A method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials

Abstract

The present invention discloses a method for in-situ improving the cycle capacity of sulfur-based polymer positive electrode materials, which belongs to the field of chemical power supply technology. The core of the method of the present invention is to prepare graphite carbon-coated lithium orthosilicate and combine it with a sulfur-based polymer positive electrode material. By heating at a certain temperature, the diffusion of elemental sulfur that is difficult to remove in the sulfur-based polymer to the carbon layer is achieved. During the charge and discharge process of the battery, lithium orthosilicate and elemental sulfur work together to generate lithium sulfate and silicon, and release lithium ions, effectively replenishing the lithium ion loss of the battery during the cycle. This technology innovatively utilizes graphite carbon-coated lithium orthosilicate, effectively eliminating the negative impact of elemental sulfur that is difficult to handle by conventional methods on the battery cycle, thereby significantly improving the battery's cycle stability and performance. After 300 cycles of long-cycle testing, the battery's capacity retention rate was 80%, and the coulombic efficiency still remained at 100%.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical power sources, and in particular relates to a method for in-situ improving the cycle capacity of a sulfur-based polymer positive electrode material. Background Art

[0002] Lithium-sulfur (Li-S) batteries have become a research hotspot in recent years due to their potential applications in a variety of fields, from portable electronic devices to electric vehicles. Sulfur, as a low-cost, abundant material with a high theoretical capacity, is considered a strong competitor to traditional metal oxide batteries and has significant advantages. However, the low conductivity of the sulfur cathode and the dissolution of lithium polysulfides generated during the charge and discharge process have always been key factors limiting the performance of lithium-sulfur batteries. In particular, the dissolution of lithium polysulfides in the electrolyte can trigger a "shuttle effect", which not only greatly reduces the cycle life of the battery, but can also induce the formation of lithium dendrites, which can then pierce the separator and cause thermal runaway, seriously affecting the safety and stability of the battery.

[0003] To address this issue, researchers have developed a new sulfur-based polymer cathode material. This material, through a "solid-solid" conversion mechanism, theoretically eliminates the shuttling effect of polysulfides, thereby significantly improving Coulombic efficiency and cycle performance. However, during the synthesis of this material, trace amounts of sulfur inevitably remain in the material's interstices. This residual sulfur is difficult to remove through conventional desulfurization methods, affecting the battery's cycle performance.

[0004] In order to overcome this technical difficulty, the present invention proposes an innovative solution. We mix carbon-coated lithium orthosilicate with the synthesized sulfur-based polymer positive electrode material and heat it at a certain temperature for a period of time. During this process, the non-structural sulfur element is induced to diffuse into the carbon layer, and at the same time reacts with the lithium orthosilicate during the positive charge and discharge process to form lithium sulfate. This chemical reaction not only effectively eliminates the negative effects of trace sulfur elements, but also significantly reduces the gas production problem inside the soft-pack battery, thereby further improving the overall performance of the lithium-sulfur battery. The implementation of this invention provides important technical support for the practical application and commercialization of lithium-sulfur batteries. Summary of the Invention

[0005] The present invention aims to solve the technical problems existing in the above-mentioned background technology and provides a method for in-situ improving the cycle capacity of sulfur-based polymer positive electrode materials.

[0006] The present invention adopts the following technical solution: a method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials, comprising the following steps:

[0007] S1, placing silicon dioxide (SiO2), lithium carbonate (Li2CO3) and a carbon source in a ball mill according to a preset appropriate molar ratio, and ball milling at an appropriate rotation speed for a specific time to obtain a uniform mixture of SiO2, Li2CO3 and the carbon source;

[0008] S2, placing the above mixture into a tube furnace and heating it in an inert gas environment to generate lithium orthosilicate coated with a graphite carbon layer after a certain reaction time;

[0009] S3, mixing the graphite carbon layer-coated lithium orthosilicate and the sulfur-based polymer in a predetermined ratio, and heating them under certain temperature conditions for a predetermined time to allow the residual sulfur element in the sulfur-based polymer to penetrate into the carbon layer, thereby producing a composite positive electrode material;

[0010] S4, mixing the obtained composite material with conductive carbon and a binder in an appropriate proportion to form a pole piece, and completing the assembly of the battery.

[0011] Preferably, the molar ratio of SiO2, Li2CO3 and carbon source in step S1 is 1:2:(0.1~5); the carbon source is selected from one or more of glucose, sucrose, fructose, cellulose, starch, dopamine, resorcinol-formaldehyde resin, polyvinyl pyrrolidone, tannic acid and citric acid; the ball milling speed ranges from 100 to 2000 rpm / min; and the ball milling duration is set at 30 to 1000 min.

[0012] Preferably, in step S2, the inert gas used includes nitrogen and argon; the temperature of the heating treatment is set between 400-900° C.; and the heating time is 30-3000 min.

