.82mAhg -1 Meanwhile, the S@PVDF has a capacity of only 1129.32 mAh g. -1 and 27.91mAh g -1 This indicates that the binder of the present invention can effectively improve the lithium polysulfide conversion capability of the battery under high-rate conditions. After the current density recovers to 0.2C, the positive electrode prepared with the binder provided in Example 3 still has 951.56 mAh g⁻¹. -1 The capacity. Due to the significant capacity difference at 5C discharge, the discharge time varies considerably. Therefore, when the rate returns to 0.2C, S@PVDF still has 997.61 mAh g. -1 The specific capacity. The above results demonstrate that the sulfur electrodes provided in Examples 6-9 have excellent fast charge / discharge capability and high power output capability, while S@PVDF has poor capability in high-power, fast charge / discharge scenarios.

[0175] Figure 6 The GITT curves of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention are shown. Compared with S@PVDF, S@Mn-PWPU has a smaller polarization voltage (charge-discharge plateau voltage difference) and a longer discharge plateau, indicating that Mn-PWPU contributes to the redox kinetics of Li-S batteries. The internal resistance during nucleation and activation is shown in the figure, ΔR. internal It can be calculated using the following formula:

[0176] ΔR internal (Ω)=|ΔV QOCV-CCV | / I applied .

[0177] Figure 7 The EIS curves of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention are shown. The EIS test reveals a semi-circular region in the high-frequency range, representing the transfer resistance (Rt) generated at the electrolyte-electrode interface. ct The transfer resistance (R) of S@Mn-PWPU ct The RΩ is 12.87, which is lower than that of S@PVDF. ct(32.61Ω). This indicates that compared to PVDF, the designed binder has higher ionic conductivity. The Mn-PWPU binder contains a large number of ion-conducting PEG segments, which can better bond the active material and conductive agent together and fix them on the current collector, improving the transport of electrons and lithium ions, resulting in lower battery resistance and better cycle performance.

[0178] Figure 8 The cyclic voltammetry curves are for the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention. Figure 8 This reflects the kinetics of the redox reaction. Peaks i and ii represent the reduction of sulfur to higher-order lithium polysulfides (LiPSs) (Li2S), respectively. n The process by which higher-order LiPSs (4≤n≤8) are reduced to lower-order LiPSs (Li2S2 and Li2S). Compared with S@PVDF, S@Mn-PWPU exhibits a smaller interval between the oxidation and reduction peaks, higher intensity, and exhibits less voltage polarization and more favorable reaction kinetics.

[0179] exist Figure 8 The conclusion that "the smaller the interval between the oxidation peak and the reduction peak, the higher the intensity, exhibiting smaller voltage polarization and more favorable reaction kinetics" can be found in the following literature:

[0180] 1.Senthil C,Kim SS,Jung H Y.Flame retardant high-power Li-S flexiblebatteries enabled by bio-macromolecular binder integrating conformalfractions[J].Nature Communications,2022,13(1):145.

[0181] Figure 9 Images of the batteries assembled from the sulfur electrode samples prepared in Example 7 and Comparative Example 1 of this invention after 200 cycles at 1C show that the S@Mn-PWPU did not detach, and there was no obvious lithium polysulfide residue on the separator; while the corresponding S@PVDF cathode showed obvious detachment, and dark yellow lithium polysulfides appeared on the separator. This indicates that the sulfur cathode prepared based on Mn-PWPU binder has significantly better stability than the sulfur cathode prepared based on PVDF.

[0182] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties, characterized in that: It is prepared by in-situ crosslinking of waterborne polyurethane resin with porphyrin / metalloporphyrin, including the following steps: The tetra(4-carboxyphenyl)porphyrin / tetra(4-carboxyphenyl)porphyrin metal complex and waterborne polyurethane resin were added to the reaction vessel at a mass ratio of 1:(1~20). A crosslinking agent was added, and the mixture was stirred thoroughly to obtain an aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties. The chemical structural formula of the waterborne polyurethane resin is as follows: ， In the formula, n = 1~100, and R1 has the following structure: ； R2 can be any of the following structures: 、 、 、 、 ； R3 can be any of the following structures, where m = 10~200: 、 、 。 2. The aqueous binder for lithium-sulfur battery electrodes according to claim 1, characterized in that: The tetra(4-carboxyphenyl)porphyrin metal complex is a metal complex formed by tetra(4-carboxyphenyl)porphyrin and any one of the following metal ions: iron ion, cobalt ion, nickel ion, and manganese ion; the tetra(4-carboxyphenyl)porphyrin metal complex is prepared by mixing tetra(4-carboxyphenyl)porphyrin with a metal salt and carrying out a metallization reaction.

3. The application of the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties as described in claim 1 in the preparation of lithium-sulfur batteries.

4. A method for preparing a sulfur electrode based on the aqueous binder for lithium-sulfur battery electrodes with electrocatalytic properties as described in claim 1, characterized in that... Includes the following steps: (1) Prepare the following raw materials by weight: 50-90 parts of carbon-sulfur complex, The electrodes use 3-20 parts of conductive carbon. 5-30 parts of the aqueous binder for lithium-sulfur battery electrodes as described in claim 1; (2) After the carbon-sulfur composite, conductive carbon for electrodes, and the aqueous binder for lithium-sulfur battery electrodes prepared in step (1) are thoroughly mixed and uniformly applied to the surface of the electrode current collector, and then dried to prepare a sulfur electrode.

5. The sulfur electrode prepared by the sulfur electrode preparation method according to claim 4.

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