Sulfide solid electrolyte, preparation method thereof and all-solid-state battery

Abstract

The invention provides a sulfide solid electrolyte, a preparation method thereof and an all-solid-state battery, and relates to the technical field of batteries. The method comprises the following steps: mixing and grinding lithium sulfide and phosphorus sulfide to obtain a non-crystallized mixture, and then carrying out first heat treatment and refining on the non-crystallized mixture to obtain a first mixture with fine particles and fine powder; meanwhile, lithium sulfide and halogen lithium salt are mixed and granulated, and a granular second mixture is obtained; and finally, obtaining the sulfide solid electrolyte according to the first mixture and the second mixture. The sulfide solid electrolyte prepared by the method has a heterogeneous halogen concentration gradient core-shell structure, and can improve the stability of air / water on the premise of not reducing the ionic conductivity, that is, the synergistic improvement of the ionic conductivity and the air / water stability is realized.

Description

Technical Field

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

[0002] Among numerous solid electrolyte materials, sulfide solid electrolytes stand out due to their extremely high ionic conductivity (up to 10⁻⁶). -3 ~10 -2 With its high energy density (S / cm) and excellent machinability, it can meet the requirements of next-generation energy storage devices for higher energy density and longer cycle life of all-solid-state batteries.

[0003] However, sulfide solid electrolytes are extremely sensitive to moisture in the air and are prone to irreversible hydrolysis, leading to a decrease in ionic conductivity and air stability, which restricts their large-scale production, processing, and practical application. Existing technologies employ halogen doping strategies to improve the ionic conductivity of sulfide solid electrolytes; however, high halogen doping reduces their air stability. Alternatively, soft acids As and Sn are used as central atoms or oxides to synthesize new sulfide solid electrolytes to improve their air / water stability, but their ionic conductivity is insufficient to meet the requirements of high-rate batteries.

[0004] In summary, providing a sulfide solid electrolyte that combines high ionic conductivity and high air / water stability is an urgent technical problem to be solved. Summary of the Invention

[0005] This application provides a sulfide solid electrolyte, its preparation method, and an all-solid-state battery to achieve a synergistic improvement in ionic conductivity and high air / water stability.

[0006] In a first aspect, embodiments of this application provide a sulfide solid electrolyte, comprising: a first mixture and a second mixture;

[0007] The first mixture comprises lithium sulfide and phosphorus sulfide, and the second mixture comprises lithium sulfide and a lithium halide salt;

[0008] The first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

[0009] In one possible implementation, the particle size of the first particle is 0.6 μm to 2 μm;

[0010] and / or;

[0011] The second particle has a particle size of 3μm to 20μm.

[0012] In one possible implementation, the phosphorus sulfide includes at least one of P2S3, P2S5, P4S4, P4S7, P4S9, and P4S6.

[0013] and / or;

[0014] The lithium halide salt includes at least one of LiCl, LiBr, LiI, and LiF.

[0015] In one possible implementation, the molar ratio of lithium sulfide to phosphorus sulfide in the first mixture is (3~3.2):1;

[0016] and / or;

[0017] The molar ratio of lithium sulfide to the halogen lithium salt in the second mixture is (0.176~19):1.

[0018] In one possible implementation, the molar ratio of the first mixture to the second mixture is 1:(1.9~2.1).

[0019] Secondly, embodiments of this application provide a method for preparing a sulfide solid electrolyte, the method comprising:

[0020] Lithium sulfide and phosphorus sulfide were mixed and ground to obtain an amorphous mixture.

[0021] After subjecting the amorphous mixture to a first heat treatment, it is then refined to obtain a first mixture;

[0022] Lithium sulfide and lithium halide salts are mixed and granulated to obtain a second mixture;

[0023] Based on the first mixture and the second mixture, a sulfide solid electrolyte is obtained;

[0024] Wherein, the first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

[0025] In one possible implementation, the granulation process includes any one of spray drying granulation, dry granulation, and wet granulation.

[0026] In one possible implementation, the particle size of the first particle is 0.6 μm to 2 μm;

[0027] and / or;

[0028] The second particle has a particle size of 3μm to 20μm.

[0029] In one possible implementation, the mixing and grinding of lithium sulfide and phosphorus sulfide to obtain an amorphous mixture includes:

[0030] Lithium sulfide and phosphorus sulfide in a molar ratio of (3~3.2):1 were placed in an inert gas atmosphere and mechanically mixed and ground to obtain the amorphous mixture.

[0031] The inert gas includes at least one of argon, nitrogen, and neon.

[0032] In one possible implementation, in the first heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 240~320℃, and the holding time is 0.5~8h.

[0033] In one possible implementation, the refining process includes at least one of mechanical grinding, ball milling, sand milling, or air jet milling.

[0034] In one possible implementation, the phosphorus sulfide includes at least one of P2S3, P2S5, P4S4, P4S7, P4S9, and P4S6.

[0035] and / or;

[0036] The lithium halide salt includes at least one of LiCl, LiBr, LiI, and LiF.

[0037] In one possible implementation, the molar ratio of lithium sulfide to phosphorus sulfide in the first mixture is (3~3.2):1;

[0038] and / or;

[0039] The molar ratio of lithium sulfide to the lithium halide salt in the second mixture is (0.176~19):1;

[0040] And / or,

[0041] The molar ratio of the first mixture to the second mixture is 1:(1.9~2.1).

[0042] In one possible implementation, obtaining the sulfide solid electrolyte based on the first mixture and the second mixture includes:

[0043] The first mixture is mixed with the second mixture to obtain a third mixture;

[0044] The third mixture is subjected to a second heat treatment to obtain a sintered body;

[0045] The sintered body is crushed and sieved to obtain the sulfide solid electrolyte.

[0046] In one possible implementation, in the second heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 400~560℃, and the holding time is 2~24h.

[0047] Thirdly, embodiments of this application provide an all-solid-state battery, including a positive electrode, a negative electrode, and a sulfide solid electrolyte as described in the first aspect and / or any possible implementation of the first aspect, and / or a sulfide solid electrolyte prepared by the second aspect and / or various possible implementations of the second aspect.

[0048] This application provides a sulfide solid electrolyte, its preparation method, and an all-solid-state battery. The method involves mixing and grinding lithium sulfide and phosphorus sulfide to obtain an amorphous mixture, thus optimizing the ion transport path. The amorphous mixture is then heat-treated and refined to obtain a first mixture with fine particles. Simultaneously, lithium sulfide is mixed with a halogen lithium salt and granulated to obtain a second mixture with larger particles. Finally, a sulfide solid electrolyte is obtained based on the first and second mixtures. The first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture. The sulfide solid electrolyte prepared by this method possesses a core-shell structure with a heterogeneous halogen concentration gradient. The halogen-rich core significantly enhances the lithium-ion migration ability and the overall ionic conductivity of the material, while the halogen-poor shell provides effective physical isolation and chemical protection for the core, greatly enhancing the stability of the sulfide solid electrolyte in air or humid environments. Ultimately, this achieves a synergistic improvement in ionic conductivity and air / water stability. Attached Figure Description

[0049] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0050] Figure 1 This is a schematic diagram of the structure of a sulfide solid electrolyte provided in this application;

[0051] Figure 2 A flowchart illustrating a method for preparing a sulfide solid electrolyte provided in this application. Figure 1 ;

[0052] Figure 3 A flowchart illustrating a method for preparing a sulfide solid electrolyte provided in this application. Figure 2 ;

[0053] Figure 4 A schematic diagram of the comparison curves of the ionic conductivity of a sulfide solid electrolyte provided in this application;

[0054] Figure 5 A schematic diagram showing the comparison curves of the ionic conductivity retention rate of a sulfide solid electrolyte provided in this application.

