A sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst, a preparation method and application thereof

Abstract

The application provides a sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst and a preparation method and application thereof, and belongs to the technical field of nanometer material preparation. First, citric acid, thiourea, a cobalt salt, selenium powder and ethanol are ultrasonically mixed to obtain a slurry material, and then the slurry material is subjected to joule heat shock in an air atmosphere to obtain a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst. The catalyst can fully exert the synergistic effect of the structural and component advantages, the two-dimensional structure endows it with a large specific surface area, meanwhile, the two-dimensional channel can promote the migration of particles and inhibit the shuttle effect of polysulfides, and the C3N4 and sulfur doping together endow it with the component advantages, wherein the C3N4 can effectively stabilize the structure of cobalt selenide, together with the sulfur doping, the catalytic activity and conductivity of the cobalt selenide are improved, the conversion of polysulfides is promoted, thereby the shuttle effect of the lithium-sulfur battery is inhibited and the stability of the cobalt selenide is improved, and excellent lithium-sulfur battery performance is exhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial preparation, and particularly relates to a sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst and a preparation method and application thereof. BACKGROUND

[0002] Lithium-sulfur batteries, as a kind of secondary batteries with extremely high energy density, have received extensive attention in the field of energy storage technology. Its theoretical energy density reaches 2600 Wh / kg, far exceeding the energy density of traditional lithium-ion batteries, making it show great application potential in the fields of electric vehicles, portable electronic devices, etc. Compared with lithium-ion batteries, lithium-sulfur batteries not only have a significant advantage in energy density, but also have great potential in reducing battery costs due to the use of low-cost and abundant sulfur materials. Although lithium-ion batteries dominate the current market, their lower energy density and high cost make lithium-sulfur batteries one of the key technologies for future development.

[0003] However, the practical application of lithium-sulfur batteries still faces many challenges, the most prominent of which include poor conductivity of sulfur, large volume change, and polysulfide shuttle effect. The polysulfide shuttle effect is a key issue in lithium-sulfur batteries, which refers to the continuous migration of dissolved high-order polysulfides in the electrolyte during charging and discharging, causing polysulfides to leave the electrode surface, thereby reducing the overall performance of the battery and shortening the cycle life. This effect seriously affects the stability and efficiency of lithium-sulfur batteries and is one of the main factors limiting their commercialization process. Therefore, how to effectively suppress the shuttle effect has become a key to improving the performance of lithium-sulfur batteries.

[0004] To address this challenge, researchers have proposed a variety of solutions, one of the most widely used strategies is to introduce catalysts to capture and convert dissolved polysulfides, thereby suppressing the shuttle effect. Cobalt selenide (CoSe2) as a potential catalyst material, due to its excellent chemical adsorption performance and catalytic ability, has become the focus of research in lithium-sulfur batteries. Cobalt selenide can effectively promote the conversion of polysulfides, reduce the migration of dissolved sulfur substances, and thus alleviate the shuttle effect.

[0005] However, the application of cobalt selenide also faces certain challenges. First, during the charging and discharging process of lithium-sulfur batteries, especially in the reduction and oxidation reactions of polysulfides, cobalt selenide will undergo certain volume expansion and contraction. This structural change may cause the crystal structure of cobalt selenide to collapse or deform, affecting its catalytic performance. Second, the cobalt (Co) element in cobalt selenide is prone to oxidation in a strong electrochemical environment. Especially under high voltage and high current operating conditions, cobalt is easily oxidized from Co(II) to Co(III), or forms unstable cobalt oxides. This process not only consumes the active components of cobalt selenide, but also damages its catalytic efficiency and battery performance. Compounding cobalt selenide with a substrate material resistant to electrochemical corrosion can enhance the stability of cobalt selenide, prevent structural changes due to chemical reactions, and reduce the deactivation of selenide. In addition, two-dimensional porosity and element doping of cobalt selenide can improve the catalytic activity of cobalt selenide, making it more effective in capturing and converting dissolved polysulfides, reducing the occurrence of shuttle effect, and improving the stability of selenide to prevent its deactivation in battery cycling. However, existing technologies often require complex process optimization of the composition and structure of cobalt selenide, which is not conducive to industrial development. For example, Chinese patent document CN117976841A discloses a sulfur-doped cobalt selenide carbon composite negative electrode material and its preparation method and application. The patent first prepares metal organic framework Co-MOF-74 through solvothermal reaction, then prepares cobalt sulfide carbon composite material through two solvothermal reactions, and finally prepares sulfur-doped cobalt carbon composite negative electrode material by calcining with selenium source in an inert atmosphere. This method has a complex preparation process, and the multi-step solvothermal reaction consumes a large amount of organic solvent, and the complex centrifugation and washing process is time-consuming and energy-consuming. Moreover, it does not involve two-dimensionalization of cobalt selenide. In addition, the selenization process requires an inert atmosphere, which requires higher equipment requirements and is not conducive to industrial production. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst, which can solve the problems of poor stability of traditional cobalt selenide in lithium-sulfur battery applications and complex composite and doping modification process of cobalt selenide material.

