Design and preparation method of a "chip-like" integrated lithium-sulfur battery

Abstract

The present invention discloses the design and preparation of an integrated lithium-sulfur battery that mimics a "chip". This invention is based on the design concept of transistor integration in a chip and designs an integrated lithium-sulfur battery that mimics a "chip". This design integrates nano-Mo2C nanoparticles and nano-sulfur into a graphene oxide matrix to synthesize a sulfur nanoreactor unit with high catalytic activity and dispersion stability for sulfur-active substances, and realizes the close series connection of isolated sulfur nanoreactors on the GO conductive network to form an extremely large integrated conductive network system. The integrated effect of each sulfur nanoreactor unit and the efficient catalysis of Mo2C are used to achieve high-energy adaptive storage and output. It is worth noting that the obtained integrated nanoreactor positive electrode has a high initial specific capacity, excellent cycle retention performance and outstanding rate performance.

Description

Technical Field

[0001] The present invention relates to the field of lithium-sulfur batteries, and in particular to a design and preparation method of a "chip-like" integrated lithium-sulfur battery. Background Art

[0002] Batteries, as a storage device that can convert chemical energy into electrical energy, have received continuous attention and development since their inception. Lithium-sulfur batteries (LSBs) are considered one of the most promising core technologies in post-lithium-ion batteries because of the theoretical specific capacity of sulfur (1672 mAh·g -1 ) and the theoretical energy density of the battery (2600 Wh·kg -1 ) is extremely high, which can overcome the limitations of intercalated oxide cathodes and graphite anodes in lithium-ion batteries. Currently, the key issue in the development of LSBs electrode materials is how to effectively improve their energy density and cycle stability.

[0003] In order to solve the above problems, many research works have focused on the exploration of materials and the design of composite material structures and morphologies. For example, the performance of electrode materials has been improved through strategies such as regulating morphology, introducing catalysts, and interface engineering, and certain results have been achieved. However, its further development has encountered some bottlenecks. As we all know, while developing materials, we need to better consider how to utilize the materials, including the overall design of the device and the performance of the materials. In order to enhance the development potential of materials in this application field, this study shifted the focus from the modification research of electrode materials to the overall design of the device, innovatively introduced the "chip integration effect", and broke through the tradition and proposed for the first time a new structural design concept of "chip-like" integrated LSBs.

[0004] The primary challenge in fabricating integrated LSBs (LSBs) that mimic "chips" is to construct the sulfur active material in the lithium-sulfur battery cathode into an independent sulfur nanoreactor. Its enclosed microenvironment creates a cavity effect, encapsulating guest molecules through binding interactions. The sulfur nanoreactor is then integrated into a conductive network, leveraging the integrated effect to maximize overall performance. To optimize the overall performance of integrated LSBs, it is necessary to rationally design a conductive network similar to the integrated circuits in chips to provide electron / ion transport pathways. Graphene oxide (GO), with its high electronic conductivity and excellent mechanical properties, offers a continuous conductive network structure suitable for high-speed ion / electron transport. Its use as a carrier for immobilizing sulfur active materials improves sulfur conductivity, mitigates its volume expansion during cycling, inhibits the shuttling effect of polysulfides (through physical and chemical adsorption), and enhances the redox kinetics of LSBs (through catalytic conversion of additional active sites), playing a key role in their application in integrated LSBs. Furthermore, to fabricate the sulfur active material into independent nano-discrete devices, it is necessary to nanosize the sulfur element and uniformly disperse and firmly anchor the nanosulfur (NS) within the conductive framework. However, NS have a high surface area and surface energy. During the preparation or charge-discharge process, NS (if randomly distributed, loosely attached, and free to move under driving force) can easily move and aggregate. In addition, the strong pushing and squeezing between NS can also cause the sulfur active material to pulverize, thereby reducing the cycling stability. Therefore, how to uniformly disperse and anchor NS and confine NS and polysulfide ions in nanoscale space to prevent their aggregation remains a major challenge in the preparation of sulfur nanoreactors.

