Transition metal supported layered metal sulfide composite materials, preparation and use thereof

Abstract

This invention belongs to the field of new energy technology, specifically relating to a layered metal sulfide composite material supported by transition metal single atoms, its preparation method, and its application. First, a layered metal sulfide is loaded onto a conductive carbon carrier, and then transition metal single atoms are loaded onto the surface of the layered metal sulfide. When this composite material is used as a sulfur carrier in a positive electrode, the prepared lithium-sulfur battery exhibits superior capacity retention, cycle stability, and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a layered metal sulfide composite material supported by a single atom of a transition metal, its preparation method, and its application. Background Technology

[0002] With the rapid development of portable wearable electronic devices, electric vehicles, large-scale energy storage power stations, aerospace, and other fields, there is an urgent need to develop secondary batteries with higher specific energy. However, the energy density of commercial lithium-ion batteries has approached its theoretical limit, thus necessitating accelerated development and research into high specific energy density battery systems. Among these, lithium-sulfur batteries, with their relatively high theoretical specific energy (2600Wh / kg), are a promising candidate. -1 This has attracted widespread attention from researchers.

[0003] Lithium-sulfur batteries use elemental sulfur as the positive electrode and metallic lithium as the negative electrode. The reaction mechanism is complex and has evolved from long-chain lithium polysulfides (Li₂S₂) to lithium sulfides. x The process of converting lithium polysulfides (4 < x < 8) to short-chain lithium sulfides involves the following: long-chain lithium polysulfides are highly soluble in ether-based electrolytes and, under the influence of an electric field and concentration gradient, easily shuttle through the membrane to the lithium metal anode side for reduction. The reduced lithium polysulfides then readily re-diffuse to the sulfur cathode side for oxidation, resulting in low capacity retention, coulombic efficiency, and poor cycle stability in lithium-sulfur batteries. Therefore, mitigating this shuttle effect of polysulfides remains a fundamental scientific problem in lithium-sulfur batteries that has long existed and has not yet been well resolved.

[0004] Chinese patent CN114149028B discloses a method for preparing molybdenum disulfide material and its application in the modification of lithium-sulfur battery separators. Although polar molybdenum disulfide exhibits strong adsorption for lithium polysulfides, its catalytic ability for the reduction reaction of lithium polysulfides is weak. This results in limited suppression of the shuttle effect in practical high-sulfur cathodes, leading to unsatisfactory battery cycle performance. Furthermore, Chinese patent CN107469855A mentions the preparation of a nitrogen-doped graphene-supported metal single-atom catalyst for energy storage materials. However, when applied to sulfur cathodes, the graphene used in this patent is expensive, leading to high costs in large-scale industrial applications. Additionally, the limited number of single-atom active sites further contributes to unsatisfactory battery cycle performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a carbon-supported layered metal sulfide composite material with transition metal single atoms and its application in the sulfur cathode of lithium-sulfur batteries. The carbon support serves to facilitate electron transport and construct the electrode channel structure; the polar layered metal sulfides not only provide abundant defect sites to anchor transition metal single atoms but also exhibit strong adsorption of lithium polysulfides; simultaneously, the sulfur-coordinated transition metal single atoms have a strong catalytic conversion effect on the dissolved polysulfides, effectively mitigating the "shuttle effect" of lithium polysulfides. When this composite material is used as a sulfur support for the cathode, the prepared lithium-sulfur battery exhibits superior capacity retention, cycle stability, and rate performance.

[0006] A method for preparing a layered metal sulfide composite material supported by a transition metal single atom includes the following steps: First, a layered metal sulfide is loaded onto a conductive carbon carrier, and then a transition metal single atom is loaded onto the surface of the layered metal sulfide.

