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CN-118079979-B - Monoatomic catalyst Co/MOFc composite material, preparation method and preparation method of room-temperature sodium-sulfur battery positive electrode material

CN118079979BCN 118079979 BCN118079979 BCN 118079979BCN-118079979-B

Abstract

The invention discloses a single-atom catalyst Co/MOFc composite material, a preparation method and a preparation method of a room-temperature sodium-sulfur battery positive electrode material, wherein the composite material is expressed as Co-N 2 O 2 /MOFc, and is a catalyst synthesized by taking a metal-organic framework Material (MOF) as a precursor and adopting a coordination form (Co-N 2 O 2 ) of single-atom cobalt, two N and two O, wherein the carbon material derived from the metal-organic framework compound accounts for 98.85-99.04 wt%, the Co accounts for 0.96-1.15 wt%, and the molar ratio of Co to N to O is 1:2:2. According to the invention, the metal organic frame material is used as a precursor, a catalyst in the coordination form of single-atom cobalt, two N and two O (Co-N 2 O 2 ) is designed and synthesized, and is used as a sulfur storage material for the first time, and is applied to the positive electrode of the room-temperature sodium-sulfur battery, so that the electrochemical performance of the room-temperature sodium-sulfur battery is effectively improved.

Inventors

  • HU PENG
  • GAO XINPENG
  • CAI BINBIN
  • CHEN YUBAO
  • XIAO FENGPING

Assignees

  • 云南师范大学

Dates

Publication Date
20260512
Application Date
20240201

Claims (8)

  1. 1. The single-atom catalyst Co/MOFc composite material is characterized in that the composite material is expressed as Co-N 2 O 2 /MOFc, and is a catalyst synthesized by adopting a metal organic framework material as a precursor and adopting a coordination form Co-N 2 O 2 of single-atom cobalt and two N and two O, wherein the carbon material derived from the metal organic framework compound accounts for 98.85-99.04 wt%, co accounts for 0.96-1.15 wt%, and the molar ratio of Co to N to O is 1:2:2; the preparation method of the monoatomic catalyst Co/MOFc composite material comprises the following steps: (1) Weighing 0.736 g of 4, 4-dimethyl-2, 2-bipyridine and 1.032, g of 4, 4-diphenyl ether dicarboxylic acid, dispersing in 130, mL of ethanol and 72, mL of NaOH, and carrying out ultrasonic treatment to obtain a solution A; (2) 0.8 g Zn (NO 3 ) 2 and 0.4 g Co (NO 3 ) 2 in ethanol of 20 mL) was dissolved to give solution B; (3) Placing the solution A into a round-bottom flask, heating to the boiling point, then adding the solution B, refluxing for 30 minutes, and performing vacuum filtration to obtain pink Co-Zn MOF; (4) Placing the Co-Zn MOF in a quartz boat, and carbonizing by using a tube furnace under the protection of argon at 600 ℃; (5) Taking out carbonized sample, putting the carbonized sample into a hydrothermal kettle lining of 20 mL, dripping prepared 12 mL diluted hydrochloric acid, screwing the hydrothermal kettle, putting the hydrothermal kettle into an electrothermal constant-temperature blast drying oven, preserving heat for 5 hours at 85 ℃ to remove ZnO and unfixed Co, carrying out suction filtration after reaction, and drying to obtain Co-N 2 O 2 /MOFc.
  2. 2. The single-atom catalyst Co/MOFc composite of claim 1, wherein the molar concentration of NaOH in step (1) is 0.1: 0.1 mol/L.
  3. 3. The single-atom catalyst Co/MOFc composite of claim 1, wherein the concentration of the dilute hydrochloric acid in step (5) is 50vol%.
  4. 4. The preparation method of the room-temperature sodium-sulfur battery positive electrode material is characterized by comprising the following steps of: (1) Grinding sulfur powder and the single-atom catalyst Co/MOFc composite material according to the mass ratio of 1:1 in a quartz mortar for a period of time, and fully and uniformly mixing the materials; (2) Then adding the mixture into a small test tube, performing ultrasonic dispersion in an ultrasonic instrument, then placing the mixture into an oven for drying at 60 ℃, taking out the mixture, placing the mixture into an eggplant bottle, and heating the mixture to 155 ℃ under the protection of argon for preserving heat for a certain time; (3) After taking out the sample, heating for a certain time at 700 ℃ in a tubular furnace in argon atmosphere to prepare a sulfur-carbon composite material; (4) Mixing the prepared sulfur-carbon composite material, a binder polyvinylidene fluoride PDVF and acetylene black in a ratio of 7:1.5:1.5, adding a solvent N-methyl pyrrolidone NMP, stirring and mixing in a quartz mortar to form uniform slurry, uniformly coating the slurry on a copper foil, and drying in a vacuum drying oven to obtain a positive plate of the sodium-sulfur battery; (5) And taking out the pole piece after cooling, and preparing the sulfur-carbon positive pole piece Co-N 2 O 2 /MOFc/S with the diameter of 12 mm by using a punching machine.
  5. 5. The method according to claim 4, wherein in the step (2), the ultrasonic dispersion time is 10 min.
  6. 6. The method of claim 4, wherein in step (2), the drying in an oven and the incubation under argon are each 12h.
  7. 7. The method according to claim 4, wherein in the step (3), the heating time period is 30 minutes.
  8. 8. The process according to any one of claims 4 to 7, wherein in step (4), drying is carried out in a vacuum oven at 60 ℃ for 12 hours.

