A selenium-doped sulfide solid-state electrolyte and a preparation method thereof

Abstract

The application discloses a Se-doped sulfide solid electrolyte and a preparation method thereof, and relates to the technical field of battery materials. The preparation method comprises the following steps: mixing a selenium source, a complexing agent and a first organic solvent to obtain a first mixed solution; mixing a lithium source, a nonmetal source and a second nonpolar organic solvent, heating the obtained second mixed solution to a first preset temperature, then adding the first mixed solution, and stirring for a first preset time; continuously heating to a second preset temperature and stirring for a second preset time; drying the obtained coprecipitate, and annealing at 300-400 DEG C to obtain the Se-doped sulfide solid electrolyte; the boiling point of the first organic solvent is less than or equal to the first preset temperature, and the boiling point of the second nonpolar organic solvent is less than or equal to the second preset temperature. The application realizes uniform doping of Se elements by adopting a double-solvent gradient evaporation technology combined with low-temperature annealing, and the prepared Se-doped sulfide solid electrolyte has higher ionic conductivity and air stability compared with undoped electrolyte.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a selenium-doped sulfide solid electrolyte and its preparation method. Background Technology

[0002] Solid-state batteries are considered a core direction for next-generation energy storage technology, and their research surge stems from the need to overcome three major bottlenecks of traditional liquid lithium-ion batteries: 1. Safety issues: Liquid electrolytes are prone to leakage and flammability, posing a risk of thermal runaway. Solid-state batteries, by using solid electrolytes instead of liquid electrolytes, reduce the risk of thermal runaway by more than 90%. 2. Energy density limitations: Liquid batteries are limited by graphite anodes (theoretical capacity of 372 mAh / g), while solid-state batteries can be adapted to lithium metal anodes (theoretical capacity of 3860 mAh / g), with the potential energy density exceeding 500 Wh / kg (compared to only 200-300 Wh / kg for traditional batteries). 3. Fast charging requirements: Solid electrolytes have shorter ion transport paths, enabling solid-state batteries to achieve fast charging in 10 minutes, while liquid batteries require more than 30 minutes.

[0003] Among the four major solid-state electrolyte technologies—oxide, sulfide, polymer, and halide—sulfide solid-state electrolytes have become the preferred solution for all-solid-state batteries due to their unique properties. Sulfide electrolytes possess the following properties: 1. Ultra-high ionic conductivity: Sulfide solid-state electrolytes (such as Li...) 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 The ionic conductivity of [a substance] can reach 25 mS / cm, far exceeding that of oxides (1–10 mS / cm) and polymers (10 mS / cm). -3 ~10 -2 (mS / cm) solid electrolyte, close to the level of liquid electrolyte (10) -2 ~10 -1 1. **Mechanical Flexibility:** Sulfide solid electrolytes can be cold-pressed into films without additional binders, and maintain close contact with the positive and negative electrode interfaces, reducing interfacial impedance. 2. **Low Density and High Compatibility:** Sulfide solid electrolytes have a density of approximately 2.5 g / cm³. 3 Significantly lower than oxide solid electrolytes (>5 g / cm³) 3 Furthermore, it exhibits excellent compatibility with lithium metal, silicon anodes, and high-nickel cathodes, making it suitable for high-energy-density electrode materials. 4. Cost optimization potential: The lithium oxysulfide phosphorus (Li7P3S) developed by Ma Cheng's team at the University of Science and Technology of China... 7.5 O 3.5 The cost is reduced to $14.42 / kg by using inexpensive raw materials (lithium hydroxide hydrate + phosphorus sulfide), a 92% reduction compared to traditional sulfides.

[0004] Despite the significant advantages of sulfide solid electrolytes (SSEs), their industrialization still faces the following key challenges: 1. Poor air stability: SSEs exposed to humid air are prone to hydrolysis, generating H2S and Li3PO4, leading to a decrease in ionic conductivity. For example, the conductivity of LPSC (lithium phosphide sulfide chloride) decreases by 50% after 24 hours of exposure to air. 2. High interfacial impedance: When SSEs come into contact with lithium metal anodes, they easily form unstable solid electrolyte interfaces (SEIs), causing dendrite growth and capacity decay (e.g., charging time increases to 45 minutes after 50 cycles). 3. Complex synthesis process: Traditional doping (such as O and F) requires high-temperature annealing, which is energy-intensive and easily damages the crystal structure. 4. Cost and scalability conflict: Raw materials such as lithium sulfide (Li2S) are expensive (≥650 USD / kg), and traditional synthesis routes are difficult to meet the demand for thousand-ton-scale production capacity.

