Preparation method and application of saop-34 molecular sieve membrane based on size effect regulation

Abstract

The application discloses a preparation method and application of a SAPO-34 molecular sieve diaphragm based on size effect regulation, which can effectively adsorb polysulfides to inhibit the "shuttle effect". Secondly, the introduction of the negative-charged molecular sieve diaphragm can prevent the migration of polysulfides from the positive side to the negative side, and the negative-charged modified diaphragm can make the lithium ion flux distribution uniform through electrostatic interaction, thereby reducing the metal negative electrode dendrite growth. In addition, the SAPO-34 molecular sieve has a micropore channel of 0.38 nm, and the larger polysulfide anions can be isolated on the positive side of the diaphragm through the sieving effect, and the smaller ions can still freely pass through the diaphragm for transmission. The project first proposes to use the SAPO-34 molecular sieve to prepare a lithium-sulfur battery diaphragm to improve the "shuttle effect" of polysulfides and help the uniform deposition of the metal negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a method for preparing a SAPO-34 molecular sieve membrane and its application. Background Technology

[0002] Currently, lithium-ion batteries are an indispensable component integrated into consumer electronics, electric vehicles, and smart grids. However, state-of-the-art lithium-ion batteries based on intercalation theory have almost reached their theoretical energy density. With increasing energy demands, the development of cost-effective and high-energy / power-density rechargeable batteries is urgently needed. Extensive research has been conducted to explore advanced electrode materials with superior energy / power density, excellent rate capability, and ultra-long cycle life. Currently, anion redox chemistry has proven to be an effective strategy for improving energy density, providing a new research direction for next-generation high-energy rechargeable batteries. Among these, lithium-sulfur batteries exhibit an excellent theoretical specific capacity (1675 mAh g⁻¹). -1 ) and energy density (2600Wh kg) -1 Sulfur, being naturally abundant, cost-effective, and environmentally friendly, is considered the closest battery system to practical application after lithium-ion batteries. However, the shuttle effect of soluble polysulfide intermediates leads to poor cycle stability, low coulombic efficiency and self-discharge performance, as well as uncontrollable dendrite growth, which restricts the commercial application of lithium-sulfur batteries. In recent years, domestic and foreign scholars have effectively alleviated the positive electrode shuttle effect and related side reactions, insufficient electrochemical reaction kinetics, and dendrite growth by designing multifunctional porous positive electrode carriers, developing novel electrolytes, modifying separators, and modifying the negative electrode surface. Among these strategies, separator modification is considered the most effective method to simultaneously suppress the "shuttle effect" of soluble polysulfides and the side reactions of the metal negative electrode. The separator, located between the sulfur positive and lithium negative electrodes, is the only pathway for the diffusion of anions and cations and plays an important role in the mass transfer process at the interface between the sulfur positive and lithium negative electrodes. Therefore, separator modification is of great significance for achieving stable operation of lithium-sulfur batteries. However, current research mainly focuses on using coatings to modify the separator, which is also limited by the problem of irreversible peeling off from the separator surface and reduced ion transport rate. How to solve these problems is an urgent problem to be solved for high-performance lithium-sulfur batteries. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the prior art by proposing a method for preparing a membrane using SAPO-34 molecular sieve and its application in lithium-sulfur battery systems.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing SAPO-34 molecular sieve membranes based on size effect regulation, characterized in that: the preparation method is as follows:

[0006] S1. Preparation of SAPO-34 molecular sieve seed crystals with a gel molar ratio of 3.0 TEA: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 60 H2O; the specific synthesis steps are as follows: Boehmite (containing 67.5 wt.% Al2O3, also known as monohydrated alumina, i.e., Al2O3·nH2O) and water are mixed and stirred for about 30 min, then phosphoric acid is added, and stirring is continued at room temperature for 2 h to form a white homogeneous gel; then, silica sol (containing 30% TEA, 1.0% P2O5, 1.0% P2O5, 0.6% SiO2, 60% H2O) is added dropwise to the above homogeneous gel. wt.% SiO2 (silica sol is an alkaline solution of silicon dioxide) was added, and after stirring for 30 min, the template agent triethylamine was added, and the mixture was stirred at room temperature for 4 h. The resulting homogeneous gel was transferred to a stainless steel crystallization vessel with a polytetrafluoroethylene liner and crystallized at 200 °C for 2 days. After crystallization, the reaction vessel was cooled, and the solid product was washed with deionized water by centrifugation until neutral. Then, it was dried overnight in an oven at 100 °C. Finally, the obtained molecular sieve powder was calcined at 600 °C for 4 h to remove the organic template agent, yielding SAPO-34 molecular sieve seed crystals.