[0055] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0057] The application background of this application is explained as follows:

[0058] With the rapid development of the electric vehicle and large-scale energy storage markets, the demand for high-energy-density and high-safety rechargeable batteries is becoming increasingly urgent. Traditional lithium-ion batteries use organic liquid electrolytes, which pose safety hazards such as easy leakage, flammability, and explosion, and their energy density is already close to the theoretical limit, making it difficult to meet the requirements of next-generation energy storage devices for higher energy density and longer cycle life. All-solid-state batteries, by using non-flammable inorganic solid electrolytes instead of organic liquid electrolytes, are considered one of the ultimate solutions for next-generation energy storage technology.

[0059] Among numerous solid electrolyte materials, sulfide solid electrolytes stand out due to their extremely high ionic conductivity (up to 10⁻⁶). -3 ~10 -2 Sulfide solid electrolytes (such as sulfide-rich silver-germanium sulfide-based Li) have attracted much attention due to their good machinability (e.g., cold pressing), which can significantly reduce the interfacial impedance between the electrolyte and the electrode, thereby improving the rate performance and cycle stability of the battery. 5.4 PS 4.4 Cl 1.6 It has poor air / water stability and is extremely sensitive to water vapor in the air. Upon exposure, it will rapidly undergo an irreversible hydrolysis reaction, generating highly toxic H2S gas and causing a sharp drop in ionic conductivity, which seriously restricts its feasibility in large-scale production, processing and practical application.

[0060] Existing technologies mostly employ homogeneous doping schemes, which cannot simultaneously achieve high ionic conductivity and high air / water stability, thus limiting the application of sulfide electrolytes in all-solid-state batteries. Specifically, the ionic conductivity of sulfide solid electrolytes can be improved by doping them with halogens (such as Cl, Br, I), for example, Li. 5.4 PS 4.4 Cl 1.6 The ionic conductivity of halogen-rich materials can reach 10. -2 S / cm. However, high halogen doping exacerbates the sensitivity of sulfide solid electrolytes to water vapor, leading to deterioration of air / water stability. To improve air / water stability, some studies have synthesized new sulfide solid electrolytes by using soft acid elements (such as As and Sn) as central atoms to replace some sulfide components (such as Li4SnS4 and Li3AsS4), for example, Li3SbS4 and Li... 3.8 Sb 0.2 Sn 0.8 S4, Li6PS5I-20%Sn, Li4Cu8Ge3S 12 These all exhibit high air / water stability in humid air. Furthermore, doping with oxides (P2O5, LiNbO3) to create a surface protective layer can also effectively improve the air / water stability of sulfide solid electrolytes. However, these strategies all have a significant drawback: they sacrifice some of the ionic conductivity of the sulfide solid electrolyte.

[0061] Although the above methods have improved the performance of sulfide solid electrolytes to some extent, their core contradiction has not been overcome: it is difficult to achieve both "high ionic conductivity" and "good air / water stability" in a single sulfide solid electrolyte.

[0062] Therefore, providing a sulfide solid electrolyte with both high ionic conductivity and excellent air / water stability, as well as its preparation method, is a key technological bottleneck for promoting the commercialization of all-solid-state batteries.

[0063] Based on the aforementioned technical problems, the inventors, in the process of researching the preparation process of sulfide solid electrolytes possessing both high ionic conductivity and excellent air / water stability, discovered that granulation treatment maintains a high halogen content in the internal bulk phase of the prepared sulfide solid electrolyte, while a low-halogen layer is constructed on the surface and near-surface regions. This ensures that the sulfide solid electrolyte exhibits high ionic conductivity, and the low-halogen layer on the surface provides relatively stable air / water stability protection for the internal bulk phase, thereby achieving a synergistic improvement in ionic conductivity and air / water stability. Based on this, this application provides a sulfide solid electrolyte, its preparation method, and an all-solid-state battery.

[0064] The technical solution of this application and how it solves the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0065] Figure 1 Here is a schematic diagram of the structure of a sulfide solid electrolyte provided in this application, as shown below. Figure 1 As shown, the sulfide solid electrolyte particles comprise a first mixture and a second mixture.

[0066] In one possible implementation, the first mixture comprises lithium sulfide and phosphorus sulfide, and the second mixture comprises lithium sulfide and a halogenated lithium salt.

[0067] Lithium sulfide (Li2S) is a particle compound composed of lithium and sulfur elements. As the core lithium and sulfur source in sulfide solid electrolytes, it can provide lithium ions required for the conduction of iodide solid electrolytes and provide the basis for the formation of the basic framework structure of sulfide solid electrolytes. Its chemical properties are active and it is easy to react with other sulfides or halogen compounds to form a composite sulfide phase with ion conduction properties.

[0068] Phosphorus sulfide is a covalent compound composed of phosphorus and sulfur elements. It serves as both a phosphorus and sulfur source in sulfide solid electrolytes. Upon reaction with Li₂S, it can form PS₄-containing compounds. 3- The tetrahedral structure of the composite sulfide is key to ensuring the high ionic conductivity of sulfide solid electrolytes.

[0069] Lithium halide salts refer to those composed of lithium cations Li. + With halide anions (such as Cl) - ,Br - I - Ionic compounds composed of lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), etc., can be introduced into sulfide solid electrolytes. By doping these halogen lithium salts with halogen anions, the crystal structure of the sulfide solid electrolyte can be regulated, the lithium ion transport channels can be optimized, and the ionic conductivity of the sulfide solid electrolyte can be significantly improved.

[0070] In another possible implementation, the first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

[0071] Specifically, by controlling the particle size difference between the first mixture and the second mixture, the smaller particles of the first mixture can fully coat the surface of the larger particles of the second mixture, forming a core-shell heterogeneous structure. For example, the first mixture is a fine powder with particle sizes in the micrometer or even submicrometer range, giving it a larger specific surface area and better dispersibility and adhesion. The second mixture is granular with particle sizes ranging from several micrometers to tens of micrometers. As the core layer structure, it possesses sufficient structural strength to support the overall shape, and its larger particle size compared to the first mixture provides a stable substrate for adhesion to the fine powder. Ultimately, a complete structure is formed with the second mixture as the core layer and the first mixture as the shell layer.