[0005] In recent years, researchers have improved the performance of sulfide solid electrolytes (SSEs) by constructing nanocoatings or through elemental doping. For example, constructing nanocoatings (such as LiF@Li₂O shells) can improve SSE performance, but the fabrication process of nanoshells is complex (e.g., high-temperature annealing or chemical vapor deposition), and achieving uniform coating is difficult, increasing costs. Specifically, the preparation of nano-Li₂O / LiF shells relies on high-temperature annealing or solution blending, which can easily lead to uneven coating or damage to the internal structure. While slow-cooling heat treatment can form LiF@Li₂O nanoshells, it is energy-intensive and difficult to scale up. Furthermore, while the addition of LiF suppresses lithium dendrites, its wide bandgap (14.2 eV) and high electronic insulation may exacerbate interfacial impedance. Another approach is to improve the performance of sulfide SSEs (such as LPSCs) through elemental doping (e.g., O, F, Cl). Doping with O and F can generate PO₄⁻ and LiF phases, improving air stability and interfacial compatibility, but reducing ionic conductivity due to electrostatic interactions. In addition, it will form strongly polarized PO- or PF- bonds, hindering Li + Migration leads to a decrease in ionic conductivity (e.g., the conductivity of LPSC-OF electrolyte is lower than that of undoped materials).

[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a selenium-doped sulfide solid electrolyte and its preparation method, which aims to solve the problem that the ionic conductivity of sulfide solid electrolytes will decrease after element doping.

[0008] The technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a selenium-doped sulfide solid electrolyte, comprising the following steps:

[0010] The selenium source, complexing agent, and first organic solvent are mixed to obtain a first mixture.

[0011] A lithium source, a non-metallic source, and a second non-polar organic solvent are mixed to obtain a second mixture; the non-metallic source includes a sulfur source.

[0012] After heating the second mixture to a first preset temperature, the first mixture is added and stirred at the first preset temperature for a first preset time. Then, the temperature is raised to a second preset temperature and stirred at the second preset temperature for a second preset time to obtain a coprecipitate.

[0013] The coprecipitate was dried and then annealed at 300–400°C to obtain the selenium-doped sulfide solid electrolyte.

[0014] Wherein, the boiling point of the first organic solvent is less than or equal to the first preset temperature, and the boiling point of the second non-polar organic solvent is less than or equal to the second preset temperature.

[0015] Optionally, the selenium source includes at least one of lithium selenate and lithium selenide;

[0016] The number of moles of selenium in the selenium source is 5% to 20% of the number of moles of the sulfide solid electrolyte.

[0017] Optionally, the complexing agent includes at least one of citric acid and polyethylene glycol; and / or,

[0018] In the first mixture, the concentration of the complexing agent is 0.1–0.5 mol / L, and the concentration of the selenium source is 1–5 mol / L; and / or,

[0019] The first organic solvent includes at least one of acetone and tetrahydrofuran.

[0020] Optionally, the lithium source includes Li₂S; and / or,

[0021] The non-metallic source also includes at least one of a phosphorus source and a chlorine source.

[0022] Optionally, the second nonpolar organic solvent includes at least one of n-hexane and cyclohexane; and / or,

[0023] In the second mixture, the total concentration of the lithium source and the non-metallic source is 0.5 to 2 mol / L.

[0024] Optionally, the first mixture is added by dripping at a rate of 1 to 5 mL / min.

[0025] Optionally, the mixture is stirred at a speed of 200–500 rpm for 5–15 min at a first preset temperature; and / or,

[0026] Stir at 200-500 rpm for 5-15 minutes at the second preset temperature.

[0027] Optionally, drying is carried out in an inert atmosphere or vacuum, the drying temperature is 100–150°C, and the drying time is 2–5 hours; and / or,

[0028] The annealing time is 1 to 2 hours.

[0029] In a second aspect, the present invention provides a selenium-doped sulfide solid electrolyte, wherein the selenium-doped sulfide solid electrolyte is prepared by the preparation method described above.

[0030] Optionally, the selenium-doped sulfide solid electrolyte includes Se-doped Li6PS5Cl or Se-doped Li 5.5 PS 4.5 Cl 1.5 .

