Preparation method of sodium sulfide carbon confinement pre-sodium coating based on monatomic catalysis

Abstract

The invention provides a preparation method of a sodium sulfide carbon confinement pre-sodium coating based on monatomic catalysis, and belongs to the technical field of sodium battery materials. Comprising the following steps: mixing cobalt phthalocyanine and melamine powder, performing ultrasonic-assisted mechanical stirring, drying and grinding to obtain composite powder; mixing with sodium sulfate and polyvinylpyrrolidone in proportion, stirring, drying and grinding to obtain precursor powder; the precursor powder is sintered in an argon atmosphere, so that sodium sulfate is converted into sodium sulfide in situ, cobalt atoms in cobalt phthalocyanine are dispersed in a carbon network in a monatomic state, and a monatomic cobalt catalysis-carbon confinement sodium sulfide composite material is prepared; mixing the composite material with a conductive agent, a first binder and a first organic solvent, and performing stirring and defoaming stirring to prepare slurry; and coating the surface of a positive electrode material with the slurry to form a sodium supplementing interface layer, and performing vacuum drying to obtain the positive electrode with the sodium pre-coating. The problems of initial cycle sodium loss and long-term cycle performance reduction of the sodium-ion battery, defects of traditional sodium salt supplementation and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of sodium battery materials technology, and in particular to a method for preparing a sodium sulfide carbon confined pre-sodium coating based on single-atom catalysis. Background Technology

[0002] Currently, lithium-ion batteries (LIBs) are the superior energy storage technology for portable devices and automotive applications. However, the scarcity and geographical limitations of lithium resources make it impossible to sustain and meet explosive market demand. Given the widespread availability and cost-effectiveness of sodium resources, sodium-ion battery (SIB) technology has emerged as a strong alternative to LIBs. In the initial cycling of SIBs, the negative electrode irreversibly consumes the limited sodium ions released from the positive electrode, leading to a decrease in initial coulombic efficiency (ICE) and consequently, energy density. Releasing the inherent full capacity of the positive electrode material throughout the battery system is a complex and challenging task. Especially when used in conjunction with mainstream hard carbon (HC) anodes, their relatively low ICE (70-90%) inevitably leads to the irreversible consumption of active sodium, resulting in a significant loss of overall cell capacity.

[0003] After long-term cycling, the reliable operation of sodium-ion batteries is hampered by structural degradation, impaired ion transport, and side reactions, leading to a decline in battery performance. For example, vanadium in sodium vanadium phosphate (NVP) may degrade at a rate of V0.05. 3+ dissolve V in the form of 4+ This leads to the collapse of the cathode material structure. Dissolved vanadium ions migrate to the anode surface, damaging the SEI layer and catalyzing sodium dendrite growth, resulting in cross-contamination. Furthermore, the migrating vanadium ions trigger continuous side reactions through redox shuttle effects. On the other hand, the parasitic irreversible reaction between exposed reactive Na and organic solvents, along with incomplete Na stripping, will collectively deplete the active Na in the cathode lattice. + in stock.

