An irradiated chemical cross-linked lithium-sulfur battery cathode and its preparation method, and a lithium-sulfur battery.

Abstract

This invention discloses an irradiated chemically cross-linked lithium-sulfur battery cathode and its preparation method, as well as the lithium-sulfur battery itself. The high-strength cathode of the lithium-sulfur battery comprises a current collector and a loading slurry, wherein the loading slurry is coated on the surface of the current collector; the loading slurry includes a polymer binder, which is a cross-linked polyacrylamide obtained by irradiation cross-linking of acrylamide monomers. This invention utilizes gamma-ray irradiation technology to achieve a uniform distribution of a three-dimensional polyacrylamide network in the sulfur cathode, effectively reducing polysulfide ion shuttle movement and avoiding repeated "hollowing out" and volume change effects in the sulfur cathode, thereby improving battery capacity and cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery cathode preparation technology, and more specifically, to an irradiated chemical cross-linked lithium-sulfur battery cathode and its preparation method, as well as a lithium-sulfur battery. Background Technology

[0002] With energy consumption steadily increasing, humanity faces a significant environmental and energy crisis. Finding new systems for energy utilization, conversion, and storage has become an urgent task. Currently, lithium-ion batteries dominate the energy storage market, finding mature applications in most digital products, electric vehicles, aircraft, power tools, and robots. However, as the actual energy density of lithium-ion batteries approaches their theoretical limit, developing novel electrochemical energy storage systems with higher energy densities than lithium-ion batteries is imperative to meet the demand for high-energy-density battery systems.

[0003] Lithium-sulfur batteries are a type of chemical power source that utilizes the electrochemical reaction between elemental sulfur and metallic lithium to convert chemical energy into electrical energy. Their theoretical specific capacity reaches 1675 mAh / g, and their theoretical energy density reaches 2600 Wh / kg, far exceeding that of traditional lithium-ion batteries. Furthermore, sulfur, the cathode material, is abundant in nature and environmentally friendly, thus making them considered one of the next generation of high-energy rechargeable batteries with promising applications. Despite these numerous advantages, key scientific problems inherent in the lithium-sulfur system limit their further commercial application.

[0004] Sulfur has poor electrical conductivity, with a conductivity of only 5.0 × 10⁻⁶. -30 S·cm -1 The weak conductivity of the positive electrode leads to low utilization of sulfur active materials, while the discharge intermediate products, polysulfides, are easily soluble in organic electrolytes, causing a "shuttle effect." This severe shuttle effect results in the loss of active materials and reduced coulombic efficiency. Furthermore, the dissolved polysulfides diffuse to the negative electrode, disrupting its operating state and negatively impacting the battery's actual performance. In particular, the significant density difference between the active material sulfur and the discharge end product Li2S causes substantial expansion and contraction of the electrode volume during charging and discharging, resulting in a large "volume change effect." This damages the integrity of the positive electrode structure, leading to poorer cycle performance.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the lithium-sulfur batteries prepared in the prior art have poor cycle performance due to the shuttle effect and volume change effect. The purpose is to provide an irradiated chemical cross-linked lithium-sulfur battery cathode and its preparation method, as well as a lithium-sulfur battery, to alleviate the volume change effect of the sulfur cathode and the shuttle effect of polysulfides, thereby improving the cycle performance and service life of the lithium-sulfur battery.

[0007] This invention is achieved through the following technical solution:

[0008] A first aspect of this application provides an irradiated chemically cross-linked lithium-sulfur battery cathode, comprising a current collector and a loading slurry, wherein the loading slurry is coated on the surface of the current collector; the loading slurry comprises a polymer binder, wherein the polymer binder is a cross-linked polyacrylamide formed by irradiation of acrylamide monomer with gamma rays.

[0009] In traditional lithium-sulfur batteries, severe shuttle effects cause loss of active material and reduced coulombic efficiency. Simultaneously, dissolved polysulfides diffuse to the negative electrode and react with lithium, disrupting the working state of the negative electrode surface and leading to poor electrode structural integrity, thus affecting battery cycle performance. This invention provides an irradiated chemically cross-linked lithium-sulfur battery cathode. Acrylamide monomers are irradiated with gamma rays to obtain a polyacrylamide binder with a high-strength three-dimensional cross-linked network. This binder not only effectively chemically adsorbs polysulfide ions but also maintains the structural integrity of the sulfur cathode during cycling, thereby improving the cycle performance and lifespan of the lithium-sulfur battery.