[0031] Beneficial effects: This invention uses a dual-solvent gradient evaporation technique combined with low-temperature annealing to achieve uniform doping of selenium, thereby preparing a selenium-doped sulfide solid electrolyte. Compared with the undoped sulfide solid electrolyte, the selenium-doped sulfide solid electrolyte has higher ionic conductivity and air stability. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the preparation method of selenium-doped sulfide solid electrolyte in this invention.

[0033] Figure 2 This is a flowchart illustrating the preparation process of Se-doped LPSC in Example 1.

[0034] Figure 3 The images show the XRD patterns of the Se-doped LPSCs prepared in Examples 1 to 5. Detailed Implementation

[0035] This invention provides a selenium-doped sulfide solid electrolyte and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0037] If the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0038] Current methods for doping sulfide solid electrolytes typically employ solid-state methods, involving mechanical ball milling of sulfide precursors and dopants followed by high-temperature sintering. However, traditional solid-state methods for preparing doped sulfide solid electrolytes suffer from low doping uniformity, easy particle agglomeration, reduced ionic conductivity, limited improvement in air stability, and high energy consumption. Therefore, this invention provides a method for preparing selenium-doped sulfide solid electrolytes, wherein, as... Figure 1 As shown, it includes the following steps:

[0039] S1. Mix the selenium source, complexing agent and first organic solvent to obtain a first mixture;

[0040] S2. A lithium source, a non-metallic source, and a second non-polar organic solvent are mixed to obtain a second mixture; the non-metallic source includes a sulfur source.

[0041] S3. After heating the second mixture to a first preset temperature, add the first mixture and stir at the first preset temperature for a first preset time. Then, continue heating to a second preset temperature and stir at the second preset temperature for a second preset time to obtain a coprecipitate. Wherein, the boiling point of the first organic solvent is ≤ the first preset temperature < the boiling point of the second non-polar organic solvent is ≤ the second preset temperature.

[0042] S4. The coprecipitate is dried and then annealed at a temperature of 300-400°C to obtain the selenium-doped sulfide solid electrolyte.

[0043] In this embodiment of the invention, the low-boiling-point first organic solvent is evaporated by stirring at a first preset temperature (higher than or equal to the boiling point of the first organic solvent, but lower than the boiling point of the second non-polar organic solvent) for a first preset time. The rapid evaporation of the low-boiling-point first organic solvent drives the combination of the selenium source and the sulfide solid electrolyte particles, avoiding the mechanical mixing inhomogeneity problem of traditional solid-phase methods. The high-boiling-point second non-polar organic solvent maintains the liquid phase environment, achieving atomic-level uniform dispersion. Then, the mixture is stirred at a second preset temperature (higher than or equal to the boiling point of the second non-polar organic solvent) for a second preset time to evaporate a portion of the second non-polar organic solvent, resulting in a co-precipitate of the selenium source and the sulfide solid electrolyte. Next, drying and low-temperature annealing are performed to obtain the selenium-doped sulfide solid electrolyte. In this embodiment of the invention, low-temperature annealing (300–400°C) enhances the chemical bonding between selenium (Se) and the sulfide solid electrolyte lattice while retaining the high ionic conductivity of the sulfide solid electrolyte, improving air stability, reducing lattice defects, and lowering energy consumption. Compared to high-temperature annealing (500-600℃), low-temperature annealing can improve air stability, reduce lattice defects, and lower energy consumption. Furthermore, adding a complexing agent can inhibit selenium source aggregation in solution, ensuring controllable doping concentration, and optimize Se chemical bonding through the soft and hard acid-base theory, thereby improving air stability.

[0044] This invention employs a dual-solvent gradient evaporation technique combined with low-temperature annealing to achieve uniform selenium doping, thus preparing a selenium-doped sulfide solid electrolyte. This avoids the localized defects caused by uneven mixing in traditional solid-phase methods. The selenium-doped sulfide solid electrolyte exhibits higher ionic conductivity and air stability compared to undoped sulfide solid electrolytes.

[0045] Traditional solid-state methods for preparing doped sulfide solid electrolytes suffer from low doping uniformity, easy particle agglomeration, ionic conductivity loss exceeding 20%, limited improvement in air stability (thin passivation layer), and high energy consumption. In contrast, the preparation method provided by this invention improves selenium doping uniformity, prevents particle agglomeration (molecular-level dispersion), enhances ionic conductivity and air stability, and consumes less energy.

