Preparation method of self-polymerized inherent microporous polymer coated sulfenyl polymer positive electrode material

Abstract

The invention belongs to the field of electrochemistry, and particularly relates to a preparation method for in-situ coating of a sulfur-based positive electrode material by using a self-polymerized microporous polymer (PIM). The method comprises the following steps: dispersing compounds with different rigidities and non-coplanar structures and a sulfur-based positive electrode material in an organic solvent according to a certain proportion, and adding a proper amount of a catalyst at a certain temperature to initiate in-situ polymerization of the compounds on the surface of the sulfur-based positive electrode material and form a coating layer; due to the irregularity and steric hindrance of the molecular chain, a polymer chain cannot form a compact accumulation structure, so that micro-pores in a micro-level are generated. In practical application, a charge-discharge test is carried out in a voltage range of 1-3V, the reversible discharge specific capacity is up to 1425.8 mAh / g under 0.2 C, the reversible discharge specific capacity is 1402.2 mAh / g after 150 cycles, and the capacity retention rate is up to 98.3%. Through the method, the volume expansion of the sulfur positive electrode is improved, polysulfur shuttling is hindered, and the battery cycle stability of the material is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry technology, and particularly relates to a preparation method of a self-polymerized intrinsic microporous polymer-coated sulfur-based polymer cathode material. Background Art

[0002] As a new generation of high-energy density energy storage system, lithium-sulfur batteries have received extensive attention and research due to their theoretically high specific capacity of up to 1675 mAh / g and energy density of 2600 Wh / kg. However, lithium-sulfur batteries face many technical challenges in practical applications. One of the most critical problems is the poor cycle stability of the battery, which is mainly due to the dissolution and diffusion of the cathode active material sulfur during charge and discharge. Specifically, the intermediate products (such as polysulfides) generated by sulfur during discharge are easily soluble in the electrolyte, resulting in the loss of active materials and thus leading to rapid capacity decay. This process not only loses the cathode material but also causes a serious shuttle effect in the electrolyte, accelerating the decline of battery performance.

[0003] Existing cathode materials, such as sulfurized polyacrylonitrile (SPAN) and carbon-sulfur composite materials (C / S), have improved the utilization rate of sulfur and cycle stability to a certain extent. SPAN chemically binds and fixes some sulfur atoms, while C / S materials physically restrict the diffusion of polysulfides using a porous carbon structure. However, these two materials still have some deficiencies in practical applications. Although SPAN has high chemical stability, its conductivity is poor, limiting the electron transfer efficiency. Although the C / S composite material has improved electron conduction through a conductive carbon network, the problem of polysulfide dissolution has not been fundamentally solved.

[0004] Therefore, there is a need to develop a preparation method for cathode materials to overcome the above technical problems. Summary of the Invention

[0005] The concept of the present invention lies in that the self-polymerized microporous polymer (PIM) can form a stable coating layer on the surface of the cathode material due to its rich microporous structure and excellent physical and chemical properties, effectively blocking the diffusion of polysulfides. In addition, the high conductivity of PIM also helps to improve the overall conductivity of the cathode material, thereby enhancing the overall electrochemical performance of lithium-sulfur batteries. Coating the SPAN or C / S cathode material with PIM can not only effectively inhibit the shuttle effect of polysulfides, reduce the loss of active materials, but also improve the conductivity of the cathode material, significantly enhancing the cycle stability and specific capacity of lithium-sulfur batteries, providing a new direction and solution idea for the technical progress of lithium-sulfur batteries.

[0006] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a sulfur-based cathode material in-situ coated with a self-polymerized microporous polymer, comprising the following steps:

[0008] S1: Take compounds with different rigid and non-coplanar structures as solvents and disperse them in an organic solvent; the structural characteristics of the above compounds make the polymer chains formed after polymerization unable to be closely packed, thus forming micropores at the molecular level;

[0009] The compounds with different rigid and non-coplanar structures include at least two of substances a to j; the molar ratio between any two different rigid and non-coplanar structure compounds is 1:(0.5 - 2); at the same time, a sulfur-based cathode material and a catalyst are added to initiate the polymerization of the compounds on the surface of the sulfur-based cathode material;

[0010]

[0011] The catalyst is any one or a mixture of two or more of triethylamine, potassium hydroxide, sodium hydroxide, boron trifluoride, p-toluenesulfonic acid, zinc chloride, aluminum chloride, and anhydrous potassium carbonate;

[0012] S2: The mixture obtained in step S1 is kept mixed and reacted to form a sulfur-based cathode material in-situ coated with a self-polymerized intrinsic microporous polymer.

