A self-supported high-load sulfur cathode and its preparation method

Abstract

This invention discloses a self-supported high-load sulfur cathode and its preparation method, comprising a self-supporting matrix, lithium polysulfides, and other lithium-containing compounds. The self-supporting matrix is ​​prepared by composite composition of a porous carbon framework, an active catalyst, and a functional polymer. The molecular structure of the lithium polysulfides is Li₂S. x 4≤x≤8; This invention is easy to implement and the process is controllable. It has good practicality and operability. The self-supporting high-load sulfur cathode prepared has multiple advantages such as high sulfur loading, good confinement ability, rapid conversion kinetics, stable structure and simple composition.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to a self-supporting high-load sulfur cathode and its preparation method. Background Technology

[0002] Lithium-sulfur batteries have become a hot research topic due to their high theoretical specific capacity and wide availability of raw materials. However, their development is limited by defects such as poor cycle stability and safety. The main problems stem from the following two aspects:

[0003] 1) Elemental sulfur is an electronic insulator with low electrochemical activity. Its conversion to lithium sulfide has a slow reaction kinetics and an approximately 80% volume expansion occurs during the electrode reaction, which can easily damage the electrode structure.

[0004] 2) The reaction intermediate lithium polysulfide is readily soluble in the electrolyte and diffuses towards the negative electrode under the influence of concentration gradient and electric field, corroding lithium metal and producing a shuttle effect, which leads to a decrease in coulombic efficiency and a short cycle life.

[0005] Current common solutions involve combining elemental sulfur with porous carbon to improve the conductivity of the electrode material and, to some extent, limit the lithium polysulfide content. However, this does not fundamentally solve the aforementioned problems, and the sulfur loading in cathodes constructed from traditional sulfur-carbon composites is low (mostly around 5 mg / cm³). 2 (within), which greatly affects the actual energy density of the battery. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a self-supporting high-load sulfur cathode and its preparation method to address the shortcomings of the prior art. This invention solves the technical problems of low active material loading, intermediate product shuttle effect, poor insulating sulfur electrochemical activity, and electrode volume expansion of traditional sulfur cathodes, and has a significant effect on improving the overall electrochemical performance of lithium-sulfur batteries.

[0007] The present invention adopts the following technical solution:

[0008] A self-supported, high-load sulfur cathode comprises a self-supporting matrix, lithium polysulfides, and other lithium-containing compounds. The self-supporting matrix is ​​prepared by combining a porous carbon framework, an active catalyst, and a functional polymer. The molecular structure of the lithium polysulfides is Li₂S. x , 4≤x≤8.

[0009] Specifically, the mass ratio of porous carbon framework, active catalyst and functional polymer is (50-70):(5-10):(20-45).

[0010] Furthermore, the functional polymer includes at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethyleneimine, polyvinyl acetate, polyvinylidene fluoride-hexafluoropropylene copolymer, polysiloxane, and polyphosphazene.

[0011] Specifically, the active catalyst contains transition metal atoms.

[0012] Specifically, the porous carbon skeleton is formed by first soaking bio-cotton material in a conductive carbon solution, and then freeze-drying and high-temperature carbonization. The mass ratio of bio-cotton material to conductive carbon before freeze-drying is (80-95):(5-20).

[0013] Furthermore, bio-cotton materials include at least one of cotton, kapok, flax, and jute.

[0014] Furthermore, conductive carbon includes at least one of graphene, fullerene, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanospheres.

[0015] Specifically, other lithium-containing compounds include at least one of LiNO3, LiODFB, LiBOB, LiPF6, LiTFSI, LiBF4, LiClO4, LiFSI, LiBETI, LiCF3SO3, LiAsF6, LiTf, LiOTf, LiBC2O4F2, LiN(FSO2)2, LiN(CF3SO2)2, LiCl, LiI, LiBr, LiF, LiFAP, LiFAB, and LiTFSM.

[0016] Specifically, the total thickness of the self-supported sulfur cathode is 300–500 μm, and the areal sulfur loading is 8–20 mg / cm². 2 .