[0004] To address the aforementioned issues, improving sodium ion utilization and optimizing interfacial performance are crucial. Existing sodium replenishment technologies mostly employ traditional sodium salts, which suffer from drawbacks such as high decomposition potential and gas generation from side reactions, making it difficult to balance sodium replenishment efficiency with interfacial stability. Therefore, developing a pre-sodiuming technology that can efficiently compensate for sodium ions, suppress side reactions, and improve cycle performance is of great significance for promoting the practical application of sodium-ion batteries. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of sodium sulfide carbon confined pre-sodium coating based on single atom catalysis, which converts sodium sulfate into sodium sulfide through carbothermal reduction at 800-900 DEG C, prevents oxidation by using inert atmosphere and discharges gas products, confines sodium sulfide in a three-dimensional carbon network to avoid agglomeration and shorten ion diffusion path, and reduces the decomposition voltage of sodium sulfide and improves the sodium supplement efficiency by means of the triple mechanism of cobalt single atom, thereby providing an efficient and stable solution for sodium supplement technology of high specific energy sodium ion battery, synergistically optimizing ion transmission and sodium supplement process, significantly enhancing the cycle stability, rate performance and high voltage resistance of sodium ion battery, and further improving the performance of sodium ion battery.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following scheme: A preparation method of sodium sulfide carbon confined pre-sodium coating based on single atom catalysis, comprising the following steps: S1, mixing cobalt phthalocyanine CoPC and melamine powder, obtaining slurry by ultrasonic assisted mechanical stirring method, and obtaining composite powder containing cobalt-nitrogen precursor after drying and grinding; S2, blending the composite powder, sodium sulfate Na2SO4 and polyvinylpyrrolidone PVP in proportion, and obtaining precursor powder containing sodium source and carbon precursor after stirring, drying and grinding; S3, sintering treatment of the precursor powder under argon atmosphere, in-situ conversion of sodium sulfate into sodium sulfide Na2S through carbothermal reduction reaction, and dispersion of cobalt atoms in cobalt phthalocyanine in single atom state in carbon network to obtain single atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material; S4, mixing the single atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material with conductive agent, first binder and first organic solvent, and performing first defoaming stirring to obtain slurry; S5, coating the slurry on the surface of the positive electrode material to form a sodium supplement interface layer, and performing first vacuum drying to obtain a positive electrode with single atom catalysis based sodium sulfide carbon confined pre-sodium coating.

[0007] Preferably, in S1, the mass ratio of the cobalt phthalocyanine CoPC to the melamine powder is 1:30, and the mixing process is carried out in ammonia water, the ultrasonic time is 4-6h, and the slurry is stirred to be viscous by mechanical stirring.

[0008] Preferably, in S1, the drying condition is vacuum drying at 75-85 DEG C for 10-12h to remove solvents and volatile components.

[0009] Preferably, in S2, the mass ratio of the composite powder, sodium sulfate and polyvinylpyrrolidone is 1:4:1, the blending process is carried out in ethanol, and the stirring temperature is 80 DEG C.

[0010] Preferably, in S2, the drying condition is vacuum drying at 69-70℃ for 6-8h, and after grinding, ball milling treatment is performed at a rotation speed of 400-600r / min.

[0011] Preferably, in S3, the heating rate of sintering treatment is 2-5℃ / min, the sintering temperature is 800-900℃, and the holding time is 2-3h.

[0012] Preferably, in S3, the argon flow rate is 60mL / min, and after sintering, a step cooling strategy is adopted: natural cooling before 500℃, and furnace cooling to room temperature after 500℃.

[0013] Preferably, in S4, the mass ratio of the single-atom cobalt catalyzed-carbon confined sodium sulfide SA-Co / Na2S@C composite material, the conductive agent and the first binder is 3-6:3-6:1; the first binder is one or more of polyvinylidene fluoride, polymethyl methacrylate or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0014] Preferably, in S4, the rotation speed of the first defoaming stirring is 400-800r / min, and the first organic solvent is N-methyl-2-pyrrolidone.

[0015] Preferably, in S5, the thickness of the sodium supplement interface layer is 5-15μm, and the first vacuum drying condition is drying at 60℃ for 12h.

[0016] According to the specific embodiments of the present application, the following technical effects are disclosed: (1) In the technical scheme of the present application, Na2SO4 is converted into Na2S by carbon thermal reduction reaction in a high temperature environment of 800-900℃. The inert atmosphere plays a protective role, on the one hand, it prevents the generated Na2S from being oxidized, on the other hand, it helps to discharge the gas products CO2 or CO generated in the reaction. The Na2S generated in situ will be uniformly confined in the three-dimensional carbon network formed by the carbonization of polyvinylpyrrolidone PVP, which can avoid the agglomeration phenomenon and shorten the path required for ion diffusion.