[0046] Specifically, during the Se doping process, on the one hand, Se doping into the lattice of the sulfide solid electrolyte causes lattice distortion, which lowers the lithium ion migration barrier and increases ionic conductivity. On the other hand, Se may also participate in the formation of the surface passivation layer, which isolates water and improves air stability (that is, the selenium-doped sulfide solid electrolyte prepared by this invention can be understood as having a core-shell structure, with the core material being a sulfide solid electrolyte doped with Se in the lattice and the shell being a passivation layer containing Se).

[0047] For example, in the preparation of Se-doped LPSCs, a dual-solvent gradient evaporation combined with low-temperature annealing achieves a uniform distribution of Se atoms in the LPSC lattice through molecular diffusion (Se substituting for P sites and / or S sites). Se doping optimizes lattice distortion by forming PSe33- or SSe22- groups (e.g., in Li6PS5Cl, after Se substituting for P, the lattice parameter change is <1.5%), reducing the lithium-ion migration barrier (ΔEa decreases from 0.6 eV to 0.3 eV), and increasing ionic conductivity to 12–15 mS / cm (at least 10% higher than undoped LPSCs). During Se doping, on the one hand, Se doping penetrates into the sulfide solid electrolyte, achieving a uniform distribution of Se atoms in the LPSC lattice (Se substituting for P sites and / or S sites). On the other hand, Se doping forms a SeO2 or Li2SeO3 passivation layer on the surface of the sulfide solid electrolyte, suppressing water decomposition reactions and improving air stability.

[0048] In step S1, in some embodiments, the selenium source, complexing agent and first organic solvent are mixed and stirred at a speed of 100-500 rpm for 15-60 min to obtain a first mixture.

[0049] In some embodiments, the selenium source includes at least one of lithium selenate and lithium selenide, but is not limited thereto.

[0050] In some embodiments, the molar amount of selenium in the selenium source is 5% to 20% of the molar amount of the sulfide solid electrolyte, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. Thus, compared to undoped sulfide solid electrolytes, ionic conductivity and air stability can be improved more effectively.

[0051] In some embodiments, the complexing agent includes at least one of citric acid and polyethylene glycol, but is not limited thereto. These complexing agents can inhibit the aggregation of selenium sources in solution, ensure controllable doping concentration, and optimize the chemical bonding of Se through the soft and hard acid-base theory, thereby improving air stability.

[0052] In some embodiments, the concentration of the complexing agent in the first mixture is 0.1–0.5 mol / L, and the concentration of the selenium source is 1–5 mol / L; for example, the concentration of the complexing agent can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L, etc. When the concentrations of the complexing agent and the selenium source are within the above ranges, the aggregation of the selenium source in the solution can be better suppressed, ensuring that the doping concentration is controllable.

[0053] In some embodiments, the first organic solvent includes at least one of acetone and tetrahydrofuran, but is not limited thereto. Acetone and tetrahydrofuran are low-boiling-point solvents, which, when combined with a high-boiling-point nonpolar solvent, i.e., a second nonpolar organic solvent, achieve dual-solvent gradient evaporation.

[0054] In step S2, in some embodiments, the lithium source, the non-metallic source and the second non-polar organic solvent are mixed and stirred at a speed of 120-200 rpm for 30-60 min to obtain the second mixture.

[0055] In some embodiments, the lithium source, the non-metallic source, and the second non-polar organic solvent are mixed according to the stoichiometric ratio of the sulfide solid electrolyte.

[0056] In some embodiments, the lithium source includes Li2S (Li2S can also be used as a sulfur source), but is not limited thereto.

[0057] In some embodiments, the non-metallic source further includes at least one of a phosphorus source and a chlorine source, but is not limited thereto. For example, the phosphorus source includes P2S5 (P2S5 can also be used as a sulfur source), and the chlorine source includes LiCl (which can also be used as a lithium source).

[0058] In some embodiments, the second nonpolar organic solvent includes at least one of n-hexane and cyclohexane, but is not limited thereto.

[0059] In some embodiments, the total concentration of the lithium source and non-metallic source in the second mixture is 0.5–2 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2 mol / L. Such concentrations facilitate the addition of the lithium source and non-metallic source, as well as subsequent stirring.

