Sulfide solid electrolyte, preparation method thereof, battery and application

Abstract

The invention relates to the technical field of electrochemistry, and provides a sulfide solid electrolyte, a preparation method thereof, a battery and application. The chemical formula of the sulfide solid electrolyte is Li7-aPS6-aXa, X is selected from at least one of Cl, Br and I, and a is greater than or equal to 1 and less than or equal to 2; wherein the sulfide solid electrolyte comprises carbon generated in situ in the synthesis process, the content of the carbon is M, and M is more than or equal to 0.03 wt% and less than or equal to 0.5 wt%. According to the method disclosed by the invention, the inert solvent is used and the solvent dosage is reduced, so that the introduction of oxygen and carbon impurities is reduced, the high purity and high ionic conductivity of the product are ensured, and meanwhile, the environmental pollution, the energy consumption and the production cost are remarkably reduced.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a sulfide solid electrolyte and a preparation method thereof, a battery containing the sulfide solid electrolyte, and applications of the battery. Background Art

[0002] Solid-state electrolytes are key materials for next-generation high-performance battery systems, and their performance directly impacts the battery's energy density, safety, and service life. Sulfide solid-state electrolytes have become a research hotspot in recent years due to their excellent ionic conductivity and electrochemical stability, particularly in all-solid-state lithium batteries.

[0003] Traditional methods for preparing sulfide solid electrolytes (LPSCs) primarily 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 alcoholic solvents to dissolve and mix the precursors, leveraging the solvent's polarity and protic properties to promote reaction uniformity. However, these solvents can react with precursors such as Li2S and P2S5, generating oxygen-containing impurities such as Li3PO4. Even when inert solvents that do not react with the precursors are used, their presence in large quantities can introduce significant carbon impurities during the calcination process. The dry process directly reacts the precursors through high-temperature calcination, avoiding the use of solvents in wet processes and reducing the generation of oxygen and carbon impurities. However, this method requires high temperature control precision and uniform mixing conditions, otherwise it can easily lead to problems such as excessively large and uneven product particle size. In the existing technology, some studies have used wet ball milling to pre-treat the precursor to improve the problems of uneven products and large particle size in the dry process. However, ball milling has problems such as high energy consumption, chemical bond breakage of the precursor during the ball milling process, and uneven reaction degree.

[0004] Furthermore, sulfide solid electrolytes generally suffer from poor air stability. When exposed to air, they easily react with moisture or oxygen, generating toxic gases such as hydrogen sulfide (H2S). This can lead to serious problems such as material structural degradation and decreased electrical conductivity, significantly limiting their safety and operability in practical energy storage devices. To address this issue, some studies have attempted to improve the air stability of sulfide solid electrolytes by coating them with protective layers (such as Li2O and Li2CO3), 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, how to improve the air stability of sulfide solid electrolytes while taking into account their ion conductivity has become the key to breaking through the bottleneck of sulfide solid electrolyte industrialization. Summary of the Invention

[0006] The purpose of this application is to provide a sulfide solid electrolyte and its preparation method, which can achieve dual optimization of the air stability and room temperature ionic conductivity of the sulfide solid electrolyte, thereby making the battery using the sulfide solid electrolyte safer and more efficient. The specific technical solution is as follows: The first aspect of the present application provides a sulfide solid electrolyte, the chemical formula of which 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%.

[0007] In some embodiments of the present application, the carbon content of the sulfide solid electrolyte is M, 0.03 wt%≤M≤0.4 wt%.

[0008] In some embodiments of the present 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.

[0009] In some embodiments of the present application, the ionic conductivity of the sulfide solid electrolyte is greater than 5.0 mS / cm.

[0010] In one embodiment of the present application, the sulfide solid electrolyte further includes at least one element selected from the group consisting of 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, and the element is introduced by doping or coating.

[0011] In one embodiment of the present application, the surface of the sulfide solid electrolyte is coated with an inert oxide layer, and 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.

[0012] A second aspect of the present application provides a method for preparing a sulfide solid electrolyte, comprising: Under an inert atmosphere, a precursor is mixed with a solvent and mechanically stirred to obtain a mixture; wherein the precursor comprises Li2S, P2S5 and a halogen-containing compound; the halogen-containing compound comprises NH4X′ and LiX″, X′ and X″ are each independently selected from at least one of Cl, Br and I; 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 an inert solvent, and the inert solvent is selected from at least one of n-hexane, benzene, toluene, cyclohexane, n-pentane, acetonitrile, cyclopentane and dimethyl carbonate; drying the mixture at room temperature and pressure in an inert atmosphere to volatilize the solvent, thereby obtaining a solid electrolyte precursor mixture; calcining the solid electrolyte precursor mixture under an inert atmosphere to obtain the 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, and 1≤a≤2.