[0017] (2) The present application introduces a single-atom catalyst to reduce the decomposition voltage of Na2S. The introduced cobalt single atom SA-Co, relying on the three action mechanisms of atomic level active site construction, electronic structure regulation and reaction path optimization, can significantly reduce the decomposition voltage of Na2S and improve the efficiency of the sodium supplement process, providing a solution with high efficiency and stability for the sodium supplement technology of high specific energy sodium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0019] Figure 1 A flowchart of a preparation method of a sodium sulfide carbon confined pre-sodium coating based on single-atom catalysis according to the present application; Figure 2 A TEM image of SA-Co / Na2S@C provided in Embodiment 1 of the present application; Figure 3 An XRD comparison chart of Embodiment 1 and Comparative Examples 1-2 provided in the present application; Figure 4 A comparison chart of half-cell charge-discharge curves of Embodiment 1 and Comparative Examples 1-2 provided in the present application; Figure 5 A comparison chart of long cycle capacity retention rates of Embodiment 1 and Comparative Examples 1-2 provided in the present application; Figure 6 A comparison chart of full-cell charge-discharge curves of Embodiment 1 and sodium vanadium phosphate NVP provided in the present application; Figure 7 A comparison chart of long cycle capacity retention rates of full cells of Embodiment 1 and sodium vanadium phosphate NVP provided in the present application. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0022] As shown in Figure 1 The present application provides a preparation method of a sodium sulfide carbon confined pre-sodium coating based on single-atom catalysis, which comprises the following steps: S1, mixing cobalt phthalocyanine CoPC and melamine powder, obtaining slurry by ultrasonic-assisted mechanical stirring method, and obtaining cobalt-nitrogen precursor-containing composite powder after drying and grinding; S2, blending the composite powder with sodium sulfate Na2SO4, polyvinylpyrrolidone PVP in proportion, after stirring, drying and grinding, a precursor powder containing a sodium source and a carbon precursor is obtained; S3, sintering treatment of the precursor powder under argon atmosphere, in-situ conversion of sodium sulfate to sodium sulfide Na2S through carbothermal reduction reaction, while cobalt atoms in cobalt phthalocyanine are dispersed in carbon network in monatomic state, obtaining single-atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material; S4, mixing the single-atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material with a conductive agent, a first binder and a first organic solvent, and performing first defoaming stirring to obtain a slurry; S5, coating the slurry on the surface of the positive electrode material to form a sodium supplement interface layer, and performing first vacuum drying to obtain a positive electrode with a single-atom catalysis-based sodium sulfide carbon confined pre-sodium coating.

[0023] In S1, the mass ratio of the cobalt phthalocyanine CoPC to the melamine powder is 1:30, and the mixing process is carried out in ammonia water, with an ultrasonic time of 4-6h, and the slurry is stirred to be viscous by mechanical stirring. The drying condition is vacuum drying at 75-85℃ for 10-12h to remove the solvent and volatile components.

[0024] In S2, the mass ratio of the composite powder, sodium sulfate and polyvinylpyrrolidone is 1:4:1, the blending process is carried out in ethanol, and the stirring temperature is 80℃. The drying condition is vacuum drying at 69-70℃ for 6-8h, and after grinding, ball milling treatment is performed with a ball milling speed of 400-600r / min.

[0025] In S3, the heating rate of the sintering treatment is 2-5℃ / min, the sintering temperature is 800-900℃, and the holding time is 2-3h. The argon flow rate is 60mL / min, and after sintering, a stepwise cooling strategy is adopted: natural cooling before 500℃ and furnace cooling to room temperature after 500℃.

[0026] In S4, the mass ratio of the single-atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material, the conductive agent and the first binder is 3-6:3-6:1; the first binder is one or more of polyvinylidene fluoride, polymethyl methacrylate or polyvinylidene fluoride-hexafluoropropylene copolymer. The stirring speed of the first defoaming stirring is 400-800r / min, and the first organic solvent is N-methyl-2-pyrrolidone.

[0027] In S5, the thickness of the sodium supplement interface layer is 5-15μm, and the first vacuum drying condition is drying at 60℃ for 12h.

[0028] Based on the above scheme, by uniformly coating SA-Co / Na2S@C on the surface of sodium vanadium phosphate (NVP) positive electrode, the coating can act as a "sodium source repository". During the first charging process, the Na2S layer decomposes in situ to release active sodium, precisely compensating for the loss of sodium in the positive electrode lattice, while the sodium polysulfide (NaPs) produced during the sodium supplementing process forms a dynamic protective layer on the positive electrode surface, inhibiting vanadium dissolution at high voltage of 4.3V. The released Na + After migration to the hard carbon (HC) negative electrode, a dense SEI is induced by solventation structure reconstruction, reducing the interface impedance, and obtaining a sodium ion battery that exhibits excellent cycle stability and rate performance.

