A method for preparing a lithium-sulfur battery cathode containing a catalyst

Abstract

The application belongs to the technical field of lithium-sulfur batteries, and discloses a preparation method of a lithium-sulfur battery positive electrode containing a catalyst. The preparation method adopts a mode in which an organic binder is dissolved and then precipitated to composite conductive carbon material and a catalyst, and the steps include: adding a metal compound catalyst, conductive carbon material B and an organic binder into an organic dispersing agent, then adding a reverse solvent deionized water to precipitate the organic binder, separating out solid substances, and obtaining a composite catalyst; then adding the composite catalyst, elemental sulfur, conductive carbon material A and an aqueous binder into deionized water, stirring into a slurry, coating on an aluminum foil, and drying to obtain the lithium-sulfur battery positive electrode containing the catalyst. The lithium-sulfur battery positive electrode containing the catalyst prepared by the method can effectively exert the catalytic effect of the catalyst on reaction intermediates, and realize high discharge specific capacity and stable long cycle performance of the lithium-sulfur battery positive electrode at a large rate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery technology, specifically relating to a method for preparing a lithium-sulfur battery cathode containing a catalyst. Background Technology

[0002] The commercialization of lithium-ion batteries has spurred the rapid development of the electric vehicle industry. Electric vehicles with a range exceeding 1000 kilometers require secondary batteries with an actual energy density exceeding 500 Wh / kg. However, due to its reaction mechanism, the actual energy density of lithium-ion batteries is generally below 400 Wh / kg, making it difficult to meet the demands of long-range electric vehicles. Lithium-sulfur batteries, with their ultra-high theoretical energy density of up to 2600 Wh / kg, have thus attracted widespread attention.

[0003] Under actual operating conditions, the reaction on the cathode side of a lithium-sulfur battery follows a multiphase, multi-electron conversion process. Specifically, during discharge, solid-phase elemental sulfur first undergoes a solid-liquid conversion, electrochemically reducing it to the soluble intermediate lithium polysulfide. The liquid-phase lithium polysulfide then undergoes a liquid-phase reduction process, ultimately resulting in a liquid-solid conversion on the conductive surface to form solid-phase lithium sulfide. This liquid-solid conversion process is a kinetically delayed step, leading to insufficient liquid-solid deposition in practical lithium-sulfur batteries and low cathode discharge specific capacity, severely hindering the practical application of lithium-sulfur batteries. Based on these issues, previous researchers have mostly adopted the method of introducing cathode catalysts to accelerate the liquid-solid conversion kinetics, thereby constructing high-energy-density lithium-sulfur batteries.

[0004] Yuan et al. introduced the conductive inorganic compound CoS2 into the cathode to accelerate the conversion kinetics of polysulfides, thereby improving the discharge specific capacity of lithium-sulfur batteries (Nano Lett. 2016, 16, 519-527). Yang et al. constructed a WS2-WO3 heterojunction catalyst, which enhanced the adsorption of polysulfides by WO3 and the conversion of polysulfides by WS2, thus simultaneously improving the mass transfer and interfacial charge transfer processes of polysulfides and increasing the discharge specific capacity of the cathode (Adv. Energy Mater. 2020, 2000091). Lv et al. constructed a grain boundary-rich MoN-Mo2N catalyst, utilizing the special electronic structure at the grain boundaries to regulate the liquid-solid deposition kinetics and deposition mode of polysulfides (Nano Energy 2022, 91, 106669). However, most studies only focus on how to construct catalytic sites with better effects, neglecting the actual catalytic effect in practical battery systems. In reality, improving the intrinsic catalytic activity of a catalytic site does not necessarily translate to a full and effective performance enhancement in a practical battery system. This is because the liquid-solid conversion reaction at the cathode occurs at the three-phase interface of the electrolyte, catalyst, and conductive carbon. Only when the catalyst has a reasonable spatial distribution, situated at the interface between the electrolyte and conductive carbon, and simultaneously in contact with both ionic and electronic pathways, can it exert a catalytic effect and improve battery performance. Therefore, strengthening the interaction between the catalyst and conductive carbon, rationally combining the catalyst and conductive carbon, and optimizing the spatial distribution of the catalyst in the cathode are crucial means to improve catalytic efficacy. In particular, developing rational composite methods for catalysts and conductive carbon holds promise for enhancing the performance of catalysts in practical battery systems.

