Preparation method and application of lithium-sulfur battery positive electrode material
The preparation of sulfur-containing polymer materials by using solid-phase sintering method of melamine, polyacrylamide and sulfur element is solved, and the capacity attenuation problem caused by lithium-sulfur battery due to lithium polysulfide shuttle effect and sulfur volume expansion is significantly improved, and the structural stability and electrochemical performance of the battery are significantly improved.
Patent Information
- Application Number
- CN202411771585.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-04
- Publication Date
- 2025-04-11
AI Technical Summary
During the charging and discharging process, lithium-sulfur batteries have a fast capacity decay due to the shuttle effect of lithium polysulfide and the volume expansion of sulfur, and are difficult to transfer electrons.
Melamine, polyacrylamide and sulfur element are used as the main raw materials to prepare high-performance sulfur-containing polymer materials through solid phase sintering. Polyacrylamide provides volume expansion space, melamine alleviates polymer agglomeration, and N atoms enhance the chemical affinity of polysulfides and reduces shuttle effects.
The structural stability and electrochemical performance of the lithium-sulfur battery positive electrode material are significantly improved, the cycle life is extended, the initial discharge specific capacity is as high as 1122mAh/g, and the capacity retention rate is as high as 93.4% after 150 cycles.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a preparation method and application of a positive electrode material for a lithium-sulfur battery. Background Art
[0002] Environmental pollution and the gradual depletion of traditional energy have become the main problems facing the development of today's society. In the process of energy transformation, due to the increasing demand for portable devices and electric vehicles, traditional lithium-ion batteries can no longer meet the requirements. Lithium-sulfur batteries have a high theoretical capacity (1675mAh g -1 ), high energy density (2600Wh kg -1 ) and low cost, and has attracted much attention.
[0003] The intermediate product lithium polysulfide (LiPSs) produced during the charge and discharge process of lithium-sulfur batteries will dissolve in the electrolyte, resulting in loss of active substances and rapid capacity decay; secondly, the insulating properties of sulfur and its products (LiS / LiS2) make it difficult for electron transfer during operation; and sulfur has a large volume expansion during the reaction, which will cause its structure to collapse and the capacity to decay rapidly.
[0004] In response to these problems, researchers have used carbon materials, transition metal-based compounds, metal framework materials, etc. as carriers to prepare sulfur-containing composites to improve their electrochemical performance. Many studies have found that sulfur-containing composites can improve the conductivity of materials, but the shuttle effect and volume expansion of LiPSs are still relatively serious, and cannot fundamentally solve the problem of capacity attenuation during battery charging and discharging. Summary of the invention
[0005] The purpose of the present invention is to solve the serious shuttle effect and volume expansion problems of sulfur-containing compounds LiPSs, and to provide a preparation method and application of lithium-sulfur battery positive electrode materials. The method selects melamine, polyacrylamide and sulfur as main raw materials, and prepares high-performance sulfur-containing polymer materials by solid phase sintering. The polymer material polyacrylamide is used as the main framework of the electrode material, which provides a certain volume expansion space for the reaction process and effectively alleviates the expansion effect of the sulfur positive electrode during the charging and discharging process. The addition of organic molecule melamine can alleviate the agglomeration of the polymer, exposing more reactive sites, and the presence of N atoms has a strong chemical affinity for polysulfides, which effectively alleviates the shuttle effect of lithium polysulfide. The present invention provides a new way to synthesize sulfur polymer materials and has broad application prospects in the field of lithium ion batteries.
[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:
[0007] A method for preparing a positive electrode material for a lithium-sulfur battery, the method comprising:
[0008] Step 1: Processing raw materials: Add polyacrylamide (PAM) and carbon nanotubes (CNT) into anhydrous ethanol, stir them ultrasonically for more than 5 hours until they are evenly dispersed, add melamine, stir them ultrasonically until they are completely dissolved, and obtain an evenly dispersed suspension;
[0009] Step 2: Preparing a precursor: Stir and heat the suspension obtained in step 1 until the anhydrous ethanol is completely evaporated, grind the obtained material sufficiently, place it in a tube furnace under an argon atmosphere at 380° C. for 3 to 5 hours, and obtain a precursor;
[0010] Step 3: Preparation of lithium-sulfur positive electrode material: Add sulfur powder to the precursor material obtained in step 2, grind it thoroughly, place it in a sealed container and keep it at 170°C for 15 to 20 hours to obtain a product, and keep the obtained product in a tubular furnace under an argon protective atmosphere at 220°C for 1 to 3 hours to remove free sulfur and obtain a lithium-sulfur positive electrode active material.