[0029] The above content will be further verified by specific embodiments to enable those skilled in the art to better understand the present application and to implement it, but the examples are not limiting to the present application.

[0030] Example 1 In this embodiment, the preparation of single-atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material includes the following steps: Step one, 0.2g of CoPc is dissolved in 25wt% ammonia water and mixed with 6g of melamine powder, and the uniform dispersion slurry system is formed by ultrasonic assisted mechanical stirring; then the mixed slurry is placed in a vacuum drying oven, and heat treated at a temperature of 70℃ for 12h to completely remove the solvent and volatile components; and the dried product is ground to obtain a composite powder.

[0031] Step two, 2g of Na2SO4, 500mg of PVP and 500mg of composite powder are blended and dissolved in anhydrous ethanol, and magnetically stirred at a temperature of 80℃ with a rotation speed of 300-500rpm until the solvent is completely volatilized; then it is placed in a vacuum drying oven at 60℃ for 8h to obtain a primary powder; then a planetary ball mill (zirconia grinding ball, ball-to-material ratio 20:1, rotation speed 400rpm) is used for 2h to obtain a uniform particle size precursor powder.

[0032] Step three, the obtained precursor powder is placed in a tube furnace, high-purity argon gas with a flow rate of 60ml / min is introduced, and the temperature is raised to 800℃ at a rate of 5℃ / min and kept constant for 2h for carbothermal reduction reaction, then the step cooling strategy is used: natural cooling before 500℃, and furnace cooling to room temperature after 500℃, finally the single-atom cobalt catalysis-carbon confined sodium sulfide SA-Co / Na2S@C composite material with three-dimensional porous carbon network confinement structure is obtained.

[0033] The SA-Co / Na2S@C composite material prepared in Example 1 was used as a sodium supplement material in a sodium ion battery for electrochemical performance testing. The process was as follows: SA-Co / Na2S@C material, polyvinylidene fluoride binder and SuperP conductive agent with a mass ratio of 8:1:1 were weighed and sequentially added to N-methyl-2-pyrrolidone (NMP) to obtain a black slurry with a solid content of 40%; then the black slurry was coated on an aluminum foil and vacuum dried at 60°C for 12 hours, and the solid content of the dried coated aluminum foil was 3.5 mg cm-2. -2 The dried coated aluminum foil was punched into a 12 mm round sheet as the positive electrode, sodium sheet as the negative electrode, Whatman GF / A as the separator between the positive and negative electrodes, and NP-035 as the electrolyte to assemble a CR2016 button cell for electrochemical performance testing.

[0034] The material of the present example was characterized by transmission electron microscopy (TEM), and the results are shown in FIG. 1. Figure 2 As can be seen from FIG. 1, the Na2S generated in situ in Example 1 is uniformly confined in the three-dimensional carbon network formed by carbonization of polyvinylpyrrolidone (PVP), avoiding agglomeration and shortening the ion diffusion path, and promoting the release of more active Na during charging and discharging. + for supplementing sodium.

[0035] Comparative Example 1 In the present comparative example, the preparation of the single-atom cobalt / sodium sulfide@carbon composite material includes the following steps: Step one, 2g of Na2SO4, 500mg of PVP, 200mg of Co(NO3)2 and 500mg of KB were blended and dissolved in anhydrous ethanol, and were magnetically stirred at a temperature of 80°C and a speed of 300-500rpm until the solvent was completely volatilized; then it was placed in a vacuum drying oven at 60°C for 8h to obtain a primary powder; then a planetary ball mill (zirconia grinding ball, ball-to-material ratio 20:1, speed 400rpm) was used to mill for 2h to obtain a uniform particle size precursor powder.

[0036] Step two, the obtained precursor powder was placed in a tube furnace, high-purity argon gas with a flow rate of 60ml / min was introduced, and the temperature was raised to 800°C at a rate of 5°C / min and kept constant for 2h for carbothermic reduction reaction, and then a step cooling strategy was used: natural cooling before 500°C and furnace cooling to room temperature after 500°C, finally obtaining a single-atom cobalt / sodium sulfide@carbon (NP-Co / Na2S@C) composite material with a three-dimensional porous carbon network confinement structure.