[0013] In some embodiments of the present application, the mechanical stirring is performed at room temperature and pressure, the stirring rate is 300-600 rpm, and the stirring time is 10-50 min.

[0014] In some embodiments of the present application, the calcination temperature is 450-600° C. and the calcination time is 5-15 hours.

[0015] In some embodiments of the present application, the solvent volatilization rate is 1.5~7.0 mg / cm 2 h, based on the total mass of the solvent, the residual rate of the solvent after volatilization is 1wt%~5wt%.

[0016] In some embodiments of the present application, during the drying process, the thickness of the solid electrolyte precursor mixture is 1 to 5 mm, and the dry specific surface area of ​​the solid electrolyte precursor mixture is 1.5 to 3 cm 2 / g.

[0017] In some embodiments of the present application, the moisture content in the inert atmosphere during the drying process is less than 10 ppm.

[0018] The third aspect of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet and the sulfide solid electrolyte described in the first aspect of the present application or the sulfide solid electrolyte prepared by the preparation method described in the second aspect of the present application.

[0019] The fourth aspect of the present application provides an application of the battery of the third aspect of the present application in an electric vertical take-off and landing aircraft.

[0020] The beneficial effects of the present application are: The present application provides a sulfide solid electrolyte and a preparation method thereof, 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, and 1≤a≤2; wherein the sulfide solid electrolyte includes carbon generated in situ during synthesis, and the content of the carbon is M, 0.03 wt%≤M≤0.5 wt%. The present 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 of the sulfide solid electrolyte. The carbon is derived from the carbonization residue of the solvent during the heat treatment process, and is uniformly doped on the surface or grain boundary of the sulfide solid electrolyte particles, forming a continuous distribution of inert carbon phase. By controlling the content of carbon in the range of 0.03wt%-0.5wt%, a layer of isolation structure can be formed on the microscale, effectively inhibiting the 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 content of carbon in this range can improve the overall electronic transmission capacity of the sulfide solid electrolyte after being compounded with the positive electrode, which is beneficial to improve the interface electron diffusion efficiency of the sulfide solid electrolyte and the positive electrode. At the same time, by adjusting the content of carbon within the range of the present application, the problems of rising electronic conductivity and declining ionic conductivity caused by excessive content of carbon can be avoided, which ensures the low electronic conductivity and high ionic conductivity of the sulfide solid electrolyte as an electrolyte. Compared with the existing technical solutions relying on the addition of exogenous carbon, the present application can simultaneously improve the air stability, electrode adaptability and ionic conductivity performance of the sulfide solid electrolyte.

[0021] Furthermore, the preparation method of the present application, by using a small amount of inert solvent and controlling the volatilization rate of the solvent, effectively reduces the introduction of oxygen impurities during the wet preparation process, such as the generation of oxide impurities such as Li3PO4, while controlling the carbon content of the sulfide solid electrolyte, which can achieve the dual optimization of the air stability of the sulfide solid electrolyte and the room temperature ionic conductivity. Moreover, by reducing the amount of solvent used, the drying can be completed by standing at room temperature and pressure, which not only reduces energy consumption but also reduces production costs. In addition, NH3 and H2S gases are generated during the roasting process, making the particles more evenly dispersed and slowing down the particle growth rate to obtain particles with smaller particle size. Furthermore, a battery comprising the sulfide solid electrolyte of the present application or the sulfide solid electrolyte prepared by the preparation method of the present application has high safety and energy density and good low-temperature performance, and can be used in electric vertical take-off and landing aircraft, especially in low-altitude economic manned electric vertical take-off and landing aircraft.

[0022] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0024] Figure 1 This is the X-ray diffraction pattern of the sulfide solid electrolyte (Li6PS5Cl) prepared in Example 1-1. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] The first aspect of the present application provides a sulfide solid electrolyte, the chemical formula of which is Li 7-a PS 6-a X a The structural formula 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%. 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 consisting of any two of these values. The carbon in this application includes but is not limited to amorphous carbon, crystalline carbon, or carbide formed after sintering an organic solvent. The inventors have found that in a synthesis system involving an inert solvent, part of the organic solvent undergoes a carbonization reaction during the drying or sintering process, generating a small amount of carbon, which is embedded or attached to the surface or grain boundary region of the sulfide solid electrolyte particles in an extremely fine form. Unlike exogenously added carbon materials, this in situ formed carbon is more evenly distributed, has a smaller particle size, and is more tightly integrated with the main structure, making it less likely to fall off or migrate. Secondly, this type of amorphous carbon structure is an electrochemically inert material, unreactive with air, water, or electrolytes at room temperature and pressure, and exhibits excellent chemical stability. When uniformly distributed in a sulfide solid electrolyte at a concentration of 0.03–0.5 wt%, it forms a localized 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 the structural degradation process.

