A solid electrolyte with ion transport regulation function and preparation method thereof

Abstract

The composition formula of the solid electrolyte with ion transport regulation function disclosed in the present invention is aNa2S‑bSb2S3‑cMnS‑dS, wherein a, b, c, d are all molar ratios, 3≤a≤3.6, 0.8≤b≤1, 0<c≤0.4, 1.6≤d≤2. The solid electrolyte has a double-phase crystal structure with cubic phase as the main phase and tetragonal phase as the auxiliary phase. The mutual conversion between the two crystalline phases will produce vacancies and reduce the electrostatic interaction between the moving ions, achieve low potential barriers and accelerate the co-migration between ions, reduce the kinetic energy on its diffusion path, thereby achieving ion transport regulation, so that the electrochemical properties and crystal structure of the solid electrolyte are improved. In addition, Sb is difficult to react with oxygen in the air, and thus the present invention can fundamentally improve the air stability of the solid electrolyte by introducing Sb. The preparation method of the solid electrolyte is simple to operate, environmentally friendly, and suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of sulfur-based solid electrolytes, and in particular to a solid electrolyte with ion transport regulating function and a preparation method thereof. Background Art

[0002] The development of sodium ion sulfur solid electrolytes is an urgent alternative to the limited reserves of lithium resources. Sodium resources are more abundant than lithium and are more evenly distributed globally. Moreover, lithium and sodium are adjacent elements of the same family with similar physical and chemical properties, and can learn from each other in technical research. Among the major solid electrolytes today, sulfide electrolytes can effectively improve the defect that oxide electrolytes can only achieve high conductivity at high temperatures. At the same time, due to the S 2- O 2- With a larger ionic radius, S 2- than O 2- The electronegativity of Na is small, which makes + They can migrate freely within sulfide solid electrolytes, resulting in higher electrical conductivity. Compared to the flammable and explosive safety issues of traditional organic electrolytes, the application of solid electrolytes can perfectly resolve these safety hazards while also significantly improving energy density and operating voltage. It is widely considered one of the most valuable technologies for next-generation energy storage.

[0003] At present, the research on sodium ion sulfur solid electrolytes is in a rapid development stage at home and abroad. In traditional solid electrolytes, the single crystal cell structure leads to a decrease in the sodium ion transmission efficiency. + Transport increases the activation energy of the reaction and significantly reduces the stability of the ion structure. By rationally modifying the unit cell structure, not only can the regulation of ion transport be achieved, but the generation of H2S by the reaction with H2O in the air can also be reduced, fundamentally improving the tolerance at room temperature.

[0004] Currently, there are two commonly used methods for preparing solid-state electrolytes: liquid-phase and solid-phase. Electrolytes prepared using the liquid-phase method often incorporate water of crystallization, making it difficult to obtain high-conductivity electrolytes. Most organic solvents are highly toxic and pose certain risks. The solid-phase method, also commonly referred to as high-energy ball milling, involves rotating small balls in a milling jar at high speed, causing them to continuously collide with the raw materials. This motion generates heat and continuously refines the raw materials to the micron level, allowing for sufficient bonding reactions between the raw materials. Currently reported inorganic sulfide electrolytes based on Na3SbS4 solid electrolytes prepared by ball milling are typically single crystalline phases of tetragonal or cubic phases and are not stable in air. These sulfide electrolytes undergo irreversible chemical reactions with oxygen, water vapor, and carbon dioxide in the air, resulting in structural changes and reduced ionic conductivity, severely limiting their application in all-solid-state sodium batteries. Therefore, the research on new sulfide solid-state sodium-ion electrolytes, particularly those with polycrystalline phases, excellent room-temperature ionic conductivity, and water stability, is highly anticipated. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a solid electrolyte with ion transport regulation function and a preparation method thereof, in view of the low electrical conductivity and poor air stability of existing single crystal phase solid electrolytes.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a solid electrolyte with ion transport regulation function, the composition formula of the solid electrolyte is aNa2S-bSb2S3-cMnS-dS, wherein a, b, c, and d are all molar ratios, 3≤a≤3.6, 0.8≤b≤1, 0<c≤0.4, and 1.6≤d≤2.

