A co-doped sodium-based sulfide solid-state electrolyte, a preparation method and application thereof

Abstract

The application relates to the technical field of solid electrolytes, in particular to a co-doped sodium-based sulfide solid electrolyte and a preparation method and application thereof, wherein a Na2S-NaD nanoeutectic precursor is prepared by pre-high-energy ball milling of a sodium source and sodium halide, then the precursor is mixed with the remaining raw materials and sintered at a low temperature of 300-450 DEG C, so that the product forms a nanocrystal-glass composite structure which cannot be obtained by a traditional high-temperature solid-phase method. The unique structure can eliminate the inherent grain boundary impedance of the crystalline material, provide isotropic and continuous three-dimensional transmission channels for sodium ions, significantly reduce the diffusion barrier, and realize ultra-high ionic conductivity far exceeding that of the same-component crystalline material. Meanwhile, the application realizes multi-element synergistic doping by adopting the main group elements M of IV / V to partially replace the position of phosphorus elements and co-substitute the cations with fixed tungsten element doping, so that the lattice can be stabilized, stress can be released, the sodium ion diffusion barrier can be reduced, and the synergistic improvement of high air stability, high structural stability and high ionic conductivity can be realized.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and in particular to a co-doped sodium-based sulfide solid electrolyte, its preparation method, and its application. Background Technology

[0002] Currently, the main methods for modifying sodium-based sulfide solid electrolytes include solution phase surface modification, physical vapor deposition coating, single-element bulk doping, and traditional high-temperature solid-phase synthesis, but all of them have obvious technical defects.

[0003] Solution-phase surface modification mainly involves immersing Na3PS4 in fluorine- or oxygen-containing solutions for coating. This process easily leads to solvent residue, particle agglomeration, uneven coating, and disruption of sodium ion conduction channels, resulting in a significant decrease in conductivity. Furthermore, organic solvents present environmental and cost issues. Physical vapor deposition (PVD) coating, on the other hand, prepares inorganic protective layers through sputtering and evaporation. This requires high-vacuum equipment, is costly, and inefficient. The coating layer is physically bonded to the substrate, making it prone to peeling and cracking, and its thickness is difficult to control precisely. Additionally, single-element bulk doping introduces only a single cation or anion, offering limited lattice manipulation and insufficient stability improvement. It easily disrupts crystal symmetry, leading to decreased ion conduction efficiency, and the doping amount is difficult to control, easily generating impurity phases. Traditional high-temperature solid-state synthesis involves directly mixing raw materials and sintering at high temperatures. This results in incomplete reactions, low product purity, easy volatilization of sulfur, deviations in stoichiometry, numerous lattice defects, and an inability to achieve precise co-doping of cations and anions.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a co-doped sodium-based sulfide solid electrolyte and its preparation method and application, aiming to solve the problems of poor air stability, easy hydrolysis and H2S release, easy structural phase transition, and low intrinsic ionic conductivity of sodium-based sulfide solid electrolyte Na3PS4 prepared by existing methods.

[0006] The technical solution of the present invention is as follows: A method for preparing a co-doped sodium-based sulfide solid electrolyte, comprising the following steps: Na2S and sodium halide are mixed to obtain the first mixed powder; The first mixed powder was subjected to inert atmosphere ball milling to obtain a pre-synthesized nano-eutectic precursor; At least one of the Group IVA and Group VA elements, a sodium source, a phosphorus source, a tungsten source, and a sulfur source are mixed with the pre-synthesized nano-eutectic precursor to obtain a second mixed powder. The second mixed powder is subjected to low-temperature sintering to obtain a sintered block; The sintered block was ground and sieved to obtain a co-doped sodium-based sulfide solid electrolyte, Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y ; Wherein, M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium; the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h.

[0007] The method for preparing the co-doped sodium-based sulfide solid electrolyte comprises: the sodium source being selected from one or more of Na2S, NaH, and Na2S2; the phosphorus source being selected from one or more of P2S5, Na3P, and Na3PS3; the tungsten source being selected from one or more of tungsten powder, WS2, WCl6, WO3, and W(CO)6; the sodium halide being selected from one or more of sodium fluoride, sodium chloride, sodium bromide, and sodium iodide; the Group IVA element source being selected from one of SnS and GeS2; and the Group VA element source being selected from one of Sb2S3, As2S3, and Bi2S3.

[0008] The method for preparing the co-doped sodium-based sulfide solid electrolyte includes an inert atmosphere ball milling process performed in a frequency conversion mode; the rotation speed of the inert atmosphere ball milling process is 400 rpm-600 rpm, and the total time of the inert atmosphere ball milling process is 6 h-12 h.

[0009] The method for preparing the co-doped sodium-based sulfide solid electrolyte, wherein the frequency conversion mode is performed in a cyclical manner, first rotating forward for 8-12 minutes, pausing for 4-6 minutes, then rotating in reverse for 8-12 minutes, pausing for 4-6 minutes.

[0010] The method for preparing the co-doped sodium-based sulfide solid electrolyte, wherein the sieving process uses a 200-300 mesh nylon sieve.

[0011] A co-doped sodium-based sulfide solid electrolyte is prepared using the same preparation method as described above; the structural formula of the co-doped sodium-based sulfide solid electrolyte is Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y Where M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium.

[0012] The co-doped sodium-based sulfide solid electrolyte, wherein the Group IVA element is selected from Sn and Ge; the Group VA element is selected from Sb, As, and Bi; and the halogen element is selected from one or more of F, Cl, Br, and I.

[0013] The co-doped sodium-based sulfide solid electrolyte, wherein the co-doped sodium-based sulfide solid electrolyte is selected from Na... 2.28 Sn 0.2 P 0.68 W 0.12 S 3.2 Br 0.8 Na 3.18 Sn 0.8 P 0.08 W 0.12 S 3.5 Br 0.5 Na 2.08 Sb 0.5 P 0.38 W 0.12 S 3.2 Cl 0.8 One of them.

[0014] Application of a co-doped sodium-based sulfide solid electrolyte in all-solid-state sodium-ion batteries.