[0027] Maintaining the carbon content of the sulfide solid electrolyte between 0.03wt% and 0.5wt% not only helps optimize the microstructure and ion conductivity of the sulfide solid electrolyte itself, but also provides advantages in interface compatibility and electronic contact for its subsequent composite with the cathode material. When the carbon content is above 0.03wt%, a small amount of uniformly distributed conductive network can be formed in the sulfide solid electrolyte, which helps improve the electron transport path in the cathode composite system and enhance the overall interfacial reaction kinetics of the secondary battery, especially under high-load cathode conditions. If the carbon content is lower than 0.03wt%, the sulfide solid electrolyte will have insufficient conductivity when composited with the cathode, resulting in poor interfacial electronic contact, which can easily lead to increased interfacial polarization and capacity decay; and when the carbon content exceeds 0.5%, the excessive distribution of carbon may form a continuous electron conduction path, destroying the electronic insulation properties of the sulfide solid electrolyte, leading to an increased risk of self-discharge and even short circuit of the secondary battery. Therefore, controlling the carbon content of the sulfide solid electrolyte within the scope of the present application can not only ensure the stability of the sulfide solid electrolyte in synthesis and structure, but also provide good interface properties for subsequent composite with the positive electrode material.

[0028] In some embodiments of the present application, the particle size of the sulfide solid-state electrolyte satisfies: 0.5 µm < D v 50 < 1.5 µm, 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 between any two of them; 2 µm < D v 90 < 2.5 µm, for example, D v 90 can be 2.0 µm, 2.1 µm, 2.3 µm, 2.5 µm, or a range between any two of them; 6 µm < D MAX < 6.5 µm, for example, D MAX can be 6.0 µm, 6.1 µm, 6.3 µm, 6.5 µm, or a range between any two of them. The particle size D v 50, D v 90 and D MAX Within the above ranges, the sulfide solid-state electrolyte has a higher bulk density.

[0029] In some embodiments of the present application, the ionic conductivity of the sulfide solid-state electrolyte is > 5.0 mS / cm (referring to the ionic conductivity measured at room temperature under 350 MPa pressure molding). The sulfide solid-state electrolyte of the present application has high ionic conductivity, and when applied to a secondary battery, it can improve the safety performance, energy density, and low-temperature performance of the secondary battery.

[0030] In the present application, Figure 1 The XRD pattern of the present application has no diffraction peak with a peak area > 150 in the range of 20°-24.7°, which proves that there is basically no lithium phosphate impurity detected in the sulfide solid-state electrolyte of the present application. The inventors believe that this is because the reaction of ammonium chloride and lithium sulfide generates NH3 and H2S gas as a protective gas when sintering, so that the sample does not react with water and oxygen, reducing the oxygen impurity in the product.

[0031] In an embodiment of the present application, the sulfide solid-state electrolyte further comprises at least one of 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 elements, which are introduced by doping or coating.

[0032] In the present application, the above-mentioned doping method includes but is not limited to introducing doping elements during the substrate and solvent mixing stage or introducing doping elements with a sintering aid during the sintering stage; the above-mentioned coating method includes but is 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.

[0033] In one embodiment of the present application, the surface of the sulfide solid electrolyte is coated with an inert oxide layer, and 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 an inert oxide layer coated on the surface can effectively improve the interface stability and air stability of the solid electrolyte. The sulfide solid electrolyte with an inert oxide layer coated on the surface is prepared by the above-mentioned coating method. For example, under an inert atmosphere, the sulfide solid electrolyte Li 7-a PS 6-a X a Mixed with at least one of the above-mentioned inert oxides, then sealed and ball-milled to obtain a sulfide solid electrolyte with an inert oxide layer on the surface. 7-a PS 6-a X a The mass ratio of the inert oxide can be 95:5 to 99.99:0.01.