[0010] In one implementation, the current collector is an aluminum foil or a carbon-coated aluminum foil.

[0011] In one implementation, the loaded slurry further includes a sulfur host material and a sulfur material, wherein the sulfur host material is composed of at least one material selected from conductive carbon material and electrocatalyst.

[0012] In one implementation, the conductive carbon material is composed of at least one material selected from Ketjen black, carbon nanotubes, acetylene black, conductive carbon black, and graphene.

[0013] In one implementation, the electrocatalyst is a metal compound and / or a metal single-atom catalyst.

[0014] A second aspect of this application also provides a method for preparing an irradiated chemically cross-linked lithium-sulfur battery cathode, the method comprising the following steps:

[0015] Obtain the current collector and the acrylamide monomer solution;

[0016] The sulfur host material, the acrylamide monomer solution, and the sulfur material are mixed evenly in a certain proportion to obtain a loaded slurry.

[0017] The loaded slurry is uniformly coated onto the current collector. After the coated current collector is naturally dried in the air, it is then placed in a vacuum oven to dry, thus obtaining an uncrosslinked sulfur positive electrode sheet.

[0018] High-strength sulfur cathode sheets were obtained by irradiating naturally dried, uncrosslinked sulfur cathode sheets with gamma rays.

[0019] In one implementation, the naturally dried current collector is placed in a vacuum oven and dried at a temperature of 60°C for 8 hours.

[0020] In one implementation, the gamma ray irradiation dose ranges from 20 to 50 kGy.

[0021] In one implementation, the thickness of the load slurry uniformly coated on the current collector ranges from 100 to 200 μm.

[0022] The high-strength positive electrode of the lithium-sulfur battery is a type of irradiated chemical cross-linked lithium-sulfur battery positive electrode as described in the first aspect of this application, or is prepared by an irradiated chemical cross-linked lithium-sulfur battery positive electrode preparation method as described in the second aspect of this application.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] This invention provides an irradiated chemically cross-linked lithium-sulfur battery cathode and its preparation method, as well as the lithium-sulfur battery itself. First, acrylamide monomer is uniformly dispersed in the cathode material, and then irradiated with gamma rays to directly obtain a high-strength sulfur cathode with cross-linked polyacrylamide as a binder. The cross-linking reaction process does not involve complex chemical additives, avoiding side reactions caused by the decomposition products of chemical additives. Simultaneously, the process of dispersing acrylamide monomer in the liquid phase before cross-linking ensures the uniformity of the final network. By controlling the dose and time of gamma ray irradiation, the polyacrylamide network in the sulfur cathode can be rationally controlled. The use of gamma ray irradiation technology achieves a uniform distribution of the three-dimensional polyacrylamide network in the sulfur cathode, which not only effectively chemically adsorbs polysulfide ions but also effectively avoids repeated "hollowing out" and volume change effects of the sulfur cathode, thereby improving the battery's capacity and cycle life. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 The charge-discharge curves of a lithium-sulfur battery using irradiated crosslinked polyacrylamide as a binder at 0.2C rate for the first and tenth cycles.

[0027] Figure 2 The specific capacity-cycle count curve of a lithium-sulfur battery using irradiated crosslinked polyacrylamide as a binder at a 0.2C rate. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention.

[0029] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0030] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Example 1

[0032] In traditional lithium-sulfur batteries, severe shuttle effect causes loss of active material and reduction of coulombic efficiency. At the same time, dissolved polysulfides diffuse to the negative electrode and react with lithium on the negative electrode, destroying the working state of the negative electrode surface, resulting in poor integrity of the electrode structure and thus affecting the battery cycle performance.

[0033] This embodiment discloses an irradiated chemically cross-linked lithium-sulfur battery cathode, which uses γ-rays to irradiate acrylamide monomers to obtain a polyacrylamide binder with a high-strength cross-linked network, thereby helping to maintain the structural integrity of the sulfur cathode during cycling and improving the cycle performance and service life of the lithium-sulfur battery.

[0034] The high-strength positive electrode of the lithium-sulfur battery disclosed in this embodiment mainly includes a current collector and a loading slurry. The loading slurry is coated on the surface of the current collector. The loading slurry includes a polymer binder, which is a cross-linked polyacrylamide obtained by irradiation cross-linking of acrylamide monomer.