[0007] S2. Nano-sized SAPO-34 molecular sieves were prepared using a hydrothermal seed-directing liquid. Aluminum isopropoxide was used as the aluminum source (source of Al2O3), phosphoric acid as the phosphorus source, tetraethyl orthosilicate as the silicon source (source of SiO2), and morpholine (MOR) as the template agent. The SAPO-34 prepared in S1 was used as the seed crystal. The synthesis steps were as follows: First, morpholine and deionized water were mixed and stirred for 15 min. Then, the SAPO-34 seed crystals were added to the mixture, and stirring was continued for 15 min. The mixture was then transferred to a stainless steel crystallization vessel with a polytetrafluoroethylene liner and placed in an oven at 80℃ for 30 h to obtain liquid seed-directing liquid A. Aluminum isopropoxide and water were mixed and stirred for 15 min, and phosphoric acid was added dropwise. Stirring was continued at room temperature. A white, uniform gel was formed at 1h. Then, tetraethyl orthosilicate was added, and stirring was continued for 1h to obtain gel precursor B. Subsequently, the cooled seed crystal guiding liquid A was added to gel precursor B, and stirring was continued at room temperature for 2h. The final molar ratio of the gel was 4.0 MOR: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 70 H2O. The obtained gel was then transferred to a 100 mL stainless steel crystallization vessel and hydrothermally crystallized at 200℃ for 2d. After crystallization, the solid product was washed with deionized water until neutral, and then dried overnight in an oven at 100℃. The resulting molecular sieve powder was calcined at 600℃ for 4h to remove the organic template agent, yielding nano-SAPO-34 molecular sieve.

[0008] S3. The nano-SAPO-34 molecular sieve obtained in step S2 is mixed with PVDF binder at a mass ratio of 9:1. After mechanical grinding for 20 min, NMP organic solvent is added dropwise and stirred thoroughly for 12 h to obtain a slurry. The slurry is then uniformly coated onto a glass plate and placed in a vacuum oven to dry at 80 °C for 12 h to remove the NMP solvent. The molecular sieve membrane is then soaked in methanol for 5 min and peeled off from the glass plate. The membrane is then dried under vacuum at 100 °C for 48 h to obtain the SAPO-34 molecular sieve membrane.

[0009] The above-prepared SAPO-34 molecular sieve membrane is used in lithium-sulfur battery systems.

[0010] The principle and beneficial effects of this invention are as follows:

[0011] First, the molecular sieve is a Lewis acid, which can effectively adsorb polysulfides and suppress the "shuttle effect". Second, the molecular sieve is composed of AlO4. - The membrane alternates periodically with SiO4 to form a negatively charged framework. Typically, highly soluble polysulfides are negatively charged in organic electrolytes. Based on the principle of electrostatic repulsion between two like charges, introducing a negatively charged molecular sieve membrane can prevent the migration of polysulfides from the positive to the negative electrode side. Furthermore, the negatively charged modified membrane promotes a uniform lithium-ion flux distribution through electrostatic interactions, thereby reducing dendrite growth in the metal anode. In addition, SAPO-34 molecular sieves have 0.38 nm microporous channels, allowing larger polysulfide anions to be isolated on the positive electrode side of the membrane, while smaller ions can still freely pass through. This invention is the first to propose using SAPO-34 molecular sieves to prepare lithium-sulfur battery membranes to improve the polysulfide "shuttle effect" and facilitate uniform deposition of the metal anode. Successful implementation of this invention will provide new insights for the design of high-efficiency lithium-sulfur battery membranes. Attached Figure Description

[0012] Figure 1 This is a scanning electron microscope image of the SAPO-34 molecular sieve of the present invention.

[0013] Figure 2 The XRD diffraction pattern of SAPO-34 molecular sieve.

[0014] Figure 3 This is a photograph of the SAPO-34 molecular sieve membrane prepared according to the present invention.

[0015] Figure 4 A comparison chart of the rate performance of lithium-sulfur batteries using commercial PE membranes and SAPO-34 molecular sieve membranes.

[0016] Figure 5 A CV comparison graph showing the performance of lithium-sulfur batteries using commercial PE membranes and SAPO-34 molecular sieve membranes.

[0017] Figure 6 A comparison of the ionic conductivity of PE membrane and SAPO-34 molecular sieve membrane.