[0007] By introducing Mn, the present invention imparts a solid electrolyte with a dual-phase crystal structure dominated by a cubic phase and supplemented by a tetragonal phase. The interconversion between the two crystal phases creates vacancies and reduces electrostatic interactions between moving ions, achieving a low potential barrier and accelerating the co-migration of ions, reducing the kinetic energy along their diffusion paths. This allows for ion transport regulation, improving both the electrochemical properties and crystal structure of the solid electrolyte. Furthermore, Sb is difficult to react with oxygen in the air, so the present invention, through the introduction of Sb, can fundamentally improve the air stability of the solid electrolyte.

[0008] By regulating the amount of MnS introduced, that is, regulating the c value, the overall performance of the solid electrolyte can be controlled. This not only improves the electrochemical performance of the solid electrolyte, but more importantly, ensures that the solid electrolyte has a dual-phase crystal structure, fundamentally improving the stability of the solid electrolyte at room temperature. Preferably, c = 0.1, 0.16, 0.2, or 0.4.

[0009] The method for preparing the solid electrolyte having ion transport regulating function comprises the following steps:

[0010] (1) weighing raw materials Na2S, Sb2S3, MnS and S in proportion, crushing and sieving them respectively under anhydrous and oxygen-free conditions under inert gas protection to obtain powdered raw materials Na2S, Sb2S3, MnS and S, placing the above powdered raw materials in a ball mill for mixed ball milling, and sieving them under anhydrous and oxygen-free conditions under inert gas protection to obtain a mixed powder;

[0011] (2) Press the mixed powder into blocks, place them in a quartz tube, and evacuate the tube to 10 -3 After Pa, melt and seal the quartz tube;

[0012] (3) The sealed quartz tube is placed in an annealing furnace, first heated to 340-640°C at a heating rate of 100°C / h, then annealed at 340-640°C for 4-12h, and then cooled to room temperature at a cooling rate of 100°C / h. The quartz tube is opened to obtain a solid electrolyte with ion transport regulation function.

[0013] Preferably, in step (1), the anhydrous and oxygen-free conditions are: the moisture content is less than 1 ppm, and the oxygen content is less than 1 ppm.

[0014] Preferably, in step (1), the sieve used for sieving has an aperture of 200 to 800 meshes, more preferably 200 to 600 meshes.

[0015] Preferably, in step (1), the conditions for the mixed ball milling treatment are: rotation speed 510 rpm, ball-to-material ratio 20:1, ball milling time 20 h, counterclockwise rotation mode, cycle setting of ball milling for 15 minutes and pause for 5 minutes, and during the ball milling period, scraping treatment is performed every 5 h.

[0016] Preferably, in step (2), the pressure used to press the mixed powder into blocks is 480 MPa, and a heating tape is wrapped around the body of the quartz tube before vacuuming to prevent deliquescence and assist in vacuuming, and the quartz tube is melt-sealed with a flamethrower.

[0017] Preferably, in step (3), annealing is performed at a temperature of 340 to 640° C. for 6 hours.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1) By introducing Mn, the present invention enables the solid electrolyte to have a dual-phase crystal structure with a cubic phase as the main phase and a tetragonal phase as the auxiliary phase. The mutual transformation between the two crystal phases will produce vacancies and reduce the electrostatic interaction between mobile ions, thereby achieving a low potential barrier and accelerating the co-migration between ions, reducing the kinetic energy on their diffusion path, thereby achieving ion transport regulation, and improving the electrochemical properties and crystal structure of the solid electrolyte. In addition, Sb is difficult to react with oxygen in the air. Therefore, by introducing Sb, the present invention can fundamentally improve the air stability of the solid electrolyte and significantly reduce the erosion of moisture and oxygen in the air on the solid electrolyte material structure.