[0015] Beneficial Effects: This invention provides a co-doped sodium-based sulfide solid electrolyte, its preparation method, and its application. The preparation method of the co-doped sodium-based sulfide solid electrolyte includes the following steps: mixing Na₂S with sodium halide to obtain a first mixed powder; subjecting the first mixed powder to inert atmosphere ball milling to obtain a pre-synthesized nano-eutectic precursor; mixing at least one of a Group IVA element source and a Group VA element source, a sodium source, a phosphorus source, a tungsten source, and a sulfur source with the pre-synthesized nano-eutectic precursor to obtain a second mixed powder; subjecting the second mixed powder to low-temperature sintering to obtain a sintered block; and grinding and sieving the sintered block to obtain the co-doped sodium-based sulfide solid electrolyte Na. 3+δ M 0.88-x P x W 0.12 S 4-y D yWherein, M is a Group IVA element and / or a Group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium; the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h. The co-doped sodium-based sulfide solid electrolyte prepared by the present invention using high-energy ball milling and low-temperature sintering processes possesses a nanocrystalline-glass composite structure, transforming the microstructure of the product from the "crystalline state" of traditional methods to a "nanocrystalline-glass composite structure." This structural change brings about a significant leap in ionic conductivity and air stability, solving the inherent problems of high grain boundary impedance, anisotropic transport, and interfacial chemical instability that have long existed in crystalline materials. Abandoning the traditional approach of directly mixing raw materials such as Na2S, P2S5, and NaCl in a single step, this invention first involves high-energy ball milling of Na2S (sodium and sulfur sources) and NaD (halogen sources, D = F, Cl, Br, I) in a specific ratio. Na2S has an antifluorite structure, while NaD has a rock salt structure; their crystal lattice types are different. Under the mechanochemical action of prolonged high-energy ball milling, ion exchange, diffusion, and structural disorder occur at the interface between the two crystals. 2- and D - Two anions were uniformly mixed and pre-organized at the nanoscale to form a highly active, partially disordered anionic sublattice Na₂S-NaD nano-eutectic precursor. The anions in the nano-eutectic precursor achieved atomic-level homogeneous mixing and were in a high-energy metastable state. This allows the target product to rapidly form at low temperatures, eliminating the need for the slow solid-phase diffusion process driven by high-temperature long-range atomic migration found in traditional methods. Furthermore, the resulting solid electrolyte exhibits a room-temperature ionic conductivity ≥30 × 10⁻⁶. -3 With a conductivity of S / cm, a conductivity retention rate of ≥50% after 24 hours of air exposure, no significant H2S release, and an electrochemical window of ≥3.3V, it can be widely used in sodium metal all-solid-state batteries, composite cathodes, solid electrolyte membranes, etc. The process is green, low-cost, and suitable for industrial production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process flow for preparing a co-doped sodium-based sulfide solid electrolyte according to the present invention. Figure 2 This is a scanning electron microscope image of the sulfide solid electrolyte of Example 1; Figure 3 The image shows a scanning electron microscope (SEM) image of the sulfide solid electrolyte of Comparative Example 3. Figure 4 The images show the XRD patterns of the sulfide solid electrolytes of Example 1 and Comparative Example 3. Detailed Implementation

[0017] This invention provides a co-doped sodium-based sulfide solid electrolyte, its preparation method, and its applications. 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 merely illustrative and not intended to limit the invention.

[0018] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0019] Against the backdrop of global energy structure transformation and rapid growth in demand for large-scale energy storage, sodium-ion batteries have become a core alternative technology for low-speed electric vehicles, grid energy storage, and base station power supplies due to their advantages such as abundant sodium resources, low cost, environmental friendliness, and high compatibility of production processes with lithium-ion batteries. Traditional sodium-ion batteries use liquid organic electrolytes, which pose safety hazards such as leakage, gas evolution, combustion, and thermal runaway, making it difficult to meet the application requirements of high safety, long cycle life, and wide temperature range.

[0020] All-solid-state sodium-ion batteries replace liquid electrolytes with solid electrolytes, fundamentally eliminating the risks of electrolyte leakage and thermal runaway. They can also be matched with sodium metal anodes, significantly improving battery energy density and cycle stability, making them a core development direction for next-generation high-safety sodium-ion batteries. Among solid-state electrolyte systems, sulfide solid electrolytes have become the system with the greatest industrialization potential due to their high room-temperature ionic conductivity, good mechanical ductility, low interfacial impedance, and ease of large-scale preparation. Na3PS4 is a typical sodium-based sulfide electrolyte with an open crystal structure, continuous sodium ion conduction pathways, and an intrinsic ionic conductivity of 10⁻⁶. -4 ~10 -3 S / cm, basically possessing sodium ion conduction.

[0021] However, Na3PS4 has three major flaws that severely limit its industrial application: 1) Extremely poor air stability: It easily undergoes hydrolysis reactions with H2O and O2 in the air to generate insulating products such as Na2S, Na3PO4, and Na2CO3, while releasing toxic H2S gas and causing a sharp decrease in ionic conductivity. 2) Insufficient structural stability: Lattice phase transitions are prone to occur during high temperature or electrochemical cycling, leading to the interruption of sodium ion conduction channels and a significant increase in grain boundary impedance; 3) Low intrinsic ionic conductivity: The pure phase has a compact cubic crystal structure with fixed and narrow primary lattice channels. There are no additional lattice defects or ion vacancies to provide transport sites, so diffusion can only occur through the bulk lattice. This results in a high diffusion barrier and low migration efficiency, with a room-temperature ionic conductivity of only 10. -4 ~10 -3 The S / cm level cannot meet the application requirements of all-solid-state sodium batteries for high ionic conductivity, which is its most critical performance shortcoming.

[0022] Therefore, developing a method for modifying sodium-based sulfide solid electrolytes to improve ionic conductivity and simultaneously enhance air stability and structural stability without reducing the intrinsic electrochemical window has become a research hotspot and a core technological bottleneck in the field of all-solid-state sodium-ion batteries.

[0023] Based on this, the present invention provides a method for preparing a co-doped sodium-based sulfide solid electrolyte, comprising the following steps: Step S10: Mix Na2S with sodium halide to obtain the first mixed powder; Step S20: The first mixed powder is subjected to inert atmosphere ball milling to obtain a pre-synthesized nano-eutectic precursor; Step S30: Mix at least one of the Group IVA element source and the Group VA element source, sodium source, phosphorus source, tungsten source, and sulfur source with the pre-synthesized nano-eutectic precursor to obtain a second mixed powder; Step S40: The second mixed powder is subjected to low-temperature sintering treatment to obtain a sintered block; Step S50: Grind and sieve the sintered block to obtain a co-doped sodium-based sulfide solid electrolyte Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y ; Wherein, M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium; the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h.

[0024] In this embodiment, the co-doped sodium-based sulfide solid electrolyte prepared by high-energy ball milling and low-temperature sintering has a nanocrystalline-glass composite structure, transforming the microstructure of the product from the "crystalline state" of traditional methods to a "nanocrystalline-glass composite structure." This structural change brings about a significant leap in ionic conductivity and air stability, solving the inherent problems of high grain boundary impedance, anisotropic transport, and interfacial chemical instability that have long existed in crystalline materials. Abandoning the traditional approach of directly mixing raw materials such as Na2S, P2S5, and NaCl in one step, this invention first performs high-energy ball milling on Na2S (sodium and sulfur sources) and NaD (halogen source, D=F, Cl, Br, I) in a certain proportion. Na2S has an antifluorite structure, while NaD has a rock salt structure; the two have different crystal lattice types. Under the mechanochemical action of long-term high-energy ball milling, ion exchange, diffusion, and structural disorder occur at the interface between the two crystals. 2- and D - Two anions are uniformly mixed and pre-organized at the nanoscale to form a highly active, partially disordered anionic sublattice Na₂S-NaD nano-eutectic precursor. The anions in the nano-eutectic precursor are atomically homogeneously mixed and in a high-energy metastable state. This allows the target product to rapidly form at low temperatures, eliminating the need for the slow solid-phase diffusion process driven by high-temperature long-range atomic migration found in traditional methods. Finally, a co-doped sodium-based sulfide solid electrolyte with a nanocrystalline-glass composite structure is obtained through low-temperature sintering. The solid electrolyte prepared using this process exhibits a room-temperature ionic conductivity ≥30 × 10⁻⁶. -3 With a conductivity of S / cm, a conductivity retention rate of ≥50% after 24 hours of air exposure, no significant H2S release, and an electrochemical window of ≥3.3V, it can be widely used in sodium metal all-solid-state batteries, composite cathodes, solid electrolyte membranes, etc. The process is green, low-cost, and suitable for industrial production.