[0060] In step S3, in some embodiments, the first mixture is added dropwise at a rate of 1–5 mL / min, such as 1 mL / min, 2 mL / min, 3 mL / min, 4 mL / min, or 5 mL / min. Adding the first mixture dropwise ensures that the first and second mixtures come into full contact and mix evenly.

[0061] Specifically, the first mixture is added dropwise to the second mixture while stirring it.

[0062] In some embodiments, the mixture is stirred at a speed of 200–500 rpm (e.g., 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm) for 5–15 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes) at a first preset temperature. This achieves rapid evaporation of the first organic solvent.

[0063] In some embodiments, the mixture is stirred at a speed of 200–500 rpm (e.g., 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or 500 rpm) for 5–15 minutes (e.g., 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes) at a second preset temperature. This allows for partial evaporation of the second nonpolar organic solvent.

[0064] In step S4, in some embodiments, drying is carried out in an inert atmosphere or vacuum, the drying temperature is 100-150°C (e.g., 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C), and the drying time is 2-5 hours (e.g., 2 hours, 3 hours, 4 hours, or 5 hours).

[0065] In some embodiments, the annealing time is 1 to 2 hours (e.g., 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2 hours, etc.).

[0066] This invention also provides a selenium-doped sulfide solid electrolyte, wherein the selenium-doped sulfide solid electrolyte is prepared using the preparation method described above.

[0067] In some embodiments, the selenium-doped sulfide solid electrolyte includes Se-doped Li6PS5Cl or Se-doped Li 5.5 PS 4.5 Cl 1.5 .

[0068] The present invention will be further described below through specific embodiments.

[0069] Example 1

[0070] This embodiment provides a Se-doped LPSC (Li 5.5 PS 4.5 Cl1.5 Preparation method of ), such as Figure 2 As shown, it includes the following steps:

[0071] Li₂Se (lithium selenide), citric acid, and acetone were mixed and placed on a magnetic stirrer. The mixture was stirred at 200 rpm for 30 minutes to obtain the first mixture. The concentration of citric acid was 0.1 mol / L and the concentration of Li₂Se was 1 mol / L.

[0072] According to Li 5.5 PS 4.5 Cl 1.5 According to the stoichiometric ratio, Li₂S, P₂S₅, LiCl and cyclohexane were mixed and placed on a magnetic stirrer and stirred at 200 rpm for 60 min (i.e., completely dispersed) to obtain a second mixture; the total concentration of Li₂S, P₂S₅ and LiCl was 1 mol / L (i.e., the concentrations of Li₂S, P₂S₅ and LiCl were 0.5 mol / L, 0.125 mol / L and 0.375 mol / L, respectively).

[0073] The second mixture was heated to 60°C using an oil bath heating device. While stirring (at 300 rpm), the first mixture was slowly added dropwise (at a rate of 2 mL / min, the amount of the first mixture added being such that the molar percentage of Se in Li₂Se was equal to the molar percentage of Li). 5.5 PS 4.5 Cl 1.5 After adding 0.05 moles of acetone, continue stirring at 60°C (300 rpm to avoid local oversaturation) for 10 minutes (to evaporate acetone; 10 minutes ensures complete evaporation). Here, the rapid evaporation of acetone is used to induce Se to bind with LPSC particles, forming a homogeneous colloidal solution.

[0074] Continue heating the colloidal solution to 100℃ and stirring at 300 rpm for 5 min to partially evaporate the cyclohexane, forming a coprecipitate of LPSC and Li2Se.

[0075] The coprecipitate was transferred to an Ar atmosphere and dried at 150°C for 5 hours to completely remove any possible residual cyclohexane and acetone.

[0076] The obtained powder was placed in a box furnace and annealed at 400°C for 2 hours to obtain Se-doped LPSC, denoted as LPSC-Se0.05.

[0077] Example 2

[0078] This embodiment provides a Se-doped LPSC (Li 5.5 PS 4.5 Cl 1.5The preparation method of ) differs from that of Example 1 only in that:

[0079] The amount of the first mixture added should be such that the molar percentage of Se in Li₂Se is equal to that of Li. 5.5 PS 4.5 Cl 1.5 The product obtained by adding 0.1 moles of the product is denoted as LPSC-Se0.1.