[0034] A second aspect of the present application provides a method for preparing a sulfide solid electrolyte, comprising: Under an inert atmosphere, the precursor and the solvent are mixed and mechanically stirred to obtain a mixture; The precursor comprises Li2S, P2S5 and a halogen-containing compound; the halogen-containing compound comprises NH4X' and LiX'', 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), the solvent is selected from inert solvents, and the inert solvents are selected from 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 formed by any two of the above values; and the mass ratio of the solvent to the precursor can be 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or a range formed by any two of the above values. When the molar ratio of NH4X' to LiX'' is within the above range, the precursor of the application will produce NH3 and H2S gas during the heat treatment process, and the NH3 and H2S gas not only can be used as a protective atmosphere during the calcination process, but also can control the growth of the sulfide solid electrolyte, so that the particle size distribution of the sulfide solid electrolyte is more uniform, the final product has a narrow particle size distribution, and the electrochemical performance of the secondary battery is improved; the mass ratio of the precursor to the solvent is limited within the above range, compared with the traditional wet process, not only the production cost is reduced, but also the environmental pollution is reduced; at the same time, by reducing the amount of solvent, the drying step only needs to be placed at room temperature and normal pressure in an inert atmosphere, which not only reduces the energy consumption, but also reduces the production cost. The solvent is selected from inert solvents, and will not react with the precursor such as Li2S and P2S5. If a non-inert solvent such as ethanol and tetrahydrofuran is selected, unavoidable side reactions will occur between the solvent and the precursor such as Li2S and P2S5, producing Li3PO4 and other oxygen impurities, which will reduce the purity of the sulfide solid electrolyte.

[0035] In the prior art, the synthesis methods of sulfide electrolytes mainly include dry method (i.e. solid phase method) and wet method (liquid phase method). The dry method usually refers to a mechanical mixing method without adding a solvent, such as high-energy ball milling, mechanical crushing and other physical means to realize the reaction excitation of the precursor. However, this method has several obvious defects: first, the mixture is not uniform, the contact interface of the raw materials is limited, which leads to uneven composition distribution or incomplete local reaction; second, the energy introduced in the ball milling or mechanical crushing process will cause the chemical bonds of the raw materials to break, which will cause the raw materials to react partially in advance, and then the reaction degree is not uniform during the subsequent sintering; third, the content of adjustable carbon cannot be introduced by controlling the carbonization by-product, which limits the improvement space of the air stability of the sulfide solid electrolyte.

[0036] On the other hand, although the typical wet process can improve mixing uniformity, polar solvents such as alcohols and ketones are often used, which have strong chemical interactions with sulfide precursors (such as P2S5 and Li2S), easily generating complexes or intermediate byproducts, increasing the risk of introducing impurities, and easily leaving reactive species during the drying process, affecting the purity and structural stability of the final product. In addition, polar solvents have a high degree of carbonization during high-temperature sintering, and the generation of carbon sources is not easy to control, which can easily lead to excessive carbon content, causing problems such as increased electronic conductivity and blocked ion channels.

[0037] In comparison, the scheme adopted in the present application selects a chemically inert, low-polarity non-reactive solvent and controls the mass ratio of the precursor to be within the range of 1:(1.5-3.5). At this ratio, the precursor can be fully dispersed in the solvent to ensure reaction uniformity, and a controllable amount of amorphous carbon (controlled within 0.03wt%-0.5wt%) can be introduced during volatilization and sintering, which can help to build a stable air barrier structure for sulfide solid-state electrolytes, improve the stability of the material in air, and avoid the problem of conductivity degradation caused by excessive carbon.

[0038] The mixture is dried at room temperature and normal pressure in an inert atmosphere to volatilize the solvent and obtain a solid-state electrolyte precursor mixture. In the preparation process of the present application, the drying step of the solvent is carried out under room temperature and normal pressure conditions, which is cooperatively designed with other key process links to achieve overall control of the structure and performance of the material.

[0039] The present application solves the problem of direct contact between the material and air from the perspective of the physical barrier effect of carbon doping. On the one hand, the carbon source is controlled: the natural volatilization process under room temperature and normal pressure conditions is mild and controllable, which helps to reduce the intensity of organic solvent volatilization, allowing some solvents to remain in the precursor and carbonize during subsequent step-by-step sintering, thereby more accurately controlling the carbon content in the material to a range of 0.03wt%-0.5wt%, ensuring uniform distribution of carbon without forming a continuous conductive network, and balancing air stability, low electronic conductivity, and high ionic conductivity.

[0040] On the other hand, the particle size is controlled: the ammonium halide in the precursor mixture of the present application can release gas at high temperatures to adjust the particle structure or form a gas-phase auxiliary sintering path, achieving particle size control and structural uniformization of the material. Under room temperature and normal pressure, ammonium halide can be effectively retained in the precursor; if high-temperature vacuum drying or other methods are used, ammonium halide is easily decomposed and volatilized, causing its function to be lost in the formal sintering stage, affecting the particle size control effect and density of the final product.

