A dynamic oxide-metal catalyst and a method for preparing the same

Abstract

The present application relates to a kind of dynamic oxide-metal catalyst and its preparation method.The preparation method of the dynamic oxide-metal catalyst includes the following steps: in pure oxygen atmosphere, with metal lithium as negative electrode, with the multi-walled carbon nanotube loaded with nano metal particles as positive electrode, with non-lithium metal salt solution as electrolyte, assemble lithium-oxygen battery, discharge by constant current until cut-off voltage, oxide is generated on the positive electrode surface of the multi-walled carbon nanotube loaded with nano metal particles, oxide-metal catalyst is obtained, the oxide is catalytically decomposed by the nano metal particles during charging, that is, dynamic oxide-metal catalyst is constructed on the positive electrode surface.

Description

Technical Field

[0001] This invention belongs to the field of lithium-oxygen battery technology and relates to a dynamic oxide-metal catalyst and its preparation method. Background Technology

[0002] Lithium-oxygen batteries have an extremely high energy density (3500 Wh•kg). -1 Lithium-oxygen batteries are considered a promising next-generation energy storage system. However, the slow oxygen reduction (ORR) and oxygen evolution (OER) kinetics of the discharge product Li₂O₂ result in low energy efficiency, short cycle life, and poor rate performance. Furthermore, prolonged charging at high voltages easily leads to the decomposition of the carbon-based material on the cathode side, forming Li₂CO₃ and other byproducts. These byproducts are difficult to decompose and accumulate on the cathode surface with each cycle, hindering electron and O₂ transport and ultimately causing battery failure. To address these issues, selecting a suitable catalyst is considered one of the most effective approaches.

[0003] In recent years, researchers have focused on developing highly efficient OER / ORR catalysts to regulate the discharge morphology of products on the cathode side and improve interfacial charge transport between the electrode and the products. However, highly catalytically active surfaces are prone to deactivation during long-term cycling, especially when the discharge specific capacity of the cathode exceeds 5000 mAh / g or a voltage-cutoff discharge-charge mode is used. Therefore, in lithium-oxygen battery research, maintaining the stability of highly active catalytic sites on the cathode side over a long period and establishing efficient interfacial charge transport channels to continuously and effectively control product morphology has become a key challenge in improving the performance of lithium-oxygen batteries. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a dynamic oxide-metal catalyst and its preparation method. During the charge-discharge cycle of a lithium-oxygen battery, a dynamic oxide-metal catalyst is constructed by forming and decomposing metastable oxides on the surface of metal nanoparticles, achieving a dynamic and reversible conversion between mobile metal ions and the solid-phase nano-metal catalytic structure. More importantly, the formed oxide-metal heterojunction possesses highly efficient charge transport channels, enhancing interfacial charge transfer and transport. This effectively regulates the morphology of lithium peroxide, reducing battery polarization, and enables the sustainable regeneration of highly active catalytic sites, improving the battery's cycle stability.

[0005] In a first aspect, the present invention provides a method for preparing a dynamic oxide-metal catalyst, comprising the following steps: in a pure oxygen atmosphere, using lithium metal as the negative electrode, multi-walled carbon nanotubes loaded with nano-metal particles as the positive electrode, and a non-lithium metal salt solution as the electrolyte, assembling a lithium-oxygen battery, discharging it under a constant current until the cutoff voltage, generating an oxide on the surface of the multi-walled carbon nanotubes loaded with nano-metal particles, thereby obtaining an oxide-metal catalyst; during the charging process, the oxide is catalytically decomposed by the nano-metal particles, that is, a dynamic oxide-metal catalyst is constructed on the surface of the positive electrode.

[0006] Preferably, a separator is included between the positive and negative electrodes; the separator is at least one of glass fiber, polyethylene, and polypropylene.

[0007] Preferably, the nano-metal particles are at least one of ruthenium, platinum, palladium, and gold nanoparticles; more preferably, the particle size of the nano-metal particles is 1 to 100 nm.