[0025] Specifically, this invention uses at least one of Group IVA and Group VA elements, along with sodium, phosphorus, tungsten, and sulfur sources as basic raw materials. First, Na₂S is mixed with sodium halide and then ball-milled under an inert atmosphere to form a nano-eutectic precursor. This precursor is then mixed with the remaining raw materials and subjected to low-temperature sintering. This invention synthesizes the target electrolyte through dry ball milling under an inert atmosphere combined with low-temperature sintering, offering advantages such as low energy consumption, high controllability, and suitability for large-scale mass production. Furthermore, the entire preparation process is completed within an argon-filled glove box, isolating water and oxygen throughout the process from raw material weighing and ball milling to sintering and post-treatment. This prevents surface hydrolysis and oxidation reactions of the sulfide electrolyte from the source, ensuring high purity and intrinsic ionic conductivity of the powder. Simultaneously, the low-temperature sintering process effectively suppresses sulfur volatilization, ensuring accurate stoichiometry and solving the problems of sulfur volatilization and impurity phase formation in traditional high-temperature solid-state methods.

[0026] In some embodiments, the sodium source is selected from one or more of Na₂S, NaH, and Na₂S₂; the phosphorus source is selected from one or more of P₂S₅, Na₃P, and Na₃PS₃; the tungsten source is selected from one or more of tungsten powder (W), WS₂ (tungsten disulfide), WCl₆, WO₃ (tungsten trioxide), and W(CO)₆; the sodium halide is selected from one or more of sodium fluoride (NaF), sodium chloride (NaCl), sodium bromide (NaBr), and sodium iodide (NaI); the Group IVA element source is selected from one of SnS (stannous sulfide) and GeS₂ (germanium sulfide); and the Group VA element source is selected from one of Sb₂S₃ (antimony trisulfide), As₂S₃ (arsenic trisulfide), and Bi₂S₃ (bismuth trisulfide). All Group IVA element sources, Group VA element sources, sodium sources, phosphorus sources, tungsten sources, and halogen sources are anhydrous, with a purity ≥99.9% and a water content ≤10 ppm. All of the aforementioned sulfur-containing substances can be used as sulfur sources to balance chemical structural formulas.

[0027] In some embodiments, in step S10, in an argon glove box with a water content ≤0.1ppm and an oxygen content ≤0.1ppm, the gas is added according to the target chemical formula Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y The stoichiometric ratio of Na2S and sodium halide was accurately weighed and ball-milled under an inert atmosphere to obtain a pre-synthesized nano-eutectic precursor. Then, at least one of the Group IVA and Group VA element sources, along with sodium, phosphorus, tungsten, and sulfur powders, were placed in an agate mortar and manually ground for 20-40 minutes to ensure that the components were mixed without significant color difference or agglomeration. Through thorough premixing under an inert atmosphere, the macroscopic uniform distribution of each raw material component was achieved, avoiding local component segregation and providing a uniform basis for the subsequent low-temperature sintering solid-phase reaction. The process was completely isolated from water and oxygen, which can inhibit the hydrolysis of raw materials and the generation of by-products from the source.

[0028] In some embodiments, the inert atmosphere ball milling process is carried out in a variable frequency mode; the rotation speed of the inert atmosphere ball milling process is 400 rpm-600 rpm, and the total time of the inert atmosphere ball milling process is 6 h-12 h.

[0029] In a preferred embodiment, the rotation speed of the inert atmosphere ball milling treatment is 400 rpm, and the total time of the inert atmosphere ball milling treatment is 7 hours.

[0030] In some embodiments, during the inert atmosphere ball milling process, the mass ratio of zirconia balls to the primary mixed powder is 5:1-10:1; preferably, the mass ratio of zirconia balls to the primary mixed powder is 8:1, which can balance mixing uniformity and lattice integrity.

[0031] In some implementations, the frequency conversion mode is performed in a cyclical manner, first rotating forward for 8-12 minutes, pausing for 4-6 minutes, then rotating in reverse for 8-12 minutes, pausing for 4-6 minutes.

[0032] In some embodiments, step S20 specifically includes: loading the primary mixed powder into a vacuum-sealed zirconia ball mill jar, adding zirconia balls at a ball-to-powder ratio of 8:1 (zirconia balls to primary mixed powder by mass); then vacuum-sealing the mill jar and loading it into a planetary ball mill, using a variable frequency mode: forward rotation for 10 minutes → pause for 5 minutes → reverse rotation for 10 minutes → pause for 5 minutes, repeating this cycle; the milling speed is 400 rpm, and the total milling time is 7 hours; the jar temperature is controlled below 60°C throughout the process to avoid overheating and decomposition of the raw materials and sulfur volatilization. After milling, the mill jar is moved into a glove box, the lid is opened to collect the powder, and it is passed through a 100-mesh nylon sieve to obtain a highly active and highly uniform precursor powder.

[0033] Specifically, high-energy dry ball milling achieves the miniaturization of raw material particles and atomic-level uniform mixing of multiple components, significantly improving solid-phase reaction kinetics; furthermore, the pulse frequency conversion mode does not introduce solvents and impurities, ensuring the crystal phase purity and ion conduction performance of the subsequent synthesized products.

[0034] In some embodiments, the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h; low-temperature sintering can effectively suppress the volatilization of sulfur and ensure accurate stoichiometry; the moderate lattice distortion brought about by tungsten doping can significantly reduce the sodium ion migration barrier, achieving a synergistic effect of high ionic conductivity and high structural stability.

[0035] In a preferred embodiment, the temperature of the low-temperature sintering treatment is 400°C, and the time of the low-temperature sintering treatment is 3 hours.

[0036] In some embodiments, step S40 specifically includes: loading the second mixed powder into a high-purity corundum crucible, gently compacting and leveling it, and transferring it into the constant temperature zone of an inert atmosphere tube furnace; then performing vacuum-argon purging of the furnace cavity 3-5 times to ensure that the water and oxygen content in the furnace is <1ppm; followed by low-temperature sintering treatment: heating to 300℃-450℃ at 2℃ / min-3℃ / min, holding at that temperature for 1h-4h to allow the raw materials to react completely and generate the target product, using W 6+ With P 5+The difference in valence states induces controllable lattice deformation, which broadens the sodium ion transport channels and improves ionic conductivity; preferably, the heating rate is 2℃ / min.

[0037] In some embodiments, the sieving process uses a 200-300 mesh nylon sieve. The nylon sieve removes large particle agglomerates, resulting in a uniformly sized nanocrystalline-glass composite co-doped sodium-based sulfide solid electrolyte.

[0038] In a preferred embodiment, the sieving process uses a 200-mesh nylon sieve.

[0039] In some embodiments, step S40 is carried out entirely in anhydrous and oxygen-free conditions to prevent the product from coming into contact with air and undergoing hydrolysis; gentle masking and sieving can ensure that the product has uniform particle size and good flowability, and can be directly used for solid-state battery assembly. The ionic conductivity and air stability meet the requirements of high-performance all-solid-state sodium batteries.

[0040] In some embodiments, the co-doped sodium-based sulfide solid electrolyte prepared by the above method is a cubic spinel type with a room temperature ionic conductivity ≥30×10⁻⁶. -3 S / cm; After exposure to an environment with a dew point of -35℃ for 24 hours, the ionic conductivity retention rate is ≥50%, there is no obvious H2S gas release, and the cubic crystal structure shows no significant change.

[0041] In some embodiments, the above preparation method can be applied to other sodium-based sulfide solid electrolyte systems, such as Na3SbS4, Na3SnPS4, Na3GePS4, etc. In terms of process, only the stoichiometric ratio of raw materials needs to be adjusted according to the target system, the tungsten doping amount is fixed at 0.12, and the ball milling and sintering process parameters remain unchanged; a complete cubic crystal structure can be obtained, the ionic conductivity retention rate is ≥60%, and the air stability is significantly improved.