[0005] Here, based on the design concept of integrated transistors in a chip, GOQDs were first used to induce the in situ growth of Mo2C nanoparticles on GO, serving as nanosulfur dispersion, anchoring, and catalytic sites. Subsequently, NS was anchored on GO and coated with GO to synthesize a S nanoreactor. This achieved the large-scale, close-coupled integration of Mo2C / NS nanoreactor units with both high dispersion stability and catalytic activity for use as high-performance LSBs cathodes. GO not only serves as a conductive network and flexible framework to enhance the electrode's conductivity and structural stability, but also provides a protective shell for the NS, providing a buffer matrix to mitigate the volume change of S and achieve its small size and high dispersion. Furthermore, Mo2C acts as a synergistic chemical "sulfur absorption" and catalytic "sulfur activation," fully leveraging the role of each nanoreactor unit and ultimately realizing the collective effect of the LSB cathode. Due to the lack of interference from neighboring units, reducing the characteristic size significantly improves the areal / volume capacity and energy density of the NS. The unique structural design enables fast charge transfer kinetics and significantly enhances the cycling performance of the cathode. This work provides new research ideas and methods for promoting the precise preparation of new energy storage devices. Summary of the Invention

[0006] In response to the above problems, the present invention provides a design concept and a design and preparation method for a "chip-like" integrated lithium-sulfur battery.

[0007] One of the purposes of the present invention is to provide a "chip-like" integrated lithium-sulfur battery positive electrode sheet, the raw materials of which include GO / Mo2C / NS positive electrode active materials, a conductive agent, a binder and a solvent.

[0008] The conductive agent is super C, the binder is PVDF, and the cosolvent includes N-methylpyrrolidone.

[0009] As a preferred technical solution of the present invention, the mass ratio of the positive electrode active material, the conductive agent and the binder is 7:2:1, wherein the mass ratio can be 8:1:1 or 7.5:1.5:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0010] As a preferred technical solution of the present invention, the positive electrode active material includes graphene oxide, Mo2C nanomaterial and sodium thiosulfate (Na2S2O3·5H2O).

[0011] A second object of the present invention is to provide a method for preparing the positive electrode active material GO / Mo2C / NS of the "chip-like" integrated lithium-sulfur battery positive electrode sheet as described in the first object, the preparation method comprising the following steps:

[0012] (1) citric acid is heated in an air atmosphere and then placed in a dialysis bag, dialyzed in ultrapure water, and then the resulting solution is freeze-dried to obtain graphene quantum dots;

[0013] (2) The solution obtained by dissolving anhydrous MoCl5 in an ice bath is mixed with graphene oxide and graphene quantum dots, and then oleylamine is injected to obtain a mixed solution. The mixed solution is heated and stirred, centrifuged, washed, freeze-dried and heated in an argon environment to obtain a Mo2C nanoparticle composite material anchored on a perforated graphene framework.

[0014] (3) Sodium thiosulfate (Na2S2O3·5H2O) and hydrochloric acid (HCl) are sequentially added to the GO / Mo2C suspension described in step (2) and stirred in an ice bath to obtain a mixed solution, and the mixed solution is centrifuged, washed, vacuum-dried, and calcined to obtain a GO / Mo2C / NS positive electrode active material;

[0015] (4) Grind and mix the positive electrode active material, conductive agent, and binder described in step (3) in a cosolvent to obtain a slurry, apply the slurry on a current collector, and vacuum dry and stamp to obtain the positive electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the XRD pattern of GO / Mo2C / NS in Example 1 of the present invention.

[0017] Figure 2 is the SEM image of GO / Mo2C / NS in Example 1 of the present invention.

[0018] Figure 3 This is a rate performance diagram of the lithium-sulfur battery in Example 1 of the present invention.

[0019] Figure 4 This is a rate performance diagram of the lithium-sulfur battery in Comparative Example 1 of the present invention.

[0020] Figure 5 This is a rate performance diagram of the lithium-sulfur battery in Comparative Example 2 of the present invention.

[0021] Figure 6 The cycling performance of the electrodes of GO / Mo2C / NS in Example 1 of the present invention, rGO / S in Comparative Example 1, and Mo2C / S in Comparative Example 2 under 0.2C constant current charge and discharge conditions is shown.

[0022] Figure 7 The charge and discharge curves of the electrodes in Example 1, Comparative Example 1 and Comparative Example 2 under constant current charge and discharge of the present invention are shown in FIG.

[0023] Figure 8 This is the EIS spectrum of the GO / Mo2C / NS electrode in Example 1 of the present invention under the 0.5C constant current charge and discharge long cycle curve.