[0080] Example 3

[0081] This embodiment provides a Se-doped LPSC (Li 5.5 PS 4.5 Cl 1.5 The preparation method of ) differs from that of Example 1 only in that:

[0082] The amount of the first mixture added should be such that the molar percentage of Se in Li₂Se is equal to that of Li. 5.5 PS 4.5 Cl 1.5 The product obtained by adding 0.15 moles of the product is denoted as LPSC-Se0.15.

[0083] Example 4

[0084] This embodiment provides a Se-doped LPSC (Li 5.5 PS 4.5 Cl 1.5 The preparation method of ) differs from that of Example 1 only in that:

[0085] The amount of the first mixture added should be such that the molar percentage of Se in Li₂Se is equal to that of Li. 5.5 PS 4.5 Cl 1.5 The product obtained by adding 0.2 moles of the product is denoted as LPSC-Se0.2.

[0086] Comparative Example 1

[0087] This embodiment provides an LPSC (Li 5.5 PS 4.5 Cl 1.5 The preparation method of ) differs from that of Example 1 only in that:

[0088] No Li2Se is added.

[0089] test:

[0090] 1. X-ray diffraction (XRD) test

[0091] The specific steps are as follows:

[0092] (1) Powder Sample Preparation

[0093] Grinding requirements: The sample is ground until the particle size is uniform (passes through a 200-mesh sieve, particle size ≤75μm) to obtain powder. The powder has no grainy feel when touched and has a texture similar to flour, in order to reduce preferred orientation and enhance the intensity of diffraction peaks.

[0094] Moisture-proof treatment: Sulfides are prone to moisture absorption and decomposition, so samples need to be ground and pressed in an inert gas (such as argon) glove box to avoid oxidation or structural damage.

[0095] Compressing method: The positive pressure method is used to fill the powder into the groove of the glass sample holder and compact it with a glass plate until the surface is flat and flush with the groove to ensure sample uniformity.

[0096] (2) Instrument setup and testing procedures

[0097] a. Instrument initialization

[0098] Circulating water system: Ensure water temperature is 17-20℃ and water pressure is 0.3-0.4MPa to prevent equipment from overheating or being damaged.

[0099] Software startup: Open the PC-based XRD control software (such as Rigaku Ultimate IV or DIFFRAC measurement system), initialize the goniometer, and confirm that the sample chamber door is closed.

[0100] b. Parameter settings

[0101] Scanning range: The standard wide-angle test range is 5° to 90°, with a step size of 0.02° and a scanning speed of 5° / min (adjusted according to the crystallinity of the sample).

[0102] Slit width: entrance slit is 0.2-0.6 mm, detector slit is 3-8 mm, optimizing resolution and signal-to-noise ratio.

[0103] X-ray conditions: Copper target Kα rays The voltage is 40kV and the current is 30mA to ensure clear diffraction peaks.

[0104] c. Sample loading and testing

[0105] Sample loading procedure: Gently open the sample chamber door, insert the sample holder into the slot, ensuring the sample surface is facing up and centered, gently close the door and confirm that the closing indicator light is on.

[0106] Start the test: Click "Start" to start the scan. Wait for the software to indicate completion and save the data (e.g., RAW or TXT format).

[0107] result Figure 3 As shown, the main crystal phase of LPSC is Li7PS6, with a steric argillaceous structure, and the phase is PDF#34-0688. Additionally, as... Figure 3As shown, doping with different proportions of Se does not affect the phase peak value of LPSC.

[0108] 2. Ionic conductivity test

[0109] The specific steps are as follows:

[0110] (1) Sample preparation

[0111] The powder is cold-pressed into sheets under a pressure of 360–500 MPa, with a thickness of approximately 0.1–1 mm and a diameter of 10–14 mm.

[0112] (2) Electrochemical impedance spectroscopy (EIS)

[0113] The sample is held in place using a blocking electrode (such as stainless steel or sputtered metal film), and an AC voltage (amplitude of 10mV, frequency range of 1MHz to 0.1Hz) is applied.

[0114] The bulk resistance R is obtained by fitting the semicircular intercept in the high-frequency region using EIS. bulk The low-frequency region reflects the interfacial resistance and the double-layer effect.

[0115] (3) Geometric parameter measurement

[0116] Thickness (L): The thickness of the compressed tablet is measured directly using a micrometer;

[0117] Area (A): Calculated based on the electrode diameter;

[0118] According to the formula Calculate the ionic conductivity σ of the corresponding material.