[0017] Another technical solution of the present invention is a method for preparing a self-supporting high-load sulfur cathode, comprising the following steps:

[0018] S1. Disperse conductive carbon uniformly in deionized water or organic solvent to prepare a conductive carbon solution; immerse the bio-cotton material in the conductive carbon solution at 25-60℃ for 12-48 hours.

[0019] S2. The conductive carbon solution obtained in step S1 is freeze-dried for 12-48 hours, and then carbonized at high temperature in an inert atmosphere to obtain a porous carbon skeleton.

[0020] S3. The active catalyst and functional polymer are ultrasonically dispersed in an organic solvent, and then the porous carbon framework obtained in step S2 is added. After vacuum drying at 50-80°C for 12-48 hours, a self-supporting matrix is ​​obtained.

[0021] S4. Mix elemental sulfur and lithium sulfide in a stoichiometric ratio of (3-7):1 and add to an organic solvent. After sufficient reaction and dissolution, prepare a lithium polysulfide solution. Then add 1% to 5% of other lithium-containing compounds by mass of the solution. Inject the lithium polysulfide solution into the self-supporting matrix obtained in step S3 to prepare a self-supporting high-load sulfur cathode.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] This invention discloses a self-supporting high-load sulfur cathode. The self-supporting matrix combines the mechanical strength of a porous carbon framework with the flexibility of functional polymers, achieving a balance of rigidity and flexibility. This buffers the volume changes of the electrode during charging and discharging, preventing structural collapse. The physical adsorption of the porous carbon framework and the chemical clamping effect of the functional polymers allow for the effective adsorption and retention of lithium polysulfides within the cathode structure, effectively suppressing lithium corrosion and shuttle effects. The three-dimensional porous carbon framework increases the contact sites with the active material, while the uniformly distributed active catalyst on the framework accelerates the redox reaction of sulfur species, promoting the conversion kinetics of lithium polysulfides. The self-supporting matrix directly accommodates the active material, eliminating the need for additional electrode auxiliaries such as current collectors, conductive agents, and binders, thus simplifying the structure and composition of traditional sulfur cathodes.

[0024] Furthermore, the mass ratio of porous carbon framework, active catalyst and functional polymer is limited to (50-70):(5-10):(20-45) to fully utilize the advantages of each component of the self-supporting matrix.

[0025] Furthermore, the functional polymers should have good flexibility to buffer the volume expansion of the electrode and maintain structural stability. At the same time, these polymers can also use the polar groups they carry to chemically anchor lithium polysulfides, so that lithium polysulfides are effectively confined within the positive electrode structure, suppressing their diffusion and shuttle between the positive and negative electrodes.

[0026] Furthermore, the active catalysts all contain transition metal atoms, including at least one of transition metal oxides, transition metal nitrides, transition metal sulfides, permetal phosphides, and transition metal single atoms. These substances can accelerate the redox kinetics of catalytic sulfur species. For the high sulfur loading electrodes involved in this invention, accelerating the conversion of lithium polysulfides and improving electrode kinetics are important measures to enhance electrochemical performance.

[0027] Furthermore, the porous carbon skeleton formed by freeze-drying and high-temperature carbonization of bio-cotton materials retains a rich 3D pore structure, providing ample space for accommodating active substances and thus improving the loading of active substances on the electrode.

[0028] Furthermore, bio-cotton materials possess a well-developed three-dimensional porous structure, and their original structural characteristics can be preserved through freeze-drying and high-temperature carbonization. Moreover, bio-cotton materials have a simple composition and low impurity content, making them highly suitable as precursors for sintering porous carbon frameworks.

[0029] Furthermore, conductive carbon materials all possess excellent electrical conductivity, which can enhance the conductivity and mechanical strength of porous carbon frameworks, and improve their electrochemical activity after sufficient contact with elemental sulfur.

[0030] Furthermore, other lithium-containing compounds can provide more lithium ions to the sulfur cathode and participate in the formation of a passivation film on the lithium anode surface, further preventing the corrosion of the lithium anode by a small amount of lithium polysulfides that may diffuse to the anode.