[0008] Preferably, the loading of surface nano-metal particles on the multi-walled carbon nanotube is 5.0 to 15.0 wt%, and more preferably 7.77 wt%.

[0009] Preferably, the non-lithium metal salt is a salt that combines with oxygen molecules to form a solid metal oxide; more preferably, the electrochemical potential of the reaction between the metal ions and oxygen in the non-lithium metal salt is higher than the electrochemical potential of the reaction between lithium ions and oxygen.

[0010] Preferably, the non-lithium metal salt is at least one selected from La, Ce, Ga, Sm, and Y salts; the La salt is at least one selected from La(NO3)3·6H2O and La(ClO4)3; the Ce salt is at least one selected from Ce(ClO4)3·6H2O, Ce(NO3)3·6H2O, and Ce(Ac)3·xH2O; the Ga salt is at least one selected from Ga(ClO4)3, Ga(NO3)3·xH2O, GaI3, GaBr3, and GaCl3; the Sm salt is at least one selected from Sm(NO3)3, Sm(Ac)3·xH2O, SmBr3, SmCl3, and SmI3; and the Y salt is Y(NO3)3·6H2O.

[0011] Preferably, the solvent of the non-lithium metal salt solution is an organic solvent, which is at least one of dimethyl sulfoxide (DMSO), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethyl carbonate, propylene carbonate, and ethylene carbonate, and is preferably dimethyl sulfoxide. Preferably, the molar concentration of the non-lithium metal salt in the non-lithium metal salt solution is 25–200 mM, and more preferably 50 mM.

[0012] Preferably, the non-lithium metal salt solution further comprises a lithium metal salt; the lithium metal salt is selected from at least one of LiNO3, LiClO4, LiTFSI, LiFSI, and LiPF6; preferably, the molar concentration of the lithium metal salt in the non-lithium metal salt solution is 0.5–2 M.

[0013] Preferably, the oxide is at least one selected from lanthanum oxide, yttrium oxide, cerium oxide, samarium oxide, and gallium oxide.

[0014] Preferably, the current density of the constant current discharge is 100-1000 mA / g, and more preferably 500 mA / g.

[0015] Preferably, the cutoff voltage is 2.4 to 4.5 V.

[0016] Preferably, the formation potential of the oxide during discharge is 2.75–3.0V, and the decomposition potential of the oxide during charging is 3.75–4.5V.

[0017] Secondly, the present invention provides a dynamic oxide-metal catalyst prepared according to the above preparation method.

[0018] Preferably, in the dynamic oxide-metal catalyst, the oxide is coated on the surface of the nano-metal particles in the form of a thin film or particles, and forms a heterojunction structure with the nano-metal particles. Beneficial effects

[0019] Compared with the prior art, the dynamic oxide-metal catalyst and its preparation method provided by the present invention have the following beneficial effects: (1) The dynamic oxide-metal catalyst provided by the present invention exhibits high catalytic performance and excellent cycle reversibility in lithium-oxygen batteries; (2) The preparation method provided by the present invention is simple, low in cost, and the composition and content of the catalyst are easy to control. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the formation and decomposition process of the dynamic La2O3-Ru catalyst in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of ruthenium loaded on multi-walled carbon nanotubes in Example 1 of the present invention; Figure 3 This is a microscopic morphology diagram of the positive electrode surface after discharge in Embodiment 1 of the present invention; Figure 4 This is a graph showing the change in La element content during the cycling process of a lithium-oxygen battery in Example 1 of the present invention; Figure 5The cycle performance of the lithium-oxygen battery in Example 1 of this invention; Figure 6 The discharge curves of this invention under different lanthanum salt concentrations are shown below. Figure 7 The cycling performance of the positive electrode of this invention with different ruthenium loadings; Figure 8 The cycle performance of the lithium-oxygen battery without lanthanum salt in Comparative Example 1 of this invention; Figure 9 The cycling performance of the lithium-oxygen battery using pure multi-walled carbon nanotubes as the positive electrode in Comparative Example 2 of this invention is shown. Detailed Implementation

[0021] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.