[0005] Therefore, there is an urgent need to provide a novel catalyst composite method to prepare catalysts and lithium-sulfur battery cathodes, thereby fully leveraging the catalytic effect of the catalysts and constructing high-performance lithium-sulfur battery systems. Summary of the Invention

[0006] This invention provides a method for preparing a catalyst-containing lithium-sulfur battery cathode, which uses an organic binder to first dissolve and then precipitate conductive carbon material and catalyst to composite the cathode. The steps include:

[0007] 1) Mix the metal compound catalyst, conductive carbon material B, and organic binder;

[0008] 2) Add the above mixture to an organic dispersant, preferably N-methylpyrrolidone, and stir to form a first slurry;

[0009] 3) Add deionized water to the first slurry to obtain the second slurry, and stir to precipitate the organic binder;

[0010] 4) Separate the solid material from the second slurry to obtain the composite catalyst; preferably, the solid material in the slurry is separated by vacuum filtration.

[0011] 5) Mix elemental sulfur, conductive carbon material A, aqueous binder, and composite catalyst to obtain a mixture;

[0012] 6) Add the mixture from step 5) to deionized water and stir thoroughly to form the third slurry;

[0013] 7) Coat the third slurry onto aluminum foil and dry it to obtain the positive electrode of a lithium-sulfur battery containing the catalyst.

[0014] In some preferred embodiments, the metal compound catalyst is selected from one or more of titanium nitride, cobalt nitride, nickel nitride, vanadium nitride, titanium carbide, or iron carbide;

[0015] and / or

[0016] The conductive carbon material B is graphene and / or carbon nanotubes;

[0017] and / or

[0018] The organic binder is polytetrafluoroethylene and / or polyvinylidene fluoride.

[0019] In some preferred embodiments, the conductive carbon material A is selected from acetylene black, Ketjen black, mesophase carbon microspheres, or activated carbon;

[0020] and / or

[0021] The water-based adhesive is selected from one of polyacrylic acid, carboxymethyl cellulose, or polyvinyl alcohol.

[0022] In some preferred embodiments, in step 1), the mass fraction of the metal compound catalyst is 65-85 wt%, the mass fraction of the organic binder is 3-5 wt%, and the balance is conductive carbon material B.

[0023] In some preferred embodiments, in step 5), the mass fraction of elemental sulfur is 65-80 wt%, the mass fraction of aqueous binder is 5-10 wt%, the mass fraction of composite catalyst is 1-10 wt%, and the balance is conductive carbon material A.

[0024] In some preferred embodiments, in step 2), the solid content of the first slurry is 10-20 wt%, preferably 15 wt%.

[0025] In some preferred embodiments, in step 3), the solid content of the second slurry is 3-7 wt%, preferably 5 wt%.

[0026] In some preferred embodiments, in step 6), the solid content of the third slurry is 10-15 wt%, preferably 12 wt%.

[0027] In some preferred embodiments, in step 7), the drying temperature is 30–80°C and / or the drying time is 2–20 hours; preferably, drying is carried out at 60°C for 12 hours.

[0028] In some preferred embodiments, the areal loading of elemental sulfur in the catalyst-containing lithium-sulfur battery cathode is 6–10 mg / cm³. 2 .

[0029] Secondly, the present invention provides a catalyst-containing lithium-sulfur battery cathode prepared by the preparation method described above.

[0030] Thirdly, the present invention also provides an application of the catalyst-containing lithium-sulfur battery cathode described above in lithium-sulfur batteries.

[0031] Fourthly, the present invention provides a lithium-sulfur battery comprising: a lithium-sulfur battery positive electrode containing a catalyst, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a lithium-sulfur battery electrolyte.

[0032] In lithium-sulfur batteries, the aforementioned lithium-sulfur battery cathode containing a catalyst is used, such that at a charge / discharge rate of 0.5C, the cathode's first discharge specific capacity is not less than 1300 mAh / g, and the number of cycles is not less than 300 when the discharge specific capacity decays to 80% of the initial value.