[0037] Comparative Example 2 In the present comparative example, the preparation of the single-atom cobalt / sodium sulfide@carbon composite material includes the following steps: Step one, 2g of Na2SO4, 500mg of PVP, 200mg of Co(NO3)2 and 500mg of KB were blended, dissolved in anhydrous ethanol, magnetically stirred at 80℃ with a speed of 300-500rpm until the solvent was completely volatilized, then placed in a vacuum drying box at 60℃ for 8h to obtain a primary powder, then a planetary ball mill (zirconia grinding ball, ball-to-material ratio 20:1, speed 400rpm) was used to mill for 2h to obtain a precursor powder with uniform particle size.

[0038] Step two, the obtained precursor powder was placed in a tube furnace, high-purity argon gas with a flow rate of 60ml / min was introduced, heated to 800℃ at a rate of 5℃ / min and kept at this temperature for 2h to perform carbothermal reduction reaction, then a staged cooling strategy was used: naturally cooled at 500℃ and cooled to room temperature with the furnace after 500℃, finally a single-atom cobalt / sodium sulfide@carbon (Na2S@C) composite material with a three-dimensional porous carbon network confined structure was obtained.

[0039] The SA-Co / Na2S@C prepared in Example 1, the NP-Co / Na2S@C prepared in Comparative Example 1 and the Na2S@C prepared in Comparative Example 2 were characterized by X-ray diffractometer (XRD), and the results are shown in Figure 3 It can be found that no (002) and (102) crystal face characteristic peaks of metallic cobalt are detected in the spectrum of SA-Co / Na2S@C, referring to Co JCPDS No. 89-4308 and Na2S JCPDS No. 23-0441, it is confirmed that cobalt is dispersed in the three-dimensional carbon network in the form of single atoms, and no metallic cobalt or nanoparticles are formed.

[0040] In addition, the SA-Co / Na2S@C prepared in Example 1, the NP-Co / Na2S@C prepared in Comparative Example 1 and the Na2S@C prepared in Comparative Example 2 were also tested for electrochemical performance, and the first circle (0.1C) charge-discharge curves were obtained, and the results are shown in Figure 4 It can be found that the first circle (0.1C) charge capacity of the SA-Co / Na2S@C battery prepared in Example 1 is as high as 486.71mAhg -1 , and the sodium supplement effect is excellent; Figure 5 The charge-discharge curves of the sodium-ion full battery assembled by using the NVP positive electrode modified by the SA-Co / Na2S@C of Example 1 (i.e. p-NVP) and the NVP positive electrode respectively as the coating material and the NVP positive electrode and the hard carbon (HC) negative electrode in the 0.5C rate range are compared, and it can be known from Figure 5 that the first circle coulombic efficiency of the NVP||HC system is 56.37%, the first circle coulombic efficiency of the p-NVP||HC system is increased to 82.70%, and the first circle discharge specific capacity of the p-NVP||HC system is 26.68mAhg -1, and the SA-Co / Na2S@C modification can effectively improve the coulombic efficiency and discharge capacity of the sodium-ion full battery in the first cycle, verifying the positive effect of the modification on improving the electrochemical performance of the sodium-ion full battery in the first cycle. Figure 6 The cycle curves of p-NVP-10 and NVP are compared in the following figure: Figure 6 It can be seen from the figure that the specific capacity retention rate of the p-NVP-10 system is 87.85% and that of the NVP system is 77.31% after 300 cycles. The p-NVP-10 system modified by SA-Co / Na2S@C has better cycle stability, and the modification strategy can effectively improve the cycle stability of the sodium-ion full battery through the synergistic effect of dynamic sodium supplementation and interface catalysis, providing strong support for optimizing the electrochemical performance and service life of the battery.

[0041] Referring to Figure 7 The p-NVP has a higher sodium ion diffusion rate than the NVP in the charge and discharge processes through the galvanostatic intermittent titration test (GITT) analysis of the p-NVP and NVP in Example 1. This indicates that the sodium polysulfide (NaPs) produced by the decomposition of SA-Co / Na2S@C can form a dynamic protective layer on the surface of the positive electrode, allowing the p-NVP to have faster sodium ion diffusion kinetics.