[0022] In this invention, multi-walled carbon nanotubes loaded with nano-metal particles are used as the lithium-oxygen battery cathode. Under a pure oxygen atmosphere, a specific non-lithium metal salt is added to the electrolyte of the lithium-oxygen battery. During discharge, oxides are generated on the surface of the carbon nanotube cathode loaded with nano-metal particles. During charging, these oxides can be catalytically decomposed. This type of oxide-metal catalyst, which can continuously form and decompose during battery cycling, is the dynamic oxide-metal catalyst.

[0023] In this invention, metal nanoparticles are loaded onto the surface of multi-walled carbon nanotubes. During discharge, oxides are generated on the surface of the metal nanoparticles, forming an oxide-metal catalyst. During charging, the metal nanoparticles effectively catalyze the decomposition of their surface oxides, thus establishing a dynamic oxide-metal catalyst during battery cycling. In this process, the nanoparticles regulate the electronic structure of the oxides, thereby establishing efficient charge transport channels. Simultaneously, the oxide-metal catalyst further modulates the electronic structure and influences Li... + Discharge intermediate products (LiO2, Li + +O2+e - →The adsorption energy of LiO2 on the positive electrode surface regulates the discharge product Li2O2(O2+2Li + +2e -→Li2O2 (actual formation potential 2.75V) growth morphology improves the extremely difficult-to-decompose cyclic Li2O2 into flocculent Li2O2, promotes the charging decomposition of Li2O2, reduces electrode polarization, improves electrochemical performance, and thus effectively improves the cycle stability of lithium oxygen battery.

[0024] The following exemplarily illustrates the preparation method of the dynamic oxide-metal catalyst provided by the present invention.

[0025] Electrolyte preparation. Select specific non-lithium metal salts and add specific concentrations of lithium salts and non-lithium metal salts to an organic solvent to obtain the electrolyte for lithium-oxygen batteries.

[0026] In an optional embodiment, the non-lithium metal salt is a salt that combines with oxygen molecules to form a solid metal oxide. The non-lithium metal salt is at least one of La, Ce, Ga, Sm, and Y salts; the La salt is at least one of La(NO3)3·6H2O and La(ClO4)3; the Ce salt is at least one of Ce(ClO4)3·6H2O, Ce(NO3)3·6H2O, and Ce(Ac)3·xH2O; the Ga salt is at least one of Ga(ClO4)3, Ga(NO3)3·xH2O, GaI3, GaBr3, and GaCl3; the Sm salt is at least one of Sm(NO3)3, Sm(Ac)3·xH2O, SmBr3, SmCl3, and SmI3; and the Y salt is Y(NO3)3·6H2O. The organic solvent is at least one selected from dimethyl sulfoxide (DMSO), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethyl carbonate, propylene carbonate, and ethylene carbonate, preferably dimethyl sulfoxide; more preferably, the molar concentration of the non-lithium metal salt in the electrolyte is 25–200 mM, preferably 50 mM. If the molar concentration of the non-lithium metal salt is too low, the content of the generated oxides is low; if the molar concentration of the non-lithium metal salt is too high, the generated oxides are difficult to decompose completely. Therefore, both excessively low and excessively high molar concentrations of the non-lithium metal salt are not conducive to the formation of a dynamic oxide-metal catalyst during long-term cycling. The lithium salt is selected from at least one selected from LiNO3, LiClO4, LiTFSI, LiFSI, and LiPF6; preferably, the molar concentration of the metallic lithium salt in the electrolyte is 0.5–2 M.