[0072] Understandably, the second mixture located in the core layer possesses halogen-rich properties due to the inclusion of lithium halide salts, and halide anions (such as Cl-) - ,Br - I - (etc.) can improve the migration ability of ions by optimizing the lithium-ion transport channel, thereby significantly improving the ionic conductivity of sulfide solid electrolytes. The halogen anions concentrated in the core layer diffuse from the core layer as the starting point, avoiding the uniform dispersion of halogen anions. As halogen anions diffuse from the core layer to the shell layer to a limited extent, due to the combined influence of internal migration resistance, lattice structure constraints and heat treatment process conditions, halogen anions cannot achieve a uniform distribution throughout the entire region. Finally, a heterogeneous concentration gradient of halogen anions is formed between the core layer and the shell layer. This not only retains the high ionic conductivity advantage brought by the halogen-rich core layer, but also ensures the air / water stability of sulfide solid electrolytes by the relatively halogen-poor dense structure of the shell layer.

[0073] The second mixture, coating the surface of the first mixture, does not contain halogenated lithium salts (halogen elements). Due to the limited diffusion of halogen anions, it belongs to the halogen-poor system and has relatively stable chemical properties, essentially providing a protective layer for the second mixture, which can improve ionic conductivity. This heterogeneous halogen concentration gradient structure, with a halogen-rich core and a halogen-poor shell, allows the sulfide solid electrolyte to effectively reduce the erosion of the halogen-rich core components by air moisture through the physical isolation and chemical protection of the shell, thus improving the air / water stability of the sulfide solid electrolyte. At the same time, it does not hinder the efficient transport of lithium ions in the core-shell structure, ultimately achieving a synergistic improvement in ionic conductivity and air / water stability.

[0074] In another possible implementation, the first particle size is 0.6 μm to 2 μm;

[0075] and / or;

[0076] The second particle size is 3μm~20μm.

[0077] Specifically, the first particle size is the particle size of the first mixture, specifically set to a fine powder range of 0.6μm to 2μm. It can be any value within the range of 0.6μm, 1μm, 1.5μm, or 2μm, to provide the first mixture with sufficient specific surface area, ensuring excellent dispersibility and surface adhesion when mixed with the second mixture. This ensures uniform and tight coverage of the second mixture surface, forming a continuous and dense coating layer, ultimately forming the shell layer in a continuous and dense core-shell structure. The second particle size is the particle size of the second mixture, specifically set to 3μm to 20μm. It can be any value within the range of 3μm, 5μm, 8μm, 10μm, 14μm, 17μm, or 20μm, to provide a stable and suitable adhesion substrate for the fine powder first mixture, forming the core layer in a continuous and dense core-shell structure. By combining a heterogeneous halogen concentration gradient design with a halogen-rich core and a halogen-poor shell, the high ionic conductivity of the sulfide solid electrolyte is ensured while also exhibiting certain air / water stability.

[0078] It should be noted that the specific values ​​of the first and second particle sizes mentioned above are for illustrative purposes only. In actual applications, they should be flexibly adjusted according to the needs of different application scenarios to achieve customized design of the performance of sulfide solid electrolytes.

[0079] In another possible implementation, phosphorus sulfide includes at least one of P2S3, P2S5, P4S4, P4S7, P4S9, and P4S6.

[0080] and / or;

[0081] Lithium halide salts include at least one of LiCl, LiBr, LiI, and LiF.

[0082] Taking phosphorus pentasulfide (P2S5) as an example, P2S5 is a commonly used phosphorus-sulfur source compound in the preparation of sulfide solid electrolytes. At room temperature, it is a yellow to yellowish-green crystalline powder with high chemical activity. It readily undergoes solid-phase or liquid-phase reactions with lithium source materials such as Li2S. The PS bonds in its molecular structure break and recombine during the reaction, reacting with the Li provided by Li2S. + Combined, forming a PS4 3- An ion conduction network with a tetrahedral structure as its basic unit contains a large number of gaps and channels for lithium ion migration, making it the fundamental structure for achieving rapid ion transport.

[0083] Taking LiCl, a lithium halide salt, as an example, LiCl is an inorganic compound that appears as white crystals or powder at room temperature. It is hygroscopic and has a relatively low melting point. It is readily soluble in polar solvents such as water, ethanol, and acetone, and its aqueous solution is neutral or weakly acidic. In sulfide solid electrolyte systems, LiCl is a commonly used lithium halide salt dopant or component to provide LiCl. + Transmission carrier, simultaneously via Cl - Modifying the crystal structure of sulfide solid electrolytes, such as disrupting the symmetry of the original sulfide lattice and forming defect sites, can lower the lithium-ion migration barrier and thus improve the ionic conductivity of the sulfide solid electrolyte. Furthermore, Cl... - atomic radius and S in sulfide system 2- There are differences, and appropriate doping can optimize the microstructure density of sulfide solid electrolytes, improve their interfacial compatibility with electrode materials, reduce interfacial impedance, and enhance the machinability of the electrolyte.

[0084] In another possible implementation, the molar ratio of lithium sulfide to phosphorus sulfide in the first mixture is (3~3.2):1;

[0085] and / or;

[0086] The molar ratio of lithium sulfide to lithium halide in the second mixture is (0.176~19):1.

[0087] For example, the molar ratio of lithium sulfide to phosphorus sulfide in the first mixture can be any value within the range of (3~3.2):1, such as 3:1, 3.1:1, 3.15:1, or 3.2:1. The selection of this molar ratio range is based on the crystal structure formation rules of the sulfide solid electrolyte and the lithium-ion transport performance requirements. The molar ratio of lithium sulfide to halide lithium salt in the second mixture can be any value within the range of (0.176~19):1, such as 0.176:1, 0.25:1, 1:1, 2.33:1, 4.5:1, 7:1, 9:1, 12.4:1, 15:1, 16.8:1, 18.5:1, or 19:1. The selection of this molar ratio range is based on balancing the lithium-ion transport efficiency, crystal structure integrity, and interfacial compatibility of the sulfide solid electrolyte. In practical applications, the molar ratio of lithium sulfide to phosphorus sulfide in the first mixture and the molar ratio of lithium sulfide to phosphorus sulfide in the second mixture can be adjusted according to the performance requirements of the target sulfide solid electrolyte (such as ionic conductivity, electrochemical window, interfacial compatibility, etc.).

[0088] In another possible implementation, the molar ratio of the first mixture to the second mixture is 1:(1.9~2.1).

[0089] For example, the molar ratio of the first mixture to the second mixture can be any value within the range of 1:(1.9~2.1), such as 1:1.9, 1:1.95, 1:2, 1:2.05, or 1:2.1. By adjusting the relative content of the first mixture (lithium sulfide and phosphorus sulfide reaction system) and the second mixture (lithium sulfide and halide lithium salt system), a balance can be achieved in crystal structure regulation, ion transport efficiency improvement, and air / water stability enhancement.

