Sulfide solid electrolyte and preparation method thereof, battery and application

Abstract

The application relates to the field of electrochemistry, and provides a sulfide solid electrolyte, a preparation method thereof, a battery and application. The sulfide solid electrolyte has a chemical formula of Li 7‑a PS 6‑ a X a X is at least one selected from Cl, Br and I, and 1<=a<=2; wherein the sulfide solid electrolyte comprises carbon generated in situ in a synthesis process, and the content of the carbon is M, 0.03 wt%<=M<=0.5 wt%. The method provided by the application reduces the introduction of oxygen and carbon impurities by using an inert solvent and reducing the solvent consumption, ensures high purity and high ionic conductivity of the product, and significantly reduces environmental pollution, energy consumption and production cost.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a sulfide solid electrolyte and its preparation method, a battery containing the sulfide solid electrolyte, and the application of the battery. Background Technology

[0002] Solid-state electrolytes are key materials for next-generation high-performance battery systems, and their performance directly affects the battery's energy density, safety, and lifespan. Due to their excellent ionic conductivity and electrochemical stability, sulfide solid-state electrolytes have become a research hotspot in recent years, especially in their application in all-solid-state lithium batteries.

[0003] Traditional methods for preparing sulfide solid electrolytes (LPSCs) mainly include wet and dry processes. However, while these processes improve the performance of sulfide solid electrolytes, they also have significant drawbacks. For example, wet processes typically use alcohol solvents to dissolve and mix precursors, utilizing the polarity and protonation of the solvents to promote reaction homogeneity. However, these solvents can undergo side reactions with precursors such as Li₂S and P₂S₅, producing oxygen-containing impurities such as Li₃PO₄. Even when using inert solvents that do not react with precursors, their large presence can introduce significant amounts of carbon impurities during calcination. Dry processes directly react precursors through high-temperature calcination, avoiding the use of solvents in wet processes and thus reducing the generation of oxygen and carbon impurities. However, this method requires high precision in temperature control and uniform mixing conditions; otherwise, it can easily lead to problems such as excessively large and uneven product particle size. In the prior art, some studies have used wet ball milling to pretreat precursors, thereby improving the problems of uneven product and large particle size in dry processes. However, ball milling has problems such as high energy consumption, chemical bond breakage of precursors during ball milling, and uneven reaction degree.

[0004] Furthermore, sulfide solid electrolytes generally suffer from poor air stability. When exposed to air, they readily react with moisture or oxygen to generate toxic gases such as hydrogen sulfide (H2S), leading to serious problems such as material structure degradation and decreased conductivity, which greatly limits their safety and operability in practical energy storage devices. To improve this issue, some studies have attempted to enhance the air stability of sulfide solid electrolytes by coating with protective layers (such as Li2O, Li2CO3, etc.), introducing exogenous inert substances, or adjusting the sintering atmosphere. However, these methods are complex, costly, or have adverse effects on the intrinsic properties of the material.

[0005] Therefore, improving the air stability of sulfide solid electrolytes while also considering their ion conductivity has become the key to breaking through the bottleneck of industrialization of sulfide solid electrolytes. Summary of the Invention

[0006] The purpose of this application is to provide a sulfide solid electrolyte and its preparation method, achieving dual optimization of the air stability and room temperature ionic conductivity of the sulfide solid electrolyte, thereby making batteries using this sulfide solid electrolyte safer and more efficient. The specific technical solution is as follows:

[0007] The first aspect of this application provides a sulfide solid electrolyte, wherein the chemical formula of the sulfide solid electrolyte is Li. 7-a PS 6-a X a X is selected from at least one of Cl, Br and I, 1≤a≤2; wherein the sulfide solid electrolyte includes carbon generated in situ during the synthesis process, and the content of the carbon is M, 0.03 wt%≤M≤0.5 wt%.

[0008] In some embodiments of this application, the carbon content of the sulfide solid electrolyte is M, where 0.03wt%≤M≤0.4wt%.

[0009] In some embodiments of this application, the particle size of the sulfide solid electrolyte satisfies: 0.5µm < D v 50 < 1.5µm, 2µm < D v 90 < 2.5µm, 6µm < D MAX <6.5µm.

[0010] In some embodiments of this application, the sulfide solid electrolyte has an ionic conductivity > 5.0 mS / cm.

[0011] In one embodiment of this application, the sulfide solid electrolyte further includes at least one element selected from O, Se, F, Mg, Ca, Sr, Zn, Sc, Sb, Si, Ge, Sn, B, Al, Ga, In, Ti, Zr, V, Nb, Cu, Ni, Mn, Cr, Ag, La, Ce, Tb, Te, Pb, As, Bi, Fe, Mo, Hf, Y, and Ru, wherein the element is introduced by doping or coating.

[0012] In one embodiment of this application, the surface of the sulfide solid electrolyte is coated with an inert oxide layer, wherein the inert oxide layer is selected from at least one of Li2O, Al2O3, V2O5, ZnO, ZrO2, TiO2, MgO, RuO2, La2O3, CeO2, HfO2, Y2O3, SiO2, B2O3, CuO, NbO2, LiNbO3, and LiAlO2.

[0013] A second aspect of this application provides a method for preparing a sulfide solid electrolyte, comprising:

[0014] Under an inert atmosphere, the precursor and solvent are mixed and mechanically stirred to obtain a mixture; wherein the precursor includes Li2S, P2S5 and a halogen-containing compound; the halogen-containing compound includes NH4X′ and LiX″, wherein X′ and X″ are each independently selected from at least one of Cl, Br and I; the molar ratio of NH4X′ and LiX″ is 1:(0~1); the mass ratio of the solvent to the precursor is 1:(1.5~3.5), and the solvent is selected from an inert solvent, wherein the inert solvent is selected from at least one of n-hexane, benzene, toluene, cyclohexane, n-pentane, acetonitrile, cyclopentane and dimethyl carbonate;

[0015] The mixture was dried at room temperature and pressure under an inert atmosphere to evaporate the solvent, yielding a solid electrolyte precursor mixture.