[0033] The beneficial effects of this invention are as follows:

[0034] 1. This invention provides a method for preparing a catalyst-containing lithium-sulfur battery cathode. An organic binder B is first dissolved in an organic dispersant N-methylpyrrolidone, followed by the addition of a metal compound catalyst and conductive carbon material B. After thorough mixing, deionized water is added as an antisolvent to precipitate the organic binder. This method effectively combines the metal compound catalyst with the conductive carbon material B, allowing the metal compound catalyst to be directionally loaded onto the high specific surface area conductive carbon material B. This induces the directional and reversible deposition of lithium sulfide on the highly conductive and high specific surface area conductive carbon material B, significantly improving the utilization rate of the active material and maintaining stability during cycling.

[0035] 2. The lithium-sulfur battery cathode containing catalyst and the composite catalyst design described in this invention can effectively leverage the catalytic effect of metal compound catalysts on reaction intermediates, enabling lithium sulfide to be fully deposited on conductive carbon materials with high specific surface area, thereby improving the utilization rate of active materials in the cathode.

[0036] 3. When the catalyst-containing cathode prepared by this invention is applied in lithium-sulfur batteries, it can achieve high discharge specific capacity and long cycle stability at a high charge-discharge rate. At a charge-discharge rate of 0.5C, the first discharge specific capacity of the cathode is not less than 1300mAh / g, and the number of cycles is not less than 300 when the discharge specific capacity decays to 80% of the initial value. Attached Figure Description

[0037] Figure 1 This is a flowchart of a method for preparing a lithium-sulfur battery cathode containing a catalyst.

[0038] Figure 2 The image shown is a scanning electron microscope (SEM) image of the composite catalyst prepared in Example 1.

[0039] Figure 3 The image shown is a scanning electron microscope (SEM) image of the catalyst-containing lithium-sulfur battery cathode prepared in Example 1. Detailed Implementation

[0040] The present invention is illustrated below with specific examples. These embodiments are provided to better understand the present invention and are by no means intended to limit the scope of the present invention.

[0041] Example 1

[0042] like Figure 1 As shown, the present invention provides a method for preparing a catalyst-containing lithium-sulfur battery cathode, which specifically includes the following steps:

[0043] Preparation of composite catalysts:

[0044] 1) Mix the metal compound catalyst, conductive carbon material B and organic binder; the mass fraction of the metal compound catalyst is 65-85 wt%, the mass fraction of the organic binder is 3-5 wt%, and the balance is the second conductive carbon material;

[0045] 2) Add the above mixture to the organic dispersant N-methylpyrrolidone and stir thoroughly to form a first slurry. The solid content of the first slurry is 15 wt%.

[0046] 3) Add deionized water as an anti-solvent to the first slurry to obtain the second slurry, thereby reducing the solid content of the second slurry to 5 wt%, and stir thoroughly to allow the organic binder to precipitate.

[0047] 4) The solid substances in the second slurry are separated by vacuum filtration to obtain the composite catalyst.

[0048] The method for preparing a lithium-sulfur battery cathode containing the above-mentioned composite catalyst includes:

[0049] 5) Mix elemental sulfur, conductive carbon material A, aqueous binder and the composite catalyst prepared in step 4) above; wherein the mass fraction of elemental sulfur is 65-80 wt%, the mass fraction of aqueous binder is 5-10 wt%, the mass fraction of composite catalyst is 1-10 wt%, and the balance is conductive carbon material A;

[0050] 6) Add the above mixture to deionized water and stir thoroughly to form a third slurry. The solid content of the third slurry is 12 wt%.

[0051] 7) The above third slurry is coated onto aluminum foil with a scraper and dried at 60°C for 12 hours to obtain the positive electrode of lithium-sulfur battery containing catalyst.

[0052] The cathode prepared using this method has a surface loading of 6–10 mg / cm³. 2 .

[0053] Specifically, titanium nitride is used as the metal compound catalyst, graphene as the conductive carbon material B of the composite catalyst, and polytetrafluoroethylene (PTFE) as the organic binder of the composite catalyst. The mass fraction of titanium nitride in the composite catalyst is 70 wt%, PTFE is 5 wt%, and graphene is 25 wt%. Figure 2 The morphology of the composite catalyst prepared by this method is shown.