[0090] This application provides a sulfide solid electrolyte, specifically a heterogeneous halogen concentration sulfide solid electrolyte with a core-shell structure. It comprises a first mixture containing lithium sulfide and phosphorus sulfide, and a second mixture containing lithium sulfide and a lithium halide salt. The first mixture coats the surface of the second mixture, and the particle size of the first mixture is smaller than that of the second mixture. This sulfide solid electrolyte effectively optimizes its crystal structure and broadens lithium-ion transport channels through the halogen anions in the second mixture located in the core layer (halogen-rich core), thereby ensuring high ionic conductivity. The stable and dense halogen-poor shell located on the surface of the core layer acts as a physical and chemical barrier, significantly reducing direct contact between the halogen-rich core layer and air, greatly improving the air / water stability of the sulfide solid electrolyte. Ultimately, this sulfide solid electrolyte achieves a synergistic improvement in ionic conductivity and air / water stability through a heterogeneous halogen concentration gradient structure with a halogen-rich core layer and a halogen-poor shell layer.

[0091] Figure 2 A flowchart illustrating a method for preparing a sulfide solid electrolyte provided in this application. Figure 1 ,like Figure 2 As shown, the method includes:

[0092] S201: Lithium sulfide and phosphorus sulfide are mixed and ground to obtain an amorphous mixture.

[0093] In this step, lithium sulfide and phosphorus sulfide are mixed and ground to obtain an amorphous mixture, meaning that the mixture lacks a long-range ordered crystal structure and may only contain short-range atomic aggregates. The amorphous structure, with its disordered atomic arrangement, creates a smoother transport environment for ion migration within the sulfide solid electrolyte. Ions do not need to overcome the inherent obstacles posed by the ordered lattice arrangement in the crystalline structure, allowing for smoother shuttle diffusion and significantly improving the ionic conductivity of the sulfide solid electrolyte. Secondly, the amorphous structure lacks distinct grain boundary divisions (grain boundary regions often become bottlenecks in ion transport, easily generating additional impedance due to structural discontinuities). Its weakening effect on grain boundaries effectively reduces interfacial resistance during ion transport, further optimizing ionic conductivity.

[0094] Optionally, lithium sulfide (Li₂S) and phosphorus sulfide (P₂S₅) in a molar ratio of (3~3.2):1 are placed in a glove box or mixing device under an inert gas atmosphere (including at least one of argon, nitrogen, and neon) and mechanically mixed and ground to obtain an amorphous mixture. For example, the molar ratio of lithium sulfide to phosphorus sulfide can be any value within the range of (3~3.2):1, such as 3:1, 3.12:1, 3.14:1, 3.16:1, 3.18:1, or 3.2:1. In addition to P₂S₅, phosphorus sulfide can also be at least one of P₂S₃, P₄S₄, P₄S₇, P₄S₉, and P₄S₆.

[0095] The grinding process in this step is used to achieve amorphization, such as mechanical grinding (mechanical ball milling). Alternatively, melt extraction can be used. The resulting amorphous mixture is a transitional form of sulfide solid electrolyte, providing a basis for the subsequent preparation of sulfide solid electrolytes with both high ionic conductivity and air / water stability.

[0096] S202: After the amorphous mixture undergoes a first heat treatment, it is then refined to obtain a first mixture.

[0097] The first heat treatment is used to promote the rearrangement of atoms or ions inside the amorphous mixture through thermal activation. On the one hand, it can eliminate the internal stress and structural defects that may remain in the mixing and grinding stage, making the short-range ordered region of the amorphous structure more uniform. On the other hand, it can moderately improve the bonding stability between atoms, avoiding performance fluctuations caused by loose structure in subsequent processing. At the same time, the heat treatment may also induce slight chemical reactions between raw materials, forming a local chemical environment that is more conducive to ion transport.

[0098] In one possible implementation, in the first heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 240~320℃, and the holding time is 0.5~8h.

[0099] For example, an amorphous mixture is placed in a sealed reaction vessel and subjected to a first heat treatment (high-temperature solid-state reaction) under inert gas protection to obtain the precursor Li3PS4. The heating rate of the first heat treatment can be any value within the range of 0.5~10℃ / min, such as 0.5℃ / min, 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, 8℃ / min, or 10℃ / min; the temperature can be any value within the range of 240~320℃, such as 240℃, 265℃, 280℃, 300℃, 305℃, 315℃, or 320℃; and the holding time can be any value within the range of 0.5~8h, such as 0.5h, 2h, 4h, 5h, 7h, or 8h.

[0100] Refining treatment is used to solve the problem of particle agglomeration that may occur after heat treatment. During the heat treatment of amorphous mixtures, due to the intensified atomic thermal motion, some fine particles are prone to sticking together and agglomerating due to the reduction of surface energy, forming agglomerates with larger sizes. This will directly affect the specific surface area of ​​the material and its dispersibility in subsequent applications. Therefore, refining treatment uses at least one physical means, such as mechanical grinding, ball milling, sand milling or air jet milling, to disperse the agglomerated particles, so that the particle size of the first mixture is controlled to the target range, making it into a fine powder. This ensures the uniformity of the material and increases the specific surface area to improve the contact efficiency with other components.

[0101] For example, the precursor Li3PS4 obtained after the first heat treatment is refined by at least one physical means, such as mechanical grinding, ball milling, sand milling, or air jet milling, to obtain a highly active fine powder precursor (first mixture). The fine powder state gives the precursor powder a large specific surface area, which can improve the contact efficiency with other components and provide a material basis for the subsequent formation of the shell layer in the core-shell structure of the sulfide solid electrolyte.

[0102] S203: Lithium sulfide and halogenated lithium salts are mixed and granulated to obtain a second mixture.

[0103] In this step, granulation is a process for processing powdered or fine granular materials into uniform particles. That is, it involves agglomerating and shaping a mixture of lithium sulfide and lithium halogen salts into granular products with specific size, shape and density through physical or chemical means.

[0104] In one possible implementation, the granulation process includes any one of spray drying granulation, dry granulation, and wet granulation.

[0105] Wet granulation refers to the process of introducing a liquid medium (such as deionized water, anhydrous ethanol, a specific organic solvent, or a solution containing a binder) into the powder raw material mixing process. By utilizing the wetting effect of the liquid and the bridging effect of the binder (if added), a liquid film is formed on the surface of the powder particles, causing them to adhere and aggregate. Then, through subsequent drying, sieving, and other steps, a granular product with a specific particle size, shape, and mechanical strength is finally obtained.

[0106] Dry granulation refers to a process technology that, without introducing any liquid medium, relies solely on mechanical external forces (such as extrusion, rolling, and impact) to act on powder raw materials, causing particles to agglomerate and form shapes through physical adsorption, van der Waals forces, or mechanical interlocking between particles, ultimately obtaining granular products with specific particle size, shape, and mechanical strength.