[0007] (1) Dissolve conductive carbon, metal salt and ligand in a certain proportion, disperse by ultrasonication and continue stirring until a homogeneous solution is formed;

[0008] (2) The above solution is subjected to closed heating treatment, and the generated carbon-supported layered metal sulfide material is recovered;

[0009] (3) The above composite material, metal salt and deionized water are mixed in a certain proportion for impregnation treatment, and the carbon-supported layered metal sulfide composite material after adsorbing metal salt is recovered.

[0010] (4) The above composite material is placed in a tube furnace for calcination to obtain a carbon-supported layered metal sulfide composite material with a single atom of transition metal.

[0011] (5) Grind the composite material obtained in step (4) with sublimed sulfur at a mass ratio of 1:2 to 9, transfer it to a sealed bottle, and heat-treat the sulfur-loaded material under an inert atmosphere to obtain a composite sulfur cathode.

[0012] The conductive carbon selected in step (1) is one or a mixture of two or more of acetylene black, carbon nanotubes, carbon fibers, and graphene.

[0013] The metal salt in step (1) includes one or a mixture of two or more of sodium molybdate, ammonium molybdate, sodium stannate, sodium niobate, and sodium titanate.

[0014] The ligand in step (1) includes one or more of the following: thiourea, cysteine, carbon disulfide, selenium, and selenourea.

[0015] The mass ratio of conductive carbon: metal salt: ligand in step (1) is 1:1 to 100:1 to 2000.

[0016] The heat treatment temperature in step (2) is 80-600℃ and the heat treatment time is 2-30h;

[0017] The ratio of the composite material in step (3) to the metal salt to the deionized water is 1:0.01 to 1:1 to 100.

[0018] The metal salt in step (3) includes one or a mixture of two or more of the following: ferric nitrate, cobalt nitrate, nickel nitrate, zinc nitrate, copper nitrate, ferric chloride, cobalt chloride, nickel chloride, zinc chloride, ferrocyanine, cobalt phthalocyanine, and nickel phthalocyanine.

[0019] The immersion temperature in step (3) is 20-100℃, and the immersion time is 1-100h;

[0020] The calcination temperature in step (4) is 300-1000℃, the calcination time is 1-10h, and the calcination atmosphere is a hydrogen-argon mixture.

[0021] In step (5), the inert atmosphere is high-purity argon or nitrogen, the heat treatment temperature is 140-300℃, and the treatment time is 12-24 hours.

[0022] The carbon-supported layered metal sulfide material with transition metal single atoms prepared in this invention, when used as a sulfur carrier, not only ensures a high sulfur loading and buffers sulfur volume expansion while providing good physical confinement for lithium polysulfides, but also ensures rapid electron transport. The layered metal sulfides not only provide defect sites for anchoring single atoms, but their polar surfaces also exhibit strong adsorption capacity for lithium polysulfides. The sulfur-coordinated transition metal single atoms have a strong catalytic effect on the redox reaction of lithium polysulfides, thereby effectively suppressing the shuttle effect and improving the cycle stability of lithium-sulfur batteries. The advantages of this invention are low raw material cost, uniform material morphology, controllable parameters, good reproducibility, mature and simple process, and mass production capability. The loading amounts of layered metal sulfides and transition metal single atoms can be adjusted and controlled through process parameters to synergistically enhance the adsorption and catalysis of lithium polysulfides. Attached Figure Description

[0023] Figure 1 This is the XRD diffraction pattern of CNT@MoS2-Fe;

[0024] Figure 2 These are transmission electron microscopy (TEM) images and elemental analysis diagrams of CNT@MoS2-Fe.