Description

Monoatomic catalyst Co/MOFc composite material, preparation method and preparation method of room-temperature sodium-sulfur battery positive electrode material Technical Field The invention relates to a single-atom catalyst Co/MOFc composite material, a preparation method and a preparation method of a room-temperature sodium-sulfur battery positive electrode material, and belongs to the technical field of room-temperature sodium-sulfur batteries (RT Na-S). Background The room temperature sodium-sulfur battery (RT Na-S) is expected to be one of the substitutes of the lithium ion battery due to low cost and high energy density. While RT Na-S cells have many of the advantages described above, research into such cells is currently under way, and there are inevitably issues that need to be resolved, which severely limit the electrochemical performance of RT Na-S cells. The problems of the current batteries are mainly as follows 1-3: (1) Poor conductivity of sulfur, the starting material for the positive electrode reaction of RT Na-S cells, and short chain sodium polysulfide, the discharge product, which results in lower electronic and ionic conductivity in the positive electrode of the cell. Meanwhile, as the long-chain sodium polysulfide Na 2Sx (x is more than or equal to 4 and less than or equal to 8) intermediate generated in the discharging process has higher solubility in the electrolyte, the long-chain sodium polysulfide Na 2Sx can reach the negative electrode along with the electrolyte penetrating through the diaphragm, and finally a part of insulating Na 2 S product is deposited on the surface of the negative electrode metal sodium to form an insulating interface, so that the conductivity of the negative electrode is also poor. (2) The shuttle effect is that the intermediate long-chain sodium polysulfide Na 2Sx (x is more than or equal to 4 and less than or equal to 8) of sulfur and Na + react can be dissolved in the organic electrolyte and smoothly pass through the diaphragm to freely shuttle between the anode and the cathode. After reaching the cathode, the long-chain sodium polysulfide can directly react with metal Na and be reduced into short-chain sodium polysulfide Na 2Sx (x is more than or equal to 1 and less than 4). As the reaction proceeds, only a portion of the short chain sodium polysulfide can again shuttle back to the sulfur positive electrode to oxidize to long chain sodium polysulfide, a process that repeatedly occurs with cycling of the battery, known as a "shuttle effect. Because only a part of the long-chain sodium polysulfide which is shuttled to the negative electrode after being reduced can be oxidized again to participate in electrochemical reaction, the rest of the long-chain sodium polysulfide can not be used as an active substance to participate in electrochemical circulation, so that the active material is gradually lost in the charge and discharge process, the battery capacity is attenuated in the electrochemical circulation process, and the circulation stability of the RT Na-S battery is obviously reduced. (3) Elemental sulfur expands in volume due to the large difference in density between elemental sulfur and the electrochemical cycle end product (Na 2 S) (2.36 g/cm 3 and 1.86g/cm 3, respectively), the elemental sulfur expands significantly during discharge and gradually recovers during charge. During electrochemical cycling, this expansion and contraction repeatedly occurs in the positive electrode portion, which easily results in collapse and damage of the positive electrode material structure, thereby significantly deteriorating the performance of the battery. Researchers have actively explored and improved on the problems with the above RT Na-S batteries. The existing main solution strategy is to use different types of conductive carbon materials (such as carbon nano tubes, carbon hollow spheres, porous carbon and the like) as sulfur-carrying materials to be compounded with active substance sulfur, so that the conductivity 4-7 of the sulfur anode is improved. Meanwhile, elemental sulfur is coated and limited by a porous structure material, so that the volume change of the elemental sulfur can be effectively relieved, and the structure of the RT Na-S positive electrode is stabilized. Part of the porous material has a certain adsorption capacity to long-chain sodium polysulfide, which is also very beneficial to reducing the shuttle effect of RT Na-S batteries. For example, wang et al designed a sulfur carrier (iMCHS) of mesoporous hollow nanocarbon sphere structure whose hollow structure can provide sufficient space to store sulfur and help to mitigate the volume change of elemental sulfur during charge and discharge. At the same time, the outer carbon shell can limit polysulfide dissolution, thereby alleviating the effects of "shuttling". Therefore, when the S@iMCHS is used as the positive electrode of the RT Na-S battery, the S@iMCHS shows good cycling stability, and th