[0107] Spray drying granulation is a special type of wet granulation. It involves breaking a mixture of lithium sulfide and halogen lithium salts (a suspension or solution in which raw material powder is dispersed in a liquid medium) into tiny droplets through an atomizing device, and then rapidly exposing the droplets to a high-temperature airflow environment. The liquid medium evaporates instantly, ultimately forming a dry, regular granular product.

[0108] For example, lithium sulfide Li2S with a molar ratio of (0.176~19):1 and lithium halide salt (LiCl) are thoroughly mixed in an inert gas atmosphere (including at least one of argon, nitrogen and neon) and granulated to obtain a second mixture within the target particle size range, providing a material basis for the shell layer of the core-shell structure of the sulfide solid electrolyte. The molar ratio of lithium sulfide (Li₂S) to lithium halogen salt (LiCl) can be any value within the range of 0.176:1, 0.25:1, 0.33:1, 0.43:1, 0.54:1, 0.67:1, 0.82:1, 1:1, 1.22:1, 1.5:1, 1.86:1, 2.33:1, 3:1, 4:1, 5.67:1, 9:1, 10.5:1, 13:1, 14.9:1, 17:1, or 19:1. In addition to LiCl, the lithium halogen salt can also be at least one of LiBr, LiI, and LiF.

[0109] S204: Based on the first mixture and the second mixture, a sulfide solid electrolyte is obtained.

[0110] For example, the molar ratio of the first mixture to the second mixture is 1:(1.9~2.1), that is, the molar ratio of the first mixture to the second mixture can be any value within the range of 1:(1.9~2.1), such as 1:1.9, 1:1.95, 1:2, 1:2.05 or 1:2.1.

[0111] Optionally, the sulfide solid electrolyte obtained from the first mixture and the second mixture has the first mixture coating the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

[0112] Understandably, the second mixture is granular, with a particle size larger than that of the first mixture (fine powder), providing a stable and suitable substrate for the subsequent coating of the first mixture onto the surface of the second mixture. Ultimately, the second mixture, possessing halogen-rich properties due to its inclusion of halogen lithium salts and granulated into particles, resides in the core layer of the sulfide solid electrolyte, providing a foundation for optimizing lithium-ion transport channels, enhancing ion migration capabilities, and thereby improving ionic conductivity.

[0113] Understandably, the first mixture, being a fine powder with smaller particle size than the second mixture (granular), provides a sufficient specific surface area, ensuring excellent dispersibility and surface adhesion when mixed with the second mixture. This allows it to uniformly and tightly coat the surface of the second mixture, forming a continuous and dense coating layer. Ultimately, the first mixture, which is a halogen-poor system compared to the second mixture due to the absence of halogenated lithium salts (halogen elements) and is located in the shell of the sulfide solid electrolyte, provides effective physical isolation and chemical protection for the second mixture in the core layer, which is used to improve ionic conductivity. This results in excellent air / water stability for the sulfide solid electrolyte. In summary, the prepared sulfide solid electrolyte achieves a synergistic improvement in ionic conductivity and air / water stability.

[0114] The method for preparing sulfide solid electrolytes provided in this application first involves mixing and grinding lithium sulfide and phosphorus sulfide to obtain an amorphous mixture. This mixture is then subjected to a first heat treatment and refining process to obtain a fine powdered first mixture. Simultaneously, lithium sulfide is mixed with a halogen lithium salt and granulated to form a granular second mixture. Finally, the first and second mixtures are combined at a specific molar ratio to form a core-shell structure sulfide solid electrolyte with a halogen concentration gradient, consisting of a halogen-rich second mixture as the core and a halogen-poor first mixture as the shell. This method achieves a synergistic improvement in ionic conductivity and air / water stability. Furthermore, the raw materials used in the preparation process are all conventional chemical raw materials, resulting in low cost. The process is primarily based on mechanical mixing and solid-state sintering, with a clear flow, requiring no complex and expensive equipment, making it easy to scale up and achieve large-scale production, and possessing extremely high potential for industrial application.

[0115] exist Figure 2 Based on the examples, in one possible implementation, the particle size of the first particle is 0.6 μm to 2 μm;

[0116] and / or;

[0117] The second particle size is 3μm~20μm.

[0118] like Figure 1As mentioned in the embodiments, exemplaryly, the first particle size can be any value within the range of 0.6μm to 2μm, such as 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.2μm, 1.3μm, 1.6μm, 1.8μm, 1.9μm, or 2μm. The second particle size can be any value within the range of 3μm to 20μm, such as 3μm, 6μm, 7μm, 9μm, 11μm, 13μm, 15μm, 16μm, 18μm, 19μm, or 20μm. The technical effects achieved by the first mixture and the second mixture through the above particle size design have been described in detail above and will not be repeated here.

[0119] Figure 3 A flowchart illustrating a method for preparing a sulfide solid electrolyte provided in this application. Figure 2 ,like Figure 3 As shown, in Figure 2 Based on the previous example, in S204: a sulfide solid electrolyte is obtained from the first mixture and the second mixture, specifically including:

[0120] S301: Mix the first mixture with the second mixture to obtain the third mixture.

[0121] Specifically, the first mixture and the second mixture are physically mixed using a mixing device, which may be at least one of a planetary ball mill, a high-efficiency mixer, a high-energy ball mill, a fusion coating machine, a high-temperature coating machine, and a drum mixer. During the mixing process, the first mixture is ensured to uniformly adhere to and coat the surface of the second mixture, thereby obtaining a third mixture.

[0122] S302: The third mixture is subjected to a second heat treatment to obtain a sintered body.

[0123] Through a second heat treatment, the fine powder of the first mixture and the granular second mixture in the third mixture undergo an interfacial reaction and structural fusion.

[0124] In one possible implementation, in the second heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 400~560℃, and the holding time is 2~24h.

[0125] For example, the third mixture is placed in a sealed reaction vessel and subjected to a second heat treatment under inert gas protection to obtain a sintered body. The heating rate of the second heat treatment can be any value within the range of 0.5~10℃ / min, such as 0.5℃ / min, 0.8℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 9℃ / min, or 10℃ / min; the temperature can be any value within the range of 400~560℃, such as 400℃, 450℃, 470℃, 490℃, 500℃, 520℃, 540℃, 555℃, or 560℃; and the holding time can be any value within the range of 2~24h, such as 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 17h, 18h, 20h, 22h, 23h, or 24h.

[0126] S303: The sintered body is crushed and sieved to obtain a sulfide solid electrolyte.

[0127] After the second heat treatment reaction is completed, the sintered body is slightly crushed and sieved to obtain a sulfide solid electrolyte with uniform particle size distribution.