[0035] First, acrylamide monomers are uniformly dispersed in the cathode slurry, and then irradiated with gamma rays to directly obtain a high-strength sulfur cathode with cross-linked polyacrylamide as a binder. The cross-linking reaction process does not involve complex chemical additives, avoiding side reactions caused by the decomposition products of chemical additives. Simultaneously, the process of dispersing acrylamide monomers in the liquid phase before cross-linking ensures the uniformity of the final network. By controlling the dose and time of gamma ray irradiation, the polyacrylamide network in the sulfur cathode can be rationally controlled. The use of gamma ray irradiation technology achieves a uniform distribution of the three-dimensional polyacrylamide network in the sulfur cathode, effectively avoiding repeated "hollowing out" and volume change effects in the sulfur cathode, thus contributing to improved battery capacity and cycle life.

[0036] The current collector is aluminum foil or carbon-coated aluminum foil. The loading slurry also includes a sulfur host material and a sulfur material, wherein the sulfur host material is composed of at least one material selected from conductive carbon material and electrocatalyst. The conductive carbon material is composed of at least one material selected from Ketjen black, carbon nanotubes, acetylene black, conductive carbon black, and graphene. The electrocatalyst is a metal compound and / or a metal single-atom catalyst.

[0037] The specific implementation process is as follows:

[0038] When the load slurry consists of a sulfur host material, a sulfur material, and a binder, and the sulfur host material is a conductive carbon material or an electrocatalyst, the thickness of the load slurry coated on the current collector is 100 μm; the mass ratio of the sulfur host material, sulfur, and binder is 10:10:1.

[0039] When the load slurry components are sulfur host material, sulfur material and binder, and the sulfur host material is conductive carbon material or electrocatalyst, the coating thickness of the load slurry is 150 μm; the mass ratio of sulfur host material, sulfur and binder is 10:20:1.5.

[0040] When the load slurry components are sulfur host material, sulfur material and binder, and the sulfur host material is conductive carbon material or electrocatalyst, the coating thickness of the load slurry is 100 μm; the mass ratio of sulfur host material, sulfur and binder is 10:10:2.

[0041] This embodiment discloses an irradiated chemically cross-linked lithium-sulfur battery cathode. An acrylamide monomer solution, a sulfur host material, and a sulfur material are uniformly mixed to obtain a loaded slurry, which is then coated onto a current collector, dried, and subsequently subjected to irradiation cross-linking. The irradiation cross-linking process does not involve complex chemical additives, avoiding side reactions caused by the decomposition products of chemical additives. Simultaneously, the pre-dispersion and subsequent cross-linking process of the liquid-phase acrylamide monomer ensures the uniformity of the final network. By controlling the dose and time of gamma-ray irradiation, the polyacrylamide network in the sulfur cathode can be rationally controlled. The use of gamma-ray irradiation technology achieves a uniform distribution of the three-dimensional polyacrylamide network in the sulfur cathode, effectively reducing lithium polysulfide shuttle, avoiding repeated "hollowing out" and volume change effects in the sulfur cathode, thereby improving the electrochemical performance of the battery.

[0042] Example 2

[0043] This embodiment discloses a method for preparing an irradiated chemically cross-linked lithium-sulfur battery cathode. The cathode sheet prepared in this embodiment is the lithium-sulfur battery cathode sheet from Example 1. The method includes the following steps:

[0044] Obtain the current collector and the acrylamide monomer solution;

[0045] The sulfur host material, the acrylamide monomer solution, and the sulfur material are mixed evenly in a certain proportion to obtain a loaded slurry.

[0046] The loading slurry is uniformly coated onto the current collector. After the current collector is naturally dried in the air, it is then placed in a vacuum oven for drying. The current collector is then placed in a vacuum oven for drying at a temperature of 60°C for 8 hours. The thickness of the loading slurry uniformly coated onto the current collector is in the range of 100–200 μm.

[0047] High-strength sulfur cathode sheets are obtained by irradiating dried, uncrosslinked sulfur cathode sheets with gamma rays. The gamma ray irradiation dose ranges from 20 to 80 kGy.