[0054] Ketjenblack was used as the conductive carbon material A, and polyacrylic acid was used as the aqueous binder for the sulfur-carbon composite cathode. The cathode material had a mass fraction of 70 wt%, polyacrylic acid 5 wt%, composite catalyst 10 wt%, and Ketjenblack 15 wt%. Figure 3 The morphology of the catalyst-containing positive electrode of the lithium-sulfur battery prepared by this method is shown.

[0055] The surface loading of elemental sulfur in the cathode prepared by this method is 8 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1510mAh / g at a discharge rate of 0.5C, and a cycle count of 504 when the discharge specific capacity decays to 80% of the initial value.

[0056] Comparative Example 1

[0057] Based on Example 1, steps 1) to 4) of the composite catalyst preparation were removed. In step 5), the composite catalyst was replaced with an equal amount of titanium nitride material and graphene in equal proportion. Other components and preparation processes remained the same as in Example 1.

[0058] The surface loading of elemental sulfur in the cathode prepared by this method is 8 mg / cm³. 2In a lithium-sulfur battery, at a discharge rate of 0.5C, the positive electrode specific capacity is 1150mAh / g, and the number of cycles is 112 when the discharge specific capacity decays to 80% of the initial value.

[0059] Table 1

[0060]

[0061] Conclusion Analysis:

[0062] The experimental results above show that, compared with Example 1, the use of composite catalyst can significantly improve the specific capacity and cycle life of lithium-sulfur batteries, thus confirming the effectiveness of the cathode used in this invention.

[0063] Example 2

[0064] Cobalt nitride was used as the metal compound catalyst. Carbon nanotubes were used as the conductive carbon material B of the composite catalyst, and polyvinylidene fluoride (PVDF) was used as the organic binder of the composite catalyst. The mass fraction of the metal compound catalyst particles in the composite catalyst was 65 wt%, PVDF was 4 wt%, and graphene was 31 wt%.

[0065] Acetylene black was used as the conductive carbon material A in the sulfur-carbon composite cathode, and carboxymethyl cellulose was used as the aqueous binder for the sulfur-carbon composite cathode. The cathode material contained 65 wt% sulfur, 10 wt% polyacrylic acid, 1 wt% composite catalyst, and 24 wt% acetylene black.

[0066] Other processes remain consistent with those in Example 1. The areal loading of elemental sulfur in the cathode prepared using this method is 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1420 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 423 cycles when the discharge specific capacity decays to 80% of the initial value.

[0067] Example 3

[0068] Based on Example 2, nickel nitride was used as the metal compound catalyst, while other components and preparation processes remained consistent with Example 2. The surface loading of elemental sulfur in the cathode prepared using this method was 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1370 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 452 cycles when the discharge specific capacity decays to 80% of the initial value.

[0069] Example 4

[0070] Based on Example 2, vanadium nitride was used as the metal compound catalyst, while other components and preparation processes remained consistent with Example 2. The areal loading of elemental sulfur in the cathode prepared using this method was 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1345 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 388 cycles when the discharge specific capacity decays to 80% of the initial value.

[0071] Example 5

[0072] Based on Example 2, titanium carbide was used as the metal compound catalyst, while other components and preparation processes remained consistent with Example 2. The areal loading of elemental sulfur in the cathode prepared using this method was 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1310 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 352 cycles when the discharge specific capacity decays to 80% of the initial value.

[0073] Example 6

[0074] Based on Example 2, iron carbide was used as the metal compound catalyst, while other components and preparation processes remained consistent with Example 2. The surface loading of elemental sulfur in the cathode prepared using this method was 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1370 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 446 cycles when the discharge specific capacity decays to 80% of the initial value.

[0075] Example 7

[0076] Based on Example 2, the metal compound catalyst used was cobalt nitride and iron carbide in a 1:1 mass ratio, while other components and preparation processes remained consistent with Example 2. The cathode prepared using this method had an elemental sulfur surface loading of 10 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1335 mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 384 cycles when the discharge specific capacity decays to 80% of the initial value.

[0077] Table 2

[0078]

[0079] Example 8

[0080] A conductive carbon material B is used as the composite catalyst. Polytetrafluoroethylene (PTFE) is used as the organic binder for the composite catalyst. The mass fraction of the metal compound catalyst particles in the composite catalyst is 85 wt%, the mass fraction of PTFE is 3 wt%, and the mass fraction of graphene is 11 wt%.