[0128] The method for preparing sulfide solid electrolytes provided in this application embodiment, in Figure 2 Based on the previous examples, the steps for combining the first mixture and the second mixture to finally obtain a sulfide solid electrolyte are further detailed. Specifically, this includes: firstly, physically mixing the finely powdered first mixture and the granular second mixture using a mechanical mixing device, causing the first mixture to uniformly adhere to the surface of the second mixture, forming a third mixture. Subsequently, the third mixture undergoes a second heat treatment, promoting a tight interfacial reaction and structural fusion between the first and second mixtures, thereby forming a dense sintered body. Finally, the sintered body is slightly crushed and sieved to obtain a sulfide solid electrolyte with uniform particles. Through this method, chemical bonding and densification of the core and shell materials at the interface are achieved, further stabilizing the gradient structure composed of a halogen-rich core and a halogen-poor shell, providing a foundation for the sulfide solid electrolyte to possess both high ionic conductivity and excellent air / water stability.

[0129] Based on the above embodiments, the prepared sulfide solid electrolyte is a binary Li2S-P2S5 system sulfide solid electrolyte. Furthermore, the preparation method provided in this application for obtaining a core-shell structured sulfide solid electrolyte with a halogen concentration gradient is also applicable to sulfide solid electrolytes of the silver-germanium sulfide type and lithium-phosphorus-sulfur-iodine type.

[0130] Among them, the chemical formulas of sulfide solid electrolytes in the Li2S-P2S5 system and thiogermanate sulfide solid electrolytes can be expressed as: xLi2S (100 - x - z) AySn zB, where 0 < x < 100, y is 0, 1 or 2, n is 2y or 2y + 1, 0 ≤ z < 100 - x, A is P 3+ or P 5+ , and B is at least one of LiCl, LiBr, LiI, Li3PO4, GeS2, P2O5, Li4SiO4, and P2S3.

[0131] The chemical formula of the lithium phosphorus sulfur iodine type sulfide solid electrolyte can be expressed as: , where when the doping element at the S site is a +5 valence element, its chemical formula is ; when the doping element at the S site is a +4 valence element, its chemical formula is . Among them, 0.01 ≤ a ≤ 2, 0.01 ≤ b ≤ 1, 0.01 ≤ c ≤ 1; A is the doping element at the P site, B is the doping element at the S site, and C is the doping element at the I site; optionally, 0.1 ≤ a ≤ 0.6, 0.1 ≤ b ≤ 0.5, 0.1 ≤ c ≤ 1. Optionally, the doping element at the S site includes O; the doping element at the I site includes Cl or Br.

[0132] This application also provides a all-solid-state battery, including a positive electrode sheet, a negative electrode sheet, and the sulfide solid electrolyte as mentioned in Figure 1 the embodiment, and / or the sulfide solid electrolyte prepared by the method as mentioned in Figure 2 or Figure 3 the embodiment.

[0133] This all-solid-state battery can be used in vehicles, aircraft, drones, and can also be used in computers, mobile phones, digital cameras, and wearable devices, etc., such as Computers, Communications, and Consumer Electronics (3C) products, providing a stable and lasting power source and power support for these electrical devices.

[0134] Due to the sulfide solid electrolyte of this all-solid-state battery having both high ionic conductivity and excellent air / water stability, it exhibits lower interfacial impedance, higher rate performance, and longer cycle life. At the same time, the sulfide solid electrolyte has a core-shell structure with a halogen concentration gradient, effectively blocking the penetration of moisture in the external environment or trace moisture remaining inside the battery into the sulfide solid electrolyte and contacting the sulfides in the core layer and shell layer; at the same time, the electronegativity of the halogen anion is stronger than that of sulfur element, which can form a more stable chemical bond with lithium ions, reducing the activity of S 2- in the sulfide and reducing its reaction with H+ The probability of binding is reduced, thereby suppressing the generation of H2S gas and greatly improving the safety of the production, transportation and use of all-solid-state batteries.

[0135] The following specific embodiments will provide a detailed description of the sulfide solid electrolyte and its preparation method provided in this application. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments are all conventional reagents, materials, and instruments in the art, and can all be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0136] Example 1

[0137] This embodiment provides a sulfide solid electrolyte, the preparation method of which includes the following steps:

[0138] 1) 13.79 g of Li2S and 44.45 g of P2S5 (the molar ratio of Li2S to P2S5 is 3:1) were placed in a glove box protected by an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm) and mechanically mixed and ground in a planetary ball mill jar at a ball milling speed of 300 rpm / min for 24 h to obtain an amorphous mixture.

[0139] 2) The amorphous mixture was loaded into a quartz crucible and transferred to a tube furnace. Under an argon flow, the temperature was increased to 250°C at 2°C / min and held for 2 hours. After natural cooling, the mixture was further refined by ball milling for 4 hours to obtain a first mixture with a particle size D50 = 1 μm.

[0140] 3) 1.84 g of Li2S and 6.78 g of LiCl (the molar ratio of Li2S to LiCl is 0.25:1) were thoroughly mixed in a glove box filled with argon gas, and the mixed powder of Li2S and LiCl was pressed into tablets under a pressure of 10 MPa using a tablet press. After being gently crushed, a second mixture with a particle size D50 = 15 μm was obtained.

[0141] 4) Mix 18g of the first mixture and 8.6g of the second mixture (the molar ratio of the first mixture to the second mixture is 1:2) in a glove box on a planetary ball mill for 2 hours to make the first mixture uniformly adhere to and coat the surface of the second mixture, thus obtaining the third mixture.

[0142] 5) The third mixture was placed in a quartz crucible and placed in a tube furnace. Under an argon flow, the temperature was increased to 430°C at 2°C / min and held for 6 hours to obtain a sintered body. After natural cooling, the sintered body was lightly ground and passed through a 400-mesh sieve to obtain a sulfide solid electrolyte. This sulfide solid electrolyte has a core-shell structure with a chlorine concentration gradient.

[0143] Example 2

[0144] This embodiment provides a sulfide solid electrolyte, the preparation method of which is basically the same as that mentioned in Example 1, specifically including the following steps:

[0145] 1) Same as step 1 in Example 1).

[0146] 2) The amorphous mixture was loaded into a quartz crucible and transferred to a tube furnace. Under an argon flow, the temperature was increased to 250°C at 2°C / min and held for 2 hours. After natural cooling, the mixture was further refined by ball milling for 4 hours to obtain a first mixture with a particle size D50 = 0.6 μm.

[0147] 3) 1.38g of Li2S, 3.6g of LiCl, and 7.38g of LiBr (the molar ratio of Li2S to lithium halogen salts (LiCl and LiBr) is 0.176:1) were thoroughly mixed in an argon-filled glove box. The mixed powder of Li2S, LiCl, and LiBr was pressed into tablets under a pressure of 10MPa using a tablet press. After being gently crushed, a second mixture with a particle size D50 = 3μm was obtained.

[0148] 4) Mix 16.2g of the first mixture and 11.6g of the second mixture (the molar ratio of the first mixture to the second mixture is 1:2.1) in a glove box on a planetary ball mill for 2 hours to make the first mixture uniformly adhere to and coat the surface of the second mixture, thus obtaining the third mixture.