[0025] Figure 3 This is a comparison chart of the cyclic voltammetry curves of lithium-sulfur batteries in Example 1 and the control group;

[0026] Figure 4This is a comparison chart of charge-discharge cycles of lithium-sulfur batteries in Example 1 and the control group; Detailed Implementation

[0027] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0028] Example 1

[0029] 100 mg of carbon nanotubes, 40 mL of deionized water, 1.8 g of ammonium molybdate, and 20 mL of CS2 were mixed thoroughly and transferred to a hydrothermal reactor. The mixture was reacted at 400°C for 4 hours under sealed conditions. The product was then filtered, washed, and dried to obtain CNT@MoS2. 100 mg of CNT@MoS2, 20 mg of ferric nitrate, and 1 mL of deionized water were ultrasonically homogenized and allowed to stand for 12 hours. After centrifugation, washing, and drying, the product was placed in a tube furnace and treated at 500°C for 3 hours under a hydrogen-argon mixed atmosphere with a hydrogen volume content of 10% to obtain the CNT@MoS2-Fe composite material. The XRD pattern of the composite material is shown below. Figure 1 As shown, obvious MoS2 diffraction peaks are visible, and no diffraction peaks belonging to Fe particles or Fe compounds are observed; the transmission electron microscopy of the composite material is as follows. Figure 2 As shown, the MoS2 sheet structure grows on the CNT surface, and no obvious Fe or Fe compound particles are observed. Meanwhile, the selected area elemental analysis results show that Fe is enriched in the MoS2 region, indicating that Fe may be anchored on the MoS2 surface in the form of single atoms.

[0030] Take 0.1g of CNT@MoS2-Fe, grind it with 0.3g of sublimed sulfur, and transfer it to a sealed reaction vessel. Heat treat it at 155℃ for 12h under nitrogen to obtain S@CNT@MoS2-Fe composite material.

[0031] Take 0.08 g of S@CNT@MoS2-Fe (S@CNT@MoS2 and S@CNT are control groups) and 0.01 g of acetylene black, add 0.2 g of polyvinylidene fluoride (PVDF, 5% by mass) solution, use N-methylpyrrolidone as solvent, grind for 1 h, then use a 200 μm scraper to coat the film on carbon-coated aluminum foil, dry at 60 °C overnight, slice, weigh, and vacuum dry at 55 °C for 24 h. Use this electrode as the positive electrode, lithium sheet as the negative electrode, Celgard 2500 as the separator, 1 M lithium bis(trifluoromethanesulfonyl)imide solution (LITFSI) as the electrolyte, 0.2 M lithium nitrate as the additive, and a mixture of 1,3-dioxolane (DOL) and dimethyl ether (DME) (volume ratio 1:1) as the solvent to assemble the battery.

[0032] The cyclic volt-ampere curve of the battery is as follows: Figure 3As shown, compared to the control groups S@CNT@MoS2 and S@CNT, the reduction peaks I and II of the S@CNT@MoS2-Fe battery exhibit more positive potentials and sharper peak shapes, indicating faster sulfur reduction kinetics. Furthermore, the oxidation peaks show a more negative potential, indicating faster lithium sulfide oxidation kinetics. This demonstrates that single-atom Fe-supported MoS2 possesses strong catalytic activity for both sulfur reduction and lithium sulfide oxidation.

[0033] The charge-discharge cycle diagram of the battery at 1C rate is as follows: Figure 4 As shown, S@CNT@MoS2-Fe exhibits the highest first-cycle discharge specific capacity, reaching 902 mAh g. -1 Furthermore, after 1000 cycles, the discharge specific capacity still remains at 586 mAh g. -1 The highest capacity retention rate was achieved at 65%, while the capacity retention rates of the control group S@CNT@MoS2 and S@CNT were only 50% and 49%, respectively. This indicates that the single-atom Fe-supported MoS2 plays a strong role in the adsorption and catalytic conversion of lithium polysulfides, effectively suppressing the shuttle effect of lithium polysulfides and improving the cycle stability of the battery.