[0027] A hydrogen-assisted carbothermic reduction method was used to load nano-metal particles onto the surface of multi-walled carbon nanotubes. Specifically, multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to an atomic ratio of Ru:C = 1:(50-150) and dissolved in acetone solution. The solution was then magnetically stirred and evaporated to dryness to obtain carbon nanotube powder coated with ruthenium acetylacetonate salt. The powder was then heated at 400℃ for 2 h in a 5% H2 / Ar atmosphere to obtain carbon nanotubes uniformly loaded with ruthenium nanoparticles.

[0028] Battery assembly. A lithium-oxygen battery was assembled using multi-walled carbon nanotubes loaded with nano-metal particles as the lithium-oxygen cathode, metallic lithium as the anode, and the aforementioned non-lithium metal salt solution as the electrolyte.

[0029] In an optional embodiment, the nano-metal particles are at least one of ruthenium, platinum, palladium, and gold nanoparticles; preferably, the particle size of the nano-metal particles is 1–100 nm. The loading of nano-metal particles on the surface of the multi-walled carbon nanotubes is 5.0–15.0 wt%. If the loading of nano-metal particles is too low, the catalytic effect on the OER / ORR reaction process is poor; if the loading of nano-metal particles is too high, the metal nanoparticles will agglomerate, affecting the activity and stability of the catalyst.

[0030] Construction of dynamic oxide-metal catalysts. The assembled battery was placed in a pure oxygen environment and allowed to stand for 6–10 hours. Then, it was discharged at a current density of 100–1000 mA / g until the cutoff voltage of 2.4–4.5V, forming oxides on the surface of the positive electrode nanoparticles, thus obtaining the oxide-metal catalyst. During the charging process, the oxides were catalyzed and decomposed by the nanoparticles, thus constructing a dynamic oxide-metal catalyst on the positive electrode surface.

[0031] In an optional embodiment, the oxide is at least one selected from lanthanum oxide, yttrium oxide, cerium oxide, samarium oxide, and gallium oxide. The formation potential of the oxide during discharge is 2.75–3.0 V, and the decomposition potential of the oxide during charging is 3.75–4.5 V.

[0032] In the dynamic oxide-metal catalyst prepared by the above method, the oxide is coated on the surface of the nano-metal particles in the form of a thin film or particles, forming a heterojunction structure with the nano-metal particles. The dynamic oxide-metal catalyst of this invention exhibits highly efficient catalytic performance and excellent cycle reversibility in lithium-oxygen batteries.

[0033] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Example 1

[0034] (1) Electrolyte preparation: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), 50 mM lanthanum nitrate hexahydrate La(NO3)3•6H2O was first dissolved in dimethyl sulfoxide (DMSO) (>99.9%), and then a molecular sieve was added to remove water. After standing for 24 h, the molecular sieve was replaced once, and the solution was left to stand for a total of 48 h. Finally, 1 M LiNO3 was added to the obtained 50 mM La(NO3)3+DMSO solution. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assembling the battery: The positive electrode of the lithium-oxygen battery is a multi-walled carbon nanotube (Ru / CNT positive electrode) loaded with ruthenium (Ru) nanoparticles, and the negative electrode is a circular lithium metal sheet with a diameter of 12 mm. The battery case is of type 2032, with the negative electrode case opening facing upwards and placed flat on the panel; the spring sheet is placed into the negative electrode case; the pad is placed on the spring sheet, and then the lithium sheet is placed in the center of the pad; the separator is placed to cover the lithium sheet, and the electrolyte is dropped onto the separator using a pipette; the positive electrode is placed in the center of the separator, and the porous positive electrode case is covered with tweezers. The battery is pressed with a button battery packaging machine to obtain a button lithium-oxygen battery. The amount of electrolyte added to the button battery is 100 μL. (4) Dynamic La2O3-Ru catalyst: The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and left to stand for 8 hours. Then it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT cathode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic La2O3-Ru catalyst on the cathode surface. Example 2