[0011] The material prepared by the present invention can provide a large number of ion transmission channels in the application of lithium-sulfur batteries to increase the ion transmission rate and enable the battery to have a high-rate charge and discharge capability. Due to the introduction of N atoms, polysulfides generated during the charge and discharge process can be bound, inhibiting their shuttle effect and improving the cycle stability of the material.
[0012] Furthermore, in step 1, the amount of PAM added is 0.2-0.5 mmol (MW-7 million), the amount of CNT added is 0.04-0.10 g, the amount of anhydrous ethanol used is 20.00-50.00 g, the purity is ≥99.5%, and the amount of melamine added is 0.05-0.15 g.
[0013] Furthermore, in step 2, the stirring and heating temperature is above 70°C.
[0014] Furthermore, in step three, the amount of sulfur powder added is 0.03-0.07 mol.
[0015] Furthermore, in step 2 and step 3, the heating rate of the tubular furnace is 2-5° C. / min.
[0016] Application of the material prepared by the above preparation method as a positive electrode material for a lithium-sulfur battery.
[0017] Compared with the prior art, the present invention has the following beneficial effects:
[0018] (1) The positive electrode material prepared by the present invention is a sulfur polymer formed by the combination of organic matter and sulfur. The flexible skeleton of the polymer can effectively alleviate the volume expansion of the electrode during the charge and discharge process, improve the structural stability of the electrode material, and provide a good structural foundation for the long cycle process.
[0019] The material prepared by the present invention provides sufficient active sites and a certain volume expansion space for S in the reaction process due to the introduction of molecules containing N atoms, and the presence of N atoms has a strong chemical affinity for polysulfides, which effectively alleviates the shuttle effect of lithium polysulfide, making it have excellent electrochemical properties. For example, at a current density of 0.3C rate, the initial discharge specific capacity of the material is as high as 1122mAh / g, and after 150 cycles, the capacity retention rate is as high as 93.4%.
[0020] The polymer used in the present invention is used as the main structure of the material. After being processed, it has good conductivity while ensuring flexibility. Organic molecules are introduced into the long-chain structure of the polymer, so that a large number of lithium ion channels are formed inside the material, which can enable lithium ions to be quickly transmitted in the material, so that it has lower resistance when used as an electrode material, thereby improving the electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 This is a cycle performance diagram of the lithium-sulfur battery positive electrode material prepared in Example 1 at a current density of 0.3C.
[0022] Figure 2 This is a cycle performance diagram of the lithium-sulfur battery positive electrode material prepared in Comparative Example 1 at a current density of 0.3C.
[0023] Figure 3 This is a cycle performance diagram of the lithium-sulfur battery positive electrode material prepared in Comparative Example 2 at a current density of 0.3C.
[0024] Figure 4 This is a charge and discharge curve diagram of the lithium-sulfur battery positive electrode material prepared in Example 1 at a current density of 0.3C.
[0025] Figure 5 This is a charge and discharge curve of the lithium-sulfur battery positive electrode material prepared in Comparative Example 1 at a current density of 0.3C.
[0026] Figure 6 This is a charge and discharge curve of the lithium-sulfur battery positive electrode material prepared in Comparative Example 2 at a current density of 0.3C.
[0027] Figure 7 This is the electrochemical impedance spectrum of the lithium-sulfur battery positive electrode material prepared in Example 1.
[0028] Figure 8 This is the electrochemical impedance spectrum of the lithium-sulfur battery positive electrode material prepared in Comparative Example 1.
[0029] Fig. 9 This is the electrochemical impedance spectrum of the lithium-sulfur battery positive electrode material prepared in Comparative Example 2. DETAILED DESCRIPTION
[0030] In order to better understand the content of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings. The following embodiments are implemented based on the technology of the present invention, and detailed implementation methods and operating steps are given, but the protection scope of the present invention is not limited to the following embodiments.
