Lithium-sulfur battery cathode material, preparation method and application thereof

Abstract

The application discloses a lithium-sulfur battery positive electrode material and a preparation method and application thereof. The method comprises the following steps: 1) dissolving terephthalic acid and FeCl3.6H2O in DMF, mixing, and obtaining a transparent orange solution; 2) carrying out a heating reaction on the transparent orange solution in an autoclave to obtain a product, which is denoted as MIL-53; 3) mixing the MIL-53 with selenium powder to obtain a mixture; and 4) annealing the mixture to obtain the lithium-sulfur battery positive electrode material. In the method, the selenium powder is used to seleniumize iron ions to generate iron selenide, the conductivity of the positive electrode material is improved, the electronic conductivity is enhanced, meanwhile, the reaction kinetics of sulfur can be catalyzed, the conversion speed of sulfur ions is improved, and the self-discharge phenomenon of the lithium-sulfur battery is inhibited to a certain extent.

Description

Technical Field

[0001] The present invention relates to the field of lithium-sulfur batteries, and in particular to a lithium-sulfur battery positive electrode material and a preparation method and application thereof. Background Art

[0002] With the continuous consumption of global fossil energy and the corresponding emission gases causing the greenhouse effect, the establishment of a clean and renewable new energy system is a key factor in achieving this goal. In the new energy system, development and storage are both very important links. The development of clean and renewable energy is gradually maturing, including wind energy, solar energy, nuclear energy, tidal energy, etc., but how to store these energies is also very important. Although the principle of the energy storage system is simple, the development of the energy storage system is very slow. This is mainly due to the lack of suitable electrode materials and electrolytes, as well as the difficulty in ensuring battery safety. In today's energy storage field, lithium-ion batteries (LIBs) occupy the vast majority of the market share and are widely used as power sources in most electronic products, drones, electric vehicles, robots and other fields. Currently, commercial lithium-ion batteries mainly use layered transition metal oxides or lithium iron phosphate as the positive electrode and graphite as the negative electrode. However, these commercial electrode active materials face the bottleneck of low specific capacity, which limits the energy density of existing lithium-ion batteries (≈300mAh g -1 ). Therefore, a more environmentally friendly, more economical and higher energy density energy storage system is needed. In addition, the resources of nickel-based and cobalt-based cathodes are scarce, expensive and relatively toxic, which also limits the large-scale application of cathode materials. Therefore, it is of great significance to develop a new generation of energy storage systems with high specific capacity, high mass / volume energy density, long life, low toxicity and low cost. Among the many new energy storage systems, the ones with high theoretical specific capacity (1675mAh g -1 ), high energy density (2600Wh kg -1 Low-cost sulfur cathode materials are attracting increasing research attention. Specifically, sulfur cathodes offer approximately 8-10 times the theoretical specific capacity of existing commercial cathode materials. Furthermore, elemental sulfur is abundant and environmentally friendly, making it highly suitable for future large-scale applications. Research and development of safe, low-cost, and high-energy-density Li-S battery energy storage systems is crucial and meaningful.

[0003] The application and development of lithium-sulfur batteries are severely hampered by the low electronic conductivity of sulfur in the cathode, the easy dissolution of lithium polysulfide produced during discharge in the electrolyte, and the volume expansion during sulfur conversion. Therefore, starting with sulfur in the cathode, deriving design principles for sulfur cathode materials based on the reaction mechanisms and failure mechanisms of the sulfur cathode is key to achieving high-performance lithium-sulfur batteries. Summary of the Invention

[0004] The present invention aims to provide a lithium-sulfur battery cathode material, its preparation method, and its application. The method provided herein selenizes iron ions to produce iron selenide, improving the conductivity of the cathode material and enhancing electronic conductivity. It also catalyzes the reaction kinetics of sulfur, increasing the conversion rate of sulfur ions and, to a certain extent, suppressing the self-discharge of lithium-sulfur batteries.

[0005] The present invention provides a method for preparing a positive electrode material for a lithium-sulfur battery, comprising the following steps: 1) dissolving terephthalic acid and FeCl3·6H2O in DMF, mixing, and obtaining a transparent orange solution;

[0006] 2) heating the transparent orange solution in an autoclave to obtain a product, designated as MIL-53;

[0007] 3) mixing the MIL-53 with selenium powder to obtain a mixture;

[0008] 4) annealing the mixture to obtain a lithium-sulfur battery cathode material.