[0031] Furthermore, the self-supporting high-load sulfur cathode has a high sulfur loading, good confinement ability, rapid conversion kinetics, stable structure, and simple composition. It can effectively solve various problems of traditional cathodes, such as low sulfur loading, lithium polysulfide shuttle effect, low electroactivity of elemental sulfur, and electrode volume expansion. It can improve the capacity, efficiency, cycle and rate performance of lithium-sulfur batteries as a whole, and can effectively improve the actual energy density of lithium-sulfur batteries, with significant practical value.

[0032] A method for preparing a self-supporting, high-load sulfur cathode is readily achievable and process-controllable, avoiding complex preparation procedures and harsh conditions, thus demonstrating good practicality and operability. One of the key technologies in this method is the freeze-drying of bio-cotton materials, which helps to better construct a stable and ideal porous carbon framework structure.

[0033] In summary, the method of the present invention is easy to implement and the process is controllable, with good practicality and operability. The self-supporting high-load sulfur cathode prepared has multiple advantages such as high sulfur loading, good confinement ability, rapid conversion kinetics, stable structure, and simple composition.

[0034] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0035] Figure 1 The cycling performance curve of the self-supporting high-load sulfur cathode prepared in Example 1 of this invention is shown.

[0036] Figure 2 The charge-discharge curve of the self-supporting high-load sulfur cathode prepared in Example 1 of this invention;

[0037] Figure 3 The above are SEM images prepared in Example 1 of the present invention, wherein (a) is a porous carbon framework and (b) is a self-supporting sulfur cathode.

[0038] Figure 4 This is a cycle performance curve of the ordinary sulfur cathode prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0041] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0042] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0043] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0044] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0045] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0046] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0047] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0048] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0049] This invention provides a self-supporting high-load sulfur cathode with a total thickness of 300–500 μm and an areal sulfur loading of 8–20 mg / cm². 2 This includes self-supporting matrix, lithium polysulfides, and other lithium-containing compounds.

[0050] The self-supporting matrix is ​​composed of a porous carbon skeleton, an active catalyst, and a functional polymer. The porous carbon skeleton is formed by first soaking bio-cotton material in a conductive carbon solution, and then freeze-drying and high-temperature carbonization. The active catalyst contains transition metal atoms.

[0051] The molecular structure of lithium polysulfide is Li2S. x (4≤x≤8).

[0052] Other lithium-containing compounds include at least one of the following: LiNO3, LiODFB, LiBOB, LiPF6, LiTFSI, LiBF4, LiClO4, LiFSI, LiBETI, LiCF3SO3, LiAsF6, LiTf, LiOTf, LiBC2O4F2, LiN(FSO2)2, LiN(CF3SO2)2, LiCl, LiI, LiBr, LiF, LiFAP, LiFAB, and LiTFSM.

[0053] This invention discloses a method for preparing a self-supporting high-load sulfur cathode, comprising the following steps:

[0054] S1. Conductive carbon is uniformly dispersed in deionized water or an organic solvent to prepare a conductive carbon solution; the bio-cotton material is immersed in the conductive carbon solution at a temperature of 25–60°C for 12–48 hours.

[0055] The mass ratio of bio-cotton material to conductive carbon before freeze-drying is (80-95):(5-20).

[0056] Conductive carbon includes at least one of graphene, fullerene, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanospheres.

[0057] Biomaterials include at least one of cotton, kapok, flax, and jute.

[0058] S2. Freeze-dry the conductive carbon solution obtained in step S1 for 12-48 hours, and then carbonize it at high temperature in a tube furnace filled with an inert atmosphere to obtain a porous carbon skeleton.

[0059] S3. The active catalyst and functional polymer are ultrasonically dispersed in an organic solvent, and then a porous carbon framework is added. After vacuum drying, a self-supporting matrix is ​​obtained. The vacuum drying temperature is 50-80℃ and the time is 12-48h.

[0060] The mass ratio of porous carbon framework, active catalyst and functional polymer is (50-70):(5-10):(20-45).

[0061] The functional polymers include at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethyleneimine, polyvinyl acetate, polyvinylidene fluoride-hexafluoropropylene copolymer, polysiloxane, and polyphosphazene.

[0062] Active catalysts include one of the following: transition metal oxides, transition metal nitrides, transition metal sulfides, permetal phosphides, and transition metal single atoms.