[0018] Figure 7 Comparison of cycle performance of lithium symmetric batteries using commercial PE membranes and SAPO-34 molecular sieve membranes at 1 mA rate and 1 mAh capacity. Detailed implementation method:

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] The preparation method of the SAPO-34 molecular sieve membrane based on size effect regulation in this embodiment of the invention is as follows: S1. Prepare SAPO-34 molecular sieve seed crystals with a gel molar ratio of 3.0 TEA: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 60 H2O; the specific synthesis steps are as follows: mix boehmite and water and stir for about 30 min, then add phosphoric acid and continue stirring at room temperature for 2 h to form a white uniform gel; then, add dropwise to the above uniform gel. After stirring the silica sol for 30 minutes, triethylamine, the template agent, was added, and the mixture was aged at room temperature for 4 hours. The resulting homogeneous gel was transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene (PTFE) and crystallized at 200°C for 2 days. After crystallization, the reaction vessel was cooled, and the solid product was washed with deionized water by centrifugation until neutral. Then, it was dried overnight in an oven at 100°C. Finally, the obtained SAPO-34 molecular sieve powder was calcined at 600°C for 4 hours to remove the organic template agent, thus preparing SAPO-34 molecular sieve seed crystals.

[0021] S2. Nano-sized SAPO-34 molecular sieves were prepared using a hydrothermal seed-directing liquid. Aluminum isopropoxide was used as the aluminum source, phosphoric acid as the phosphorus source, tetraethyl orthosilicate as the silicon source, and morpholine as the template agent. The SAPO-34 prepared in S1 was used as the seed crystal. The synthesis steps were as follows: First, morpholine and deionized water were mixed and stirred for 15 min. Then, the SAPO-34 seed crystals were added to the mixture, and stirring was continued for 15 min. The mixture was then transferred to a crystallization vessel and dried in a dynamic oven at 80°C for 30 h to obtain liquid seed-directing liquid A. Aluminum isopropoxide and water were mixed and stirred for 15 min, and phosphoric acid was added dropwise. Stirring was continued at room temperature for 1 h to form a white... A uniform gel was formed; then, tetraethyl orthosilicate was added, and stirring was continued for 1 hour to obtain gel precursor B; subsequently, the cooled seed crystal guiding liquid A was added to gel precursor B, and stirring was continued at room temperature for 2 hours. The final molar ratio of the obtained gel was 4.0 MOR: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 70 H2O; then the obtained gel was transferred to a 100 mL stainless steel crystallization vessel and hydrothermally crystallized at 200 °C for 2 days; after crystallization, the solid product was washed until neutral, and then dried overnight in an oven at 100 °C. The resulting molecular sieve powder was calcined at 600 °C for 4 hours to remove the organic template agent.

[0022] Preparation of the lithium-sulfur battery separator: 450 mg of SAPO-34 molecular sieve powder was mixed with 50 mg of PVDF binder and mechanically ground for 20 min. Then, 0.3 mL of NMP organic solvent was added dropwise, and the mixture was stirred thoroughly for 12 h to obtain a slurry. This slurry was uniformly coated onto a glass plate and dried in a vacuum oven at 80 °C for 12 h to remove the NMP solvent. The molecular sieve membrane was then immersed in methanol for about 5 minutes and peeled off from the glass plate. The prepared separator was then dried under vacuum at 100 °C for 48 h to obtain the SAPO-34 molecular sieve separator. Before use, the membrane was cut into pieces with a diameter of 17 mm. The thickness of the separator was approximately 30-35 μm.

[0023] The electron microscope images and diffraction patterns of the SAPO-34 molecular sieve prepared in this embodiment are shown in the figure. Figure 1 and 2 As can be seen from the figure, the synthesized SAPO-34 has a chalcogenide (CHA) topological structure and is a smooth cubic crystal, such as... Figure 1 As shown. Figure 2 The high diffraction peak intensities indicate that the obtained samples are all pure-phase SAPO-34 molecular sieves with good crystallinity.

[0024] The rate performance comparison between the SAPO-34 molecular sieve membrane prepared in this embodiment and the traditional commercial PE membrane in lithium-sulfur batteries is shown in the figure. Figure 4As shown in the figure, the battery using the SAPO-34 molecular sieve membrane exhibits excellent rate performance, achieving 618 mA hg even at an ultra-high rate of 10C. -1 The high reversibility demonstrates its high rate performance. Furthermore, when the current is switched back to 0.1C, the reversible capacity can recover to 916mAh g. -1 It exhibits high reversibility and long-lasting electrochemical performance, in stark contrast to the performance of lithium-sulfur batteries using PE separators.

[0025] The CV comparison chart of the SAPO-34 molecular sieve membrane and the traditional PE membrane in lithium-sulfur batteries prepared in this embodiment is shown below. Figure 5 As shown in the figure, compared with batteries using PE membranes, batteries using SAPO-34 molecular sieve membranes exhibit higher cathode and anode peak current densities at different scan rates, along with lower anode peak voltages and the highest cathode peak voltages. This indicates that SAPO-34 molecular sieve membranes contribute to faster charge / discharge kinetics, resulting in significant improvements in specific capacity and reduction of polarization.