[0042] Therefore, by using the above-mentioned preparation method of a sodium sulfide carbon confined pre-sodium coating based on single-atom catalysis, sodium sulfide is converted from sodium sulfate at 800-900°C through carbothermal reduction, the inert atmosphere is used to prevent oxidation and discharge gas products, the sodium sulfide is confined in the three-dimensional carbon network to avoid agglomeration and shorten the ion diffusion path, and the triple mechanism of cobalt single atoms is used to reduce the decomposition voltage of sodium sulfide and improve the sodium supplementation efficiency, thereby providing an efficient and stable solution for the sodium supplementation technology of high specific energy sodium-ion batteries, synergistically optimizing the ion transmission and sodium supplementation processes, significantly enhancing the cycle stability, rate performance and high-voltage resistance of sodium-ion batteries, and further improving the performance of sodium-ion batteries.

[0043] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts of each embodiment can be referred to each other.

[0044] The principles and implementation modes of the present application are described by using specific examples in this paper, and the above embodiment description is only used to help understand the method and core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In view of the above, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis, characterized in that, Includes the following steps: S1. Cobalt phthalocyanine CoPC is mixed with melamine powder and a slurry is obtained by ultrasonic-assisted mechanical stirring. After drying and grinding, a composite powder containing cobalt-nitrogen precursor is obtained. S2. The composite powder is mixed with sodium sulfate (Na2SO4) and polyvinylpyrrolidone (PVP) in a certain proportion, and after stirring, drying and grinding, a precursor powder containing sodium source and carbon precursor is obtained. S3. The precursor powder is sintered under an argon atmosphere to convert sodium sulfate into sodium sulfide Na2S in situ through a carbothermal reduction reaction. At the same time, the cobalt atoms in cobalt phthalocyanine are dispersed in the carbon network in a single-atom state to obtain a single-atom cobalt catalytic-carbon confined sodium sulfide SA-Co / Na2S@C composite material. S4. The single-atom cobalt-catalyzed-carbon-confined sodium sulfide SA-Co / Na2S@C composite material is mixed with a conductive agent, a first binder and a first organic solvent, and then subjected to first degassing and stirring to obtain a slurry. S5. The slurry is coated onto the surface of the cathode material to form a sodium-supplemented interface layer, and then dried under a first vacuum to obtain a cathode with a sodium sulfide carbon confined pre-sodium coating based on single-atom catalysis.

2. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S1, the mass ratio of cobalt phthalocyanine CoPC to melamine powder is 1:30, and the mixing process is carried out in ammonia water, with ultrasonic time of 4-6 hours, and the slurry is made viscous by mechanical stirring.

3. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S1, the drying conditions are vacuum drying at 75-85°C for 10-12 hours to remove solvents and volatile components.

4. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S2, the mass ratio of the composite powder, sodium sulfate, and polyvinylpyrrolidone is 1:4:1, and the blending process is carried out in ethanol at a stirring temperature of 80°C.

5. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S2, the drying conditions are vacuum drying at 69-70℃ for 6-8 hours, followed by ball milling at a speed of 400-600 r / min.

6. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S3, the heating rate of the sintering process is 2-5℃ / min, the sintering temperature is 800-900℃, and the holding time is 2-3h.

7. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S3, the argon flow rate is 60 mL / min. After sintering, a segmented cooling strategy is adopted: natural cooling before 500℃, and cooling to room temperature with the furnace after 500℃.

8. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S4, the mass ratio of the single-atom cobalt catalytic-carbon confined sodium sulfide SA-Co / Na2S@C composite material, the conductive agent, and the first binder is 3-6:3-6:1; the first binder is one or more of polyvinylidene fluoride, polymethyl methacrylate, or polyvinylidene fluoride-hexafluoropropylene copolymer.

9. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S4, the first degassing stirring speed is 400-800 r / min, and the first organic solvent is N-methyl-2-pyrrolidone.

10. The method for preparing a sodium sulfide carbon-confined pre-sodium coating based on single-atom catalysis according to claim 1, characterized in that, In S5, the thickness of the sodium-supplementing interface layer is 5-15 μm, and the first vacuum drying condition is drying at 60°C for 12 hours.

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