[0063] S4. Mix elemental sulfur and lithium sulfide in a stoichiometric ratio of (3-7):1, then add to an organic solvent. After sufficient reaction and dissolution, prepare a lithium sulfide solution. Add other lithium-containing compounds at a mass percentage of 1-5%. Inject the above solution into the self-supporting substrate obtained in step S3 to prepare a self-supporting high-load sulfur cathode.

[0064] Other lithium-containing compounds include at least one of the following: LiNO3, LiODFB, LiBOB, LiPF6, LiTFSI, LiBF4, LiClO4, LiFSI, LiBETI, LiCF3SO3, LiAsF6, LiTf, LiOTf, LiBC2O4F2, LiN(FSO2)2, LiN(CF3SO2)2, LiCl, LiI, LiBr, LiF, LiFAP, LiFAB, and LiTFSM.

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0066] Example 1

[0067] Cotton sheets were soaked in an aqueous graphene solution and kept at 60°C for 12 hours, with a mass ratio of cotton sheets to graphene of 80:20. The solution was then freeze-dried for 48 hours and then carbonized at high temperature in a sealed tube furnace filled with argon to obtain a porous carbon framework.

[0068] MoS2 and PVDF-HFP were ultrasonically dispersed in NMP, and then a porous carbon framework was added. The mass ratio of the porous carbon framework, MoS2 and PVDF-HFP was 70:10:20. After vacuum drying at 60℃ for 12 hours, a self-supporting matrix was obtained.

[0069] Elemental sulfur and lithium sulfide were mixed in a molar ratio of 7:1 and then added to a DME / DOL (volume ratio 1:1) mixed solvent. After sufficient reaction and dissolution, a lithium sulfide solution (with 2 wt% LiNO3 added) was prepared. This solution was then injected into a self-supporting substrate to obtain a self-supporting high-load sulfur cathode with a thickness of 380 μm and an areal sulfur loading of 10.5 mg / cm². 2 .

[0070] Example 2

[0071] Kapok was soaked in a multi-walled carbon nanotube solution and kept at 25°C for 48 hours. The mass ratio of kapok to multi-walled carbon nanotubes was 95:5. The kapok was then freeze-dried for 24 hours.

[0072] The porous carbon framework, MoN, and PVDF were dried in a mass ratio of 60:5:35 at 50°C under vacuum for 48 hours.

[0073] The molar ratio of elemental sulfur to lithium sulfide is 3:1, and the amount of LiFSI added is 5%.

[0074] The self-supported positive electrode has a thickness of 300 μm and an area sulfur loading of 8 mg / cm². 2 .

[0075] The remaining preparation conditions were the same as in Example 1.

[0076] Example 3

[0077] Flax was soaked in a carbon nanofiber solution and kept at 25°C for 24 hours. The mass ratio of flax to carbon nanofiber was 90:10. The flax was then freeze-dried for 12 hours.

[0078] The porous carbon framework, CoSe2, and PEO were dried in a mass ratio of 50:5:45 at 80°C under vacuum for 12 hours.

[0079] The molar ratio of elemental sulfur to lithium sulfide is 5:1, and the amount of LiCF3SO3 added is 1%.

[0080] The self-supported cathode thickness reaches 500μm, and the sulfur loading is 20mg / cm². 2 .

[0081] The remaining preparation conditions were the same as in Example 1.

[0082] Comparative Example 1

[0083] Elemental sulfur and lithium sulfide were mixed in a molar ratio of 7:1 and then added to a DME / DOL (volume ratio 1:1) mixed solvent. After sufficient reaction and dissolution, a lithium sulfide solution (with 2 wt% LiNO3 added) was prepared. This solution was then injected into a commercial carbon cloth matrix to obtain a sulfur cathode control sample with a thickness of 250 μm and an areal sulfur loading of -5 mg / cm². 2 .