[0149] 5) The third mixture was placed in a quartz crucible and then in a tube furnace. Under an argon flow, the temperature was increased to 475°C at 2°C / min and held for 12 hours to obtain a sintered body. After natural cooling, the sintered body was lightly ground and passed through a 400-mesh sieve to obtain a sulfide solid electrolyte. This sulfide solid electrolyte has a core-shell structure with a chlorine-bromine mixed concentration gradient.

[0150] Example 3

[0151] This embodiment provides a sulfide solid electrolyte, the preparation method of which is basically the same as that mentioned in Example 1, specifically including the following steps:

[0152] 1) 14.24 g of Li2S and 44.45 g of P2S5 (the molar ratio of Li2S to P2S5 is 3.1:1) were placed in a glove box protected by argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm) and mechanically mixed and ground in a planetary ball mill jar at a ball milling speed of 300 rpm / min for 24 h to obtain an amorphous mixture.

[0153] 2) The amorphous mixture was loaded into a quartz crucible and transferred to a tube furnace. Under an argon flow, the temperature was increased to 250°C at 2°C / min and held for 2 hours. After natural cooling, the mixture was further refined by ball milling for 4 hours to obtain a first mixture with a particle size D50 = 2 μm.

[0154] 3) Mix 8.73g of Li2S and 0.43g of LiCl (molar ratio of Li2S to LiCl is 19:1) thoroughly in a glove box filled with argon gas, and use a tablet press to press the mixed powder of Li2S and LiCl into tablets under a pressure of 10MPa. After gently crushing, a second mixture with a particle size D50=20μm is obtained.

[0155] 4) Mix 16.2g of the first mixture and 7.83g of the second mixture (the molar ratio of the first mixture to the second mixture is 1:1.9) in a glove box on a planetary ball mill for 2 hours to make the first mixture uniformly adhere to and coat the surface of the second mixture, thus obtaining the third mixture.

[0156] 5) Same as step 5 in Example 1), the final obtained sulfide solid electrolyte has a core-shell structure with a chlorine concentration gradient.

[0157] Example 4

[0158] This embodiment provides a sulfide solid electrolyte, the preparation method of which is basically the same as that mentioned in Example 1, specifically including the following steps:

[0159] 1) 14.7g of Li2S and 44.45g of P2S5 (the molar ratio of Li2S to P2S5 is 3.2:1) were placed in a glove box protected by an argon atmosphere (H2O < 0.1ppm, O2 < 0.1ppm) and mechanically mixed and ground in a planetary ball mill jar at a ball milling speed of 300rpm / min for 24h to obtain an amorphous mixture.

[0160] 2) Same as step 2 in Example 1.

[0161] 3) 2.3g of Li2S and 6.36g of LiCl (the molar ratio of Li2S to LiCl is 0.33:1) were thoroughly mixed in a glove box filled with argon gas, and the mixed powder of Li2S and LiCl was pressed into tablets under a pressure of 10MPa using a tablet press. After being gently crushed, a second mixture with a particle size D50=5μm was obtained.

[0162] 4) Mix 16.2g of the first mixture and 7.79g of the second mixture (the molar ratio of the first mixture to the second mixture is 1:2) in a glove box on a planetary ball mill for 2 hours to make the first mixture uniformly adhere to and coat the surface of the second mixture, thus obtaining the third mixture.

[0163] 5) The third mixture was placed in a quartz crucible and placed in a tube furnace. Under an argon flow, the temperature was increased to 480°C at 2°C / min and held for 6 hours to obtain a sintered body. After natural cooling, the sintered body was lightly ground and passed through a 400-mesh sieve to obtain a sulfide solid electrolyte. This sulfide solid electrolyte has a core-shell structure with a chlorine concentration gradient.

[0164] Comparative Example 1

[0165] This embodiment provides a sulfide solid electrolyte, the preparation method of which includes the following steps:

[0166] 1) 13.79 g of Li2S, 44.45 g of P2S5 and 6.78 g of LiCl were placed in a glove box under argon atmosphere protection (H2O < 0.1 ppm, O2 < 0.1 ppm) and mechanically mixed and ground in a planetary ball mill jar at a ball milling speed of 300 rpm / min for 24 h to obtain an amorphous mixture with a particle size D50 = 4 μm.

[0167] 2) The amorphous mixture was placed in a quartz crucible and then in a tube furnace. Under an argon flow, the temperature was increased to 430°C at 2°C / min and held for 6 hours to obtain a sintered body. After natural cooling, the sintered body was lightly ground and passed through a 400-mesh sieve to obtain a sulfide solid electrolyte.

[0168] Comparative Example 2

[0169] This embodiment provides a sulfide solid electrolyte, the preparation method of which is basically the same as that mentioned in Example 1, specifically including the following steps:

[0170] 1) Same as step 1 in Example 1).

[0171] 2) Same as step 2 in Example 1.

[0172] 3) 1.84 g of Li2S and 6.78 g of LiCl (the molar ratio of Li2S to LiCl is 0.25:1) were thoroughly mixed in a glove box filled with argon to obtain a second mixture in powder form with a D50 of 30 μm.

[0173] 4) Mix 18g of the first mixture with 8.6g of the second mixture (the molar ratio of the first mixture to the second mixture is 1:2) directly to obtain a homogeneous third mixture.

[0174] 5) Same as step 5 in Example 1), the final obtained sulfide solid electrolyte does not have a core-shell structure with a halogen concentration gradient (because it was not granulated in step 3), so the first mixture and the second mixture are both fine powders.

[0175] Comparative Example 3

[0176] This embodiment provides a sulfide solid electrolyte, the preparation method of which is basically the same as that mentioned in Example 1, and the preparation method includes the following steps:

[0177] 1) Place 13.79g of Li2S and 44.45g of P2S5 (the molar ratio of Li2S to P2S5 is 3:1) in a glove box protected by argon atmosphere (H2O < 0.1ppm, O2 < 0.1ppm) and grind thoroughly by hand to obtain a manually ground mixture.

[0178] 2) The hand-ground mixture was placed into a quartz crucible and transferred to a tube furnace. Under an argon flow, the temperature was increased to 250°C at 2°C / min and held for 2 hours. After natural cooling, the mixture was crushed and refined to obtain a first mixture with a particle size D50 = 10 μm.

[0179] 3) Same as step 3 in Example 1.

[0180] 4) Same as step 4 in Example 1.

[0181] 5) Same as step 5 in Example 1), the final obtained sulfide solid electrolyte has a core-shell structure with a chlorine concentration gradient (because it was not sufficiently refined in step 2, so the core-shell structure with a chlorine concentration gradient of the sulfide solid electrolyte is not very effective).