[0013] Preferably, in step S3, the mass ratio of the graphite carbon layer-coated lithium orthosilicate to the sulfur-based polymer is set between (0.01 and 10):100; the heating temperature range is 50-200°C; the heating duration is 20-3000 min; and the sulfur-based polymer positive electrode material is sulfided polyacrylonitrile, sulfided polyaniline, sulfided polytetravinylpyridine, sulfided polyacrylic acid, sulfided 1,3-diisopropenylbenzene, sulfided poly(3-hexylthiophene-2,5-diyl), sulfided 1,3-diethynylbenzene, sulfided aminophenol-formaldehyde resin, and sulfided poly(1, 2, 4, 5-4 amino)benzene.

[0014] Preferably, in step S4, the optional conductive carbon includes acetylene black, carbon nanotubes, Super P and Ketjen black; the binder is selected from PAA, CMC, SBR, guar gum, PVDF and LA133; the mass ratio of the positive electrode material, the conductive carbon and the binder is 7:2:1, 8:1:1 or 9:0.5:0.5.

[0015] Preferably, it is used in lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

[0016] Beneficial effects of the present invention:

[0017] (1) The method described in this patent can significantly improve the cycling capacity of sulfur-based polymer cathode materials. This is because the above steps successfully penetrate the residual trace sulfur element in the sulfur-based polymer into the carbon layer, which helps to reduce the negative effects of non-structural sulfur on the battery during the cycling process and enhance the stability of the cathode material, thereby improving the cycle life of the battery.

[0018] (2) During the charge and discharge process, the sulfur element fixed in the carbon layer on the surface of lithium orthosilicate reacts with lithium orthosilicate to form lithium sulfate, while releasing lithium ions and Si elements. Lithium ions have the function of replenishing lithium ions, while Si will play a role in consolidating the CEI membrane and enhancing the cycle capacity of the battery.

[0019] (3) The raw materials used in the present invention, such as silicon dioxide and lithium carbonate, are relatively common and low-cost, and the preparation process does not involve the use of toxic and hazardous substances. Therefore, the method is both economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the electrochemical long cycle data diagram of Example 1;

[0021] Figure 2 This is the electrochemical long cycle data diagram of Example 4. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Example

[0023] 1 mol of silicon dioxide (SiO2), 2 mol of lithium carbonate (Li2CO3), and 0.1 mol of glucose were used as carbon sources. The SiO2, Li2CO3, and glucose were placed in a ball mill at 600 rpm / min and milled for 300 minutes to obtain a uniform mixture. The mixture was then placed in a tube furnace and heated to 750°C for 120 minutes under an argon atmosphere to produce lithium orthosilicate coated with a graphite carbon layer. The graphite carbon-coated lithium orthosilicate was then mixed with polyacrylonitrile sulfide in a mass ratio of 1:99. The mixture was heated at 120°C for 60 minutes to allow the residual sulfur in the polyacrylonitrile sulfide to penetrate the carbon layer, thereby producing a composite cathode material. The resulting composite cathode material was then mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 7:2:1 to form a slurry. The slurry was evenly coated on aluminum foil, dried, and cut into electrodes of appropriate sizes. The battery was assembled in a dry glove box using electrolytes and separators commonly used in lithium-ion batteries. Charge and discharge tests of the assembled lithium-ion battery revealed a capacity retention rate of 80% after 300 cycles, while the coulombic efficiency remained at 100%. Example

[0024] 1 mol of silicon dioxide (SiO2), 2 mol of lithium carbonate (Li2CO3), and 0.5 mol of glucose were used as carbon sources. The SiO2, Li2CO3, and glucose were placed in a ball mill at 800 rpm / min and milled for 120 minutes to obtain a uniform mixture. The mixture was then placed in a tube furnace and heated to 700°C for 60 minutes under an argon atmosphere to produce graphite-coated lithium orthosilicate. The graphite-coated lithium orthosilicate was then mixed with polyacrylonitrile sulfide in a mass ratio of 5:95. The mixture was then heated at 120°C for 40 minutes to allow the residual sulfur in the polyacrylonitrile sulfide to penetrate the carbon layer, thereby producing a composite cathode material. The resulting composite cathode material was then mixed with carbon nanotubes and La133 in a mass ratio of 8:1:1 to form a slurry. The slurry was evenly coated on aluminum foil, dried, and cut into electrodes of appropriate sizes. The battery was assembled in a dry glove box using electrolytes and separators commonly used in lithium-ion batteries. Charge and discharge tests of the assembled lithium-ion battery revealed a capacity retention rate of 83% after 300 cycles, while the coulombic efficiency remained at 100%. Example

