Preparation method of cobalt aluminate modified diaphragm and application of cobalt aluminate modified diaphragm in lithium-sulfur battery

Abstract

The invention belongs to the technical field of lithium-sulfur battery diaphragms, and discloses a preparation method of a cobalt aluminate modified diaphragm and application of the cobalt aluminate modified diaphragm in a lithium-sulfur battery, and the preparation method comprises the following steps: step 1, dissolving aluminum nitrate, cobalt nitrate, triammonium citrate and ethylene glycol in deionized water, uniformly mixing, and then carrying out oil bath heating to obtain gel; 2, the gel obtained in the step 1 is transferred to a muffle furnace to be heated, then cooled to the room temperature and taken out, and cobalt aluminate is obtained; step 3, uniformly mixing cobalt aluminate with conductive carbon black and a polyvinylidene fluoride adhesive, grinding, then adding N-methyl pyrrolidone to prepare slurry, and then smearing the slurry on a diaphragm to obtain a cobalt aluminate modified diaphragm; the material disclosed by the invention not only can effectively inhibit shuttling of lithium polysulfide, but also can promote rapid transmission of lithium ions, so that the cycle performance of the lithium-sulfur battery is finally improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-sulfur battery separator preparation technology, specifically relating to a method for preparing a cobalt aluminate modified separator and its application in lithium-sulfur batteries. Background Technology

[0002] Among various rechargeable batteries, lithium-sulfur batteries are widely recognized as one of the most promising next-generation high-performance power batteries due to their extremely high theoretical specific capacity (1675 mAh g⁻¹) and energy density (2600 Wh kg⁻¹), as well as the wide availability, low cost, and environmental friendliness of sulfur cathode materials. Despite these numerous potential advantages, the commercialization of lithium-sulfur batteries still faces several challenges. Among these, the "shuttle effect" of lithium polysulfides has become a key obstacle to the development of lithium-sulfur batteries. Designing modified materials with adsorption and catalytic conversion capabilities for lithium polysulfides is crucial to suppressing the "shuttle effect" and improving the performance of lithium-sulfur batteries.

[0003] In lithium-sulfur batteries, the separator plays a crucial role. Located between the positive and negative electrode materials, it not only prevents direct electron transfer to avoid internal short circuits but also provides the necessary channels for ion transport. However, commonly used separators in lithium-sulfur batteries generally suffer from large pore sizes, allowing polysulfide molecules to easily pass through, thus failing to effectively suppress the diffusion and "shuttle" phenomenon of lithium polysulfides. Therefore, functional modification of the separator is achieved by coating its surface with a modifier that can confine, block, or catalyze lithium polysulfides. This modification method is of great significance for suppressing the "shuttle effect" and improving the electrochemical cycle stability of lithium-sulfur batteries. Summary of the Invention

[0004] This invention provides an application of cobalt aluminate modified separator in lithium-sulfur batteries and its preparation method, utilizing...

[0005] The unique structure of cobalt aluminate modifies the separator to effectively suppress the shuttle effect of lithium polysulfides in lithium-sulfur batteries, promote the rapid transport of lithium ions, and improve the cycle performance of lithium-sulfur batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] Step S1: Dissolve 5.5 mmol aluminum nitrate, 11 mmol cobalt nitrate, 33.75 mmol triammonium citrate and 24 ml ethylene glycol in 25 ml deionized water to form a homogeneous solution. Then heat the homogeneous suspension in an oil bath to obtain a gel.

[0008] Step S2: Place the gel obtained in step S1 into a crucible, transfer it to a muffle furnace for heating, and then cool it to room temperature before removing it to obtain cobalt aluminate;

[0009] Step S3: Mix the cobalt aluminate obtained in step S2 with conductive carbon black and polyvinylidene fluoride adhesive evenly and grind it. Then add N-methylpyrrolidone to make a slurry. Then coat the slurry onto a commercial PP membrane and vacuum dry it overnight at 65°C. Cut the coated membrane into pieces to obtain a cobalt aluminate modified membrane.