[0042] In some embodiments, the inert atmosphere ball milling treatment can be tailored to different production scale requirements, selecting appropriate ball milling equipment, including planetary ball mills, horizontal stirred ball mills, and continuous ball mills. Planetary ball mills have a grinding jar volume of 50-100 mL, suitable for small-batch preparation during the research and development stage. Horizontal stirred ball mills or continuous ball mills can achieve continuous feeding and discharging, increasing production capacity by more than 10 times, suitable for ton-scale mass production. All of these methods can achieve atomic-level uniform mixing of raw materials, ensuring uniform distribution of dopant elements, complete crystal structure of the product, and good performance consistency.

[0043] In some embodiments, the low-temperature sintering treatment can be carried out in a tube furnace, or it can be performed using rapid sintering processes such as microwave sintering, spark plasma sintering (SPS), and hot pressing sintering. Depending on the specific sintering process, the sintering time can be shortened, the sintering temperature lowered, and the crystallization rate and product density increased. All of the above sintering conditions can effectively suppress sulfur volatilization, ensure accurate stoichiometry, and guarantee that the product's ionic conductivity and structural stability meet requirements, making it suitable for high-efficiency mass production.

[0044] In addition, the present invention also provides a co-doped sodium-based sulfide solid electrolyte, which is prepared using the same method as the co-doped sodium-based sulfide solid electrolyte; the structural formula of the co-doped sodium-based sulfide solid electrolyte is Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y Where M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium.

[0045] In this embodiment, the present invention prepares a Na₂S-NaD nano-eutectic precursor by pre-milling a sodium source with sodium halide using high-energy ball milling. Simultaneously, it employs a strategy of partially substituting phosphorus sites with group IV / V main elements (M) and co-substituting with tungsten-doped cations to construct the general formula Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y This achieves the following technical effects: 1) Enhancing ion conduction based on valence state modulation and lattice distortion mechanisms: W 6+ With P 5+ Significant differences in valence states can induce moderate and controllable lattice deformation in the Na3PS4 lattice, broadening the three-dimensional transport channels of sodium ions, reducing the migration barrier, and significantly improving the room temperature ionic conductivity.

[0046] 2) Structural design based on the hard and soft acid-base theory (HSAB): partial substitution of P by introducing Group IVA elements and / or Group VA elements (medium-strong acids). 5+ (Hard acid), reducing the system's resistance to hard base O 2- Its affinity inhibits hydrolysis; and, through the partial substitution of S by the halide anion (hard base) 2- (Soft alkali) reduces the system's dependence on H + The affinity of the element inhibits H2S formation at its source. Simultaneously, multi-element synergistic doping stabilizes the crystal lattice, releases stress, and lowers the sodium ion diffusion barrier, achieving a synergistic improvement in high air stability, high structural stability, and high ionic conductivity.

[0047] 3) Eliminating grain boundary resistance and improving ionic conductivity: In the nanocrystalline-glass composite structure, the material is a thermodynamically disordered long-range and ordered short-range "frozen liquid." This structure eliminates grains and grain boundaries in traditional materials, providing a continuous, uniform, and grain boundary-free three-dimensional transport network for sodium ions. The ion conduction path is isotropic and not limited by grain orientation, allowing the macroscopic ionic conductivity to approach or even exceed the intrinsic values ​​of crystalline materials, achieving an order-of-magnitude improvement.

[0048] Specifically, the performance improvement of the co-doped sodium-based sulfide solid electrolyte provided by this invention comes from the synergistic effect of lattice channel modulation, valence state-induced distortion, and soft / hard acid / base optimization, specifically including: 1) Tungsten doping: Lattice deformation is achieved by utilizing valence state differences, thereby widening ion channels and improving ion conductivity.

[0049] In the target product, P has a +5 valence, while W has a +6 valence, showing a significant difference in valence state; W 6+ Occupying a P site will cause local charge imbalance, rearrangement of bond lengths and bond angles, and moderate and controllable micro-deformation of the lattice.

[0050] This non-destructive, low-distortion lattice manipulation can achieve the following: widening of sodium ion transport channels and increasing ion migration space; lowering the sodium ion diffusion barrier and increasing migration rate; forming more defect conduction paths and increasing carrier concentration and mobility; suppressing lattice phase transitions and maintaining structural stability during high temperature and cycling; and, by fixing the tungsten doping amount to 0.12, the distortion level is optimized, which significantly improves ionic conductivity without destroying the integrity of the crystal framework.

[0051] 2) Co-doping with Group IVA elements and / or Group VA elements M: Synergistically regulates the lattice and enhances air stability.

[0052] By utilizing group IV / V main elements and W to jointly regulate the lattice, the channel size and stress distribution are further optimized; based on the hard-soft acid-base theory (HSAB), a portion of the hard acid P is replaced with a moderately strong acid cation. 5+ Reduce the material's susceptibility to O2 in the air 2- It has affinity and inhibits hydrolysis.

[0053] 3) Nanocrystalline-glass composite structure: low grain boundaries, improving ionic conductivity.

[0054] Na₂S and sodium halides have different lattice types (antifluorite structure vs. rock salt structure). High-energy ball milling can cause ion exchange and structural disorder at the interface between the two, forming a highly active non-equilibrium precursor. This precursor can be used as a "seed" or "skeleton template" in subsequent low-temperature sintering to guide the target product to precipitate in the form of nanocrystals, rather than growing into a complete crystal.

[0055] In some embodiments, the Group IVA element is selected from Sn and Ge; the Group VA element is selected from Sb, As, and Bi; and the halogen element is selected from one or more of F, Cl, Br, and I. A synergistic co-doping system is achieved using Group I / V elements + tungsten + halogen cations and anions, with Group I / V elements partially replacing P sites, combined with W... 6+ A ternary synergistic regulatory strategy involving cation doping and partial substitution of S sites by halogen anions; simultaneously, combining the hard and soft acid-base theory (HSAB) to replace hard acid P with moderately strong acid cations. 5+ Hard base halogen substitutes soft base S 2- It inhibits hydrolysis and H2S release at the source, and simultaneously achieves a synergistic improvement in three properties: high ionic conductivity, high air stability, and high structural stability.

[0056] Furthermore, this invention also utilizes precise tungsten doping lattice manipulation based on valence state differences, and designs W based on the lattice structure and ion conduction characteristics of the Na3PS4 matrix. 6+ A precise ratio with a fixed doping amount of 0.12 was achieved using W. 6+ With P 5+ The difference in valence states induces moderate and controllable micro-deformation in the crystal lattice. Without destroying the integrity of the main cubic crystal system structure, it effectively broadens the three-dimensional transport channels of sodium ions and reduces the ion diffusion barrier. This fundamentally solves the contradiction of "difficulty in balancing conductivity improvement and structural stability" in traditional single doping, and achieves a significant improvement in ionic conductivity.

[0057] In some implementations, a complex doping system is adopted, consisting of mixed Group IV / V main elements (such as Sb+Sn, Sn+Ge) and mixed halogens (such as Cl+Br, Br+I). The ratio of the complex elements can be adjusted according to performance requirements. The complexation of multiple elements can achieve more precise lattice stress control and acid-base characteristic optimization, further improving the air stability and ionic conductivity of the electrolyte, adapting to the performance requirements of different application scenarios, with no significant change in the cubic crystal structure, and the ionic conductivity retention rate is ≥60%.