[0041] Therefore, the selected drying condition of the present application is not only to simplify the process and reduce the energy consumption, but also to realize the key node of balancing between the controllable introduction of carbon content and the preservation of reaction activity. The setting of this condition is closely related to the overall material design goal, which is different from the conventional selection in the prior art for the sake of convenience or default operation setting.

[0042] firing the solid-state electrolyte precursor mixture in an inert atmosphere to obtain the sulfide solid-state electrolyte; wherein the chemical formula of the sulfide solid-state 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.

[0043] In some embodiments of the present application, according to the chemical formula Li 7-a PS 6- a X a Adjust 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-state electrolyte is Li6PS5X; when the molar ratio of Li2S, P2S5 and NH4X' is 5.75:1:2.5, the synthesized sulfide solid-state electrolyte is Li 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-state 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-state 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-state 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-state electrolyte is Li6PS5X; when the molar ratio of Li2S, P2S5, NH4X' and LiX" is 5.5:1:1:1, the synthesized sulfide solid-state electrolyte is Li6PS5X.

[0044] In some embodiments of the present application, the mechanical stirring is carried out at room temperature and pressure, the rate of the mechanical stirring is 300-600 rpm, for example, the rate of the mechanical stirring can be 300 rpm, 350 rpm, 400 rpm, 480 rpm, 520 rpm, 600 rpm or a range defined by any two of the above values; the time of the mechanical stirring is 10-50 min, for example, the time of the mechanical stirring can be 10 min, 20 min, 30 min, 40 min, 50 min or a range defined by any two of the above values. By regulating the mixing mode of the precursor and the solvent, the temperature, pressure and stirring rate of the mechanical stirring within the above ranges, the reaction between the substrates during stirring can be avoided, ensuring that the substrates undergo sufficient and uniform solid-phase reaction only in the sintering stage, which is conducive to the preparation of sulfide solid electrolyte, improves the purity and uniformity of the sulfide solid electrolyte, and further improves the ionic conductivity of the sulfide solid electrolyte. When other mixing modes (such as ultrasonic dispersion, etc.), high-temperature and high-pressure mechanical stirring or too high stirring speed (for example, greater than 600 rpm) are used, the substrates may react with each other, resulting in uneven reaction during the subsequent preparation of the sulfide solid electrolyte, which in turn affects the ionic conductivity of the sulfide solid electrolyte. The time of the mechanical stirring in the present application is limited within the above range, which can make the components mix uniformly and contact more fully, thereby obtaining higher ionic conductivity.

[0045] In some embodiments of the present application, the temperature of the calcination is 450-600°C, and the time is 5-15 h. For example, the temperature of the calcination can be 450°C, 500°C, 550°C, 600°C or a range defined by any two of the above values, and the time of the calcination can be 5 h, 8 h, 10 h, 12 h, 15 h or a range defined by any two of the above values.

[0046] In some embodiments of the present application, the rate of the solvent evaporation is 1.5-7.0 mg / cm 2 ·h. For example, the rate of the solvent evaporation can be 1.5 mg / cm 2 ·h, 3 mg / cm 2 ·h, 4.5 mg / cm 2 ·h, 6 mg / cm 2 ·h, 7.0 mg / cm 2 ·h or a range defined by any two of the above values. The inventors have found in their research that the rate of the solvent evaporation in the present application is limited within the above range, which can avoid too fast solvent evaporation and the formation of cavities in the mixture, thereby further improving the ionic conductivity and overall performance of the electrolyte.

[0047] In some embodiments of the present application, the residual solvent content after volatilization is 1 wt% to 5 wt% based on the total mass of the solvent. The inventors discovered that controlling the residual solvent content within the range of the present application can provide an appropriate carbon content while introducing less carbon impurities during the calcination process. This results in a higher purity sulfide solid electrolyte and further improves the ionic conductivity of the electrolyte.

[0048] In some embodiments of the present application, the solvent volatilization rate is regulated during the drying process so that the thickness of the solid electrolyte precursor mixture is controlled to be 1-5 mm, and the dry specific surface area of ​​the solid electrolyte precursor mixture is 1.5-3 cm 2 / g. In this application, the material is a thin, planar layer (for example, granules or flakes spread in a beaker). The dry specific surface area is calculated as: dry area divided by the mass of the precursor mixture; dry area is the surface area of ​​the material in direct contact with the drying medium (inert atmosphere). By controlling the thickness and dry specific surface area, the drying rate of the material can be adjusted, thereby affecting the residual solvent content and thus regulating the carbon content.

[0049] In some embodiments of the present 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 scope of the present application can better prevent the sulfide electrolyte and its raw materials from deteriorating.