[0016] The solid electrolyte precursor mixture was calcined under an inert atmosphere to obtain the sulfide solid electrolyte.

[0017] The chemical formula of the sulfide solid electrolyte is Li. 7-a PS 6-a X a X is selected from at least one of Cl, Br and I, and 1≤a≤2.

[0018] In some embodiments of this application, mechanical stirring is carried out at room temperature and pressure, the stirring rate is 300~600 rpm, and the stirring time is 10~50 min.

[0019] In some embodiments of this application, the calcination temperature is 450~600℃ and the time is 5~15h.

[0020] In some embodiments of this application, the solvent evaporation rate is 1.5~7.0 mg / cm³. 2 h, based on the total mass of the solvent, the residual rate of the solvent after evaporation is 1wt%~5wt%.

[0021] In some embodiments of this application, during the drying process, the thickness of the solid electrolyte precursor mixture is 1-5 mm, and the drying specific surface area of ​​the solid electrolyte precursor mixture is 1.5-3 cm². 2 / g.

[0022] In some embodiments of this application, the moisture content in the inert atmosphere during the drying process is less than 10 ppm.

[0023] A third aspect of this application provides a battery comprising a positive electrode, a negative electrode, and a sulfide solid electrolyte as described in the first aspect of this application, or a sulfide solid electrolyte prepared by the preparation method described in the second aspect of this application.

[0024] The fourth aspect of this application provides the application of the battery described in the third aspect of this application in an electric vertical takeoff and landing aircraft.

[0025] The beneficial effects of this application are:

[0026] This application provides a sulfide solid electrolyte and its preparation method, wherein the chemical formula of the solid electrolyte is Li. 7-a PS 6-a X a X is selected from at least one of Cl, Br, and I, 1 ≤ a ≤ 2; wherein the sulfide solid electrolyte includes carbon generated in situ during the synthesis process, and the carbon content is M, 0.03 wt% ≤ M ≤ 0.5 wt%. This application improves the air stability and room temperature ionic conductivity of the sulfide solid electrolyte by introducing an appropriate amount of carbon during the preparation process. The carbon originates from the carbonization residue of the solvent during heat treatment and is uniformly doped onto the surface or grain boundaries of the sulfide solid electrolyte particles, forming a continuously distributed but non-conductive inert carbon phase. By controlling the carbon content within the range of 0.03 wt%–0.5 wt%, an isolation structure can be formed at the microscale, effectively inhibiting direct contact between the sulfide and moisture in the air, thereby significantly improving the air stability of the sulfide solid electrolyte and delaying its decomposition reaction at room temperature. The carbon content within this range can enhance the overall electron transport capability after the sulfide solid electrolyte is combined with the cathode, which is beneficial for improving the interfacial electron diffusion efficiency between the sulfide solid electrolyte and the cathode. Meanwhile, by controlling the carbon content within the scope of this application, problems such as increased electronic conductivity and decreased ionic conductivity caused by excessive carbon content can be avoided, thus ensuring the low electronic conductivity and high ionic conductivity of the sulfide solid electrolyte as an electrolyte. Compared with existing technical solutions that rely on adding exogenous carbon, this application can achieve a synergistic improvement in air stability, electrode compatibility, and ionic conductivity performance of the sulfide solid electrolyte.

[0027] Furthermore, the preparation method of this application, by using a small amount of inert solvent and controlling the solvent evaporation rate, effectively reduces the introduction of oxygen impurities during the wet preparation process, such as the generation of oxide impurities like Li3PO4. Simultaneously, by controlling the carbon content of the sulfide solid electrolyte, it achieves dual optimization of improved air stability and room-temperature ionic conductivity of the sulfide solid electrolyte. Moreover, by reducing the amount of solvent used, drying can be completed by standing at room temperature and pressure, which not only reduces energy consumption but also lowers production costs. In addition, NH3 and H2S gases are generated during calcination, resulting in more uniform particle dispersion and slowing down particle growth, leading to smaller particle size. Furthermore, batteries containing the sulfide solid electrolyte of this application or those prepared by the method of this application possess high safety, energy density, and good low-temperature performance, making them suitable for use in electric vertical takeoff and landing (EVTOL) aircraft, especially in low-altitude economical manned EVTOL aircraft.

[0028] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0030] Figure 1 The X-ray diffraction pattern of the sulfide solid electrolyte (Li6PS5Cl) prepared in Example 1-1 is shown. Detailed Implementation