[0035] (1) Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), 25 mM La(NO3)3·6H2O was added to the dimethyl sulfoxide lithium oxygen battery electrolyte, and then molecular sieve was added to remove water. After standing for 24 h, the molecular sieve was replaced once, and the electrolyte was left to stand for a total of 48 h. Finally, 1 M LiNO3 was added to the electrolyte. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assemble the battery: Assemble a lithium-oxygen battery using the electrolyte prepared in step (1) and the positive electrode prepared in step (2), following the same steps as in Example 1; (4) The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and left to stand for 8 hours. Then it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT positive electrode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic La2O3-Ru catalyst on the surface of the positive electrode. Example 3

[0036] (1) Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), 200 mM La(NO3)3·6H2O was added to the dimethyl sulfoxide lithium oxygen battery electrolyte, and then molecular sieve was added to remove water. After standing for 24 h, the molecular sieve was replaced once, and the electrolyte was left to stand for a total of 48 h. Finally, 1 M LiNO3 was added to the electrolyte. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assemble the battery: Assemble a lithium-oxygen battery using the electrolyte prepared in step (1) and the positive electrode prepared in step (2), following the same steps as in Example 1; (4) The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and left to stand for 8 hours. Then it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT positive electrode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic La2O3-Ru catalyst on the surface of the positive electrode. Example 4

[0037] (1) Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), 25 mM La(NO3)3·6H2O was added to the dimethyl sulfoxide lithium oxygen battery electrolyte, and then molecular sieve was added to remove water. After standing for 24 h, the molecular sieve was replaced once, and the electrolyte was left to stand for a total of 48 h. Finally, 1 M LiNO3 was added to the electrolyte. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:150, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 5.32wt%). (3) Assemble the battery: Assemble a lithium-oxygen battery using the electrolyte prepared in step (1) and the positive electrode prepared in step (2), following the same steps as in Example 1; (4) The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and left to stand for 8 hours. Then it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT positive electrode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic La2O3-Ru catalyst on the surface of the positive electrode. Example 5

[0038] (1) Preparation of electrolyte: In a glove box filled with argon (moisture < 0.1 ppm, oxygen < 0.1 ppm), 25 mM La(NO3)3·6H2O was added to the dimethyl sulfoxide lithium oxygen battery electrolyte, and then molecular sieve was added to remove water. After standing for 24 h, the molecular sieve was replaced once, and the electrolyte was left to stand for a total of 48 h. Finally, 1 M LiNO3 was added to the electrolyte. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:50, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 14.42wt%). (3) Assemble the battery: Assemble a lithium-oxygen battery using the electrolyte prepared in step (1) and the positive electrode prepared in step (2), following the same steps as in Example 1; (4) The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and left to stand for 8 hours. Then it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT positive electrode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic La2O3-Ru catalyst on the surface of the positive electrode. Example 6

[0039] (1) Electrolyte preparation: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), add 50 mM lanthanum perchlorate La(ClO4)3 and 1 M LiNO3 to the dimethyl sulfoxide-based lithium oxygen battery electrolyte; (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assemble the battery: Use the electrolyte prepared in step (1) and the positive electrode prepared in step (2) to assemble a lithium-oxygen battery, the steps are the same as in Example 1; (4) Dynamic La2O3-Ru catalyst: The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and allowed to stand for 8 hours. Then, it was discharged at a current density of 500 mA / g until it reached 2.75 V. A thin film of La2O3 was formed on the surface of the Ru / CNT cathode, thus obtaining the La2O3-Ru heterojunction catalyst. During the charging process, La2O3 was catalyzed and decomposed by Ru, that is, a dynamic La2O3-Ru catalyst was constructed on the cathode surface. Example 7