[0020] 2) The preparation method of the present invention obtains a mixed powder through mixed ball milling, and the mixed powder is pressed into blocks, which can effectively promote the amorphous part of the electrolyte to fill the crystalline gap, further eliminate the grain boundary resistance, and improve the ionic conductivity; the raw material mixture pressed into blocks is vacuum annealed, so that the reaction can be fully carried out to obtain a bulk solid electrolyte with a dense structure and uniform element distribution. Compared with the traditional liquid phase method, the preparation method of the present invention is simple to operate, environmentally friendly, and easy to heat treat and crystallize. This method can simply and quickly obtain a uniform and air-stable bulk solid electrolyte. The preparation method of the present invention is suitable for large-scale production, and the obtained bulk solid electrolyte has comprehensive properties such as excellent ionic conductivity, high air tolerance and low activation energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of sample powders of solid electrolytes with different c values ​​at room temperature (25°C);

[0022] Figure 2 XRD patterns of the sample powders of Example 2 obtained by annealing at different temperatures (0°C, 340°C, 440°C, 540°C) for 6 h;

[0023] Figure 3 The Raman spectra of the sample powder of Example 2 obtained by annealing at different temperatures (0°C, 340°C, 440°C, 540°C) for 6 h;

[0024] Figure 4 This is the EDX spectrum of the sample powder of Example 2 obtained by annealing at 540°C;

[0025] Figure 5 Impedance diagrams of the sample powder of Example 2 obtained by annealing at different temperatures (240°C, 340°C, 440°C, 540°C, 640°C) for 6 h;

[0026] Figure 62 is a curve showing the change in H2S release as a function of exposure time at 48% relative humidity for the sample powder of Example 2 and the sample powder of the comparative example annealed at 540°C;

[0027] Figure 7 The graph shows the change in conductivity of the sample powder of Example 2 and the sample powder of the comparative example annealed at 540° C. after being exposed to air for 4 days. DETAILED DESCRIPTION

[0028] The composition formula of the solid electrolyte with ion transport control function of the present invention is aNa2S-bSb2S3-cMnS-dS, wherein a, b, c, and d are molar ratios of 3≤a≤3.6, 0.8≤b≤1, 0<c≤0.4, and 1.6≤d≤2. The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0029] 3 g of each of the solid electrolytes for the comparative example and Examples 1 to 4 were prepared using the method of the present invention using the following raw material ratios and identical preparation parameters (annealing temperature of 540°C and annealing time of 6 h). The samples were cylindrical tablets with a diameter of 10 mm and a thickness of approximately 1 to 2 mm. The raw material purities used were: Na2S - 95%, Sb2S3 - 99%, MnS - 98%, and S - 99.99%.

[0030] Comparative example: c=0, Na2S=1.000g, Sb2S3=1.452g, S=0.548g, MnS=0g.

[0031] Example 1: c = 0.1, Na2S = 1.053 g, Sb2S3 = 1.380 g, S = 0.549 g, MnS = 0.018 g.

[0032] Example 2: c = 0.16, Na2S = 1.083g, Sb2S3 = 1.338g, S = 0.549g, MnS = 0.030g.

[0033] Example 3: c = 0.2, Na2S = 1.104g, Sb2S3 = 1.309g, S = 0.550g, MnS = 0.037g.

[0034] Example 4: c = 0.4, Na2S = 1.207g, Sb2S3 = 1.167g, S = 0.551g, MnS = 0.075g.

[0035] The samples of the comparative example and examples 1 to 4 were processed into powders and subjected to XRD analysis at room temperature (25°C). The results are shown in FIG. Figure 1 .

[0036] For the above embodiment 2, its chemical formula can be expressed as Na 3.24 Mn 0.08 Sb 0.92 S4. According to the same raw material ratio as in Example 2, multiple samples of Example 2 were prepared and annealed at different temperatures (0°C, 340°C, 440°C, 540°C) for 6 h to obtain the XRD patterns of the sample powders. Figure 2 , Raman spectrum test results are shown in Figure 3 .from Figure 2 It can be seen that when the annealing temperature gradually increases, the double peaks merge into a single peak. These asymmetric single peaks mean that the cubic phase and the tetragonal phase coexist in the sample. Figure 3 It can be seen that the Raman peak position does not change significantly at different annealing temperatures, indicating that the twin-phase sample structure has high heat resistance, and the change in the wavenumber shift and intensity of the Raman spectrum confirms the doping effect. Figures 1 to 3 The microstructure of the solid electrolyte can be evaluated, proving that the sample structure is stable and successfully prepared, providing a guarantee for the transmission of sodium ions. Figure 4 This is the EDX spectrum of the sample powder of Example 2 obtained by annealing at 540°C. Figure 4 The mapping of different elements on the sample surface was detected by energy dispersive spectroscopy. The elements were evenly distributed on the sample surface, further proving the stability of the dual-phase sample. On the electrochemical workstation, AC complex impedance was used to study the electrochemical properties of the sample powder obtained by annealing at different temperatures (240℃, 340℃, 440℃, 540℃, 640℃) for 6h. The results are shown in Figure 2. Figure 5 The results show that the lowest resistance of the sample powder obtained when the annealing temperature is 540℃ is 54Ω, corresponding to the conductivity of 2.05×10 -3 S / cm.