[0058] In some embodiments, the co-doped sodium-based sulfide solid electrolyte is selected from Na. 2.28 Sn 0.2 P 0.68 W 0.12 S 3.2 Br0.8 Na 3.18 Sn 0.8 P 0.08 W 0.12 S 3.5 Br 0.5 Na 2.08 Sb 0.5 P 0.38 W 0.12 S 3.2 Cl 0.8 One of them.

[0059] In addition, the present invention also provides an application of a co-doped sodium-based sulfide solid electrolyte in an all-solid-state sodium-ion battery.

[0060] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0061] Example 1 This embodiment synthesizes a nanocrystalline-glass composite structure of co-doped sodium-based sulfide solid electrolyte Na. 2.38 Sb 0.2 P 0.68 W 0.12 S 3.5 Cl 0.5 The specific steps are as follows: Step 1: In an argon inert atmosphere glove box, accurately weigh Na2S and NaCl according to a stoichiometric ratio of 1:1; Step 2: Place the above raw materials in a zirconia ball mill jar, add zirconia balls at a ball-to-material mass ratio of 8:1, seal and evacuate to a vacuum state; Step 3: Ball milling was performed using pulse frequency conversion mode at a speed of 400 rpm, with forward rotation for 10 min, pause for 5 min, and reverse rotation for 10 min, for a total ball milling time of 7 h, to obtain Na2S-NaCl nano eutectic precursor; Step 4: Weigh the remaining Na2S, P2S5, Sb2S3, WS2 and Na2S-NaCl nano-eutectic precursor precisely according to the stoichiometric ratio, mix them evenly, put them into an alumina crucible, place them in a vacuum tube furnace, evacuate and purge with argon gas 3 to 5 times. Step 5: Low-temperature sintering: Heat to 400℃ at a rate of 2℃ / min and hold for 3 hours, then allow to cool naturally to room temperature; Step 6: Grind the sintered product in a glove box and sieve it through a 200-mesh nylon sieve to obtain Na. 2.38 Sb 0.2 P 0.68 W0.12 S 3.5 Cl 0.5 Sulfide solid electrolyte powder.

[0062] Example 2 The difference between this embodiment and Example 1 is that in step 1, NaCl is replaced with NaBr, and in step 4, Sb₂S₃ is replaced with SnS, ultimately yielding a material with the chemical formula Na. 3.18 Sn 0.8 P 0.08 W 0.12 S 3.5 Br 0.5 A sulfide solid electrolyte.

[0063] Comparative Example 1 The difference between this comparative example and Example 1 is that SnS raw material is not added in step 4. Instead, Na2S, P2S5, WS2, and Na2S-NaCl nano-eutectic precursor are weighed in stoichiometric proportions to obtain the final product with the chemical formula Na. 2.08 P 0.88 W 0.12 S 3.2 Cl 0.8 A sulfide solid electrolyte.

[0064] Comparative Example 2 The difference between this comparative example and Example 1 is that step 1, the pre-synthesis of Na2S-NaCl nano-eutectic precursor, is omitted; in step 4, P2S5 and NaCl raw materials are not added; only Na2S, Sb2S3, and WS2 are weighed in stoichiometric ratios, and subjected to high-energy ball milling and low-temperature sintering to finally obtain the chemical formula Na... 2.88 Sb 0.88 W 0.12 S4 is a sulfide solid electrolyte.

[0065] Comparative Example 3 The difference between this comparative example and Example 1 is that step 1, the pre-synthesis of Na2S-NaCl nano-eutectic precursor, is omitted. Instead, all raw materials Na2S, P2S5, Sb2S3, WS2, and NaCl are weighed according to stoichiometric ratios and subjected to high-energy ball milling and conventional high-temperature solid-state sintering (550°C) to finally obtain Na2S-NaCl nano-eutectic precursor. 2.38 Sb 0.2 P 0.68 W 0.12 S 3.5 Cl 0.5 Sulfide solid electrolyte.

[0066] The ionic conductivity of the sulfide solid electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 was tested, and the electrochemical window for antioxidant capacity was characterized. The results are shown in Table 1, and are detailed below: The sulfide solid electrolyte was exposed to a fixed dew point of -35℃ for a certain period of time, and the ionic conductivity of the powder was tested. The specific test method for ionic conductivity is as follows: 1. Sample preparation Ultrafine Na3M1 x W x S4 series sulfide electrolyte powder is cold-pressed into sheets at a pressure of 360–500 MPa, with a thickness of approximately 0.1–1 mm and a diameter of 10–14 mm.

[0067] The thickness needs to be measured using a micrometer.

[0068] 2. Electrochemical Impedance Testing (EIS) The sample is held in place using a blocking electrode (such as stainless steel or sputtered metal film), and an AC voltage (amplitude 10mV, frequency range 1MHz to 0.1Hz) is applied.

[0069] The bulk resistance Rbulk is obtained by fitting the semicircular intercept in the high-frequency region using EIS, while the low-frequency region reflects the interfacial resistance and the double-layer effect.

[0070] 3. Geometric parameter measurement Thickness (LL): The thickness of the compressed tablet is measured directly using a micrometer; Area (AA): Calculated based on the electrode diameter; According to the formula Calculate the ionic conductivity of the corresponding material.

[0071] Table 1

[0072] As shown in Table 1: 1) Example 1 has the best overall performance. In this embodiment, a Na₂S-NaCl nanocrystalline eutectic precursor was first obtained by ball milling under an inert atmosphere. Its atomic arrangement is long-range disordered, lacking the concepts of grains and grain boundaries. The entire material is a continuous and homogeneous ion transport medium, in which sodium ions diffuse isotropically without needing to cross any grain boundary barriers. In the nanocrystalline-glass composite structure, the highly ionicly conductive nanocrystalline phase is uniformly dispersed within the amorphous glass matrix. The glass matrix not only provides a flexible interface connection, eliminating the rigid grain boundary resistance found in traditional crystalline materials, but also forms additional fast ion transport channels at the interface through the space charge effect at the nanocrystalline / glass interface. Furthermore, it combines a P-based framework with Sb... 3+ Low doping ratio +W 6+ Quantitative doping synergistic modification systems allow P-based and Sb-based systems to achieve synergistic modification. 3+ W 6+The functions of these components are mutually compatible, ensuring excellent performance across all three core indicators: ionic conductivity, air stability, and electrochemical window. This makes it the optimal comprehensive solution for all-scenario, all-solid-state sodium batteries, with high ionic conductivity (3.9 × 10⁻⁶). -2 S / cm): Sb 3+ It is a moderately strong acid with an ionic radius of 0.76 Å, and is similar to P. 5+ Significant radius differences exist at (0.34 Å), and low-proportion heterovalent substitution induces controllable lattice distortion, which broadens the Na... + The three-dimensional transport channel avoids excessive lattice defects and channel structure collapse caused by high-ratio substitution; W 6+ Quantitative doping and P 5+ To create a difference in valence state, an appropriate amount of Na is introduced. + Vacancy, reducing Na + A diffusion barrier helps improve ion migration efficiency; it retains 68% of the P-based framework, and the PS bond energy (319 kJ / mol) is much higher than the Sb-S bond energy (295 kJ / mol), making it suitable for Na. + The transmission provides a stable lattice channel structure, avoiding conductivity attenuation caused by loose channels.