[0040] (1) Electrolyte preparation: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), add 100 mM samarium nitrate Sm(NO3)3 and 1 M LiNO3 to the dimethyl sulfoxide lithium oxygen battery electrolyte; (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assemble the battery: Use the electrolyte prepared in step (1) and the positive electrode prepared in step (2) to assemble a lithium-oxygen battery, the steps are the same as in Example 1; (4) Dynamic Sm2O3-Ru catalyst: The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and allowed to stand for 8 hours. Then, it was discharged at a current density of 500 mA / g until it reached 2.75 V. Sm2O3 was formed on the surface of the Ru / CNT cathode, thus obtaining the Sm2O3-Ru heterojunction catalyst. During the charging process, Sm2O3 was catalyzed and decomposed by Ru, that is, a dynamic Sm2O3-Ru catalyst was constructed on the cathode surface. Example 8

[0041] (1) Electrolyte preparation: In a glove box filled with argon (moisture content < 0.1 ppm, oxygen content < 0.1 ppm), add 50 mM yttrium nitrate hexahydrate Y(NO3)3•6H2O to the dimethyl sulfoxide-based lithium oxygen battery electrolyte, then add molecular sieve to remove water, let stand for 24 h, then replace the molecular sieve once, and let stand for a total of 48 h. Finally, add 1 M LiNO3 to the obtained 50 mM Y(NO3)3+DMSO solution. (2) Preparation of the positive electrode: Multi-walled carbon nanotubes and ruthenium acetylacetonate were weighed according to the atomic ratio of Ru:C=1:100, dissolved in acetone solution, and then evaporated to dryness by magnetic stirring to obtain carbon nanotube powder coated with ruthenium acetylacetonate. Then, it was kept at 400℃ for 2 h in 5% H2 / Ar atmosphere to obtain multi-walled carbon nanotubes loaded with nano metal particles (loading amount of 7.77wt%). (3) Assemble the battery: Use the electrolyte prepared in step (1) and the positive electrode prepared in step (2) to assemble a lithium-oxygen battery, the steps are the same as in Example 1; (4) Dynamic Y2O3-Ru catalyst: The assembled battery was placed in a pure oxygen environment (moisture < 0.1 ppm) and allowed to stand for 8 hours. Then, it was discharged at a current density of 500 mA / g until it reached 2.75 V. Y2O3 was formed on the surface of the Ru / CNT cathode, thus obtaining the Y2O3-Ru heterojunction catalyst. During the charging process, Y2O3 was catalyzed and decomposed by Ru, thus constructing a dynamic Y2O3-Ru catalyst on the cathode surface. Comparative Example 1

[0042] The assembly process of the lithium-oxygen battery in Comparative Example 1 is the same as that in Example 1, except that in step (1), no La salt was added to the electrolyte, and only 1M LiNO3 was added to the DMSO solution. Comparative Example 2

[0043] The assembly process of the lithium-oxygen battery in Comparative Example 2 is the same as that in Example 1, except that in step (2), the positive electrode is pure multi-walled carbon nanotubes.

[0044] Figure 1 This is a schematic diagram illustrating the formation and decomposition process of the dynamic La2O3-Ru catalyst in Example 1 of this invention. As shown in the figure, when lanthanum salt is added to the lithium-oxygen battery electrolyte, during discharge, La2O3 (in thin film or particulate form) with a high reaction potential first deposits on the Ru / CNT surface (La2O3 is generated on both the surface of nano-metal particles and multi-walled carbon nanotubes); after charging, La2O3 decomposes under the catalysis of ruthenium metal, converting into La2O3. 3+ The form returns to the electrolyte. This continuously forms and decomposes lanthanum oxide on the surface of metallic ruthenium, ensuring the continuous regeneration of highly active catalytic sites, balancing the high activity and stability of the catalyst, and improving the electrochemical performance of lithium-oxygen batteries.

[0045] Figure 2 This is a scanning electron microscope (SEM) image of ruthenium loaded on multi-walled carbon nanotubes in Example 1 of the present invention. As shown in the figure, the particle size of the ruthenium nanoparticles loaded on the multi-walled carbon nanotubes is 1.5–3.5 nm.