[0037] To detect the air stability of the sample, the air stability of the sample of Example 2 obtained by annealing at 540°C was tested using an H2S gas sensor. 150 mg of powder sample, a hydrogen sulfide detector, and a small fan were placed in a 1.95 L sealed container. The relative humidity was controlled at 48% and the temperature was maintained at 25°C for testing. The H2S content was collected at regular intervals depending on the rate at which the sample released H2S, and a relationship graph between the hydrogen sulfide content released by the sample and time was obtained. Figure 6 The curves of the H2S release of the sample powder of Example 2 and the sample powder of the comparative example annealed at 540°C and 48% relative humidity as a function of exposure time are shown. Figure 6 It can be seen that the H2S release of the two is 0.6cm 3 / g and 0.37cm 3 / g. Compared with the comparative example sample, the H2S generation amount of the sample powder of Example 2 was significantly reduced by 38.3%. Figure 7The conductivity curves of the sample powder of Example 2 and the sample powder of the comparative example annealed at 540°C after being exposed to air for 4 days are shown in FIG. Figure 7 It can be seen that the electrical conductivity of the two is 0.5×10 -3 S / cm and 0.27×10 -3 S / cm, compared with the comparative example sample, the conductivity of the sample powder of Example 2 is increased by 45%.

Claims

1. A solid electrolyte with ion transport regulation function, characterized in that: The chemical formula of the solid electrolyte is Na 3.24 Mn 0.08 Sb 0.92 S4, the solid electrolyte has a twin-phase crystal structure with a cubic phase as the main phase and a tetragonal phase as the auxiliary phase.

2. The method for preparing the solid electrolyte with ion transport regulating function according to claim 1, characterized in that: The following steps are involved: (1) Raw materials Na2S, Sb2S3, MnS and S are weighed in proportion, and the raw materials are crushed and sieved under an inert gas-protected, anhydrous and oxygen-free conditions to obtain powdered raw materials Na2S, Sb2S3, MnS and S. The powdered raw materials are placed in a ball mill for mixed ball milling, and sieved under an inert gas-protected, anhydrous and oxygen-free conditions to obtain a mixed powder; (2) Press the mixed powder into a block, place it in a quartz tube, and evacuate the tube to 10 -3 After Pa, melt and seal the quartz tube; (3) Place the melt-sealed quartz tube in an annealing furnace, first heat it to 340~640℃ at a heating rate of 100℃ / h, then anneal it at 340~640℃ for 4~12h, and then cool it to room temperature at a cooling rate of 100℃ / h. Open the quartz tube to obtain a solid electrolyte with ion transport regulation function.

3. The method for preparing a solid electrolyte having an ion transport regulating function according to claim 2, wherein: In step (1), the anhydrous and oxygen-free conditions are: the moisture content is less than 1 ppm and the oxygen content is less than 1 ppm.

4. The method for preparing a solid electrolyte having an ion transport regulating function according to claim 2, wherein: In step (1), the sieve used for sieving has an aperture of 200-800 mesh.

5. The method for preparing a solid electrolyte having an ion transport regulating function according to claim 2, wherein: In step (1), the conditions for the mixed ball milling treatment are: rotation speed 510 rpm, ball-to-material ratio 20:1, ball milling time 20 h, counterclockwise rotation mode, cycle setting of ball milling for 15 minutes and pause for 5 minutes, and during the ball milling period, scraping treatment is performed every 5 h.

6. The method for preparing a solid electrolyte having an ion transport regulating function according to claim 2, wherein: In step (2), the pressure used to press the mixed powder into blocks is 480 MPa, and before vacuuming, the body of the quartz tube is wrapped with a heating tape and the quartz tube is melt-sealed with a flamethrower.

7. The method for preparing a solid electrolyte having an ion transport regulating function according to claim 2, wherein: In step (3), annealing is performed at a temperature of 340-640°C for 6 hours.

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