[0009] In the above method, the mass ratio of the terephthalic acid to the FeCl3·6H2O can be 0.20-0.25:0.35-0.40; specifically, it can be 0.23:0.37. When it is 0.23:0.37, an octahedral morphology is obtained, and changing the ratio will produce a spindle-shaped morphology;

[0010] The volume ratio of the mass of the terephthalic acid and FeCl3·6H2O to the DMF can be 0.55-0.65 g:60-65 mL; specifically, it can be 0.6 g:60-65 ml.

[0011] In the above method, the mixing is carried out by ultrasonic treatment;

[0012] The ultrasonic treatment time may be 0.5 to 1 hour, specifically 1 hour or 0.75 to 1 hour.

[0013] In the above method, the temperature of the heating reaction can be 145° C. to 155° C., specifically 150° C., the time can be 3.8 to 4.2 hours, specifically 4 hours, and the pressure can be 0.1 MPa to 10 MPa.

[0014] In the above method, the post-treatment of the heating reaction is as follows: cooling, centrifugal washing, and drying at 60-80°C.

[0015] In the above method, the mass ratio of the MIL-53 to the selenium powder can be 0.6:2-2.5. The selenium powder plays a role in selenization. Generally, in order to ensure complete selenization, the selenium powder is excessive and the mass of the selenium powder is at least twice that of MIL-53.

[0016] In the method, the mixing time can be 15-30 min, and specifically can be 20 min.

[0017] The mixing method is selected from at least one of grinding, ultrasonic-assisted dispersion and mechanical stirring.

[0018] In the method, the annealing conditions are as follows: annealing at 450-550 DEG C at a rate of 4-6 DEG C / min in a N2 environment for 3-5 h.

[0019] The application further provides the lithium-sulfur battery cathode material prepared by the method.

[0020] The application further provides a lithium-sulfur battery, wherein the cathode of the lithium-sulfur battery is made of the lithium-sulfur battery cathode material.

[0021] The application does not have special requirements for the size of the cathode material, and the size known by those skilled in the art can be used.

[0022] The application has the following beneficial effects:

[0023] 1. The method provided by the application uses selenium powder to seleniumize iron ions to generate iron selenide, improves the conductivity of the cathode material, enhances the electronic conductivity, and can catalyze the reaction kinetics of sulfur, improve the conversion speed of sulfur ions, and to a certain extent, inhibit the self-discharge of the lithium-sulfur battery.

[0024] 2. After the selenium powder and MIL-53 are fully ground, they are heated to 500 DEG C under the protection of N2, so that the two are fully reacted, and the cathode material better plays a catalytic role.

[0025] 3. The preparation method provided by the application is simple, the raw materials are cheap and easy to obtain, and the operation is convenient; the lithium-sulfur battery cathode material prepared by the method has excellent conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The XRD of the lithium-sulfur battery cathode material prepared in Example 1 and the comparative example of the application;

[0027] Figure 2 The SEM of the lithium-sulfur battery cathode material prepared in Example 1 of the application;

[0028] Figure 3 The cyclic voltammogram of the lithium-sulfur battery cathode material prepared in Example 1 of the application at a scanning speed of 0.2 mV / s;

[0029] Figure 4 The impedance spectrum of the lithium-sulfur battery cathode material prepared in Example 1 of the application;

[0030] Figure 5 100 cycles of the lithium-sulfur battery cathode material prepared in Example 1 at a current of 0.2C;

[0031] Figure 6 500 cycles of the lithium-sulfur battery cathode material prepared in Example 1 at a current of 0.5C;

[0032] Figure 7 the second cycle charge-discharge curve of the lithium-sulfur battery cathode material prepared in Example 1 at a current of 0.5C;

[0033] Figure 8 the rate performance of the lithium-sulfur battery cathode material prepared in Example 1; DETAILED DESCRIPTION

[0034] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0035] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0036] Example 1

[0037] The present embodiment provides a preparation method of a lithium-sulfur battery cathode material.