[0081] Activated carbon is used as the conductive carbon material A in the sulfur-carbon composite cathode, and polyvinyl alcohol is used as the aqueous binder for the sulfur-carbon composite cathode. The mass fraction of the cathode sulfur material is 80 wt%, the mass fraction of polyvinyl alcohol is 6 wt%, the mass fraction of the composite catalyst is 7 wt%, and the mass fraction of activated carbon is 7 wt%.

[0082] Other processes remain consistent with those in Example 1. The surface loading of elemental sulfur in the cathode prepared using this method is 6 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1350mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 359 cycles when the discharge specific capacity decays to 80% of the initial value.

[0083] Example 9

[0084] Based on Example 8, the conductive carbon material B in the cathode material is mesophase carbon microspheres, while other components and preparation processes remain consistent with Example 8. The areal loading of elemental sulfur in the cathode prepared by this method is 6 mg / cm³. 2 It can achieve a positive electrode specific capacity of 1380mAh / g at a discharge rate of 0.5C in lithium-sulfur batteries, and 374 cycles when the discharge specific capacity decays to 80% of the initial value.

[0085] Table 3

[0086]

Claims

1. A method for preparing a lithium-sulfur battery cathode containing a catalyst, characterized in that the steps include... The method comprises the following steps: 1) mixing a metal compound catalyst, an electrically conductive carbon material B and an organic binder; The metal compound catalyst is selected from one or more of titanium nitride, cobalt nitride, nickel nitride, vanadium nitride, titanium carbide or iron carbide; the electrically conductive carbon material B is graphene and / or carbon nanotube; and the organic binder is polytetrafluoroethylene and / or polyvinylidene fluoride; In the step 1), the mass fraction of the metal compound catalyst is 65-85 wt%, the mass fraction of the organic binder is 3-5 wt%, and the rest is the electrically conductive carbon material B; 2) adding an organic dispersant to the mixture obtained in the step 1) to form a first slurry by stirring; in the step 2), the solid content of the first slurry is 10-20 wt%; 3) adding deionized water to the first slurry to obtain a second slurry, and stirring to precipitate the organic binder; in the step 3), the solid content of the second slurry is 3-7 wt%; 4) separating the solid substance from the second slurry to obtain a composite catalyst; 5) mixing elemental sulfur, an electrically conductive carbon material A, a water-based binder and the composite catalyst to obtain a mixture; 6) adding the mixture obtained in the step 5) to deionized water to form a third slurry by stirring; in the step 6), the solid content of the third slurry is 10-15 wt%; 7) coating the third slurry on an aluminum foil and drying to obtain a lithium-sulfur battery cathode containing a catalyst.

2. The production method according to claim 1, wherein The electrically conductive carbon material A is selected from one of acetylene black, ketjen black, mesocarbon microbeads or activated carbon; and / or The water-based binder is selected from one of polyacrylic acid, carboxymethyl cellulose or polyvinyl alcohol.

3. The production method according to claim 1, characterized by, In the step 5), the mass fraction of the elemental sulfur is 65-80 wt%, the mass fraction of the water-based binder is 5-10 wt%, the mass fraction of the composite catalyst is 1-10 wt%, and the rest is the electrically conductive carbon material A.

4. The production method according to claim 1, characterized by, In the step 2), the solid content of the first slurry is 15 wt%; and / or The organic dispersant comprises N-methyl pyrrolidone; and / or In the step 3), the solid content of the second slurry is 5 wt%; and / or In the step 6), the solid content of the third slurry is 12 wt%.

5. The production method according to claim 1, characterized by, The elemental sulfur in the lithium-sulfur battery cathode containing catalyst has a surface loading of 6-10 mg / cm 2 .

6. A lithium-sulfur battery cathode containing a catalyst prepared by the method of any one of claims 1-5.

7. Use of the lithium-sulfur battery cathode containing a catalyst of claim 6 in a lithium-sulfur battery.

8. A lithium-sulfur battery comprising: the lithium-sulfur battery cathode containing a catalyst of claim 6, an anode, a separator disposed between the cathode and the anode, and a lithium-sulfur battery electrolyte.

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