[0050] The third aspect of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, and the sulfide solid electrolyte described in the first aspect of the present application, or a sulfide solid electrolyte prepared by the preparation method described in the second aspect of the present application. Application of the sulfide solid electrolyte of the present application or the sulfide solid electrolyte prepared by the preparation method of the present application in a secondary battery greatly improves the safety, energy density, and low-temperature performance of the secondary battery.

[0051] This application does not impose any special restrictions on the positive electrode sheet and the negative electrode sheet in the battery, as long as they can achieve the purpose of this application.

[0052] The fourth aspect of the present application provides the application of the battery described in the third aspect of the present application in electric vertical take-off and landing aircraft, including but not limited to low-altitude economic manned electric vertical take-off and landing aircraft, which can improve the flight endurance, safety performance and extreme environment resistance of the spacecraft. At the same time, the long-life battery can reduce the maintenance frequency and cost of the aircraft. Example

[0053] Hereinafter, examples and comparative examples are presented to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis. "Normal temperature" is 25 ± 5°C, "normal pressure" is 101.325 kPa, and "overnight" is 12 to 24 h.

[0054] Test methods and equipment: Test of ion conductivity In an argon-filled glove box, 100 mg of solid electrolyte powder was weighed and placed in a mold cell with a 9 mm diameter stainless steel sheet at both ends, and was press-molded at a pressure of 200 MPa and 350 MPa, respectively, to test two sets of data. The thickness of the electrolyte sheet was measured to be 1 mm by a thickness gauge, and an AC impedance spectrum test was performed using a mold cell. The bulk impedance of the electrolyte was measured by electrochemical impedance spectroscopy (EIS). The bulk impedance of the electrolyte was measured by applying a direct current (DC) polarization voltage of 1 V on an electrochemical workstation (ChenHua, CHI630E), with an amplitude of 50 mV and a frequency range of 1 Hz to 10 MHz. The ion conductivity of the electrolyte material was calculated from the bulk impedance value of the electrolyte and the ion conductivity formula, as follows:

[0055] wherein σ is the ion conductivity, with a unit of S · cm –1 ; L is the thickness of the electrolyte sheet, with a unit of cm; R is the bulk impedance of the electrolyte, with a unit of Ω; and S is the effective contact area between the stainless steel sheet and the electrolyte, with a unit of cm 2 .

[0056] Test of carbon content A LECO CS744 high-frequency infrared carbon-sulfur instrument was used for the test, and a standard sample with a known carbon content was used to calibrate the instrument to ensure the accuracy and repeatability of the test. During the test, an appropriate amount of the sulfide solid electrolyte was added to the crucible of the instrument and mixed with a fluxing agent to facilitate complete combustion. The sulfide solid electrolyte was rapidly combusted by high-frequency induction heating, and the generated gas entered the infrared detection system to detect the concentration of carbon dioxide, and then the carbon content was calculated.

[0057] Test of particle size distribution A Zeiss Sigma 300 scanning electron microscope (SEM) was used to observe the surface morphology and particle size distribution of the sulfide solid electrolyte. The sample was mounted on a sample stage and placed in a vacuum chamber. SEM parameters such as the accelerating voltage, beam intensity, and working distance were adjusted to optimize imaging. Surface morphology information was acquired using a secondary electron detector. Image J software was used to measure and analyze the particle size distribution of the sulfide solid electrolyte in the SEM images.

[0058] Control and testing methods of solvent evaporation rate At room temperature, pressure and inert atmosphere, by using different evaporation containers (such as evaporating dishes, beakers), the thickness of the solid electrolyte precursor mixture is controlled to be 1~5mm, and the dry specific surface area per gram of the solid electrolyte precursor mixture is controlled to be 1.5~3cm 2 To control the rate of solvent evaporation. After the precursor mixture evaporates for x hours, the mass of the mixture before and after evaporation, m0 and m1, is determined by weighing. m0 minus m1 is the amount of solvent evaporated during the evaporation time. Dividing this by the evaporation time x and the dry specific surface area S gives the solvent evaporation rate v. .

[0059] Air stability test Air stability is mainly described by the amount of hydrogen sulfide produced by sulfide solid electrolytes upon air exposure.

[0060] Hydrogen sulfide production test: At 40% humidity and 25°C, place a sulfide solid electrolyte (mass m) and a hydrogen sulfide detector in a sealed reaction vessel (volume V). Ensure the container is airtight. Record the reading of the hydrogen sulfide detector at regular intervals (10 minutes) to obtain the gas concentration c. Calculate the hydrogen sulfide production per unit mass of sample based on the gas concentration c, the reaction vessel volume V, and the mass m of the sulfide solid electrolyte. Hydrogen sulfide production = (c × V) / m, in cm 3 / g.