[0046] Figure 3 This is a microscopic morphology diagram of the positive electrode surface after discharge in Example 1 of the present invention. As can be seen from the figure, La2O3 with a wide interplanar spacing (d=2.258 Å) tends to form on the surface of carbon nanotubes; while (103) La2O3 with a smaller interplanar spacing is grown on the (101) crystal surface of ruthenium nanoparticles, thereby constructing a La2O3-Ru heterojunction catalyst.

[0047] Figure 4 This is a graph showing the change in La element content during the cycling process of the lithium-oxygen battery in Example 1 of the present invention. As can be seen from the graph, the discharge curve of Example 1 shows a clear high-potential plateau before 2.75 V, which is the lanthanum-oxygen reaction plateau (4La). 3+ +3O2 + 12e - →2La₂O₃). When discharged to 2.75 V, the La content was 9.6 times that of Ru, indicating that La₂O₃ is mainly generated at high potentials of 2.75–3.0 V. At the lower potential plateau around 2.75 V, the lithium-oxygen reaction (O₂ + 2Li₂O₃) occurs. + +2e -→Li₂O₂). During charging, the lanthanum content remained essentially unchanged before 3.5 V, but gradually decreased after 3.75 V, eventually reaching a La:Ru ratio of approximately 2:1. This indicates that the La₂O₃-Ru heterojunction catalyst first catalyzes the decomposition of Li₂O₂ on its surface, and then the decomposition of La₂O₃ occurs only between 3.75 and 4.5 V. This demonstrates that the La₂O₃-Ru heterojunction catalyst can be effectively decomposed during the cycling process of a lithium-oxygen battery, thereby continuously and dynamically forming new active catalytic sites.

[0048] Figure 5 The figure shows the cycle performance of the lithium-oxygen battery in Example 1 of this invention. As can be seen from the figure, the lithium-oxygen battery using the dynamic La2O3-Ru heterojunction catalyst can stably cycle for 46 times at an ultra-high cutoff capacity of 5000 mAh / g.

[0049] Figure 6 The figures show the discharge curves of the present invention under different lanthanum salt concentrations. As can be seen from the figures, at different lanthanum salt concentrations, La... 3+ The size of the high-potential reaction plateau formed by the reaction with oxygen differs, and the size of the plateau is positively correlated with the concentration of lanthanum salt. Without the addition of any lanthanum salt, no high electrochemical reaction plateau appears in the discharge curve; as the concentration of lanthanum salt increases, the high electrochemical reaction plateau gradually widens, indicating the formation of more La₂O₃.

[0050] Figure 7 The figure shows the cycle performance of the cathode with different ruthenium loadings. As can be seen from the figure, the different ruthenium loadings on the cathode have a certain impact on the cycle performance of the lithium-oxygen battery. When the loading is 14.42 wt%, the lithium-oxygen battery can stably cycle for 23 cycles; when the loading is 5.32 wt%, the lithium-oxygen battery can stably cycle for 19 cycles; and when the loading is 7.77 wt%, the lithium-oxygen battery can stably cycle for at least 33 cycles. The results indicate that if the loading of the nano-metal particles is too low, the catalytic effect on the OER / ORR reaction process is poor; if the loading of the nano-metal particles is too high, it will cause the metal nanoparticles to agglomerate, affecting the activity and stability of the catalyst. Therefore, both too low and too high ruthenium loadings on the cathode will affect the cycle stability of the lithium-oxygen battery.

[0051] Figure 8 The figure shows the cycle performance of the lithium-oxygen battery without lanthanum salt in Comparative Example 1 of this invention. As can be seen from the figure, in the electrolyte without any lanthanum salt, relying solely on the catalytic ability of the ruthenium particles, the lithium-oxygen battery can only cycle 20 times at an ultra-high cutoff capacity of 5000 mAh / g.