[0031] Embodiment 1:
[0032] (1) Processing of raw materials: 0.20 g of polyacrylamide and 0.05 g of carbon nanotubes were added to 30.00 g of anhydrous ethanol, and ultrasonically stirred for 5 h until they were evenly dispersed. 0.09 g of melamine was added, and ultrasonically stirred for 1 h until they were completely dissolved to obtain a uniformly dispersed suspension.
[0033] (2) Preparing a precursor: The suspension obtained in step (1) is stirred and heated until the solvent is completely evaporated. The obtained material is fully ground and placed in a tube furnace under an argon atmosphere at 380° C. for 5 h to obtain a material precursor.
[0034] (3) Preparation of lithium-sulfur positive electrode material: sulfur powder is added to the precursor material obtained in step (2) (the ratio of the amount of sulfur powder added to the amount of the precursor product obtained is 7:3), and after sufficient grinding, it is placed in a sealed container and kept at 170° C. for 18 hours to obtain a product, and the obtained product is kept at 220° C. for 2 hours in a tubular furnace under an argon protective atmosphere to remove free sulfur, thereby obtaining a lithium-sulfur positive electrode material.
[0035] Comparative Example 1:
[0036] (1) Processing raw materials: 0.20 g of polyacrylamide and 0.05 g of carbon nanotubes were added to 30.00 g of anhydrous ethanol, and ultrasonically stirred for 5 h until they were evenly dispersed to obtain a uniformly dispersed suspension.
[0037] (2) Preparing a precursor: The suspension obtained in step (1) is stirred and heated until the solvent is completely evaporated. The obtained material is fully ground and placed in a tube furnace under an argon atmosphere at 380° C. for 5 h to obtain a material precursor.
[0038] (3) Preparation of lithium-sulfur positive electrode material: sulfur powder is added to the precursor material obtained in step (2) (the ratio of the amount of sulfur powder added to the amount of the precursor product obtained is 7:3), and after sufficient grinding, it is placed in a sealed container and kept at 170° C. for 18 hours to obtain a product, and the obtained product is kept at 220° C. for 2 hours in a tubular furnace under an argon protective atmosphere to remove free sulfur, thereby obtaining a lithium-sulfur positive electrode material.
[0039] Comparative Example 2:
[0040] (1) Processing raw materials: 0.09 g of melamine and 0.05 g of carbon nanotubes were added to 30.00 g of anhydrous ethanol, and ultrasonically stirred for 5 h until they were evenly dispersed to obtain a uniformly dispersed suspension.
[0041] (2) Preparing a precursor: The suspension obtained in step (1) is stirred and heated until the solvent is completely evaporated. The obtained material is fully ground and placed in a tube furnace under an argon atmosphere at 380° C. for 5 h to obtain a material precursor.
[0042] (3) Preparation of lithium-sulfur positive electrode material: sulfur powder is added to the precursor material obtained in step (2) (the ratio of the amount of sulfur powder added to the amount of the precursor product obtained is 7:3), and after sufficient grinding, it is placed in a sealed container and kept at 170° C. for 18 hours to obtain a product, and the obtained product is kept at 220° C. for 2 hours in a tubular furnace under an argon protective atmosphere to remove free sulfur, thereby obtaining a lithium-sulfur positive electrode material.
[0043] The three materials prepared above were mixed with conductive carbon black and PVDF in a ratio of 8:1:1 at room temperature, with NMP as the slurry dispersant and aluminum foil as the current collector to prepare the positive electrode sheet. Then, a metal lithium sheet was used as the counter electrode, and the electrolyte consisted of 1M LiN(CF3SO2)2 and 0.1M anhydrous lithium nitrate in a 1:1 mixed solvent of 1,3-dioxolane and diethylene glycol dimethyl ether. The battery was assembled in an argon-filled glove box and the electrochemical performance was tested at room temperature.