[0038] First, 0.23 g of terephthalic acid and 0.37 g of FeCl3·6H2O were dissolved in 60 mL of DMF, and then the mixture was ultrasonically treated for 1 hour to obtain a transparent orange solution, which was poured into an autoclave and heated at 150°C for 4 h. After cooling, centrifugal washing and drying at 80°C, MIL-53 was obtained. 2 g of selenium powder was added to the prepared MIL-53, and the mixture was ground for 20 min. The mixture was then annealed at 500°C under N2 at a rate of 5°C / min for 4 h to obtain the final product, which was used as a lithium-sulfur battery cathode material.

[0039] Example 2

[0040] The present embodiment provides a preparation method of a lithium-sulfur battery cathode material.

[0041] First, 0.24 g of terephthalic acid and 0.37 g of FeCl3·6H2O were dissolved in 60 mL of DMF, and then the mixture was ultrasonically treated for 1 hour to obtain a transparent orange solution, which was poured into an autoclave and heated at 150°C for 4 h. After cooling, centrifugal washing and drying at 80°C, MIL-53 was obtained. 2 g of selenium powder was added to the prepared MIL-53, and the mixture was ground for 20 min. The mixture was then annealed at 500°C under N2 at a rate of 5°C / min for 4 h to obtain the final product, which was used as a lithium-sulfur battery cathode material.

[0042] Example 3

[0043] This embodiment provides a method for preparing a positive electrode material for a lithium-sulfur battery.

[0044] First, 0.23g of terephthalic acid and 0.37g of FeCl3·6H2O were dissolved in 65mL of DMF. The mixture was then sonicated for 1 hour to obtain a transparent orange solution, which was then poured into an autoclave and heated at 150°C for 4 hours. After cooling, the solution was centrifuged and washed, and then dried at 80°C to obtain MIL-53. 2g of selenium powder was added to the prepared MIL-53, and the two were mixed and ground for 20 minutes. The mixture was then annealed at 500°C at 5°C / min in a nitrogen atmosphere for 4 hours to obtain the final product, which was used as a positive electrode material for lithium-sulfur batteries.

[0045] Example 4

[0046] This embodiment provides a method for preparing a positive electrode material for a lithium-sulfur battery.

[0047] First, 0.23g of terephthalic acid and 0.37g of FeCl3·6H2O were dissolved in 60mL of DMF. The mixture was then sonicated for 1 hour to obtain a transparent orange solution, which was then poured into an autoclave and heated at 150°C for 4 hours. After cooling, the solution was centrifuged and washed, and then dried at 60°C to obtain MIL-53. 2g of selenium powder was added to the prepared MIL-53, and the two were mixed and ground for 20 minutes. The mixture was then annealed at 500°C at 5°C / min in a nitrogen atmosphere for 4 hours to obtain the final product, which is used as a positive electrode material for lithium-sulfur batteries.

[0048] Example 5

[0049] This embodiment provides a method for preparing a positive electrode material for a lithium-sulfur battery.

[0050] First, 0.23g of terephthalic acid and 0.37g of FeCl3·6H2O were dissolved in 60mL of DMF. The mixture was then sonicated for 1 hour to obtain a transparent orange solution, which was then poured into an autoclave and heated at 150°C for 4 hours. After cooling, the solution was centrifuged and washed, and then dried at 80°C to obtain MIL-53. 2.3g of selenium powder was added to the prepared MIL-53, and the two were mixed and ground for 20 minutes. The mixture was then annealed at 500°C at 5°C / min in a nitrogen atmosphere for 4 hours to obtain the final product, which is used as a positive electrode material for lithium-sulfur batteries.

[0051] Comparative Example 1

[0052] This embodiment provides a method for preparing a positive electrode material for a lithium-sulfur battery.

[0053] First, 0.23 g of terephthalic acid and 0.37 g of FeCl3·6H2O were dissolved in 60 mL of DMF. Then, the mixture was ultrasonicated for 1 h to obtain a transparent orange solution, which was poured into an autoclave and heated at 150 °C for 4 h. After cooling, it was centrifuged and washed, and dried at 80 °C to obtain MIL-53.

[0054] Comparative Example 1 does not involve mixing MIL-53 with selenium powder and then calcining it at high temperature to form a selenide. This results in poor conductivity, a severe shuttle effect, and significant self-discharge in the resulting battery. MIL-53 has poor conductivity before calcination, resulting in poor electrode performance.