[0007] To achieve this purpose, the technical solution of the present application is:

[0008] A preparation method of sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst, comprising the following steps:

[0009] (1) Mix citric acid, thiourea, cobalt salt, selenium powder and ethanol, and ultrasonic treatment to obtain a slurry material as a pyrolysis precursor;

[0010] (2) The above slurry material is placed in a graphite sample table groove of a Joule heat rapid heating device, and Joule heat treatment is carried out under an air atmosphere to obtain a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst.

[0011] Further, in the step (1), the molar ratio of citric acid, thiourea, cobalt salt and selenium powder is 1:2-4:0.3-0.4:0.5-2.

[0012] Further, in the step (1), the cobalt salt is one of cobalt chloride, cobalt nitrate and cobalt sulfate.

[0013] Further, in the step (1), the usage ratio of citric acid to ethanol is 1 mmol:5-10 mL.

[0014] Further, in the step (1), the ultrasonic power is 80-90 W, and the ultrasonic time is 20-50 min.

[0015] Further, in the step (2), the Joule heat treatment condition is: a heat treatment temperature of 650-850 DEG C, a heating rate of 1000-3000 DEG C / s, and a treatment number of 3-10 times. The Joule heat shock is that the temperature is raised from room temperature to the target temperature, and then naturally cooled to room temperature, which is represented as one time.

[0016] Another object of the present application is to provide a sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst prepared by the above method.

[0017] Still another object of the present application is to provide an application of the sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst prepared by the above method, which is used as an active component and is compounded with elemental sulfur and applied to a lithium-sulfur battery.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The present application adopts a Joule heat rapid calcination process under an air atmosphere, has the significant advantages of simple equipment operation, fast heating rate and low energy consumption compared with the traditional cobalt selenide material compounding and doping modification method, and does not require inert atmosphere protection in the process, which is beneficial to industrialization and large-scale production, and shows good industrial application prospect.

[0020] 2. The present application uses citric acid and ethanol to optimize the morphology and structure of the catalyst. The gas generated by citric acid in the Joule heat process promotes the formation of vacuoles in the liquid metal chelate. The vacuoles effectively inhibit the sintering of the catalyst and promote the formation of a two-dimensional porous structure as a pore-forming agent and a template. Ethanol provides a reducing and protective atmosphere during rapid heating and cooling, prevents the oxidation of CoSe2 into Co3O4, and promotes the effective doping of sulfur, thereby ensuring the structural integrity and excellent electrochemical performance of the material.

[0021] 3. The sulfur-doped C3N4-CoSe2 prepared by the method of the present application is a lithium-sulfur battery cathode catalyst with a two-dimensional sheet structure, which fully plays the synergistic effect of structure and composition. The two-dimensional sheet structure provides a large specific surface area (61.29-72.35 m² / g) and a two-dimensional channel, significantly improves the exposure of active sites, promotes particle migration, and effectively inhibits the shuttle effect of polysulfides, thereby improving the cycle stability and rate performance of lithium-sulfur batteries.