[0044] The electrochemical performance of the battery assembled from the material prepared in Example 1 tested at a current density of 0.3C is as follows: Figure 1 and Figure 4 As shown, the electrochemical impedance spectrum of the test is as follows Figure 7 The electrochemical performance of the battery assembled from the material prepared in Comparative Example 1 tested at a current density of 0.3C is shown in Figure 2 and Figure 5 As shown, the electrochemical impedance spectrum of the test is as follows Figure 8 The electrochemical performance of the battery assembled from the material prepared in Comparative Example 2 tested at a current density of 0.3C is shown in Figure 3 and Figure 6 As shown, the electrochemical impedance spectrum of the test is as follows Fig. 9 shown.
[0045] from Figure 1 , Figure 2 , Figure 3It can be found that the material prepared in Example 1 has a discharge specific capacity and a capacity retention rate that are significantly better than the material performance of Comparative Examples 1 and 2. The material prepared in Example 1 has an initial discharge specific capacity of up to 1122 mAh / g, and after 150 cycles, the capacity retention rate is as high as 93.4%, and the capacity decay rate of each cycle is only 0.045%, indicating that the lithium-sulfur battery positive electrode material prepared in Example 1 has good electrochemical cycle performance.
[0046] The charge and discharge curves of the material prepared in Comparative Example 2 are as follows: Figure 6 As shown, it can be found that at the starting point of the charging curve, the curve shows a trend of first increasing and then decreasing, indicating that the electrochemical polarization is large; the charge and discharge curve of the material prepared in Comparative Example 1 is as follows Figure 5 As shown, the discharge curve shows a relatively large concave slope at 2.0V, showing a certain electrochemical polarization; in comparison, the charge and discharge curve of the material prepared in Example 1 is as follows Figure 4 As shown, the charge and discharge curves are relatively smooth, indicating that the material can provide a large number of lithium ion diffusion channels and improve the electrochemical performance of the battery.
[0047] Figure 7 , Figure 8 and Fig. 9 The electrochemical impedance spectra of the electrode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown. It can be found that the material prepared in Example 1 shows the minimum value for both the charge transfer resistance represented by the semicircle part and the ion diffusion resistance represented by the straight line part. This shows that the electrode material prepared in Example 1 can accelerate the ion diffusion rate and charge transfer rate, so that it has good electrochemical performance.
Claims
1. A method for preparing a positive electrode material for a lithium-sulfur battery, characterized in that: The method is: Step 1: Processing raw materials: Add polyacrylamide (PAM) and carbon nanotubes (CNT) into anhydrous ethanol, stir them ultrasonically for more than 5 hours until they are evenly dispersed, add melamine, stir them ultrasonically until they are completely dissolved, and obtain an evenly dispersed suspension; Step 2: Preparing a precursor: Stir and heat the suspension obtained in step 1 until the anhydrous ethanol is completely evaporated, grind the obtained material sufficiently, place it in a tube furnace under an argon atmosphere at 380° C. for 3 to 5 hours, and obtain a precursor; Step 3: Preparation of lithium-sulfur positive electrode material: Add sulfur powder to the precursor material obtained in step 2, grind it thoroughly, place it in a sealed container and keep it at 170°C for 15 to 20 hours to obtain a product, and keep the obtained product in a tubular furnace under an argon protective atmosphere at 220°C for 1 to 3 hours to remove free sulfur and obtain a lithium-sulfur positive electrode active material.
2. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, wherein: In step 1, the amount of PAM added is 0.2-0.5 mmol (MW-7 million), the amount of CNT added is 0.04-0.10 g, the amount of anhydrous ethanol used is 20.00-50.00 g, the purity is ≥99.5%, and the amount of melamine added is 0.05-0.15 g.
3. The method for preparing the positive electrode material of a lithium-sulfur battery according to claim 1, characterized in that: In step 2, the stirring and heating temperature is above 70°C.
4. The method for preparing a positive electrode material for a lithium-sulfur battery according to claim 1, characterized in that: In step 3, the amount of sulfur powder added is 0.03-0.07 mol.
5. The method for preparing the positive electrode material of a lithium-sulfur battery according to claim 1, characterized in that: In step 2 and step 3, the heating rate of the tubular furnace is 2-5°C / min.
6. Use of a material prepared by the preparation method according to any one of claims 1 to 5 as a positive electrode material for a lithium-sulfur battery.