[0061] Example 1-1 Under an inert atmosphere, Li2S, P2S5, and NH4Cl were weighed in a molar ratio of 6:1:2 as precursors, and 1 kg of n-hexane and 3 kg of the above precursors (mass ratio of solvent:precursor = 1:3) were stirred at 400 rpm for 0.5 h at room temperature and pressure to obtain a mixture; The mixture was placed in a glove box under an argon atmosphere at room temperature and pressure overnight to evaporate the solvent. The solvent evaporation rate was controlled at 5 mg / cm 2 h, so that the residual solvent content is less than 5 wt % to obtain a sulfide solid electrolyte precursor mixture; The sulfide solid electrolyte precursor mixture was transferred to a quartz tube, which was sealed with a sealing film. The quartz tube was placed in a nitrogen-filled tube furnace. After removing the sealing film, the solid was heated at 550 o C for 10 h to obtain a sulfide solid electrolyte (Li6PS5Cl), whose X-ray diffraction pattern is as follows Figure 1 shown.

[0062] Example 1-2 to Example 1-6 Except for adjusting the mass ratio of the solvent to the precursor according to Table 1, the rest is the same as Example 1-1.

[0063] Example 1-7 to Example 1-13 Except for adjusting the solvent type according to Table 1, the rest is the same as Example 1-1.

[0064] Example 1-14 to Example 1-16 Except for adjusting the type of NH4X' according to Table 1, the rest is the same as Example 1-1.

[0065] Example 1-17 to Example 1-20 Except for adjusting the precursor molar ratio according to Table 1, the rest is the same as Example 1-1.

[0066] Example 1-21 to Example 1-22 Except for adjusting the type of LiX″ according to Table 1, the rest is the same as Example 1-19.

[0067] Example 2-1 to Example 2-8 Except for adjusting the calcination temperature and calcination time according to Table 2, the rest is the same as Example 1-1.

[0068] Example 3-1 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. 0.5 mm zirconium beads were added (ball-to-material ratio of 2:1). After sealing the ball mill, the mixture was ball milled at 500 rpm for 6 h in a Changsha Tianchuang powder planetary ball mill to obtain the sample Li6PS5Cl@0.02Li2O.

[0069] Example 3-2 Except for adjusting the coating oxide to TiO2 according to Table 3, the rest is the same as Example 3-1.

[0070] Comparative Example 1 to Comparative Example 2 Except for adjusting the mass ratio of the solvent to the precursor according to Table 1, the rest is the same as Example 1-1.

[0071] Comparative Example 3 Except for adjusting the solvent type according to Table 1, the rest is the same as Example 1-1.

[0072] Comparative Example 4 The process was the same as Example 1-1 except that the mixture was placed in a glove box under an inert atmosphere at room temperature and pressure overnight. The process was changed to placing the mixture in a vacuum oven at room temperature with a vacuum degree of -0.09 MPa overnight.

[0073] Comparative Example 5 The process is the same as Example 1-1 except that “the mixture is placed in a glove box under an inert atmosphere at room temperature and pressure overnight” is adjusted to “the mixture is transferred to a tube furnace filled with argon and heated at 80° C. for 5 h”.

[0074] Comparative Example 6 (1) Under an inert atmosphere, lithium sulfide, phosphorus pentasulfide, and lithium chloride were weighed as precursors in a molar ratio of 5:1:2. 1 kg of acetonitrile and 3 kg of the precursors were ball-milled at 500 rpm for 300 min to obtain a mixture. The mixture was vacuum-dried at 40°C (-0.09 MPa) for 8 h and wet-milled for 1 h to obtain the reactant.

[0075] (2) The material obtained in step (1) was dried, subjected to a first heat treatment at 200°C for 5 hours to remove residual carbon, and subjected to a second heat treatment at 550°C in an Ar atmosphere for 12 hours to allow the reactant to crystallize.

[0076] (3) The solvent obtained in step (3) was ball-milled with acetonitrile for 2 hours, and then centrifuged at 4000 rpm for 1 hour. The upper layer of the solution was removed for purification, and vacuum dried for 12 hours to prepare a sulfide solid electrolyte.

[0077] Comparative Example 7 Except for adjusting the solvent type according to Table 1, the rest is the same as Example 1-1.