[0022] 4. The present application realizes the component advantage of the material by C3N4 and sulfur doping. C3N4 effectively stabilizes the CoSe2 structure, and sulfur doping improves the catalytic activity and conductivity of the material. The two synergistically promote the electrochemical conversion of polysulfides, further enhancing the stability and reaction reversibility of the catalyst. The cathode material prepared in the examples can achieve a first cycle discharge capacity of 945.8-1010.2 mAh / g at a 1C rate, and the capacity retention rate after 500 cycles is 75.4-80.2%. At a 5C rate, it can still reach 632.4-685.9 mAh / g, showing excellent rate performance and cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 X-ray powder diffraction (XRD) pattern of C3N4-CoSe2 prepared in Example 1;

[0024] Figure 2 Scanning electron microscope (SEM) image and element distribution (EDS Mapping) image of C3N4-CoSe2 prepared in Example 1;

[0025] Figure 3 Nitrogen adsorption-desorption (N2-BET) pattern of C3N4-CoSe2 prepared in Example 1;

[0026] Figure 4 Electrochemical long cycle performance test chart of lithium-sulfur battery cathode material prepared in Example 1 at a 1C rate;

[0027] Figure 5 Electrochemical performance test chart of lithium-sulfur battery cathode material prepared in Example 1 at different rates. DETAILED DESCRIPTION

[0028] The present application will be further described below in conjunction with the drawings and specific examples, so that those of ordinary skill in the art can better understand the implementation of the present application, but the protection scope of the present application is not limited thereto.

[0029] The raw materials used in the embodiments of the present application are commercially available materials unless otherwise specified; all technical and scientific terms used in the present application have the same meanings as generally understood by those skilled in the art unless otherwise specified.

[0030] In various embodiments of the specific embodiments of the present application, the Joule heat rapid heating device used is composed of a gas circuit device, a vacuum pump, a graphite sample table, a temperature control system, and a data acquisition system. Among them, the model is CIS-JH3.3-P, the output voltage is 0-40V, the output current is 0-500A, the temperature measurement range is 0-3000°C, the power supply is 380V / 30A, and the current ramping time is 1ms. Example 1

[0031] (1) 1 mmol of citric acid, 3 mmol of thiourea, 0.35 mmol of cobalt chloride, 1 mmol of selenium powder were added to a glass bottle, then 7 mL of ethanol was added, and after 85W ultrasonic treatment for 30 min, a slurry material was obtained as a pyrolysis precursor;

[0032] (2) 5 mL of the above slurry material was placed in the graphite sample table groove of the Joule heat rapid heating device, and Joule heat treatment was carried out in air atmosphere, the Joule heat heating temperature was 750°C, the heating rate was 1600°C / s, the Joule heat shock times were 6, and the cooling was carried out, thereby obtaining a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst. Example 2

[0033] (1) 1 mmol of citric acid, 2 mmol of thiourea, 0.3 mmol of cobalt chloride, and 0.5 mmol of selenium powder were added to a glass bottle, then 5 mL of ethanol was added, and after 80W ultrasonic treatment for 50 min, a slurry material was obtained;

[0034] (2) 5 mL of the above slurry material was placed in the graphite sample table groove of the Joule heat rapid heating device, and Joule heat treatment was carried out in air atmosphere, the Joule heat heating temperature was 650°C, the heating rate was 1000°C / s, the Joule heat shock times were 10, and the cooling was carried out, thereby obtaining a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst. Example 3

[0035] (1) 1 mmol of citric acid, 4 mmol of thiourea, 0.4 mmol of cobalt chloride, and 2 mmol of selenium powder were added to a glass bottle, then 10 mL of ethanol was added, and after 90W ultrasonic treatment for 20 min, a slurry material was obtained;

[0036] (2) Put 5 mL of the above slurry material into the graphite sample table groove of the Joule heat rapid heating device, and perform Joule heat treatment under an air atmosphere, the Joule heat heating temperature is 850℃, the temperature rising rate is 3000℃ / s, the Joule heat shock times is 3 times, and cooling, so that a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst is obtained. Example 4

[0037] Example 4 is different from example 1 in that in step (1), cobalt chloride is replaced by cobalt nitrate, and the rest of the method is the same as example 1, and a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst is prepared. Example 5

[0038] Example 5 is different from example 1 in that in step (1), cobalt chloride is replaced by cobalt sulfate, and the rest of the method is the same as example 1, and a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst is prepared. Comparative example 1

[0039] (1) Put 1 mmol of citric acid, 3 mmol of thiourea, 0.35 mmol of cobalt chloride, and 1 mmol of selenium powder into a glass bottle, then add 7 mL of ethanol, and ultrasonic for 30 min at 90W, and then vacuum dry to obtain a first solid material as a pyrolysis precursor;