[0013] Preferably, in step S1, the organic solvent is any one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), chloroform, dichloromethane (DCM), dimethylacetamide, cyclohexane, and anhydrous toluene.

[0014] Preferably, in step S1, the mass ratio of the solute in the organic solvent is 1% - 10%.

[0015] Preferably, the molar ratio between the catalyst and the solute compound is 1:(0.2 - 4).

[0016] Preferably, in step S1, the sulfur-based cathode material is at least one of sulfurized polyacrylonitrile, sulfurized polyacrylic acid, sulfurized polyaniline, and carbon-sulfur composite materials.

[0017] Preferably, the self-polymerized intrinsic microporous polymer includes substances A to F.

[0018]

[0019] Preferably, the mass ratio of the formed self-polymerized intrinsic microporous polymer to the added sulfur-based cathode material is (0.01 - 3):10.

[0020] In a second aspect, the present invention provides a self-polymerized inherently microporous polymer-coated sulfur-based cathode material, which is prepared by using the preparation method described in any one of the first aspects.

[0021] In a third aspect, there is provided an application of the self-polymerized inherently microporous polymer-coated sulfur-based cathode material described in the second aspect as a cathode in a lithium metal battery, a lithium-ion battery, a sodium-ion battery, a sodium metal battery, a potassium-ion battery, or a potassium metal battery.

[0022] Preferably, the negative electrode of the battery is a lithium metal, a sodium metal, or a potassium metal compound; and the separator is a PP, PE, PP / PE / PP / , PETE, or PEO separator.

[0023] Beneficial effects achieved by the present invention:

[0024] (1) Improve the utilization rate of sulfur: The self-polymerized inherently microporous polymer formed on the surface of the sulfur-based cathode material has a high specific surface area and a rich microporous structure, which helps to uniformly disperse sulfur and its sulfide products, increase the exposed area of sulfur, thereby improving the sulfur utilization rate in the battery and enhancing the capacity and energy density of the battery.

[0025] (2) Improve the safety of the battery: By using a combination of rigid and non-coplanar structure monomers, the present invention can significantly improve the mechanical strength and thermal stability of the polymer while maintaining a high porosity, reduce the pulverization and shedding of the electrode material, enhance the structural stability of the electrode, improve the safety of the battery, and extend the battery life.

[0026] (3) Inhibit the dissolution and migration of polysulfides: During the charge and discharge process of a lithium-sulfur battery, the generated polysulfides are easily dissolved in the electrolyte, resulting in the loss of active substances and a decrease in cycle stability. The microporous structure of the inherently microporous polymer can effectively adsorb and fix polysulfides, inhibit their dissolution and migration in the electrolyte, thereby reducing the "shuttle effect" and improving the cycle life and stability of the battery.

[0027] (4) Enhance the electrochemical performance: The self-polymerized inherently microporous polymer-coated sulfur-based cathode material can provide rich conductive channels, enhancing the electron and ion transport performance of the electrode. This helps to improve the rate performance and charge and discharge speed of the battery, meeting the requirements of fast charge and discharge.

[0028] (5) Economical, recyclable, and easy to produce on a large scale: The self-polymerized inherently microporous polymer-coated sulfur-based cathode material prepared by this method is not only economical and efficient but also in line with the concept of green production. In addition, this technology also has the potential to be easily realized for large-scale production, providing new possibilities for the sustainable development of the battery industry. Description of the Drawings

[0029] Figure 1Cycling data of the battery in Embodiment 1 of the present invention;

[0030] Figure 2 Cycling data of the battery of the comparative example in the present invention. Detailed implementation manners

[0031] To facilitate the understanding of the present invention, the following will comprehensively and meticulously explain it in combination with the embodiments and the accompanying drawings of the specification. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0032] Embodiment 1