[0031] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0032] The first aspect of this application provides a sulfide solid electrolyte, wherein the chemical formula of the sulfide solid electrolyte is Li. 7-a PS 6-a X a The structural formula is Li 7-a PS 6-a X aX is selected from at least one of Cl, Br, and I, 1 ≤ a ≤ 2; wherein the sulfide solid electrolyte includes carbon generated in situ during the synthesis process, and the carbon content is M, 0.03 wt% ≤ M ≤ 0.5 wt%. Preferably, 0.03 wt% ≤ M ≤ 0.4 wt%. For example, M can be 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or a range of any two of these values. The carbon in this application includes, but is not limited to, amorphous carbon, crystalline carbon, or carbides formed after sintering with organic solvents. The inventors have discovered that in a synthesis system involving inert solvents, some organic solvents undergo a carbonization reaction during drying or sintering, generating a small amount of carbon. This carbon is embedded or attached in an extremely fine form to the surface or grain boundary region of the sulfide solid electrolyte particles. Unlike exogenously added carbon materials, this in-situ formed carbon has a more uniform distribution, smaller particle size, and is more tightly bound to the main structure, making it less prone to detachment or migration. Secondly, this type of amorphous carbon structure is an electrochemically inert material that does not react with air, water, or electrolytes at room temperature and pressure, exhibiting excellent chemical stability. When it is uniformly distributed in sulfide solid electrolytes at a content of 0.03–0.5 wt%, it can form a local shielding structure or buffer layer at the microscopic level of the sulfide solid electrolyte, effectively isolating the particle surface from direct contact with active components in the air (such as H2O and O2), thereby reducing the surface hydrolysis reaction rate, inhibiting the generation of harmful gases (such as H2S), and slowing down the structural degradation process.

[0033] Maintaining the carbon content of sulfide solid electrolytes (SSEs) between 0.03 wt% and 0.5 wt% not only helps optimize the microstructure and ion conductivity of the SSE itself, but also provides advantages in interfacial compatibility and electronic contact for subsequent composites with cathode materials. When the carbon content is above 0.03 wt%, a small, uniformly distributed conductive network can be formed in the SSE, which helps improve the electron transport path in the cathode composite system and enhances the overall interfacial reaction kinetics of the secondary battery, especially under high cathode load conditions. If the carbon content is below 0.03 wt%, the SSE has insufficient conductivity when composited with the cathode, resulting in poor interfacial electronic contact and easily leading to increased interfacial polarization and capacity decay. When the carbon content exceeds 0.5%, excessive carbon distribution may form continuous electron conduction paths, compromising the electronic insulation properties of the SSE and increasing the risk of self-discharge or even short circuits in the secondary battery. Therefore, controlling the carbon content of the sulfide solid electrolyte within the range of this application can ensure the stability of the sulfide solid electrolyte in synthesis and structure, and also provide good interfacial performance for subsequent composite with cathode materials.

[0034] In some embodiments of this application, the particle size of the sulfide solid electrolyte satisfies: 0.5µm < D v 50 < 1.5µm, for example, D v 50 can be 0.5 µm, 0.7 µm, 0.9 µm, 1.2 µm, 1.5 µm, or a range of any two of these values; 2 µm < D v 90 < 2.5µm, for example, D v 90 can be 2.0 µm, 2.1 µm, 2.3 µm, 2.5 µm, or a range of any two of these values; 6 µm < D MAX <6.5µm, for example, D MAX The particle size D can be 6.0 µm, 6.1 µm, 6.3 µm, 6.5 µm, or a range of any two of these values. The sulfide solid electrolyte of this application has a particle size D... v 50. D v 90 and D MAX Within the aforementioned range, sulfide solid electrolytes exhibit high packing density.

[0035] In some embodiments of this application, the ionic conductivity of the sulfide solid electrolyte is >5.0 mS / cm (referring to the ionic conductivity measured under pressure of 350 MPa at room temperature). The sulfide solid electrolyte of this application has high ionic conductivity, and its application in secondary batteries can improve the safety performance, energy density, and low-temperature performance of secondary batteries.

[0036] In this application, Figure 1 The XRD pattern showed no diffraction peaks with an area greater than 150 in the 2θ range of 20° to 24.7°, proving that lithium phosphate impurities were essentially undetectable in the sulfide solid electrolyte of this application. The inventors believe this is because ammonium chloride reacts with lithium sulfide during sintering to generate NH3 and H2S gases, which act as protective gases to prevent the sample from reacting with water and oxygen, thus reducing oxygen impurities in the product.

[0037] In one embodiment of this application, the sulfide solid electrolyte further includes at least one of the elements selected from O, Se, F, Mg, Ca, Sr, Zn, Sc, Sb, Si, Ge, Sn, B, Al, Ga, In, Ti, Zr, V, Nb, Cu, Ni, Mn, Cr, Ag, La, Ce, Tb, Te, Pb, As, Bi, Fe, Mo, Hf, Y, and Ru, wherein the elements are introduced by doping or coating.

[0038] In this application, the doping methods include, but are not limited to, introducing doping elements during the substrate and solvent mixing stage or introducing doping elements with sintering aids during the sintering stage; the coating methods include, but are not limited to, forming a coating layer containing doping elements on the surface of the sulfide solid electrolyte by ball milling, vapor deposition or atomic spraying.

[0039] In one embodiment of this application, the surface of the sulfide solid electrolyte is coated with an inert oxide layer, wherein the inert oxide layer is selected from at least one of Li₂O, Al₂O₃, V₂O₅, ZnO, ZrO₂, TiO₂, MgO, RuO₂, La₂O₃, CeO₂, HfO₂, Y₂O₃, SiO₂, B₂O₃, CuO, NbO₂, LiNbO₃, and LiAlO₂. The sulfide solid electrolyte with the inert oxide layer coated on its surface can effectively improve the interfacial stability and air stability of the solid electrolyte. The sulfide solid electrolyte with the inert oxide layer coated on its surface is prepared using the above coating method. Exemplarily, under an inert atmosphere, the sulfide solid electrolyte Li… 7-a PS 6-a X a The mixture is combined with at least one of the aforementioned inert oxides, then sealed and ball-milled to obtain a sulfide solid electrolyte with an inert oxide layer on its surface. The sulfide solid electrolyte is Li... 7-a PS 6-a X a The mass ratio of the inert oxide to the inert oxide can be 95:5 to 99.99:0.01.