[0010] Furthermore, in step S1, the molar ratio of cobalt nitrate to aluminum nitrate is 2:1.

[0011] Further, in step S1, deionized water is added first, then cobalt nitrate and ammonium citrate are added and stirred for 10 minutes until completely dissolved, then aluminum nitrate is added and stirred until dissolved, and finally ethylene glycol is added, and the homogenized suspension is heated in an oil bath at 120°C for 10 hours.

[0012] Further, in step S2, the gel obtained in step S1 is heated in a muffle furnace at 800°C for 2 hours at a heating rate of 5°C min⁻¹.

[0013] Further, in step S3, the cobalt aluminate obtained in step S2 is mixed evenly with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 7:2:1 and ground for 30 minutes.

[0014] Application of cobalt aluminate modified separator prepared by the above-described method in lithium-sulfur batteries.

[0015] Furthermore, the assembly of lithium-sulfur batteries includes the following steps:

[0016] Step S4: Mix CNTs and sulfur (S) thoroughly in carbon disulfide (CS2) solvent. Heat and sonicate the mixture until viscous, then place it in an oven to dry.

[0017] Step S5: Under argon protection, the mixture is heated and held at the same temperature twice, and finally cooled naturally to obtain S / CNT;

[0018] Step S6: Mix S / CNT, conductive carbon black and polyvinylidene fluoride adhesive evenly and grind them. Then add N-methylpyrrolidone to make a slurry. Then coat the slurry onto aluminum foil and vacuum dry it overnight at 65°C. Cut the coated aluminum foil into sheets to obtain the positive electrode sheet.

[0019] Step S7: Cut the positive electrode material obtained in step S6 into a circular sheet to obtain the positive electrode sheet. Cut the cobalt aluminate modified separator obtained in step S6 of claim 1 to obtain the battery separator. In an argon-filled glove box, assemble the negative electrode shell, electrolyte, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, gasket, spring sheet, and positive electrode shell in that order to finally prepare the button battery.

[0020] Further, in step S4, CNT and sulfur are mixed evenly in a ratio of 1:2 and CS2 solution is added. The mixed solution is heated at 70°C and sonicated until it becomes viscous, and then placed in an oven and dried at 70°C for 12 hours.

[0021] Further, in step S20, the mixture is first heated to 155°C and held for 10 hours, then heated to 200°C and held for 2 hours.

[0022] Further, in step S30, the S / CNTs obtained in step S20 are mixed evenly with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 7:2:1 and ground for 30 minutes.

[0023] Compared with the prior art, the present invention provides an application of cobalt aluminate modified separator in lithium-sulfur batteries and its preparation method, which has the following beneficial effects:

[0024] The unique structure of cobalt aluminate endows the modified separator with multiple functions, including: (1) a separator with excellent lithium polysulfide adsorption capacity can effectively suppress the battery shuttle effect, thereby reducing the loss of active material and improving the coulombic efficiency of the battery; (2) good lithium polysulfide catalysis can promote the reactivation of "dead sulfur" on the separator surface, increase sulfur utilization, and further improve the energy density of the battery; (3) high ion transport capacity can ensure the rapid transport of lithium ions during the battery charge and discharge process, reduce the internal resistance of the battery, and thus improve the power density of the battery. With these excellent characteristics, the composite function of the separator can significantly improve the electrochemical performance of the battery, including higher specific capacity, better rate charge and discharge capability, and longer cycle life, laying a solid foundation for the commercial application of lithium-sulfur batteries. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope (SEM) image of the cobalt aluminate material according to an embodiment of the invention;

[0026] Figure 2 This is the X-ray photoelectron energy (XPS) Co 2p spectrum of the cobalt aluminate material according to the invention embodiment;

[0027] Figure 3 This is a cycle performance diagram of a battery assembled with a cobalt aluminate modified separator according to an embodiment of the present invention;

[0028] Figure 4 This is a rate loop performance diagram of a battery assembled with a cobalt aluminate modified separator according to an embodiment of the present invention. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0030] A method for preparing a cobalt aluminate modified membrane includes the following steps:

[0031] Step S1: Dissolve 5.5 mmol aluminum nitrate, 11 mmol cobalt nitrate, 33.75 mmol triammonium citrate and 24 ml ethylene glycol in 25 ml deionized water to form a homogeneous solution. Then heat the homogeneous suspension in an oil bath at 120°C for 10 h to obtain a gel.