[0033] 0.8 mmol of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 0.8 mmol of tetrafluoroterephthalonitrile, 6.4 mmol of anhydrous potassium carbonate, 120 mL of N,N-dimethylformamide (DMF), and sulfonated polyacrylonitrile (5 g) were added to a four-necked flask equipped with a stirrer, a thermometer, and an adapter. Stir at room temperature for 20 min to ensure that the monomers are fully dissolved. Then, place it in a constant temperature water bath at 50 °C and heat and stir for 23 h. After the reaction is completed, filter off the precipitate to obtain a material of sulfonated polyacrylonitrile in-situ coated with an intrinsically microporous polymer.

[0034] The above-prepared material of sulfonated polyacrylonitrile coated with an intrinsically microporous polymer was used as the positive electrode material, lithium metal was selected as the negative electrode, and a PP separator was used as the battery separator. According to the conventional battery assembly process, the positive electrode, negative electrode, and separator were assembled into a lithium metal battery. Charge-discharge tests were carried out in the voltage range of 1-3 V. At 0.2 C, the reversible discharge specific capacity was as high as 1425.8 mAh / g. After 150 cycles, the reversible discharge specific capacity was 1402.2 mAh / g, and the capacity retention rate was as high as 98.3%.

[0035] Comparative example

[0036] The sulfonated polyacrylonitrile material without any treatment was taken as the positive electrode material for comparative tests. Lithium metal was selected as the negative electrode, and a PP separator was used as the battery separator. According to the conventional battery assembly process, the positive electrode, negative electrode, and separator were assembled into a lithium metal battery. Charge-discharge tests were carried out in the voltage range of 1-3 V. At 0.2 C, the reversible discharge specific capacity was as high as 1401.1 mAh / g. After 150 cycles, the reversible discharge specific capacity was 1267.2 mAh / g, and the capacity retention rate was 90.4%.

Claims

1. A method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer, characterized in that: The following steps are involved: S1: taking compounds with different rigidities and non-coplanar structures as solvents and dispersing them in organic solvents; The compounds with different rigidities and non-coplanar structures include at least two of substances a to j; the molar ratio between any two compounds with different rigidities and non-coplanar structures is 1:(0.5-2); and sulfur-based positive electrode materials and catalysts are added at the same time; The catalyst is any one of triethylamine, potassium hydroxide, sodium hydroxide, boron trifluoride, p-toluenesulfonic acid, zinc chloride, aluminum chloride, and anhydrous potassium carbonate, or a mixture of two or more thereof; S2: The mixture obtained in step S1 is kept mixed and reacted to form a sulfur-based positive electrode material in situ coated with a self-polymerized intrinsic microporous polymer.

2. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: In step S1, the organic solvent is any one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), chloroform, dichloromethane (DCM), dimethylacetamide, cyclohexane, and anhydrous toluene.

3. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: In step S1, the mass proportion of the solute in the organic solvent is 1%-10%.

4. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: The molar ratio between the catalyst and the solute compound is 1:(0.2-4).

5. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: In step S1, the sulfur-based positive electrode material is at least one of sulfided polyacrylonitrile, sulfided polyacrylic acid, sulfided polyaniline, and a carbon-sulfur composite material.

6. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: The self-polymerizing intrinsically microporous polymer includes substances A-F.

7. The method for preparing a sulfur-based positive electrode material in situ coated with a self-polymerized microporous polymer according to claim 1, characterized in that: The mass ratio of the formed self-polymerized intrinsic microporous polymer to the added sulfur-based positive electrode material is (0.01-3):

10.

8. A self-polymerized intrinsic microporous polymer in-situ coated sulfur-based positive electrode material, prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the self-polymerized inherently microporous polymer in-situ coated sulfur-based positive electrode material as claimed in claim 8 as a positive electrode in lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

10. The use of the self-polymerized intrinsic microporous polymer in-situ coated sulfur-based positive electrode material according to claim 9, characterized in that: The negative electrode of the battery is a lithium metal, sodium metal or potassium metal compound; the separator is a PP, PE, PP / PE / PP / , PETE or PEO separator.

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