[0040] A second aspect of this application provides a method for preparing a sulfide solid electrolyte, comprising:

[0041] Under an inert atmosphere, the precursor and solvent are mixed and mechanically stirred to obtain a mixture;

[0042] The precursor includes Li₂S, P₂S₅, and a halogen-containing compound; the halogen-containing compound includes NH₄X′ and LiX″, where X′ and X″ are each independently selected from at least one of Cl, Br, and I; for example, when NH₄X′ is NH₄Cl, LiX″ can be LiBr or LiI; the molar ratio of NH₄X′ to LiX″ is 1:(0~1); the mass ratio of the solvent to the precursor is 1:(1.5~3.5), and the solvent is selected from inert solvents, specifically at least one of n-hexane, benzene, toluene, cyclohexane, n-pentane, acetonitrile, cyclopentane, and dimethyl carbonate; for example, the molar ratio of NH₄X′ to LiX″ can be 1:0, 1:0.5, 1:1, or a range consisting of any two of these values; the mass ratio of the solvent to the precursor can be... The ratio is 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, or any two of these ratios. The molar ratio of NH4X′ to LiX″ is within this range. During the heat treatment of the precursor, NH3 and H2S gases are generated. These gases not only serve as a protective atmosphere during calcination but also regulate the growth of the sulfide solid electrolyte, resulting in a more uniform particle size distribution and a narrower particle size distribution in the final product, which is beneficial for improving the electrochemical performance of the secondary battery. The mass ratio of the precursor to the solvent is limited to the above range. Compared with traditional wet processes, this not only reduces production costs but also reduces environmental pollution. Furthermore, by reducing the amount of solvent used, the drying step only requires static standing at room temperature and pressure under an inert atmosphere, which reduces energy consumption and production costs. The solvent is selected from inert solvents and will not react with precursors such as Li2S and P2S5. If non-inert solvents such as ethanol and tetrahydrofuran are selected, unavoidable side reactions will occur between these solvents and precursors such as Li2S and P2S5, producing oxygen impurities such as Li3PO4, which leads to a decrease in the purity of the sulfide solid electrolyte.

[0043] In existing technologies, the synthesis methods of sulfide electrolytes mainly include two types of processes: dry methods (i.e., solid-phase methods) and wet methods (liquid-phase methods). Dry methods usually refer to mechanical mixing without adding solvents, such as high-energy ball milling and mechanical pulverization, to achieve the reaction activation of precursors. However, this type of method has several obvious drawbacks: First, the mixing is uneven, and the contact interface of the raw materials is limited, resulting in uneven component distribution or incomplete local reactions; second, the energy introduced during ball milling or mechanical pulverization can cause the chemical bonds of the raw materials to break, resulting in the raw materials reacting partially in advance, which in turn leads to uneven reaction during subsequent sintering; third, it is impossible to introduce adjustable carbon content by controlling carbonization byproducts, which limits the potential for improving the air stability of sulfide solid electrolytes.

[0044] On the other hand, while typical wet processes can improve mixing uniformity, they often use polar solvents such as alcohols and ketones, which have strong chemical interactions with sulfide precursors (such as P2S5 and Li2S), easily forming complexes or intermediate byproducts, increasing the risk of introducing impurities. Furthermore, reactive species are prone to remain during the drying process, affecting the purity and structural stability of the final product. In addition, polar solvents exhibit high carbonization during high-temperature sintering, making carbon source generation difficult to control and easily leading to excessively high carbon content, causing problems such as increased electronic conductivity and blocked ion channels.

[0045] In contrast, the approach adopted in this application selects a chemically inert, low-polarity, non-reactive solvent and controls its mass ratio to the precursor within the range of 1:(1.5–3.5). This ratio ensures sufficient dispersion of the precursor in the solvent, guaranteeing reaction uniformity, while also introducing a controllable amount of amorphous carbon (controlled at 0.03wt%–0.5wt%) during volatilization and sintering. This constructs a stable air barrier structure for the sulfide solid electrolyte, improving the material's stability in air, and simultaneously avoiding conductivity degradation caused by excessive carbon.

[0046] The mixture is dried at room temperature and pressure and in an inert atmosphere to evaporate the solvent, thereby obtaining a solid electrolyte precursor mixture. In the preparation process of this application, the solvent drying step is carried out under room temperature and pressure conditions and is designed in conjunction with other key process steps to achieve comprehensive control over the material structure and properties.

[0047] This application addresses the issue of direct contact between materials and air from the perspective of "the physical barrier effect of carbon doping." One aspect is the regulation of the carbon source: the natural volatilization process under ambient temperature and pressure is mild and controllable, which helps reduce the intensity of organic solvent volatilization. This allows some solvent to remain in the precursor, undergoing carbonization during subsequent stepwise sintering. This enables more precise control of the carbon content in the material, stabilizing it within the range of 0.03wt%–0.5wt%. This ensures uniform carbon distribution without forming a continuous conductive network, balancing air stability, low electronic conductivity, and high ionic conductivity.

[0048] On the other hand, particle size control: the ammonium halide in the precursor mixture of this application can release gas at high temperatures to adjust the particle structure or form a gas-phase assisted sintering path, thereby achieving particle size control and structural homogenization. When dried at room temperature and pressure, the ammonium halide can be effectively retained in the precursor; however, if high-temperature vacuum drying or other methods are used, the ammonium halide is prone to premature decomposition and volatilization, causing its function to be lost during the formal sintering stage, affecting the particle size control effect and density of the final product.