[0040] (2) Put 50 mg of the first solid material into the graphite sample table groove of the Joule heat rapid heating device, and perform Joule heat treatment under an air atmosphere, the Joule heat heating temperature is 750℃, the temperature rising rate is 1600℃ / s, the Joule heat shock times is 6 times, and cooling, so that comparative example 1 is obtained. Comparative example 2

[0041] Comparative example 2 is different from example 1 in that in step (1), citric acid is not used, and the rest of the method is the same as example 1, and a lithium-sulfur battery positive electrode catalyst is prepared. Comparative example 3

[0042] Comparative example 3 is different from example 1 in that in step (2), the Joule heat heating method is changed to muffle furnace calcination, and the specific heating conditions are 750℃ calcination in a muffle furnace for 1h, and the temperature rising rate is 10℃ / min, and the rest of the method is the same as example 1.

[0043] Application example 1

[0044] The lithium-sulfur battery positive electrode materials obtained in examples 1-5 and comparative examples 1-3 are mixed with sublimed sulfur according to a mass ratio of 1:4, and then loaded into a sealed container, heated at 170℃ for 12h to perform sulfur solidification, and a sulfur-solidified positive electrode material is obtained.

[0045] The sulfur-immobilized positive electrode material was used as the positive electrode of lithium-sulfur battery, Celgard 2300 porous polypropylene membrane was used as the separator, lithium foil was used as the negative electrode, and the electrolyte (1 mol / L lithium bis (trifluoromethanesulfonyl) imide and 0.2 mol / L lithium nitrate and 1,3-dioxolane and 1,2-dimethoxyethane (1:1 by volume) mixed solution) was used to assemble the button cell in the glove box filled with inert atmosphere. The electrochemical cycling performance test was carried out on the CT-4008-5A6V system at 1C rate, and the test results are shown in Table 1.

[0046] XRD test, energy dispersive spectrometer (EDS) and N2-BET test were carried out on examples 1-5 and comparative examples 1-3, wherein the XRD and EDS test results are shown in the form of phase composition, and the test results of N2-BET are shown in the form of specific surface area, and the test results are shown in Table 1:

[0047]

[0048] As can be seen from Table 1, the composition of the pyrolysis precursor, citric acid and heating method will affect the composition and structure of the material.

[0049] When the pyrolysis precursor is a slurry material containing ethanol solvent, ethanol can act as a reducing agent and a protective atmosphere to prevent CoSe2 from being oxidized to Co3O4 during rapid heating by Joule heat, and is conducive to the doping of S. Therefore, the composition of example 1 is S-doped C3N4-CoSe2, while in comparative example 1, ethanol is removed by vacuum drying first, and S doping is not achieved during the subsequent Joule heat treatment, in addition, some Co3O4 will also appear, resulting in poor electrochemical performance of comparative example 1.

[0050] The main purpose of citric acid is to optimize the morphology and structure of the catalyst. Citric acid contains acid ions, which can undergo chelation with cobalt ions and disperse cobalt ions. During rapid heating by Joule heat, citric acid undergoes thermal decomposition to produce a large amount of gas, which can cause a large number of vacuoles inside the liquid metal chelate (mainly cobalt ion-urea and cobalt ion-citric acid are liquefied by heating) in the system. These vacuoles not only act as pore-forming agents to inhibit the sintering of the catalyst, but also act as template agents to promote the formation of two-dimensional materials, so that two-dimensional porous materials with large specific surface area can be prepared. Therefore, examples 1-5 exhibit larger specific surface area than comparative example 2. It is this structural advantage that makes the examples exhibit excellent catalytic performance.

[0051] The heating method is an important factor affecting the catalyst component and structure. Due to the rapid heating characteristics of Joule heat, the decomposition of thiourea and the reaction of selenium powder and cobalt ions are relatively fast during the heating process, which can quickly form S-doped C3N4-CoSe2. Ethanol in the pyrolysis precursor forms a protective atmosphere. At the same time, the cooling speed of the Joule heat device is relatively fast. Before the protective atmosphere disappears, S-doped C3N4-CoSe2 has already dropped to a relatively low temperature, which can prevent S-doped C3N4-CoSe2 from being oxidized by air to form C3N4 and Co3O4, thereby showing poor electrochemical performance.