[0073] Excellent air stability (65% retention rate over 24 hours): Optimized dual acid-base matching based on the HSAB theory to suppress hydrolysis at its source: Sb 3+ Low-ratio substitution of P in moderately strong acids 5+ Hard acid: The system's acid composition was adjusted from "pure hard acid" to "hard acid + moderately strong acid," initially optimizing the overall acid-base balance and reducing P. 5+ With OH in water molecules - The binding activity of Sb, while 3+ With S 2- The binding energy is higher, reducing S 2- Dissociation and release of H2S gas; Cl - Hard base replaces part of S 2- The soft alkali method adjusts the system's base type from "pure soft alkali" to "soft alkali + hard alkali," further enhancing the acid-base balance and transforming the system into a thermodynamically stable system of "hard acid-hard alkali, moderately strong acid-soft alkali." Simultaneously, Cl... - The large ionic radius forms a dense, hard base protective layer on the surface of the electrolyte particles, physically blocking the intrusion of water and oxygen molecules into the crystal lattice, further inhibiting hydrolysis; the medium-proportion P-based framework maintains the integrity of the crystal structure, allowing Sb to... 3+ With Cl - The HSAB optimization effect can be effectively utilized, avoiding excessive defects and easy water and oxygen permeability problems caused by P-free or low P-based materials.

[0074] A high electrochemical window (3.3V): achieves dual protection through P-based antioxidant dominance and halogen antioxidant compensation, perfectly balancing antioxidant capacity and conductivity enhancement: retaining a high 68% P-based backbone, P... 5+ At its highest oxidation state, phosphorus cannot lose any more electrons during electrochemical oxidation, exhibiting no oxidizing activity and thus not becoming an active site for oxidation reactions. It is the core of the system's antioxidant capacity, determining the basic upper limit of the electrochemical window; Sb 3+ Although it is in a non-maximum valence state (maximum valence +5), and although a small proportion of substitution introduces a small number of oxidation active sites, its oxidation activity is much lower than that of Sn. 4+ (Highest price +6), with minimal weakening of the system's antioxidant capacity; Cl - The oxidation potential is much higher than that of S. 2- , replacing part of S 2- This increased the overall oxidation potential of the system, while Cl - The formed surface protective layer can physically block the diffusion of oxidation reactions from the particle surface to the interior, fully compensating for Sb. 3+ The slight loss of antioxidant capacity introduced keeps the electrochemical window at 3.3V, which fully meets the requirements of mainstream medium-to-high voltage sodium cathode materials (such as Na3V2(PO4)3, NaNi). 0.5 Mn 0.5 Application requirements (O2, operating voltage 3.0~3.8V).

[0075] 2) Example 2 exhibits the best ionic conductivity, but its antioxidant capacity is slightly reduced. In this embodiment, Na2S-NaBr nano-eutectic precursors were first obtained by ball milling under an inert atmosphere. Both processes eliminated the rigid grain boundary resistance found in traditional crystalline materials. The material structure consisted of a low-proportion P-based framework + Sn. 4+ High proportion of W doped 6+ The core characteristic of quantitative doping modification systems is that they achieve a peak increase in ionic conductivity at the cost of sacrificing a small amount of antioxidant capacity: the optimal ionic conductivity is 4.1 × 10⁻⁶. -2 S / cm): Sn 4+ It is a moderately strong acid with an ionic radius of 0.69 Å, and is similar to P. 5+ Significant radius differences exist, and high-proportion heterovalent substitution induces severe lattice distortion, greatly broadening the Na1 crystal. + A three-dimensional transmission channel is introduced simultaneously, along with a large amount of Na. + Empty space, let Na + The migration path is smoother and the diffusion barrier is significantly reduced; W 6+ Trace doping further enhances the lattice distortion effect, helping to improve Na + Migration efficiency; although only 8% of the P-based framework is retained, it can still provide basic support for the lattice structure and prevent Sn from spreading. 4+The complete replacement causes the channel to collapse completely, ensuring the stability of high conductivity.

[0076] Excellent air stability (61% retention rate over 24 hours): Sn 4+ High-proportion substitution of P in moderately strong acids 5+ Hard acid, achieving initial optimization of acid-base balance, reducing hydrolysis reactivity; Br - Hard base replaces part of S 2- The soft alkali achieves secondary enhancement and optimization, while simultaneously forming a surface protective layer to block water and oxygen. Dual HSAB optimization maintains excellent air stability; however, due to Sn... 4+ The high substitution ratio introduces a large number of lattice defects, and water and oxygen molecules can slightly invade the interior of the lattice from the defects, resulting in an air stability that is slightly lower than that of the comparative example 1, but still far superior to the halogen-free or pure phase system.

[0077] Antioxidant capacity slightly reduced (electrochemical window 3.1V): only 8% of the P-based backbone is retained, P 5+ The dominant antioxidant effect is significantly weakened, and the core foundation for the system's antioxidant function is missing; Sn 4+ Sn is not in its highest oxidation state; a high proportion of substitution introduces a large number of oxidation active sites. During electrochemical oxidation, Sn... 4+ It easily loses electrons and is oxidized to Sn. 6+ This becomes the "core trigger point" for the oxidation reaction, accelerating the overall oxidative decomposition of the electrolyte; although Br - The high oxidation potential can compensate for oxidation losses, but its compensatory effect cannot offset the low P-group + high Sn content. 4+ The resulting weakening of antioxidant capacity reduces the electrochemical window to 3.5V, slightly lower than in Example 2, but still meets the application requirements of medium-voltage cathode materials.

[0078] 3) Comparative Example 1 showed excellent antioxidant properties, but its air stability was relatively low. This comparative example differs from Example 1 in that it features a high proportion of P-based skeleton + W. 6+ The core feature of quantitative doping modification system is to maximize the retention of the intrinsic advantages of P-based framework. However, due to the intrinsic hard acid hydrolysis tendency of P-based structure, the vacuolation stability is limited and the ionic conductivity is low.

[0079] Air stability limited (26%): High P basic characteristic hydrolysis tendency: 88% high proportion of P groups form hard acid aggregation effect, P 5+ Hard acid reacts with OH- in water molecules - The tendency to bind is an intrinsic property, Cl - The modification effect can only "inhibit" rather than "eliminate", so the system still has a certain degree of hydrolysis reactivity.

[0080] Excellent antioxidant capacity (3.3V): P-group allows P 5+Its dominant antioxidant role makes it the case with the best antioxidant capacity and the widest antioxidant window among all doped systems: the high proportion of P-based components provides sufficient P. 5+ It has no oxidizing activity; the system has almost no oxidizing active sites, and the oxidation reaction is carried out by only a small amount of unsubstituted S. 2- Oxidation-initiated; Cl - The high oxidation potential further enhances the system's oxidative decomposition potential, thus helping to strengthen its antioxidant capacity; W 6+ It is in its highest oxidation state, has no oxidative activity, and does not introduce additional active sites, thus having a wide electrochemical window.

[0081] 4) Comparative Example 2 has poor performance. This case study involves a P-based skeleton with Sb. 3+ Total replacement + W 6+ The quantitatively doped system, lacking the two essential characteristics of a "P-based framework" and a "nano-eutectic precursor," suffers from decreased air stability, reduced electrochemical window, and slightly higher ionic conductivity (2.6 × 10⁻⁶). -2 S / cm): Although Sb 3+ Replacement causes lattice distortion, but no P-based framework provides stable lattice channels; Limited air stability (37% retention rate over 24 hours): relying solely on Sb 3+ The single HSAB optimization of medium-strong acids and the secondary enhancement optimization of halogen-free hard bases have limited improvement in acid-base matching and cannot fundamentally inhibit hydrolysis reactions. The worst antioxidant capacity (electrochemical window 2.8V): lacks a phosphorus-based backbone, completely losing phosphorus. 5+ The core antioxidant function of the system is determined solely by the Sb-S bond; Sb 3+ As a non-maximum oxidation state, total substitution introduces a large number of oxidation active sites, and without the antioxidant compensation effect of halogens, Sb... 3+ It is easily and rapidly oxidized to Sb 5+ Meanwhile, the Sb-S bond is easily oxidized and broken, the crystal structure collapses rapidly, and the electrochemical window is only 2.9V, which cannot match any medium- to high-voltage sodium cathode material.