[0049] Therefore, the drying conditions selected in this invention not only simplify the process and reduce energy consumption, but are also a key point in achieving a balance between controllable carbon introduction and retention of reactivity. This condition setting is closely related to the overall material design goals, unlike the conventional choices in existing technologies that are set for convenience or default operation.

[0050] The solid electrolyte precursor mixture was calcined under an inert atmosphere to obtain the sulfide solid electrolyte.

[0051] The chemical formula of the sulfide solid electrolyte is Li. 7-a PS 6-a X a X is selected from at least one of Cl, Br and I, and 1≤a≤2.

[0052] In some embodiments of this application, based on the chemical formula Li of the target product sulfide solid electrolyte... 7-a PS 6- a X a Adjusting the molar ratio of the precursors, for example, when the molar ratio of Li₂S, P₂S₅, and NH₄X′ is 6:1:2, the synthesized sulfide solid electrolyte is Li₆PS₅X; when the molar ratio of Li₂S, P₂S₅, and NH₄X′ is 5.75:1:2.5, the synthesized sulfide solid electrolyte is Li₂S₅X. 5.75 PS 4.75 X 1.25 When the molar ratio of Li₂S, P₂S₅, and NH₄X′ is 5.5:1:3, the synthesized sulfide solid electrolyte is Li 5.5 PS 4.5 X 1.5 When the molar ratio of Li₂S, P₂S₅, and NH₄X′ is 5.25:1:3.5, the synthesized sulfide solid electrolyte is Li 5.25 PS 4.25 X 1.75 When the molar ratio of Li2S, P2S5, and NH4X′ is 5:1:4, the synthesized sulfide solid electrolyte is Li5PS4X2; when the molar ratio of Li2S, P2S5, NH4X′, and LiX″ is 5.75:1:1.5:0.5, the synthesized sulfide solid electrolyte is Li6PS5X; when the molar ratio of Li2S, P2S5, NH4X′, and LiX″ is 5.5:1:1:1, the synthesized sulfide solid electrolyte is Li6PS5X.

[0053] In some embodiments of this application, mechanical stirring is carried out at room temperature and pressure, and the stirring rate is 300-600 rpm. For example, the stirring rate can be 300 rpm, 350 rpm, 400 rpm, 480 rpm, 520 rpm, 600 rpm, or any combination of two of these values. The stirring time is 10-50 min. For example, the stirring time can be 10 min, 20 min, 30 min, 40 min, 50 min, or any combination of two of these values. By controlling the mixing method of the precursor and solvent, and the temperature, pressure, and stirring rate of the mechanical stirring within the above ranges, reactions between the substrates during stirring can be avoided, ensuring that a sufficient and uniform solid-phase reaction occurs only during the sintering stage. This is beneficial for the preparation of sulfide solid electrolytes, improving the purity and uniformity of the sulfide solid electrolytes, and thus improving the ionic conductivity of the sulfide solid electrolytes. When other mixing methods are used (such as ultrasonic dispersion), mechanical stirring under high temperature and pressure, or excessively high rotation speeds (e.g., greater than 600 rpm), reactions may occur between the substrates, leading to uneven reaction in the subsequent preparation of sulfide solid electrolytes, which in turn affects the ionic conductivity of the sulfide solid electrolytes. In this application, the mechanical stirring time is limited to the above-mentioned range, which ensures uniform mixing and more thorough contact of the components, thereby achieving higher ionic conductivity.

[0054] In some embodiments of this application, the calcination temperature is 450~600℃ and the time is 5~15h. For example, the calcination temperature can be 450℃, 500℃, 550℃, 600℃ or any two of these values, and the calcination time can be 5h, 8h, 10h, 12h, 15h or any two of these values.

[0055] In some embodiments of this application, the solvent evaporation rate is 1.5~7.0 mg / cm³. 2 •h. For example, the solvent evaporation rate can be 1.5 mg / cm³. 2 ·h, 3 mg / cm 2 ·h, 4.5 mg / cm 2 ·h、6 mg / cm 2 ·h, 7.0mg / cm 2 •h can be a range consisting of any two of these values. The inventors discovered in their research that limiting the solvent evaporation rate within the above range in this application can prevent excessively rapid solvent evaporation and the formation of cavities in the mixture, thereby further improving the ionic conductivity and overall performance of the electrolyte.

[0056] In some embodiments of this application, the residual rate of the solvent after evaporation is 1wt% to 5wt% based on the total mass of the solvent. The inventors discovered during their research that controlling the solvent residual rate within the range of this application not only provides a suitable carbon content but also introduces fewer carbon impurities during the calcination process, resulting in a sulfide solid electrolyte with high purity, further improving the ionic conductivity of the electrolyte.

[0057] In some embodiments of this application, the solvent evaporation rate is controlled during the drying process to maintain the thickness of the solid electrolyte precursor mixture at 1-5 mm, and the dried specific surface area of ​​the solid electrolyte precursor mixture is 1.5-3 cm². 2 / g. In this application, the material is a thin planar layer (e.g., granular or flake-like material spread in a beaker), and the drying specific surface area = drying area / mass of the precursor mixture; the drying area = the surface area of ​​the material in direct contact with the drying medium (inert atmosphere). By controlling the thickness and drying specific surface area, the drying rate of the material can be adjusted, thereby affecting the solvent residue and achieving the adjustment of the carbon content.

[0058] In some embodiments of this application, the moisture content in the inert atmosphere during the drying process is less than 10 ppm. Controlling the moisture content in the inert atmosphere during the drying process within the range specified in this application can better prevent the deterioration of the sulfide electrolyte and its raw materials.