[0052] Figure 9The figure shows the cycle performance of a lithium-oxygen battery using pure multi-walled carbon nanotubes as the positive electrode in Comparative Example 2 of this invention. As can be seen from the figure, in the electrolyte with added lanthanum salt, the La2O3 generated on the surface of the carbon nanotubes is difficult to be effectively catalyzed and decomposed, leading to a continuous increase in battery polarization, ultimately resulting in only 19 cycles.

[0053] The above description represents only some preferred embodiments of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content and spirit of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a dynamic oxide-metal catalyst, characterized in that, Includes the following steps: In a pure oxygen atmosphere, a lithium-oxygen battery is assembled using lithium metal as the negative electrode, multi-walled carbon nanotubes loaded with nano-metal particles as the positive electrode, and a non-lithium metal salt solution as the electrolyte. After being discharged at a constant current until the cutoff voltage, an oxide is generated on the surface of the multi-walled carbon nanotubes loaded with nano-metal particles, thus obtaining an oxide-metal catalyst. During the charging process, the oxide is catalytically decomposed by the nano-metal particles, that is, a dynamic oxide-metal catalyst is constructed on the surface of the positive electrode.

2. The preparation method according to claim 1, characterized in that, The nano-metal particles are at least one of ruthenium, platinum, palladium, and gold nanoparticles; preferably, the particle size of the nano-metal particles is 1 to 100 nm. The loading of surface nano-metal particles on the multi-walled carbon nanotubes is 5.0 to 15.0 wt%, preferably 7.77 wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The non-lithium metal salt is a salt that combines with oxygen molecules to form a solid metal oxide; preferably, the electrochemical potential of the reaction between the metal ions and oxygen in the non-lithium metal salt is higher than that of the reaction between lithium ions and oxygen.

4. The preparation method according to any one of claims 1-3, characterized in that, The non-lithium metal salt is at least one of La, Ce, Ga, Sm, and Y salts; the La salt is at least one of La(NO3)3·6H2O and La(ClO4)3; the Ce salt is at least one of Ce(ClO4)3·6H2O, Ce(NO3)3·6H2O, and Ce(Ac)3·xH2O; the Ga salt is at least one of Ga(ClO4)3, Ga(NO3)3·xH2O, GaI3, GaBr3, and GaCl3; the Sm salt is at least one of Sm(NO3)3, Sm(Ac)3·xH2O, SmBr3, SmCl3, and SmI3; and the Y salt is Y(NO3)3·6H2O.

5. The preparation method according to any one of claims 1-4, characterized in that, The solvent for the non-lithium metal salt solution is an organic solvent, which is at least one of dimethyl sulfoxide (DMSO), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethyl carbonate, propylene carbonate, and ethylene carbonate, preferably dimethyl sulfoxide. Preferably, the molar concentration of the non-lithium metal salt in the non-lithium metal salt solution is 25–200 mM, and more preferably 50 mM.

6. The preparation method according to any one of claims 1-5, characterized in that, The non-lithium metal salt solution also contains a lithium metal salt; the lithium metal salt is selected from at least one of LiNO3, LiClO4, LiTFSI, LiFSI, and LiPF6; preferably, the molar concentration of the lithium metal salt in the non-lithium metal salt solution is 0.5 to 2 M.

7. The preparation method according to any one of claims 1-6, characterized in that, The oxide is at least one of lanthanum oxide, yttrium oxide, cerium oxide, samarium oxide, and gallium oxide.

8. The preparation method according to any one of claims 1-7, characterized in that, The current density of the constant current discharge is 100-1000 mA / g, preferably 500 mA / g; the cutoff voltage is 2.4-4.5V.

9. The preparation method according to any one of claims 1-8, characterized in that, The formation potential of the oxide during discharge is 2.75–3.0V, and the decomposition potential of the oxide during charging is 3.75–4.5V.

10. A dynamic oxide-metal catalyst prepared by the method according to any one of claims 1-9, characterized in that, In the dynamic oxide-metal catalyst, the oxide is coated on the surface of the nano-metal particles in the form of a thin film or particles, and forms a heterojunction structure with the nano-metal particles.

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