[0055] Performance Testing

[0056] The XRD analysis of the lithium-sulfur battery cathode materials prepared in Example 1 and Comparative Example 1 can be compared with the JCPDS NO.74-0247 and JCPDS NO.73-1123 standard cards. The results are as follows: Figure 1 As shown by Figure 1 It can be seen that compared with Comparative Example 1, Example 1 of the present invention successfully synthesized iron selenide.

[0057] like Figure 2 As shown, the embodiment 1 was observed by scanning electron microscopy, and the morphology maintained the framework of MIL-53 with a highly rough surface.

[0058] The positive electrode materials obtained in Examples 1, 2, 3, 4, 5 and the comparative example were cut into circular shapes with a diameter of 12 mm and directly used as the positive electrode of a lithium-sulfur battery. Metallic lithium was used as the negative electrode. The electrolyte used contained 1.0 M lithium bis(trifluoromethoxysulfonyl) (LiTFSI) and 5% LiNO3 in 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1. The cells were assembled into 2025 button cells in a glove box. The electrochemical performance was tested in the voltage range of 1.7 to 2.8 V using an electrochemical workstation and a battery testing system. The test results are shown in Table 1.

[0059] Table 1 Performance comparison of different examples and comparison samples

[0060]

[0061] Figure 3 This is the cyclic voltammogram of a full battery assembled from the cathode material prepared in Example 1. There are two obvious pairs of reduction and oxidation peaks in the figure.

[0062] Figure 4 The impedance spectrum shows that the battery has a small internal resistance.

[0063] Figure 5 、 6The cycle image shows that the coulombic efficiency of the battery remains at around 100% at the 500th cycle, showing good cycle stability.

[0064] Figure 7 The discharge voltage profile of Example 1 presented shows two typical plateaus, which are the result of the formation of higher-order polysulfides around 2.3V and the formation of final products around 2.0-2.1V.

[0065] Figure 8 The rate performance of Example 1 is shown, and it can be seen that Example 1 has better rate performance.

[0066] The results of the above examples and comparative examples demonstrate the feasibility of the preparation strategy proposed in the present invention, along with the simplicity, ease of implementation, and high operability of the preparation method, enabling the low-cost production of high-performance cathode materials for lithium-sulfur batteries. Selenization of iron ions to form iron selenide improves the conductivity of the cathode material, enhancing its low electronic conductivity. It also catalyzes the reaction kinetics of sulfur, increasing the conversion rate of sulfur ions and, to a certain extent, suppressing the self-discharge of lithium-sulfur batteries.

[0067] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium-sulfur battery, characterized in that: The method comprises the following steps: 1) dissolving terephthalic acid and FeCl3·6H2O in DMF, mixing the mixture, and obtaining a transparent orange solution; The mass ratio of the terephthalic acid to the FeCl3·6H2O is 0.23:0.37; 2) heating the transparent orange solution in an autoclave to obtain a product, designated as MIL-53; The post-treatment of the heating reaction is as follows: cooling, centrifugation, washing, and drying at 80°C; 3) mixing the MIL-53 with selenium powder to obtain a mixture; The mass ratio of the MIL-53 to the selenium powder is 0.6:2-2.5; 4) annealing the mixture to obtain a positive electrode material for a lithium-sulfur battery; The annealing conditions are as follows: annealing at 450-550° C. and 4-6° C. / min in a N 2 environment for 3-5 h.

2. The method according to claim 1, wherein The volume ratio of the terephthalic acid and FeCl3·6H2O to the DMF is 0.55-0.65 g:60-65 mL.

3. The method according to claim 1 or 2, characterized in that The mixing is carried out by ultrasonic treatment; the time of the ultrasonic treatment is 0.5 to 1 h.

4. The method according to claim 1 or 2, wherein The heating reaction temperature is 145° C. to 155° C., the reaction time is 3.8 to 4.2 h, and the pressure is 0.1 MPa to 10 MPa.

5. The method according to claim 1 or 2, characterized in that The mixing time is 15 to 30 minutes; The mixing method is selected from at least one of grinding, ultrasonic-assisted dispersion and mechanical stirring.

6. A lithium-sulfur battery cathode material prepared by the method according to claims 1-5.

7. A lithium-sulfur battery, characterized in that: The positive electrode of the lithium-sulfur battery is made of the lithium-sulfur battery positive electrode material according to claim 6.

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