[0048] Understandably, the preparation method should be adjusted accordingly when different materials are used. For example, the following preparation methods are examples:

[0049] 1. When preparing a positive electrode and lithium-sulfur battery with the components of conductive carbon black Super P, irradiated crosslinked polyacrylamide, and nano-sulfur, such as Figure 1 and Figure 2As shown: First, a 5 wt.% acrylamide solution was prepared according to technical requirements. 0.5 g of acrylamide monomer was weighed and 9.5 g of deionized water was added, and the mixture was magnetically stirred for 30 min. 500 mg of Super P and 500 mg of nano sulfur powder were weighed and stirred in a degassing machine for 30 min. The mixture was then ground in a mortar for 20 min. 1 g of the 5 wt.% acrylamide solution and 1 g of deionized water were added to the resulting powder, and the mixture was stirred in a degassing machine for 1 h to obtain the positive electrode slurry. The slurry was uniformly coated onto a dry aluminum foil current collector using a 150 μm scraper, with a coating thickness of 150 μm. After the slurry solidified, it was vacuum dried at 60 °C for 8 h. The resulting dried positive electrode sheet was irradiated under gamma rays with an irradiation dose of 30 KGy. The resulting positive electrode sheet was cut into 13 mm diameter round pieces using a cutting machine for the assembly of lithium-sulfur batteries.

[0050] 2. When preparing a positive electrode and lithium-sulfur battery with components of V2O3 electrocatalyst, irradiated crosslinked polyacrylamide, and nano-sulfur: First, prepare a 5wt.% acrylamide solution according to technical requirements. Weigh 0.5g of acrylamide monomer, add 9.5g of deionized water, and stir magnetically for 30min; weigh 500mg of V2O3 electrocatalyst and 500mg of nano-sulfur powder, mix and stir in a degassing machine for 30min, then grind in a mortar for 20min. Add 2g of 5wt.% acrylamide solution to the obtained powder, mix and stir in a degassing machine for 1h to obtain a positive electrode slurry; uniformly coat the slurry onto a dry aluminum foil current collector using a 150μm scraper, with a coating thickness of 150μm, and vacuum dry at 60℃ for 8h after the slurry has cured; irradiate the obtained dried positive electrode under gamma rays with an irradiation dose of 35KGy; cut the obtained electrode into 13mm diameter round pieces using a cutting machine for lithium-sulfur battery assembly.

[0051] 3. When preparing positive electrode sheets and lithium-sulfur batteries with components of conductive carbon black Super P, chemically cross-linked polyacrylamide, and nano-sulfur: first synthesize chemically cross-linked polyacrylamide hydrogel according to technical requirements. Weigh 5g of acrylamide monomer, add 94g of deionized water, and stir magnetically for 20min. Then add 0.2g of ammonium persulfate and 0.005g of N,N-methylenebisacrylamide, stir magnetically for 20min, seal, and degas under vacuum for 5min. Add 25μL of tetramethylethylenediamine and let stand for 8 hours. Weigh 500mg of Super P and 500mg of nano sulfur powder, mix and stir in a degassing machine for 30min, then grind in a mortar for 20min. Add 1g of 5wt.% chemically crosslinked polyacrylamide and 1g of deionized water to the powder, mix and stir in a degassing machine for 1h to obtain a positive electrode slurry. Coat the slurry evenly on a dry aluminum foil current collector with a thickness of 100μm using a 100μm scraper. After the slurry has cured, vacuum dry at 60℃ for 8h. Cut the obtained electrode sheet into positive electrode sheets with a diameter of 13mm using a cutting machine for the assembly of lithium-sulfur batteries.

[0052] 4. When preparing a positive electrode and lithium-sulfur battery with conductive carbon black Super P, PVDF, and nano-sulfur as components: First, prepare PVDF with a concentration of 5 wt.% according to technical requirements. Weigh 0.5 g of PVDF, add 9.5 g of N-methylpyrrolidone, and stir magnetically for 24 h; weigh 500 mg of Super P and 500 mg of nano-sulfur powder, mix and stir in a degassing machine for 30 min, then grind in a mortar for 20 min. Add 1 g of 2 wt.% PVDF and 1.5 g of N-methylpyrrolidone to the obtained powder, mix and stir in a degassing machine for 1 h to obtain a positive electrode slurry; uniformly coat the slurry onto a dry aluminum foil current collector with a thickness of 150 μm using a 150 μm scraper, and vacuum dry at 60 °C for 8 h after the slurry has cured; cut the obtained electrode into round pieces with a diameter of 13 mm using a cutting machine for the assembly of lithium-sulfur batteries.