[0082] 5) Comparative Example 3 serves as the baseline control, with poor air stability / conductivity. Both this case and Example 1 have the chemical formula Na. 2.38 Sb 0.2 P 0.68 W 0.12 S 3.5 Cl 0.5 Comparative Example 1, using the traditional high-temperature solid-state method (sintering at 550℃ for 6 hours), produced a highly crystalline material with a room-temperature ionic conductivity of only 2.7 × 10⁻⁶. -²S / cm, conductivity decreased to 1.053×10 after 24 hours of air exposure. - The conductivity was 2 S / cm, with a retention rate of only 39%. In contrast, Example 1, using the Na2S-NaCl nano-eutectic precursor pre-synthesis and low-temperature sintering method of this invention (400℃ for 3 hours), produced a nanocrystalline-glass composite structure, with a room-temperature ionic conductivity jumping to 3.9 × 10⁻⁶. - The conductivity was 2.65 × 10⁻⁶ S / cm, nearly 1.5 times that of Comparative Example 3; after 24 hours of air exposure, the conductivity still reached 2.65 × 10⁻⁶. - ² S / cm, with a retention rate of up to 68%, which is 2.5 times that of Comparative Example 3.

[0083] The sulfide solid electrolytes of Example 1 and Comparative Example 3 were characterized by scanning electron microscopy as follows: 1) Sample preparation (core step of inert gas protection) Pretreatment environment: The entire process is carried out in an Ar gas glove box (O2 / H2O content ≤0.1ppm) to avoid exposing the sample to air.

[0084] Sample type adaptation: bulk / sintered sheet: Powder sample: Fix the silicon wafer to the sample stage with conductive adhesive, and spray the powder sample onto the surface of the conductive adhesive; 2) Instrument preparation and vacuum optimization Instrument selection: SEM: Field emission scanning electron microscope (FE-SEM), resolution ≥1nm; EDS detector: Silicon drift detector (SDD), energy resolution ≤129eV.

[0085] Instrument warm-up and calibration: Turn on the SEM host, EDS system and vacuum system, and preheat for 30 minutes; EDS energy calibration: Calibrate using standard samples to ensure accurate positions of characteristic peaks for S (2.31 keV) and P (2.01 keV); Vacuum requirement: Sample chamber vacuum ≥ 1×10 -4 Pa.

[0086] Sample transfer and installation: Use a sealed sample transfer box (fill the sample into the glove box and then seal it) to reduce exposure time (≤30 seconds). Quickly place the sample stage into the SEM sample chamber, ensuring that the center of the sample is aligned with the electron beam scanning area; Close the sample chamber door and start the vacuum process (wait 15 minutes until the vacuum indicator light turns green).

[0087] 3) SEM parameter optimization (adapting to LPSC insulation + easy hydrolysis characteristics) Morphological observation and regional location: Magnification: First observe the overall morphology at low magnification (100×) to confirm that there is no hydrolysis (no white flocculent deposits) and no fragmentation; Then adjust to medium-high magnification (2000×) and select a flat area without pores / cracks as the ROI; Accelerating voltage: 12kV (a key parameter to balance signal strength and sample stability). Working distance: 10mm (balancing signal strength and spatial resolution); Beam current: 3nA (to ensure signal strength while avoiding sample damage); Manually optimize focus and astigmatism to ensure clear images of the ROI area (no blur or ghosting).

[0088] Measures to suppress charge accumulation: If charge still accumulates, reduce the accelerating voltage to 9kV, increase the beam current to 4nA, or turn on the "low vacuum mode" of the SEM (vacuum degree 15Pa).

[0089] 4) EDS Mapping parameter settings (for LPSC element characteristics) Element channel selection: Required elements: Li (Kα, 0.05keV), P (Kα, 2.01keV), S (Kα, 2.31keV), Ge (Lα, 9.89keV, if present); Optional element: O (Kα, 0.52 keV, used to determine whether the sample is hydrolyzed).

[0090] Key acquisition parameter settings: Pixel dwell time: 15ms / pixel (Li element signal is weak, so sufficient time is required); Scan resolution: 1024×1024 pixels (to ensure detailed element distribution); Count rate control: Target 3000 cps (counts per second); Acquisition mode: "NetMap" (Net Count Mode), automatically removes background noise.

[0091] Pre-scan before data acquisition: Perform two rapid pre-scans of the ROI region (dwell time 5ms) and observe the count rate of each element; If the Li element count rate is <50cps, adjust the parameters (extend the residence time to 18ms or increase the beam current to 4nA). If no significant peak overlap is confirmed, adjust the element channel energy window if necessary.

[0092] 5) Mapping data acquisition and monitoring Start data collection: In the EDS software, click "Mapping" → "Start Data Acquisition" and record the current parameters; Acquisition time: Approximately 20 minutes (1024×1024 pixels, 15ms / pixel); Real-time monitoring: Count rate curve: Remains stable between 2000 and 4000 cps; SEM images: If increased charge accumulation or whitening of the sample surface (signs of hydrolysis) is observed, terminate the test immediately.

[0093] Data collection complete: Save the original data (.azt / .emd format) and export the element distribution image; Close the EDS acquisition interface, but keep the SEM image interface open to observe the sample status.

[0094] 6) Data Analysis and Precautions Key aspects of data analysis: Qualitative analysis: Confirm whether the distribution of Li, P, S, and Ge is uniform, and observe the distribution of O element to determine whether hydrolysis has occurred; Semi-quantitative analysis: Comparison of P, S, and Ge signal intensities in different regions to assess the uniformity of distribution (Li is only used for qualitative judgment); Data processing: background subtraction, adjusting image contrast to highlight differences in element distribution, and superimposing P and S element images to observe co-distribution.

[0095] The scanning electron microscope image of the sulfide solid electrolyte in Example 1 is shown below. Figure 2 As shown, the scanning electron microscope image of the sulfide solid electrolyte of Comparative Example 3 is as follows. Figure 3 As shown, Example 1 exhibits a loose, porous aggregate morphology of irregular, spherical particles. The particle crystallization state is a mixture of amorphous phase and slight lattice distortion. There is no severe agglomeration between particles; they are distributed as independent particles with weak connections. This is due to the controllable lattice distortion induced by low-proportion Sb doping and Cl. - The combined effect of halogen modification inhibiting excessive aggregation.

[0096] Comparative Example 3 exhibits a dense, blocky aggregate morphology with a highly complete pure-phase cubic crystal form. The crystal form is fully developed and the grains are densely arranged. There are no obvious gaps between the grains, and they are in a densely packed state, which is a direct manifestation of the intrinsic crystal growth characteristics.

[0097] The sulfide solid electrolytes of Example 1 and Comparative Example 3 were characterized by XRD, and the phase analysis methods are as follows: 1) Sample preparation Powder Sample Preparation Grinding requirements: The sulfide powder must be ground to a uniform particle size (passing through a 200-mesh sieve, particle size ≤75μm), with no grainy feel to the touch, similar to the texture of flour, in order to reduce preferred orientation and enhance the intensity of diffraction peaks.