[0078] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0079] Table 1

[0080] Table 2

[0081] Table 3

[0082] As can be seen from Table 1, the mass ratio of the solvent to the 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 specified 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. The type of solvent is within the scope of this application, which can avoid the reaction of the solvent with the precursor to generate oxygen-containing impurities such as Li3PO4, thereby further improving the purity and ionic conductivity of the sulfide solid electrolyte; in the halogen-containing compound, the type of X is within the scope of this application, and the sulfide solid electrolyte has high purity and ionic conductivity; the particle size distribution is within the scope of this application, so that the sulfide solid electrolyte has a high packing density, thereby further improving its ionic conductivity; the molar ratio of NH4X′ and LiX″ is controlled within the above range, and NH3 and H2S gases can be generated during the heat treatment process. NH3 and H2S gases not only serve as protective atmospheres during the roasting process, but also can regulate the growth of the sulfide solid electrolyte, making the particle size dispersion of the sulfide solid electrolyte more uniform, and the final product particle size distribution is narrow, which is beneficial to improving the electrochemical performance of the secondary battery.

[0083] As can be seen from Table 2, the mechanical stirring rate, mechanical stirring time, calcination temperature and time are within the range of this application, which can enable the substrate to react completely and the halogen ions (such as chloride ions) to be basically doped into the unit cell, thereby appropriately increasing the unit cell parameters and improving the ionic conductivity. Figure 1 This is the X-ray diffraction pattern of the sulfide solid electrolyte (Li6PS5Cl) prepared in Example 1-1, in which there is no diffraction peak of Li3PO4.

[0084] As can be seen from Table 3, the conductivity of the sulfide solid electrolyte coated with an inert oxide layer is not significantly reduced, but the addition of the oxide layer can effectively isolate the sulfide from contact with moisture in the air, effectively improving the interface stability and air stability of the solid electrolyte.

[0085] In summary, the sulfide solid electrolyte of the present application has a small particle size distribution, high purity and high ionic conductivity. Further, the preparation method of the present application avoids the reaction of the solvent with the precursor to generate Li3PO4 and other oxygen impurities by using a small amount of inert solvent, alleviates the carbonization phenomenon occurring in the subsequent calcination process, reduces the introduction of oxygen and carbon impurities, and improves the purity of the sulfide solid electrolyte. Moreover, by reducing the amount of solvent, the drying step can be completed by standing at room temperature and normal pressure, which not only reduces energy consumption, but also reduces production costs, while reducing the burden of organic waste gas emission and solvent treatment during production. Further, the battery comprising the sulfide solid electrolyte of the present application or the sulfide solid electrolyte prepared by the preparation method of the present application has high safety and energy density and good low-temperature performance, and can be applied to electric vertical take-off and landing aircraft, for example, low-altitude economic manned electric vertical take-off and landing aircraft.

[0086] The above description is merely preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present 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 , 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%.

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 greater than 5.0 mS / cm.

5. The sulfide solid electrolyte according to claim 1, characterized in that The sulfide solid electrolyte also includes at least one of 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 elements, and the elements are introduced by doping or coating.

6. The sulfide solid electrolyte according to claim 1, characterized in that The surface of the sulfide solid electrolyte is coated with an inert oxide layer, and 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.

7. A method for preparing a sulfide solid electrolyte, characterized in that: include: Under an inert atmosphere, a precursor is mixed with a solvent and mechanically stirred to obtain a mixture; wherein the precursor comprises Li2S, P2S5 and a halogen-containing compound; the halogen-containing compound comprises NH4X′ and LiX″, X′ and X″ are each independently selected from at least one of Cl, Br and I; 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 an inert solvent, and the inert solvent is selected from at least one of n-hexane, benzene, toluene, cyclohexane, n-pentane, acetonitrile, cyclopentane and dimethyl carbonate; drying the mixture at room temperature and pressure in an inert atmosphere to volatilize the solvent, thereby obtaining a solid electrolyte precursor mixture; calcining the solid electrolyte precursor mixture under an inert atmosphere to obtain the 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, and 1≤a≤2.

8. The preparation method according to claim 7, 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.

9. The preparation method according to claim 7, characterized in that The calcination temperature is 450-600° C., and the calcination time is 5-15 hours.

10. The preparation method according to claim 7, characterized in that The solvent evaporation rate is 1.5~7.0 mg / cm 2 h, based on the total mass of the solvent, the residual rate of the solvent after volatilization is 1wt%~5wt%.

11. The preparation method according to claim 7, 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 cm 2 / g.

12. The preparation method according to claim 7, characterized in that The moisture content in the inert atmosphere during the drying process is less than 10 ppm.

13. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the sulfide solid electrolyte according to any one of claims 1 to 6, or comprises the sulfide solid electrolyte prepared by the preparation method according to any one of claims 7 to 12.

14. Use of the battery according to claim 13 in an electric vertical take-off and landing aircraft.

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