[0059] A third aspect of this application provides a battery comprising a positive electrode, a negative electrode, and a sulfide solid electrolyte as described in the first aspect of this application, or a sulfide solid electrolyte prepared by the preparation method described in the second aspect of this application. Applying the sulfide solid electrolyte of this application or the sulfide solid electrolyte prepared by the preparation method of this application to a secondary battery significantly improves the safety, energy density, and low-temperature performance of the secondary battery.

[0060] This application does not impose any special limitations on the positive and negative electrode plates in the battery, as long as they can achieve the purpose of this application.

[0061] The fourth aspect of this application provides the application of the battery described in the third aspect of this application in electric vertical takeoff and landing (EVTOL) aircraft, including but not limited to its application in low-altitude economic manned EVTOL aircraft, which can improve the flight endurance, safety performance and extreme environment resistance of the spacecraft, while the long-life battery can reduce the maintenance frequency and cost of the aircraft. Example

[0062] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Unless otherwise specified, "parts" and "%" are mass standards. "Room temperature" is 25±5℃, "atmospheric pressure" is 101.325 kPa, and "overnight" is 12~24h.

[0063] Test methods and equipment:

[0064] Measurement of ionic conductivity

[0065] In an argon-filled glove box, 100 mg of solid electrolyte powder was weighed and placed in a mold battery with stainless steel sheets at both ends, each with a diameter of 9 mm. The battery was then pressurized at 200 MPa and 350 MPa, and two sets of data were tested. The thickness of the electrolyte sheet was measured to be 1 mm using a thickness gauge. AC impedance spectroscopy was performed using the mold battery. The bulk impedance of the electrolyte was determined using electrochemical impedance spectroscopy (EIS). On an electrochemical workstation (ChenHua, CHI630E), a DC polarization voltage of 1 V was applied to measure the bulk impedance, with an amplitude of 50 mV and a frequency range of 1 Hz to 10 MHz. The ionic conductivity of the electrolyte material was calculated based on the bulk impedance value and the ionic conductivity formula, as follows:

[0066]

[0067] Where σ is the ionic conductivity, with units of S·cm –1 L is the thickness of the electrolyte sheet, in cm; R is the electrolyte impedance, in Ω; S is the effective contact area between the stainless steel sheet and the electrolyte, in cm². 2 .

[0068] Carbon content testing

[0069] The test was conducted using a LECO CS744 high-frequency infrared carbon-sulfur analyzer. The instrument was calibrated using standard samples with known carbon content to ensure accuracy and repeatability. During the test, an appropriate amount of the sulfide solid electrolyte was added to the instrument's crucible and thoroughly mixed with flux to promote complete combustion. High-frequency induction heating caused the sulfide solid electrolyte to burn rapidly. The generated gas entered the infrared detection system to detect the carbon dioxide concentration, thereby calculating the carbon content.

[0070] Particle size distribution testing

[0071] The surface morphology and particle size distribution of the sulfide solid electrolyte were observed using a Zeiss Sigma 300 scanning electron microscope (SEM). The sample was fixed on the sample stage and placed in a vacuum chamber. SEM parameters such as accelerating voltage, beam current intensity, and working distance were adjusted to optimize imaging. Surface morphology information was acquired using a secondary electron detector. ImageJ software was used to measure and statistically analyze the particle size of the sulfide solid electrolyte in the SEM images to obtain its particle size distribution.

[0072] Methods for controlling and testing solvent evaporation rate

[0073] Under normal temperature and pressure and inert atmosphere, by using different evaporation containers (such as evaporating dishes and beakers), the thickness of the solid electrolyte precursor mixture was controlled at 1~5 mm, and the dry specific surface area per gram of the solid electrolyte precursor mixture was controlled at 1.5~3 cm². 2 The solvent evaporation rate is controlled by adjusting the concentration of the precursor mixture. After evaporating the precursor mixture for x hours, the masses m0 and m1 of the mixture before and after evaporation are determined by weighing. The amount of solvent evaporated during that evaporation time is m0 minus m1. Dividing this by the evaporation time x and the dry specific surface area S yields the solvent evaporation rate v. .

[0074] Air stability test

[0075] Air stability is primarily described by the amount of hydrogen sulfide produced by the sulfide solid electrolyte upon air exposure.

[0076] Hydrogen sulfide generation test: Under 40% air humidity and 25℃, a sulfide solid electrolyte of mass m and a hydrogen sulfide detector are placed together in a sealed reaction vessel of volume V. The vessel is ensured to be airtight. The reading of the hydrogen sulfide detector is recorded at fixed time intervals (10 min) to obtain the gas concentration c. Based on the gas concentration c, the reaction vessel volume V, and the mass m of the sulfide solid electrolyte, the hydrogen sulfide generation per unit mass of sample is calculated. Hydrogen sulfide generation = (c × V) / m, in cm³. 3 / g.

[0077] Example 1-1

[0078] Under an inert atmosphere, Li₂S, P₂S₅ and NH₄Cl in a molar ratio of 6:1:2 were weighed as precursors. 1 kg of n-hexane and 3 kg of the above precursors (solvent:precursor mass ratio = 1:3) were stirred at 400 rpm for 0.5 h at room temperature and pressure to obtain a mixture.

[0079] The mixture was placed overnight in a glove box under an argon atmosphere at room temperature and pressure to allow the solvent to evaporate, with the evaporation rate controlled at 5 mg / cm³. 2·h, so that the solvent residue is less than 5wt%, and a mixture of sulfide solid electrolyte precursors is obtained;

[0080] The sulfide solid electrolyte precursor mixture was transferred to a quartz tube, sealed with a sealing film, and then placed in a nitrogen-filled tube furnace. After removing the sealing film, the solid was heated at 550°C. o Heating at C for 10 h yielded a sulfide solid electrolyte (Li6PS5Cl), and its X-ray diffraction pattern is shown below. Figure 1 As shown.