[0098] Moisture-proof treatment: Sulfides are prone to moisture absorption and decomposition, so they need to be ground and pressed in an inert gas (such as argon) glove box to avoid oxidation or structural damage.

[0099] Preparation of bulk or thin film samples 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.

[0100] 2) Instrument setup and testing procedures Instrument initialization 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.

[0101] 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.

[0102] Parameter settings Scanning range: standard wide-angle test range 5°-90°, step size 0.02°, scanning speed 5° / min (adjusted according to sample crystallinity).

[0103] Slit width: entrance slit 0.2-0.6mm, detector slit 3-8mm, optimizing resolution and signal-to-noise ratio.

[0104] X-ray conditions: copper target Kα rays (λ=1.5418Å), voltage 40kV, current 30mA, to ensure clear diffraction peaks.

[0105] Sample loading and testing 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 that the scan is complete and save the data (e.g., RAW or TXT format).

[0107] XRD results are as follows Figure 4 As shown, compared with the original Na3PS4 material, Example 1 shows a new peak, indicating that elemental doping has been performed.

[0108] In summary, this invention provides a co-doped sodium-based sulfide solid electrolyte, its preparation method, and its application. The preparation method of the co-doped sodium-based sulfide solid electrolyte includes the following steps: mixing Na₂S with sodium halide to obtain a first mixed powder; subjecting the first mixed powder to inert atmosphere ball milling to obtain a pre-synthesized nano-eutectic precursor; mixing at least one of a Group IVA element source and a Group VA element source, a sodium source, a phosphorus source, a tungsten source, and a sulfur source with the pre-synthesized nano-eutectic precursor to obtain a second mixed powder; subjecting the second mixed powder to low-temperature sintering to obtain a sintered block; and grinding and sieving the sintered block to obtain the co-doped sodium-based sulfide solid electrolyte Na₂S. 3+δ M 0.88-x P x W 0.12 S 4-y D y Wherein, M is a Group IVA element and / or a Group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium; the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h. The co-doped sodium-based sulfide solid electrolyte prepared by the present invention using high-energy ball milling and low-temperature sintering processes possesses a nanocrystalline-glass composite structure, transforming the microstructure of the product from the "crystalline state" of traditional methods to a "nanocrystalline-glass composite structure." This structural change brings about a significant leap in ionic conductivity and air stability, solving the inherent problems of high grain boundary impedance, anisotropic transport, and interfacial chemical instability that have long existed in crystalline materials. Abandoning the traditional approach of directly mixing raw materials such as Na2S, P2S5, and NaCl in a single step, this invention first involves high-energy ball milling of Na2S (sodium and sulfur sources) and NaD (halogen sources, D = F, Cl, Br, I) in a specific ratio. Na2S has an antifluorite structure, while NaD has a rock salt structure; their crystal lattice types are different. Under the mechanochemical action of prolonged high-energy ball milling, ion exchange, diffusion, and structural disorder occur at the interface between the two crystals. 2- and D - Two anions were uniformly mixed and pre-organized at the nanoscale to form a highly active, partially disordered anionic sublattice Na₂S-NaD nano-eutectic precursor. The anions in the nano-eutectic precursor achieved atomic-level homogeneous mixing and were in a high-energy metastable state. This allows the target product to rapidly form at low temperatures, eliminating the need for the slow solid-phase diffusion process driven by high-temperature long-range atomic migration found in traditional methods. Furthermore, the resulting solid electrolyte exhibits a room-temperature ionic conductivity ≥30 × 10⁻⁶. -3With a conductivity of S / cm, a conductivity retention rate of ≥50% after 24 hours of air exposure, no significant H2S release, and an electrochemical window of ≥3.3V, it can be widely used in sodium metal all-solid-state batteries, composite cathodes, solid electrolyte membranes, etc. The process is green, low-cost, and suitable for industrial production.

[0109] 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 co-doped sodium-based sulfide solid electrolyte, characterized in that, Including the following steps: Na2S and sodium halide are mixed to obtain the first mixed powder; The first mixed powder was subjected to inert atmosphere ball milling to obtain a pre-synthesized nano-eutectic precursor; At least one of the Group IVA and Group VA elements, a sodium source, a phosphorus source, a tungsten source, and a sulfur source are mixed with the pre-synthesized nano-eutectic precursor to obtain a second mixed powder. The second mixed powder is subjected to low-temperature sintering to obtain a sintered block; The sintered block was ground and sieved to obtain a co-doped sodium-based sulfide solid electrolyte, Na. 3+δ M 0.88- x P x W 0.12 S 4-y D y ; Wherein, M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium; the temperature of the low-temperature sintering treatment is 300℃-450℃, and the time of the low-temperature sintering treatment is 1h-4h.

2. The method for preparing the co-doped sodium-based sulfide solid electrolyte according to claim 1, characterized in that, The sodium source is selected from one or more of Na2S, NaH, and Na2S2; the phosphorus source is selected from one or more of P2S5, Na3P, and Na3PS3; the tungsten source is selected from one or more of tungsten powder, WS2, WCl6, WO3, and W(CO)6; the sodium halide is selected from one or more of sodium fluoride, sodium chloride, sodium bromide, and sodium iodide; the Group IVA element source is selected from SnS and GeS2; and the Group VA element source is selected from Sb2S3, As2S3, and Bi2S3.

3. The method for preparing the co-doped sodium-based sulfide solid electrolyte according to claim 1, characterized in that, The inert atmosphere ball milling treatment is carried out in a variable frequency mode; the rotation speed of the inert atmosphere ball milling treatment is 400rpm-600rpm, and the total time of the inert atmosphere ball milling treatment is 6h-12h.

4. The method for preparing the co-doped sodium-based sulfide solid electrolyte according to claim 3, characterized in that, The frequency conversion mode is to first rotate forward for 8-12 minutes, pause for 4-6 minutes, then rotate in reverse for 8-12 minutes, pause for 4-6 minutes, and repeat in a cyclical manner.

5. The method for preparing the co-doped sodium-based sulfide solid electrolyte according to claim 1, characterized in that, The sieving process uses a 200-300 mesh nylon sieve.

6. A co-doped sodium-based sulfide solid electrolyte, characterized in that, The co-doped sodium-based sulfide solid electrolyte is prepared using the method described in any one of claims 1-5; the structural formula of the co-doped sodium-based sulfide solid electrolyte is Na. 3+δ M 0.88-x P x W 0.12 S 4-y D y Where M is a group IVA element and / or a group VA element, 0 < x ≤ 0.88; D is a halogen element, 0 ≤ y ≤ 0.8; δ is determined by valence equilibrium.

7. The co-doped sodium-based sulfide solid electrolyte according to claim 6, characterized in that, The group IVA element is selected from Sn and Ge; the group VA element is selected from Sb, As, and Bi; and the halogen element is selected from one or more of F, Cl, Br, and I.

8. The co-doped sodium-based sulfide solid electrolyte according to claim 6, characterized in that, The co-doped sodium-based sulfide solid electrolyte is selected from Na... 2.28 Sn 0.2 P 0.68 W 0.12 S 3.2 Br 0.8 Na 3.18 Sn 0.8 P 0.08 W 0.12 S 3.5 Br 0.5 Na 2.08 Sb 0.5 P 0.38 W 0.12 S 3.2 Cl 0.8 One of them.

9. The application of a co-doped sodium-based sulfide solid electrolyte as described in any one of claims 6-8 in an all-solid-state sodium-ion battery.

Images