[0024] Figure 9 CV curves of GO / Mo2C / NS in Example 1 of the present invention, rGO / S in Comparative Example 1, and Mo2C / S in Comparative Example 2 at 1 mV s−1. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0026] Example 1:

[0027] This embodiment provides a method for preparing a positive electrode sheet of a lithium-sulfur battery that imitates a "chip", comprising the following steps:

[0028] (1) Graphene quantum dots (GOQDs) were prepared from the bottom up by using pyrolyzed citric acid (CA). 5 g of CA was placed in a 10 ml beaker and heated to 200 °C. CA was initially liquefied, and then the liquid was continuously heated. The color of the liquid changed from colorless to light yellow and then to orange within 30 min. The color change was attributed to the formation of GOQDs. The obtained orange liquid was dialyzed in ultrapure water for 48 h using a dialysis bag with a molecular weight of 1000 Da to remove excess unreacted CA. The liquid in the dialysis bag was then frozen and dried to obtain GOQDs;

[0029] (2) Preparation of GO / Mo2C: First, 50 mg of anhydrous MoCl5 (99.9%) was added to 1 ml of deionized water and stirred in an ice bath until dissolved to obtain a mixed solution. Then, 60 mL of GO dispersion (2 mg / mL) and 30 ml of GOQDs (2 mg / mL) aqueous dispersion were slowly added to the above mixed solution. Then, 0.5 mL of oleylamine was slowly injected and the mixture was heated at 75 °C and stirred for 3 h to obtain GO / Mo2C. x O solution.

[0030] (3) The solution obtained in step (2) was centrifuged at 6000-8000 rpm for 5 min; the precipitate was collected by washing with deionized water 5 times, and the precipitate was placed in a refrigerator for 6 h and then dried in a vacuum freeze dryer for 48 h to obtain the intermediate product GO / Mo x The intermediate product after O hydrolysis (GO / MoO x ) was washed with deionized water several times and then freeze-dried for 48 h to obtain the intermediate product GO / MoxO.

[0031] (4) The intermediate product obtained in step (3) was placed in a tubular furnace, and argon was introduced for 20 minutes. Then, the intermediate product was calcined under argon conditions at a heating rate of 5°C / min to 700°C, and the temperature was maintained for 1.5 hours. After the temperature was cooled to room temperature, a Mo2C nanoparticle composite material anchored on a perforated graphene oxide framework (GO / Mo2C) was obtained.

[0032] (5) 0.15 mg of GO / Mo2C composite material was added to 15 ml of deionized water and stirred for 0.5 h to obtain a Mo2C / GO suspension. 0.923 g of sodium thiosulfate (Na2S2O3·5H2O) was added to the above suspension and stirred in an ice bath for 0.5 h to obtain a mixed solution precursor. Then 0.4 ml of hydrochloric acid (HCl) was slowly added to the above mixed solution precursor and continued to stir for 0.5 h. The mixture was washed with deionized water several times and vacuum dried at 60 °C for 48 h to obtain the positive electrode active material GO / Mo2C / NS of the "chip" integrated lithium-sulfur battery positive electrode sheet.

[0033] (6) The above-mentioned positive electrode active material, super C conductive agent, and PVDF were added to N-methylpyrrolidone solvent in a mass ratio of 7:2:1, and then ground and mixed to obtain a slurry. The slurry was evenly coated on 304 stainless steel foil using a coater, and then placed in an oven at 60°C for 24 hours to remove the solvent. Finally, it was punched into positive electrode sheets with a diameter of 16 mm using a cutting machine for use.

[0034] (7) The electrochemical performance of the S-type cathode was tested using a Cr-2025 button cell. The cell assembly was performed in an argon-filled glove box. The anode was a lithium sheet, and the cathode and anode sheets were connected to aluminum and nickel sheets, respectively, and separated by a Celgard 2400 membrane.

[0035] Comparative Example 1:

[0036] This comparative example provides a method for preparing a positive electrode sheet rGO / S for a lithium-sulfur battery, comprising the following steps:

[0037] In this comparative example, the method for preparing the graphene oxide dispersion and the method for preparing the positive electrode sheet are the same as those in Example 1.

[0038] In this comparative example, 0.5 g of GO dispersion (2 mg / ml) and 2 g of sublimed sulfur were stirred at room temperature to obtain a mixture. The mixture was then transferred to a polytetrafluoroethylene-lined autoclave. The mixed solution was maintained at 155°C in an oven for 10 hours. After cooling to room temperature, it was washed multiple times with deionized water and finally dried in a 60°C oven under vacuum for 48 hours to obtain the positive electrode active material rGO / S.