[0053] 5. When preparing a positive electrode and flexible lithium-sulfur pouch battery with the composition of conductive carbon black Super P, irradiated crosslinked polyacrylamide, and nano-sulfur: First, prepare a 5wt.% acrylamide solution according to technical requirements. Weigh 0.5g of acrylamide monomer, add 9.5g of deionized water, and stir magnetically for 30min; weigh 500mg of Super P and 500mg of nano-sulfur powder, mix and stir in a degassing machine for 30min, then grind in a mortar for 20min. Add 1g of 5wt.% acrylamide solution and 1g of deionized water to the obtained powder, mix and stir in a degassing machine for 1h to obtain a positive electrode slurry; uniformly coat the slurry onto a dry aluminum foil current collector with a coating thickness of 150μm using a 150μm scraper, and vacuum dry at 60℃ for 8h after the slurry has cured; irradiate the obtained dried positive electrode under gamma rays with an irradiation dose of 30KGy; cut the obtained electrode into square pieces with a side length of 3cm for lithium-sulfur battery assembly.

[0054] Therefore, in this embodiment, the acrylamide monomer solution, sulfur host material, and sulfur material are uniformly mixed to obtain a loaded slurry, which is then coated onto the current collector, dried, and then subjected to irradiation crosslinking. The irradiation crosslinking process does not involve complex chemical additives, thus avoiding side reactions caused by the decomposition products of chemical additives. Simultaneously, the process of first dispersing and then crosslinking the acrylamide monomer in the liquid phase ensures the uniformity of the final network. By controlling the dose and time of gamma-ray irradiation, the polyacrylamide network in the sulfur cathode can be rationally controlled. The use of gamma-ray irradiation technology achieves a uniform distribution of the three-dimensional polyacrylamide network in the sulfur cathode, effectively reducing polysulfide ion shuttle movement and avoiding repeated "hollowing out" and volume change effects in the sulfur cathode, thereby contributing to improved battery capacity and cycle life.

[0055] In this embodiment, solid-phase crosslinking of binder monomer molecules is performed by irradiation crosslinking, which simplifies the preparation method of polymer binder. The resulting polyacrylamide binder has a uniform and controllable network structure and no additional chemical additives are introduced.

[0056] The irradiated crosslinked polyacrylamide three-dimensional network in the high-strength cathode of the lithium-sulfur battery provided in this embodiment is uniformly distributed in the sulfur cathode, which can effectively avoid repeated "hollowing out" and volume change effects of the sulfur cathode, and is conducive to improving the battery capacity and cycle life.

[0057] Example 3

[0058] This embodiment discloses a lithium-sulfur battery, wherein the positive electrode in the lithium-sulfur battery is the positive electrode prepared in Embodiment 1.

[0059] In a dry MIKROUNA glove box filled with argon gas, the battery was assembled in the following order: positive electrode, separator, lithium sheet, gasket, and spring. The positive electrode is the positive electrode sheet prepared in this embodiment. The battery assembly is a 2032 button cell, and the separator is Celgrad2500. The electrolyte used for battery assembly is a lithium-sulfur electrolyte prepared by dissolving 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) containing 2 wt.% LiNO3 in a mixture of ethylene glycol dimethyl ether and 1,3-dioxolane at a volume ratio of 1:1.

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an irradiated chemically cross-linked lithium-sulfur battery cathode, characterized in that, The method steps include: Obtain the current collector and the acrylamide monomer solution; The sulfur host material, the acrylamide monomer solution, and the sulfur material are mixed evenly in a certain proportion to obtain a loaded slurry. The loaded slurry is uniformly coated onto the current collector. After the coated current collector is naturally dried in the air, it is then placed in a vacuum oven to dry, thus obtaining an uncrosslinked sulfur positive electrode sheet. High-strength sulfur positive electrode sheet is obtained by irradiating the dried uncrosslinked sulfur positive electrode sheet with gamma rays to crosslink the acrylamide monomer to form crosslinked polyacrylamide. The naturally dried sulfur positive electrode sheet was placed in a vacuum oven and dried at 60°C for 8 hours. The gamma ray irradiation dose ranges from 20 to 80 kGy; The load slurry is uniformly coated on the current collector with a thickness ranging from 100 to 200 μm.

2. An irradiated chemical cross-linked lithium-sulfur battery cathode, characterized in that, The irradiated chemical cross-linked lithium-sulfur battery cathode is prepared using the irradiated chemical cross-linked lithium-sulfur battery cathode preparation method as described in claim 1.

3. A lithium-sulfur battery, characterized in that, The high-strength positive electrode of the lithium-sulfur battery is prepared using the irradiation chemical crosslinking type lithium-sulfur battery positive electrode preparation method as described in claim 1.

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