[0026] The comparison of the ionic conductivity of the SAPO-34 molecular sieve membrane and the traditional PE membrane prepared in this embodiment is shown in the figure below. Figure 6 As shown in the figure, the SAPO-34 molecular sieve membrane can regulate the uniform deposition of lithium ions and inhibit the growth of lithium dendrites. The results indicate that the ionic conductivity of the SAPO-34 molecular sieve membrane for lithium ions is much higher than that of the PE membrane.

[0027] The comparison chart of the cycle performance of the SAPO-34 molecular sieve membrane prepared in this embodiment and the traditional PE membrane used in the lithium symmetric battery at 1mA rate and 1mAh capacity is shown in the figure. Figure 7 As shown in the figure, the SAPO-34 molecular sieve membrane, with its high specific surface area, uniform nanochannels, and negative charge, facilitates ion diffusion kinetics, promotes uniform lithium-ion flux, thereby regulating uniform lithium deposition and suppressing side reactions. The SAPO-34 battery exhibits low voltage hysteresis without significant voltage fluctuations after 8000 hours of cycling, demonstrating its significant potential for ensuring uniform lithium deposition. However, the PE membrane exhibits unstable voltage hysteresis, unstable voltage fluctuations, and a large overpotential after 350 hours of cycling, indicating uneven lithium deposition / stripping.

[0028] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope of the present invention, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing SAPO-34 molecular sieve membranes based on size effect regulation, characterized in that: The preparation method is as follows: S1. Preparation of SAPO-34 molecular sieve seed crystals with a gel molar ratio of 3.0 TEA: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 60 H2O; the specific synthesis steps are as follows: Boehmite and water are mixed and stirred for 30 min, then phosphoric acid is added, and stirring is continued at room temperature for 2 h to form a white homogeneous gel; then, silica sol is added dropwise to the above homogeneous gel, and stirring is continued for 30 min, followed by the addition of the template agent triethylamine, and stirring is carried out at room temperature for 4 h; The resulting homogeneous gel was transferred to a stainless steel crystallization vessel lined with polytetrafluoroethylene and crystallized at 200°C for 2 days. After crystallization, the reaction vessel was cooled, and the solid product was washed with deionized water by centrifugation until neutral. Then, it was dried overnight in an oven at 100°C. Finally, the obtained molecular sieve powder was calcined at 600°C for 4 hours to remove the organic template agent, yielding SAPO-34 molecular sieve seed crystals. S2. Nano-sized SAPO-34 molecular sieves were prepared using a hydrothermal seed-directing liquid. Aluminum isopropoxide was used as the aluminum source, phosphoric acid as the phosphorus source, tetraethyl orthosilicate as the silicon source, and morpholine as the template agent. The SAPO-34 prepared in S1 was used as the seed crystal. The synthesis steps were as follows: First, morpholine and deionized water were mixed and stirred for 15 min. Then, the SAPO-34 seed crystals were added to the mixture, and stirring was continued for 15 min. The mixture was then transferred to a stainless steel crystallization vessel with a polytetrafluoroethylene liner and placed in an oven at 80°C for 30 h to obtain liquid seed-directing liquid A. Aluminum isopropoxide and water were mixed and stirred for 15 min, and phosphoric acid was added dropwise. Stirring was continued at room temperature for 1 h to form a white, uniform gel. Then, tetraethyl orthosilicate was added, and stirring was continued for 1 hour to obtain gel precursor B. Subsequently, the cooled seed crystal guiding liquid A was added to gel precursor B, and stirring was continued at room temperature for 2 hours. The final molar ratio of the obtained gel was 4.0 MOR: 1.0 Al2O3: 1.0 P2O5: 0.6 SiO2: 70 H2O. The obtained gel was then transferred to a 100 mL stainless steel crystallization vessel and hydrothermally crystallized at 200 °C for 2 days. After crystallization, the solid product was washed with deionized water until neutral, and then dried overnight in an oven at 100 °C. The resulting molecular sieve powder was calcined at 600 °C for 4 hours to remove the organic template agent, resulting in nano-SAPO-34 molecular sieve. S3. The nano-SAPO-34 molecular sieve obtained in step S2 is mixed with PVDF binder at a mass ratio of 9:

1. After mechanical grinding for 20 min, NMP organic solvent is added dropwise. After stirring thoroughly for 12 h, a slurry is obtained. The slurry is then uniformly coated onto a glass plate and placed in a vacuum oven to dry at 80°C for 12 h to remove the NMP solvent. The prepared molecular sieve membrane was soaked in methanol for 5 minutes and then peeled off from the glass plate; the prepared membrane was then dried under vacuum at 100°C for 48 hours to obtain the SAPO-34 molecular sieve membrane.

2. The application of the SAPO-34 molecular sieve membrane prepared as claimed in the lithium-sulfur battery system.

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