[0034] Example 2

[0035] Take 100 mg of graphene, 40 mL of deionized water, 0.2 g of sodium stannate and 20 mL of CS2, mix them evenly and transfer them to a hydrothermal reactor. Under sealed conditions, react at 400 degrees Celsius for 4 h. Filter, wash and dry the product to obtain black G@SnS2. Take 100 mg of G@SnS2, 20 mg of cobalt chloride and 1 mL of deionized water, sonicate them evenly and let them stand for 12 h. Then centrifuge, wash and dry the product and place it in a tube furnace. Under the protection of a hydrogen-argon mixed atmosphere with a hydrogen volume content of 10%, treat it at 500 degrees Celsius for 3 h to obtain G@SnS2-Co composite material.

[0036] The sulfur melting and electrode coating were the same as in Example 1. Battery cycle tests showed that the S@G@SnS2-Co cathode had the best cycle stability, indicating that the single-atom Co-supported SnS2 had a strong adsorption and catalytic conversion effect on lithium polysulfides, effectively suppressing the shuttle effect of lithium polysulfides.

[0037] Example 3

[0038] Take 100 mg of carbon fiber, 50 mL of deionized water, 0.2 g of sodium niobate and 0.5 g of thiourea, mix them evenly and transfer them to a hydrothermal reactor. Under sealed conditions, react at 200 degrees Celsius for 12 h. Filter, wash and dry the product to obtain black CNF@NbS2. Take 100 mg of CNF@NbS2, 20 mg of nickel phthalocyanine and 1 mL of deionized water, sonicate them evenly and let them stand for 12 h. Then centrifuge, wash and dry the product and place it in a tube furnace. Under the protection of a hydrogen-argon mixed atmosphere with a hydrogen volume content of 10%, treat it at 500 degrees Celsius for 3 h to obtain CNF@NbS2-Ni composite material.

[0039] The sulfur melting and electrode coating were the same as in Example 1. Battery cycle tests showed that the S@CNF@NbS2-Ni cathode had the best cycle stability, indicating that the single-atom Ni-supported NbS2 had a strong adsorption and catalytic conversion effect on lithium polysulfides, effectively suppressing the shuttle effect of lithium polysulfides.

[0040] Example 4

[0041] Take 100 mg of carbon nanotubes, 40 mL of deionized water, 0.2 g of sodium titanate and 20 mL of CS2, mix them evenly and transfer them to a hydrothermal reactor. Under sealed conditions, react at 400 degrees Celsius for 4 h. Filter, wash and dry the product to obtain black CNT@TiS2. Take 100 mg of CNT@TiS2, 20 mg of cobalt nitrate and 1 mL of deionized water, sonicate them evenly and let them stand for 12 h. Then centrifuge, wash and dry the product and place it in a tube furnace. Under the protection of a hydrogen-argon mixed atmosphere with a hydrogen volume content of 10%, treat it at 500 degrees Celsius for 3 h to obtain CNT@TiS2-Co composite material.

[0042] The sulfur melting and electrode coating were the same as in Example 1. Battery cycle tests showed that the S@CNT@TiS2-Co cathode had the best cycle stability, indicating that the TiS2 supported by single-atom Co had a strong adsorption and catalytic conversion effect on lithium polysulfides, effectively suppressing the shuttle effect of lithium polysulfides.

[0043] Example 5

[0044] 100 mg of carbon nanotubes, 40 mL of deionized water, 1.8 g of ammonium molybdate, 1 g of selenium, and 20 mL of CS2 were mixed evenly and transferred to a hydrothermal reactor. Under sealed conditions, the mixture was reacted at 400 °C for 4 h. The product was filtered, washed, and dried to obtain black CNT@MoSe2. 100 mg of CNT@MoSe2, 20 mg of ferric nitrate, and 1 mL of deionized water were ultrasonically homogenized and allowed to stand for 12 h. After centrifugation, washing, and drying, the product was placed in a tube furnace and treated at 500 °C for 3 h under a hydrogen-argon mixed atmosphere with a hydrogen volume content of 10% to obtain CNT@MoSe2-Fe composite material.