[0039] Comparative Example 2:

[0040] This comparative example provides a method for preparing a positive electrode sheet Mo2C / S for a lithium-sulfur battery, comprising the following steps:

[0041] In this comparative example, the method for preparing the positive electrode sheet is the same as that in Example 1.

[0042] In this comparative example, 0.5 g of Mo2C and 2 g of sublimed sulfur were added to 60 ml of deionized water and stirred at room temperature to obtain a mixture. The mixture was transferred to a polytetrafluoroethylene-lined autoclave, and the mixed solution was kept at a temperature of 155°C in an oven for 10 h. After the temperature was cooled to room temperature, it was washed several times with deionized water and finally dried in a 60°C oven under vacuum for 48 h to obtain the positive electrode active material Mo2C / S.

Claims

1. A design and preparation method for a "chip-like" integrated lithium-sulfur battery positive electrode sheet, characterized in that: The following steps are involved: Step S1, preparing graphene quantum dots (GOQDs) from the bottom up by using pyrolyzed citric acid (CA), heating 5g of citric acid to 200°C in an air atmosphere for 30 minutes to obtain an orange solution containing graphene quantum dots. The obtained solution was placed in a dialysis bag and dialyzed in deionized water for 48 hours. The obtained solution was then freeze-dried to obtain GOQDs; Step S2, dissolving 50 mg of anhydrous MoCl5 in deionized water in an ice bath with stirring for 20 min to obtain a mixed solution; Step S3, mixing 120 mg of graphene oxide (GO) with 60 ml of deionized water, and ultrasonicating the mixture in an ultrasonic machine for 30 min to obtain a 2 mg / ml graphene oxide dispersion; Step S4, mixing 60 mg of GOQDs prepared in step S1 with 30 ml of deionized water and ultrasonicating for 30 min to obtain a GOQDs aqueous dispersion; Step S5: slowly add the GO dispersion obtained in step S3 and the GOQDs aqueous dispersion obtained in step S4 to the mixed solution obtained in step S3, and then slowly add 0.5 ml of oleylamine and heat to 75 ° C and stir for 3 h to obtain GO / Mo x O solution; Step S6: centrifuge the solution obtained in step S5 at 6000-8000 rpm for 5 min; wash the solution with deionized water several times to obtain a precipitate, freeze the solution in a refrigerator for 6 h, and then dry the solution in a vacuum freeze dryer for 48 h to obtain the intermediate product GO / Mo. x O; Step S7, placing the intermediate product obtained in step S6 in a tube furnace, first introducing argon for 20 minutes, then calcining under argon at a heating rate of 5°C / min to 700°C, maintaining the temperature for 1.5 hours, and cooling to room temperature to obtain a Mo2C nanoparticle composite material GO / Mo2C anchored on a perforated graphene oxide framework; Step S8, the GO / Mo2C composite material obtained in step S7 is mixed with deionized water and stirred at room temperature for 0.5 h to dissolve to obtain a Mo2C / HG suspension with a concentration of 100 mg / ml, and then 0.923 g of sodium thiosulfate is added to the above suspension and stirred in an ice bath for 0.5 h, and then 0.4 ml of hydrochloric acid is slowly added and stirred in an ice bath for 0.5 h. Finally, the precipitate is collected by centrifugation and washed with deionized water, and then placed in an oven at 60°C under vacuum and dried for 48 h to obtain the "chip" integrated composite material GO / Mo2C / NS.

2. The GO / Mo2C / NS composite material prepared by the method according to claim 1, characterized in that: Application as positive electrode material for "chip-like" integrated lithium-sulfur battery positive electrode sheets.

3. A positive electrode material for a positive electrode sheet of a "chip-like" integrated lithium-sulfur battery, characterized in that: Obtained by the preparation method according to claim 1.

4. A "chip-like" integrated lithium-sulfur battery, characterized in that: The active material of the positive electrode sheet is the GO / Mo2C / NS composite material according to claim 2, and the lithium-sulfur battery further includes a negative electrode sheet, a separator and an electrolyte.

5. The lithium-sulfur battery according to claim 4, characterized in that The negative electrode sheet includes a lithium negative electrode; the separator includes a Celgard 2400 separator; and the electrolyte includes 1M LITFSI dissolved in a DOL / DME electrolyte containing 1wt% LiNO3.

Images