[0084] The sulfur cathode obtained in the above embodiments was used to assemble lithium into a lithium-sulfur battery. Constant current charge-discharge tests were conducted at a rate of 0.2C, a potential window of 1.7–2.8V, and 50 cycles. The relevant data are summarized in Table 1. Figure 1 , Figure 2 Figure 3 and Figure 4 Compared with ordinary sulfur cathodes made of commercially available carbon cloth, the sulfur cathode of this invention has significant advantages in terms of sulfur loading, reversible capacity and cycle stability, and the overall battery performance is excellent.

[0085] Table 1 Performance test results of the examples and comparative examples

[0086]

[0087] In summary, the present invention provides a self-supporting high-load sulfur cathode and its preparation method. The self-supporting high-load sulfur cathode has multiple advantages such as high sulfur loading, good confinement ability, rapid conversion kinetics, stable structure, and simple composition. It can effectively solve various problems of traditional sulfur cathodes, such as low active material loading, intermediate product shuttle effect, poor insulating sulfur electrolytic activity, and electrode volume expansion. The preparation method is easy to implement and the process is controllable, with good practicality and operability.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-supporting high-load sulfur cathode, characterized in that, This includes a self-supporting matrix, lithium polysulfides, and other lithium-containing compounds. The self-supporting matrix is ​​prepared by combining a porous carbon framework, an active catalyst, and functional polymers. The molecular structure of lithium polysulfides is Li₂S. x , 4≤x≤8, the porous carbon skeleton is formed by first soaking the bio-cotton material in the conductive carbon solution, and then freeze-drying and high-temperature carbonization. The mass ratio of the bio-cotton material and the conductive carbon before freeze-drying is (80~95):(5~20).

2. The self-supporting high-load sulfur cathode according to claim 1, characterized in that, The mass ratio of porous carbon framework, active catalyst and functional polymer is (50~70): (5~10): (20~45).

3. The self-supporting high-load sulfur cathode according to claim 2, characterized in that, The functional polymers include at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polyethyleneimine, polyvinyl acetate, polyvinylidene fluoride-hexafluoropropylene copolymer, polysiloxane, and polyphosphazene.

4. The self-supporting high-load sulfur cathode according to claim 1, characterized in that, Active catalysts contain transition metal atoms.

5. The self-supporting high-load sulfur cathode according to claim 1, characterized in that, Biomaterials include at least one of cotton, kapok, flax, and jute.

6. The self-supporting high-load sulfur cathode according to claim 1, characterized in that, Conductive carbon includes at least one of graphene, fullerene, carbon nanofibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanospheres.

7. The self-supporting high-load sulfur cathode according to claim 1, characterized in that, Other lithium-containing compounds include at least one of LiNO3, LiODFB, LiBOB, LiPF6, LiTFSI, LiBF4, LiClO4, LiFSI, LiBETI, LiCF3SO3, LiAsF6, LiTf, LiOTf, LiBC2O4F2, LiN(FSO2)2, LiN(CF3SO2)2, LiCl, LiI, LiBr, LiF, LiFAP, LiFAB, and LiTFSM.

8. The self-supporting high-load sulfur cathode according to any one of claims 1 to 7, characterized in that, The total thickness of the self-supported sulfur cathode is 300~500μm, and the sulfur loading is 8~20mg / cm². 2 .

9. A method for preparing a self-supporting high-load sulfur cathode according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Disperse conductive carbon uniformly in deionized water or organic solvent to prepare a conductive carbon solution; immerse the bio-cotton material in the conductive carbon solution at 25~60℃ for 12~48h. S2. Freeze-dry the conductive carbon solution obtained in step S1 for 12~48h, and then carbonize it at high temperature in an inert atmosphere to obtain a porous carbon skeleton. S3. The active catalyst and functional polymer are ultrasonically dispersed in an organic solvent, and then the porous carbon framework obtained in step S2 is added. After vacuum drying at 50~80℃ for 12~48h, a self-supporting matrix is ​​obtained. S4. Mix elemental sulfur and lithium sulfide in a stoichiometric ratio of (3~7):1 and add to an organic solvent. After sufficient reaction and dissolution, prepare a lithium polysulfide solution. Then add 1%~5% of other lithium-containing compounds by mass of the solution. Inject the lithium polysulfide solution into the self-supporting matrix obtained in step S3 to prepare a self-supporting high-load sulfur cathode.

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