[0052] Figure 1 The XRD pattern of Example 1 is shown in the figure. It can be seen from the figure that the characteristic peaks of Example 1 are consistent with the standard cards of CoSe2 and C3N4.

[0053] Figure 2 The SEM and EDS patterns of Example 1 are shown in the figure. It can be seen from the figure that Example 1 is mainly a two-dimensional porous sheet structure, and the elements C, N, Se, Co and S are uniformly distributed on the nanoporous sheet. Figure 1 According to the results, Example 1 is mainly S-doped C3N4-CoSe2 porous nanosheet.

[0054] Figure 3 The N2-BET pattern of Example 1 is shown in the figure. It can be seen from the figure that Example 1 has a rich mesoporous structure, and the specific surface area is 65.36 m 2 / g.

[0055] Figure 4 The electrochemical performance test figure of the lithium-sulfur battery positive electrode material prepared in Example 1 at 1C rate is shown in the figure. It can be seen from the figure that the positive electrode material shows a first cycle discharge of 1010.2 mAh / g. After 500 cycles, the capacity is maintained at 810.2 mAh / g, the average capacity decay rate per cycle is 0.0396%, and the capacity retention rate is 80.2%. Compared with the examples, the comparative examples exhibit lower first cycle discharge capacity and higher capacity decay rate at 1C and 5C rates. The main reasons for the excellent performance of the examples are as follows: the two-dimensional porous structure of the examples gives them a large specific surface area, which can expose more active sites. At the same time, the two-dimensional channels can promote particle migration and inhibit the shuttle effect of polysulfides. The components of the examples are jointly endowed with advantages, in which C3N4 can effectively stabilize the structure of CoSe2, and sulfur doping can jointly improve the catalytic activity and conductivity of cobalt selenide, promote the conversion of polysulfides, and thereby inhibit the shuttle effect of lithium-sulfur batteries and improve the stability of CoSe2.

[0056] Figure 5The electrochemical performance chart of the lithium-sulfur battery cathode material prepared in Example 1 at different rates. As can be seen from the figure, Example 1 exhibits good rate performance, reaching 1323.5 mAh / g, 1037.6 mAh / g, and 685.9 mAh / g at 0.1C, 1C, and 5C rates, respectively, and then the capacity returns to 1285.7 mAh / g after switching to 0.1C at a 5C current density, with a capacity recovery rate of 97.1%, indicating that the lithium-sulfur battery cathode material prepared in Example 1 has highly reversible electrochemical performance.

[0057] The above examples serve to illustrate the essential content of the present application, but do not limit the protection scope of the present application. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and protection scope of the technical solutions of the present application.

Claims

1. A method for preparing a sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst, characterized in that, The method comprises the following steps: (1) mixing citric acid, thiourea, cobalt salt, selenium powder and ethanol, and performing ultrasonic treatment to obtain a slurry material; (2) directly performing joule heat treatment on the slurry material in an air atmosphere to obtain a two-dimensional sulfur-doped C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst; In the step (2), the joule heat treatment is performed at a temperature of 650-850 DEG C and a heating rate of 1000-3000 DEG C / s for 3-10 times; In the step (1), the molar ratio of citric acid, thiourea, cobalt salt and selenium powder is 1:2-4:0.3-0.4:0.5-2, and the ratio of the amount of citric acid to ethanol is 1 mmol:5-10 mL.

2. The method for preparing sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst according to claim 1, characterized in that, In the step (1), the cobalt salt is one of cobalt chloride, cobalt nitrate and cobalt sulfate.

3. The method for preparing sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst according to claim 1, characterized in that, In the step (1), the ultrasonic treatment is performed at a power of 80-90 W for 20-50 min.

4. A sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst characterized by, The lithium-sulfur battery positive electrode catalyst prepared by the method of any one of claims 1-3 has a two-dimensional sheet structure, and the specific surface area provided by the two-dimensional sheet structure is 61.29-72.35 m² / g.

5. Use of the sulfur-doped C3N4-CoSe2 lithium-sulfur battery cathode catalyst according to claim 4, characterized in that, The C3N4-CoSe2 lithium-sulfur battery positive electrode catalyst is used as an active component and is compounded with elemental sulfur to be applied to a lithium-sulfur battery positive electrode.

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