[0081] Examples 1-2 to Examples 1-6

[0082] Except for adjusting the mass ratio of solvent to precursor according to Table 1, everything else is the same as in Example 1-1.

[0083] Examples 1-7 to Examples 1-13

[0084] Except for adjusting the solvent type according to Table 1, everything else is the same as in Example 1-1.

[0085] Examples 1-14 to Examples 1-16

[0086] Except for adjusting the type of NH4X′ according to Table 1, the rest is the same as in Example 1-1.

[0087] Examples 1-17 to Examples 1-20

[0088] Except for adjusting the precursor molar ratio according to Table 1, everything else is the same as in Example 1-1.

[0089] Examples 1-21 to 1-22

[0090] Except for adjusting the type of LiX″ according to Table 1, the rest is the same as in Examples 1-19.

[0091] Examples 2-1 to 2-8

[0092] Except for adjusting the roasting temperature and roasting time according to Table 2, the rest is the same as in Example 1-1.

[0093] Example 3-1

[0094] In an inert atmosphere, Li6PS5Cl and Li2O prepared in Example 1-1 at a specific mass ratio (99.98:0.02) were weighed and transferred to a ball mill jar. Zirconium beads of 0.5 mm were added (ball-to-material ratio of 2:1). After sealing the ball mill jar, it was ball milled at 500 rpm for 6 h on a Changsha Tianchuang powder planetary ball mill to obtain sample Li6PS5Cl@0.02Li2O.

[0095] Example 3-2

[0096] Except for adjusting the coating oxide to TiO2 according to Table 3, the rest is the same as in Example 3-1.

[0097] Comparative Examples 1 to 2

[0098] Except for adjusting the mass ratio of solvent to precursor according to Table 1, everything else is the same as in Example 1-1.

[0099] Comparative Example 3

[0100] Except for adjusting the solvent type according to Table 1, everything else is the same as in Example 1-1.

[0101] Comparative Example 4

[0102] Except for changing the phrase "the mixture was placed overnight in a glove box under inert atmosphere at room temperature and pressure" to "the mixture was placed overnight in a vacuum oven at room temperature with a vacuum degree of -0.09 MPa", the rest was the same as in Examples 1-1.

[0103] Comparative Example 5

[0104] Except for changing "the mixture was placed overnight in a glove box under an inert atmosphere at room temperature and pressure" to "the mixture was transferred to a tube furnace with argon gas and heated at 80°C for 5 hours", the rest is the same as in Example 1-1.

[0105] Comparative Example 6

[0106] (1) Under an inert atmosphere, lithium sulfide, phosphorus pentasulfide and lithium chloride in a molar ratio of 5:1:2 were weighed as precursors. 1 kg of acetonitrile and 3 kg of the above precursors were ball-milled at 500 rpm for 300 min to obtain a mixture. The mixture was vacuum dried at 40 °C for 8 h (-0.09 MPa) and then wet-milled for 1 h to obtain the reactants.

[0107] (2) The substance obtained in step (1) is dried, and a first heat treatment is performed at 200°C for 5 hours to remove residual carbon. A second heat treatment is performed at 550°C under an Ar atmosphere for 12 hours to allow the reactants to crystallize and grow.

[0108] (3) The solvent obtained in step (3) is ball-milled with acetonitrile for 2 hours, centrifuged at 4000 rpm for 1 hour, the upper layer of solution is removed for purification, and vacuum dried for 12 hours to prepare sulfide solid electrolyte.

[0109] Comparative Example 7

[0110] Except for adjusting the solvent type according to Table 1, everything else is the same as in Example 1-1.

[0111] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116] Table 3

[0117]

[0118] As can be seen from Table 1, the mass ratio of solvent to precursor within the range of this application can effectively reduce the carbon content in the solid sulfide electrolyte, thereby further improving its purity and ionic conductivity; the carbon content within the range of this application can reduce the negative impact of excessive carbon impurity content on lithium-ion transport, thereby improving the ionic conductivity of the sulfide solid electrolyte. Within the scope of this application, the solvent type can avoid the reaction between the solvent and the precursor to generate oxygen-containing impurities such as Li3PO4, thereby further improving the purity and ionic conductivity of the sulfide solid electrolyte. Among the halogen-containing compounds, type X is within the scope of this application, and the sulfide solid electrolytes all have high purity and ionic conductivity. The particle size distribution is within the scope of this application, which makes the sulfide solid electrolyte have a high packing density, thereby further improving its ionic conductivity. By controlling the molar ratio of NH4X′ and LiX″ within the above range, NH3 and H2S gases can be generated during the heat treatment process. NH3 and H2S gases not only serve as a protective atmosphere during calcination, but also regulate the growth of the sulfide solid electrolyte, making the particle size distribution of the sulfide solid electrolyte more uniform, and the final product has a narrower particle size distribution, which is beneficial to improving the electrochemical performance of the secondary battery.

[0119] As can be seen from Table 2, the mechanical stirring rate, mechanical stirring time, calcination temperature and time within the range of this application can ensure that the substrate reaction is complete and that halide ions (such as chloride ions) are basically doped into the unit cell, thereby appropriately increasing the unit cell parameters and increasing the ionic conductivity. Figure 1 The X-ray diffraction pattern of the sulfide solid electrolyte (Li6PS5Cl) prepared in Example 1-1 is shown, in which there is no diffraction peak of Li3PO4.