[0032] Step S2: Place the gel obtained in step S1 into a crucible, transfer it to a muffle furnace, and heat it in air at 800℃ for 2 hours at a heating rate of 5℃ min⁻¹. After cooling to room temperature, remove the gel to obtain cobalt aluminate. The scanning electron microscope (SEM) image of cobalt aluminate is shown below. Figure 1 As shown, the X-ray photoelectron energy (XPS) Co 2p spectrum of cobalt aluminate is as follows: Figure 2 As shown;

[0033] Step S3: The cobalt aluminate obtained in Step S2 was mixed evenly with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 7:2:1 and ground for 30 min. Then, N-methylpyrrolidone was added to prepare a slurry. The slurry was then coated onto a commercial PP diaphragm and vacuum dried overnight at 65°C. The coated diaphragm was trimmed into discs with a diameter of 19 mm, and the modified diaphragm was harvested.

[0034] The application of the tetranitrophthalocyanine nickel-modified separator prepared by the above-described method in lithium-sulfur batteries includes the following steps in the assembly of the lithium-sulfur battery:

[0035] Step S4: Mix CNT and sulfur in a 1:2 ratio and add CS2 solution. Heat the mixture at 70°C while sonicating until it becomes viscous. Then place it in an oven and dry at 70°C for 12 hours.

[0036] Step S5: Under argon protection, the mixture is first heated to 155°C and held for 10 hours, then heated to 200°C and held for 2 hours. Finally, it is naturally cooled to obtain S / CNT.

[0037] Step S6: Mix S / CNT with conductive carbon black and polyvinylidene fluoride binder at a mass ratio of 7:2:1 and grind for 30 minutes. Then add N-methylpyrrolidone to make a slurry. Coat the slurry onto aluminum foil and vacuum dry it overnight at 65°C. Cut the coated aluminum foil into round pieces with a diameter of 16 mm to obtain the positive electrode sheet.

[0038] Step S7: Cut the positive electrode material obtained in step S6 into a circular sheet to obtain the positive electrode sheet. Cut the cobalt aluminate modified separator obtained in step S6 of claim 1 to obtain the battery separator. In an argon-filled glove box, assemble the negative electrode shell, electrolyte, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, gasket, spring sheet, and positive electrode shell in that order to finally prepare the button battery.

[0039] The button cell battery obtained in step S7 was left to stand for 12 hours, and then charge-discharge tests were conducted at different rates. The test conditions were a constant temperature environment of 30℃, with a window starting voltage of 1.7V and a termination voltage of 2.8V. Figure 3 This is a graph showing the cycle performance of the button cell. Figure 4 The graph shows the rate performance of the button cell. It can be seen from the graph that the button cell has high initial discharge specific capacity and capacity retention at different rates. The battery assembled with the modified separator has good rate performance, charge and discharge performance and good cycle life.

[0040] The above-described embodiments are merely illustrative of specific implementations of the present invention. These specific embodiments and their detailed descriptions are for illustrative purposes only and do not limit the scope of protection. For those skilled in the art, modifications and improvements can be made without departing from the technical concept of this application or the technical solution of the present invention, and such modifications and improvements all fall within the protection scope of this application or the present invention. Furthermore, the scope of protection claimed in this application is determined by the claims, and the specific embodiments in the specification can be used to interpret the claims.