[0119] The ionic conductivity of the samples from Examples 1 to 4 and Comparative Example 1 was tested after being placed in air for 0 h, 2 h, 4 h, 8 h and 24 h, respectively. The results are shown in Table 1.

[0120] Table 1. Results of Ion Conductivity Test

[0121]

[0122] Among them, the ionic conductivity when placed in air for 0 hours is the ionic conductivity test performed directly on the prepared sample.

[0123] It can be seen that Se doping significantly improves the ionic conductivity and air stability of LPSCs compared to undoped LPSCs. Specifically, the ionic conductivity of Se-doped LPSCs ranges from 9.125 to 12.096 mS / cm, an increase of 21.5% to 32.6% compared to undoped LPSCs. After being exposed to air for 24 hours, Se-doped LPSCs retain approximately 40% of their conductivity, while undoped LPSCs retain only 23.1% of their conductivity. This demonstrates that Se doping significantly improves the air stability of LPSCs.

[0124] In summary, this invention provides a selenium-doped sulfide solid electrolyte and its preparation method. This invention employs a dual-solvent gradient evaporation technique combined with low-temperature annealing to achieve uniform doping of selenium, thereby preparing a selenium-doped sulfide solid electrolyte. Compared with undoped sulfide solid electrolytes, the selenium-doped sulfide solid electrolyte exhibits higher ionic conductivity and air stability.

[0125] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a selenium-doped sulfide solid electrolyte, characterized in that, Includes the following steps: The selenium source, complexing agent, and first organic solvent are mixed to obtain a first mixture. A lithium source, a non-metallic source, and a second non-polar organic solvent are mixed to obtain a second mixture; the non-metallic source includes a sulfur source. After heating the second mixture to a first preset temperature, the first mixture is added and stirred at the first preset temperature for a first preset time. Then, the temperature is raised to a second preset temperature and stirred at the second preset temperature for a second preset time to obtain a coprecipitate. The coprecipitate was dried and then annealed at 300–400°C to obtain the selenium-doped sulfide solid electrolyte. Wherein, the boiling point of the first organic solvent is less than or equal to the first preset temperature, and the boiling point of the second non-polar organic solvent is less than or equal to the second preset temperature. The complexing agent includes at least one of citric acid and polyethylene glycol; The selenium-doped sulfide solid electrolyte has a core-shell structure, with the core material being a sulfide solid electrolyte doped with Se in the crystal lattice, and the shell being a passivation layer containing Se. The first organic solvent includes at least one of acetone and tetrahydrofuran; The second nonpolar organic solvent includes at least one of n-hexane and cyclohexane.

2. The preparation method according to claim 1, characterized in that, The selenium source includes at least one of lithium selenate and lithium selenide. The number of moles of selenium in the selenium source is 5% to 20% of the number of moles of the sulfide solid electrolyte.

3. The preparation method according to claim 1, characterized in that, In the first mixture, the concentration of the complexing agent is 0.1–0.5 mol / L, and the concentration of the selenium source is 1–5 mol / L.

4. The preparation method according to claim 1, characterized in that, The lithium source includes Li₂S; and / or, The non-metallic source also includes at least one of a phosphorus source and a chlorine source.

5. The preparation method according to claim 1, characterized in that, In the second mixture, the total concentration of the lithium source and the non-metallic source is 0.5–2 mol / L.

6. The preparation method according to claim 1, characterized in that, The first mixture is added by dripping at a rate of 1–5 mL / min.

7. The preparation method according to claim 1, characterized in that, Stir at a speed of 200–500 rpm for 5–15 min at the first preset temperature; and / or, Stir at 200–500 rpm for 5–15 minutes at the second preset temperature.

8. The preparation method according to claim 1, characterized in that, Drying is carried out in an inert atmosphere or vacuum, at a temperature of 100–150°C, for a time of 2–5 hours; and / or, The annealing time is 1 to 2 hours.

9. A selenium-doped sulfide solid electrolyte, characterized in that, The selenium-doped sulfide solid electrolyte is prepared using the preparation method described in any one of claims 1-8.

10. The selenium-doped sulfide solid electrolyte according to claim 9, characterized in that, The selenium-doped sulfide solid electrolyte includes Se-doped Li6PS5Cl or Se-doped Li 5.5 PS 4.5 Cl 1.5 .

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