[0045] The sulfur melting and electrode coating were the same as in Example 1. Battery cycle tests showed that the S@CNT@MoSe2-Fe cathode had the best cycle stability, indicating that the single-atom Fe-supported MoSe2 had a strong adsorption and catalytic conversion effect on lithium polysulfides, effectively suppressing the shuttle effect of lithium polysulfides.

Claims

1. A method for preparing a transition metal-supported layered metal sulfide composite material, comprising first loading layered metal sulfides onto conductive carbon as a carrier, and then loading transition metal single atoms onto the surface of the layered metal sulfides; including the following steps: (1) Mix the conductive carbon, metal salt and ligand evenly in the liquid phase; (2) The above solution is subjected to closed heating treatment, and the generated carbon-supported layered metal sulfide material is recovered; (3) The above carbon-supported layered metal sulfide material, metal salt and deionized water are mixed and impregnated, and the carbon-supported layered metal sulfide composite material after adsorbing metal salt is recovered. (4) The above composite material is placed in a tube furnace for calcination to obtain a carbon-supported layered metal sulfide composite material with a single atom of transition metal. (5) Grind the composite material obtained in step (4) with sublimed sulfur at a mass ratio of 1:2~9, transfer it to a container, and heat-treat the sulfur-loaded material under an inert atmosphere to obtain a composite sulfur cathode.

2. The preparation method according to claim 1, characterized in that: The conductive carbon selected in step (1) is one or a mixture of two or more of acetylene black, carbon nanotubes, carbon fibers, and graphene. The metal salt in step (1) includes one or a mixture of two or more of sodium molybdate, ammonium molybdate, sodium stannate, sodium niobate, and sodium titanate; The ligand in step (1) includes one or more of the following: thiourea, cysteine, carbon disulfide, selenium, and selenourea. The mass ratio of conductive carbon: metal salt: ligand in step (1) is 1:1~100:1~2000.

3. The preparation method according to claim 2, characterized in that: The mass ratio of conductive carbon: metal salt: ligand in step (1) is 1:1~20:1~400.

4. The preparation method according to claim 1, characterized in that: The heat treatment temperature in step (2) is 80~600 ℃; the heat treatment time is 2~30 h.

5. The preparation method according to claim 1, characterized in that: In step (3), the ratio of carbon-supported layered metal sulfide material, metal salt, and deionized water is 1:0.01~1:1~100. The metal salt in step (3) includes one or more of the following: iron nitrate, cobalt nitrate, nickel nitrate, zinc nitrate, copper nitrate, iron chloride, cobalt chloride, nickel chloride, zinc chloride, iron phthalocyanine, cobalt phthalocyanine, and nickel phthalocyanine. The immersion temperature in step (3) is 20~100 ℃; the immersion time is 1~100 h.

6. The preparation method according to claim 5, characterized in that: In step (3), the ratio of carbon-supported layered metal sulfide material, metal salt, and deionized water is 1:0.1~0.3:1~20. The immersion temperature in step (3) is 20~50 ℃; the immersion time is 1~20 h.

7. The preparation method according to claim 1, characterized in that: The calcination temperature in step (4) is 300~1000 ℃, the calcination time is 1~10 h, and the calcination atmosphere is a hydrogen-argon mixture with a hydrogen volume content of 5-80%.

8. The preparation method according to claim 1, characterized in that: The calcination temperature in step (4) is 400~600℃ and the calcination time is 2~4 h.

9. The preparation method according to claim 1, characterized in that: In step (5), the inert atmosphere is high-purity argon and / or nitrogen, the heat treatment temperature is 140 ~ 300 ℃, and the treatment time is 12 ~ 24 hours.

10. A layered metal sulfide composite material supported on a single transition metal atom, obtained by any of the preparation methods of claims 1-9.

11. The application of the layered metal sulfide composite material supported by a single transition metal atom as described in claim 10 as a positive electrode active material in the sulfur positive electrode of a lithium-sulfur battery.

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