Claims

1. A method for preparing a cobalt aluminate modified diaphragm, characterized in that, Includes the following steps: Step S1: Dissolve 5.5 mmol aluminum nitrate, 11 mmol cobalt nitrate, 33.75 mmol triammonium citrate and 24 ml ethylene glycol in 25 ml deionized water to form a homogeneous solution. Then heat the homogeneous suspension in an oil bath to obtain a gel. Step S2: Place the gel obtained in step S1 into a crucible, transfer it to a muffle furnace for heating, and then cool it to room temperature before removing it to obtain cobalt aluminate; Step S3: The cobalt aluminate obtained in step S2 is mixed evenly with conductive carbon black and polyvinylidene fluoride adhesive and ground. Then, N-methylpyrrolidone is added to make a slurry. The slurry is then coated onto a commercial polypropylene (PP) membrane and vacuum dried overnight at 65°C. The coated membrane is then cut into pieces to obtain a cobalt aluminate modified membrane.

2. The method for preparing a cobalt aluminate modified membrane according to claim 1, characterized in that: In step S1, the molar ratio of cobalt nitrate to aluminum nitrate is 2:

1.

3. The method for preparing a cobalt aluminate modified membrane according to claim 1, characterized in that: In step S1, deionized water is added first, followed by cobalt nitrate and ammonium citrate. The mixture is stirred for 10 minutes until completely dissolved. Then aluminum nitrate is added and stirred until dissolved. Finally, ethylene glycol is added, and the homogenized suspension is heated in an oil bath at 120°C for 10 hours.

4. The method for preparing a cobalt aluminate modified membrane according to claim 1, characterized in that: In step S2, the gel obtained in step S1 is heated in a muffle furnace at 800°C for 2 h at a heating rate of 5°C min⁻¹.

5. The method for preparing a cobalt aluminate modified membrane according to claim 1, characterized in that: In step S3, the cobalt aluminate obtained in step S2 is mixed with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 7:2:1 and then ground for 30 minutes.

6. The application of the cobalt aluminate modified separator prepared by the preparation method of any one of claims 1 to 5 in lithium-sulfur batteries.

7. The application of the cobalt aluminate modified separator prepared by the method described in claim 6 in lithium-sulfur batteries, characterized in that, Includes the following steps: Step S4: Mix CNTs and sulfur (S) thoroughly in carbon disulfide (CS2) solvent. Heat and sonicate the mixture simultaneously, then place it in an oven to dry. Step S5: Under argon protection, the mixture is heated and held at the same temperature twice, and finally cooled naturally to obtain S / CNT; Step S6: Mix S / CNT, conductive carbon black and polyvinylidene fluoride (PVDF) binder evenly and grind them. Then add N-methylpyrrolidone (NMP) to make a slurry. Then coat the slurry onto aluminum foil and vacuum dry it overnight at 65 °C. Cut the coated aluminum foil into sheets to obtain the positive electrode sheet. Step S7: Cut the positive electrode material obtained in step S6 into a circular sheet to obtain the positive electrode sheet. Cut the cobalt aluminate modified separator obtained in step S6 of claim 1 to obtain the battery separator. In an argon-filled glove box, assemble the negative electrode shell, electrolyte, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, gasket, spring sheet, and positive electrode shell in that order to finally prepare the button battery.

8. The application of the cobalt aluminate modified separator prepared by the method described in claim 7 in lithium-sulfur batteries, characterized in that: In step S4, CNT and sulfur are mixed evenly in a ratio of 1:2 and CS2 solution is added. The mixture is heated and sonicated at 70°C until it becomes viscous, and then placed in an oven and dried at 70°C for 12 h.

9. The application of the cobalt aluminate modified separator prepared by the method described in claim 7 in lithium-sulfur batteries, characterized in that: In step S5, the mixture is first heated to 155°C and held for 10 h, then heated to 200°C and held for 2 h.

10. The application of the cobalt aluminate modified separator prepared by the method described in claim 7 in lithium-sulfur batteries, characterized in that: In step S6, the S / CNTs obtained in step S5 are mixed with conductive carbon black and polyvinylidene fluoride adhesive at a mass ratio of 7:2:1 and then ground for 30 minutes.

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