[0120] As can be seen from Table 3, the conductivity of sulfide solid electrolytes coated with an inert oxide layer does not decrease significantly. However, the addition of the oxide layer can effectively isolate the sulfide from moisture in the air, thereby improving the interfacial stability and air stability of the solid electrolyte.

[0121] In summary, the sulfide solid electrolyte of this application exhibits a small particle size distribution, high purity, and high ionic conductivity. Furthermore, the preparation method of this application, by using a small amount of inert solvent, avoids the reaction between the solvent and the precursor to generate oxygen impurities such as Li3PO4, thus mitigating carbonization during subsequent calcination, reducing the introduction of oxygen and carbon impurities, and improving the purity of the sulfide solid electrolyte. Moreover, by reducing the amount of solvent used, the drying step can be completed by standing at room temperature and atmospheric pressure, which not only reduces energy consumption but also lowers production costs, while simultaneously reducing the emissions of organic waste gas and the burden of solvent treatment during the production process. Furthermore, batteries containing the sulfide solid electrolyte of this application or those prepared by the method of this application possess high safety and energy density, as well as good low-temperature performance, and can be applied to electric vertical takeoff and landing (EVTOL) aircraft, such as low-altitude economical manned EVTOL aircraft.

[0122] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A sulfide solid electrolyte, characterized in that, The chemical formula of the sulfide solid electrolyte is Li 7-a PS 6- a X a The sulfide solid electrolyte is selected from at least one of Cl, Br, and I, where 1 ≤ a ≤ 2; wherein the sulfide solid electrolyte includes carbon generated in situ during the synthesis process, the carbon content being M, where 0.03 wt% ≤ M ≤ 0.5 wt%, and the preparation method of the sulfide solid electrolyte is as follows: Under an inert atmosphere, the precursor and solvent are mixed and mechanically stirred to obtain a mixture; wherein the precursor includes Li2S, P2S5 and a halogen-containing compound; the halogen-containing compound includes NH4X′ and LiX″, wherein X′ and X″ are each independently selected from at least one of Cl, Br and I; the molar ratio of NH4X′ and LiX″ is 1:(0~1); the mass ratio of the solvent to the precursor is 1:(1.5~3.5), and the solvent is selected from an inert solvent, wherein the inert solvent is selected from at least one of n-hexane, benzene, toluene, cyclohexane, n-pentane, acetonitrile, cyclopentane and dimethyl carbonate; The mixture was dried at room temperature and pressure under an inert atmosphere to evaporate the solvent, yielding a solid electrolyte precursor mixture. The solid electrolyte precursor mixture was calcined under an inert atmosphere to obtain the sulfide solid electrolyte. The chemical formula of the sulfide solid electrolyte is Li. 7-a PS 6-a X a X is selected from at least one of Cl, Br and I, where 1 ≤ a ≤ 2; The solvent evaporates at a rate of 1.5–7.0 mg / cm³. 2 h, based on the total mass of the solvent, the residual rate of the solvent after evaporation is 1wt%~5wt%.

2. The sulfide solid electrolyte according to claim 1, characterized in that, The carbon content is M, 0.03wt%≤M≤0.4wt%.

3. The sulfide solid electrolyte according to claim 1, characterized in that, The particle size of the sulfide solid electrolyte satisfies: 0.5µm < D v 50 < 1.5µm, 2µm < D v 90 < 2.5µm, 6µm < D MAX <6.5µm.

4. The sulfide solid electrolyte according to claim 1, characterized in that, The ionic conductivity of the sulfide solid electrolyte is >5.0 mS / cm.

5. The sulfide solid electrolyte according to claim 1, characterized in that, The mechanical stirring is carried out at room temperature and pressure, the stirring rate is 300~600 rpm, and the stirring time is 10~50 min.

6. The sulfide solid electrolyte according to claim 1, characterized in that, The roasting temperature is 450~600℃ and the time is 5~15h.

7. The sulfide solid electrolyte according to claim 1, characterized in that, During the drying process, the thickness of the solid electrolyte precursor mixture is 1-5 mm, and the dry specific surface area of ​​the solid electrolyte precursor mixture is 1.5-3 cm². 2 / g.

8. The sulfide solid electrolyte according to claim 1, characterized in that, The moisture content in the inert atmosphere during the drying process is less than 10 ppm.

9. A modified sulfide solid electrolyte, characterized in that, The modified sulfide solid electrolyte, based on the sulfide solid electrolyte of claim 1, further includes at least one of the following elements: O, Se, F, Mg, Ca, Sr, Zn, Sc, Sb, Si, Ge, Sn, B, Al, Ga, In, Ti, Zr, V, Nb, Cu, Ni, Mn, Cr, Ag, La, Ce, Tb, Te, Pb, As, Bi, Fe, Mo, Hf, Y, and Ru, wherein the elements are introduced by doping or coating.

10. A modified sulfide solid electrolyte, characterized in that, The modified sulfide solid electrolyte has an inert oxide layer coated on the surface of the sulfide solid electrolyte of claim 1, wherein the inert oxide layer is selected from at least one of Li2O, Al2O3, V2O5, ZnO, ZrO2, TiO2, MgO, RuO2, La2O3, CeO2, HfO2, Y2O3, SiO2, B2O3, CuO, NbO2, LiNbO3, and LiAlO2.

11. A battery, characterized in that, It includes a positive electrode, a negative electrode, and a sulfide solid electrolyte as described in any one of claims 1 to 8, or includes a modified sulfide solid electrolyte as described in any one of claims 9 to 10.

12. The application of the battery according to claim 11 in an electric vertical takeoff and landing aircraft.

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