[0025] 1 mol of silicon dioxide (SiO2), 2 mol of lithium carbonate (Li2CO3), and 1 mol of glucose were used as carbon sources. The SiO2, Li2CO3, and glucose were placed in a ball mill at 400 rpm / min and milled for 600 minutes to obtain a uniform mixture. The mixture was then placed in a tube furnace and heated to 800°C for 300 minutes under an argon atmosphere to produce graphite-carbon-coated lithium orthosilicate. The graphite-carbon-coated lithium orthosilicate was then mixed with polyacrylonitrile sulfide in a mass ratio of 10:90. The mixture was then heated at 120°C for 60 minutes to allow the residual sulfur in the polyacrylonitrile sulfide to penetrate the carbon layer, thereby producing a composite cathode material. The resulting composite cathode material was then mixed with Super P and PAA in a mass ratio of 8:1:1 to form a slurry. The slurry was evenly coated on aluminum foil, dried, and cut into electrodes of appropriate sizes. The battery was assembled in a dry glove box using electrolytes and separators commonly used in lithium-ion batteries. Charge and discharge tests of the assembled lithium-ion battery revealed a capacity retention rate of 86% after 300 cycles, while the coulombic efficiency remained at 100%. Example

[0026] This example serves as a comparative example. The resulting sulfided polyacrylonitrile was mixed with Super P and PAA in a mass ratio of 8:1:1 to form a slurry. This slurry was evenly coated on aluminum foil, dried, and cut into appropriately sized electrode sheets. The battery was assembled in a dry glove box using electrolytes and separators commonly used in lithium-ion batteries. After 230 cycles, the assembled lithium-ion battery exhibited a capacity retention rate of 17%, while maintaining a coulombic efficiency of 98%.

[0027] The above is a detailed introduction to a method for in-situ improving the cycling capacity of sulfur-based polymer positive electrode materials provided by the present invention. It is worth noting that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical details recorded in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. Any equivalent replacements, modifications, etc. made within the core ideas and principles of the present invention should be included in the scope of protection of the present invention. Unless otherwise defined, all professional terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased on the market or can be prepared by existing methods.

Claims

1. A method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials, characterized in that: The following steps are involved: S1, placing silicon dioxide (SiO2), lithium carbonate (Li2CO3) and a carbon source in a ball mill according to a preset appropriate molar ratio, and ball milling at an appropriate rotation speed for a specific time to obtain a uniform mixture of SiO2, Li2CO3 and the carbon source; S2, placing the above mixture into a tube furnace and heating it in an inert gas environment to generate lithium orthosilicate coated with a graphite carbon layer after a certain reaction time; S3, mixing the graphite carbon layer-coated lithium orthosilicate and the sulfur-based polymer in a predetermined ratio, and heating them under certain temperature conditions for a predetermined time to allow the residual sulfur element in the sulfur-based polymer to penetrate into the carbon layer, thereby producing a composite positive electrode material; S4, mixing the obtained composite material with conductive carbon and a binder in an appropriate proportion to form a pole piece, and completing the assembly of the battery.

2. The method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials according to claim 1, characterized in that: The molar ratio of SiO2, Li2CO3 and carbon source in step S1 is 1:2:(0.1~5); the carbon source is selected from one or more of glucose, sucrose, fructose, cellulose, starch, dopamine, resorcinol-formaldehyde resin, polyvinyl pyrrolidone, tannic acid and citric acid; the ball milling speed ranges from 100 to 2000 rpm / min; and the ball milling duration is set at 30 to 1000 min.

3. The method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials according to claim 1, characterized in that: In step S2, the inert gases used include nitrogen and argon; the temperature of the heating treatment is set between 400-900° C.; and the heating time is 30-3000 min.

4. The method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials according to claim 1, characterized in that: In step S3, the mass ratio of the graphite carbon layer-coated lithium orthosilicate to the sulfur-based polymer is set between (0.01 and 10):100; the heating temperature range is 50-200°C; the heating duration is 20-3000 min; and the sulfur-based polymer positive electrode material is sulfided polyacrylonitrile, sulfided polyaniline, sulfided polytetravinylpyridine, sulfided polyacrylic acid, sulfided 1,3-diisopropenylbenzene, sulfided poly(3-hexylthiophene-2,5-diyl), sulfided 1,3-diethynylbenzene, sulfided aminophenol-formaldehyde resin, and sulfided poly(1, 2,4, 5-4 amino)benzene.

5. The method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials according to claim 1, characterized in that: In step S4, the optional conductive carbon includes acetylene black, carbon nanotubes, Super P and Ketjen black; the binder is selected from PAA, CMC, SBR, guar gum, PVDF and LA133; the mass ratio of the positive electrode material, the conductive carbon and the binder is 7:2:1, 8:1:1 or 9:0.5:0.

5.

6. The method for in-situ improving the cycle capacity of sulfur-based polymer cathode materials according to claim 1, characterized in that: Used in lithium metal batteries, lithium ion batteries, sodium ion batteries, sodium metal batteries, potassium ion batteries, and potassium metal batteries.

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