[0182] Test Example 1

[0183] Ionic conductivity test: 100 mg of sulfide solid electrolyte was weighed and placed in a mold. A pressure of 360 MPa was applied to press it into an electrolyte sheet with a diameter of 10 mm. Under pressure, the impedance value of the sulfide solid electrolyte was measured using an electrochemical workstation with electrochemical impedance spectroscopy (EIS) at room temperature (25 °C). The real part of the minimum absolute value of multiple impedance phase angles was taken as the effective impedance value. The ionic conductivity of the sulfide solid electrolyte was calculated using this resistance value. The calculation formula is: ,in, L represents the ionic conductivity (mS / cm), L represents the thickness of the electrolyte sheet (cm), R represents the effective impedance of the sulfide solid electrolyte obtained by the EIS method (Ω), and S represents the cross-sectional area of ​​the electrolyte sheet (cm²). 2 ).

[0184] Test Example 2

[0185] Air / water stability test: After the ionic conductivity test, 100 mg of sulfide solid electrolyte was sampled and exposed to a dry room with a dew point of 25℃ and -30℃ for 30 min. After the standing period, the ionic conductivity was retested and the retention rate of ionic conductivity was calculated.

[0186] The test results for ionic conductivity and air / water stability are shown in Table 1.

[0187] Table 1. Test results of ionic conductivity and air / water stability

[0188]

[0189] Based on Table 1, the following conclusions can be drawn:

[0190] The sulfide solid electrolyte and its preparation method provided in this application can achieve a synergistic improvement in ionic conductivity and air / water stability, that is, improving one performance without sacrificing the other key performance. Specifically, the ionic conductivity of Examples 1 to 4 (all referring to the ionic conductivity or ionic conductivity retention rate of the sulfide solid electrolyte provided in the examples, which will not be repeated below) reaches 8 mS / cm, 10.2 mS / cm, 1.5 mS / cm and 7.5 mS / cm, respectively, with the ionic conductivity of Example 2 reaching as high as 10.2 mS / cm, which is at a high level. The corresponding air / water stability (measured by ionic conductivity retention rate) remains above 83%, and the ionic conductivity retention rates of Examples 1 and 3 reach 88.75% and 92.00%, respectively, demonstrating excellent stability. It should be noted that the ionic conductivity of Example 3 is relatively low (1.5 mS / cm), which is due to the small amount of lithium halide salt added. This result further confirms the positive effect of lithium halide salt on improving ionic conductivity.

[0191] In contrast, although the ionic conductivity of some comparative examples (such as 8.1 mS / cm in comparative example 2) was close to that of some examples in comparative examples 1 to 3, their air / water stability was significantly worse, and the highest ionic conductivity retention rate was only 70.37%, which was significantly lower than the ionic conductivity retention rate of the examples. Furthermore, the ionic conductivity of Example 1 is 8 mS / cm, which is basically at the same level as that of Comparative Example 2 (8.1 mS / cm). The difference in ionic conductivity between the two is small, and both exhibit good ion transport performance. However, in terms of air / water stability, the ionic conductivity retention rate of Example 1 is as high as 88.75%, while that of Comparative Example 2 is only 70.37%. The ionic conductivity retention rate of Example 1 is far superior to the latter two, clearly demonstrating that this technology significantly improves the air / water stability of the electrolyte without reducing the ionic conductivity. This fully illustrates that the core-shell structured sulfide solid electrolyte with halogen concentration gradient provided in this application achieves simultaneous optimization of ionic conductivity and air / water stability, breaking the bottleneck of traditional sulfide electrolytes where both are difficult to balance.

[0192] Figure 4 A schematic diagram of the comparative ionic conductivity of a sulfide solid electrolyte provided in this application is shown below. Figure 4 As shown, the ionic conductivity of Comparative Example 1 (homogeneous sulfide solid electrolyte) and Example 1 (core-shell structured sulfide solid electrolyte with halogen concentration gradient) is displayed. The horizontal and vertical axes represent impedance-related parameters. Under the same test conditions, the curve corresponding to Example 1 is closer to the origin region, and its impedance value is significantly lower than that of Comparative Example 1. Considering the inverse relationship between ionic conductivity and impedance, this further indicates that the ionic conductivity of Example 1 is significantly higher than that of Comparative Example 1.

[0193] Figure 5 A schematic diagram of the comparison curves showing the retention rate of ionic conductivity of a sulfide solid electrolyte provided in this application is shown below. Figure 5 As shown, the ionic conductivity retention rates of the sulfide solid electrolytes of Comparative Example 1 and Example 1 after exposure to a constant dew point dry room (-30°C) for a certain period of time are illustrated. The horizontal and vertical axes represent impedance-related parameters. As the impedance parameters corresponding to the exposure time increase, the impedance value of Comparative Example 1 increases more rapidly, and its final impedance is significantly higher than that of Example 1. Considering the inverse relationship between ionic conductivity and impedance, this indicates that under the same dry room exposure conditions, the ionic conductivity of Comparative Example 1 decreases more severely, while the ionic conductivity retention rate of Example 1 is higher.

[0194] In summary, the sulfide solid electrolyte and its preparation method provided in this application can improve the stability of air / water without reducing the ionic conductivity. That is, the core-shell structured sulfide solid electrolyte with halogen concentration gradient provided in this application achieves a synergistic improvement in ionic conductivity and air / water stability.

[0195] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A sulfide solid electrolyte, characterized in that, include: The first mixture and the second mixture; The first mixture comprises lithium sulfide and phosphorus sulfide, and the second mixture comprises lithium sulfide and a lithium halide salt; The first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

2. The sulfide solid electrolyte according to claim 1, characterized in that, The first particle has a particle size of 0.6 μm to 2 μm; and / or; The second particle has a particle size of 3μm to 20μm.

3. The sulfide solid electrolyte according to claim 1 or 2, characterized in that, The phosphorus sulfide includes at least one of P2S3, P2S5, P4S4, P4S7, P4S9 and P4S6. and / or; The lithium halide salt includes at least one of LiCl, LiBr, LiI, and LiF.

4. The sulfide solid electrolyte according to claim 1 or 2, characterized in that, The molar ratio of lithium sulfide to phosphorus sulfide in the first mixture is (3~3.2):1; and / or; The molar ratio of lithium sulfide to the halogen lithium salt in the second mixture is (0.176~19):

1.

5. The sulfide solid electrolyte according to claim 1 or 2, characterized in that, The molar ratio of the first mixture to the second mixture is 1:(1.9~2.1).

6. A method for preparing a sulfide solid electrolyte as described in any one of claims 1 to 5, characterized in that, The method includes: Lithium sulfide and phosphorus sulfide were mixed and ground to obtain an amorphous mixture. After subjecting the amorphous mixture to a first heat treatment, it is then refined to obtain a first mixture; Lithium sulfide and lithium halide salts are mixed and granulated to obtain a second mixture; Based on the first mixture and the second mixture, a sulfide solid electrolyte is obtained; Wherein, the first mixture coats the surface of the second mixture, and the first particle size of the first mixture is smaller than the second particle size of the second mixture.

7. The method according to claim 6, characterized in that, The granulation process includes any one of spray drying granulation, dry granulation, and wet granulation.

8. The method according to claim 6 or 7, characterized in that, The first particle has a particle size of 0.6 μm to 2 μm; and / or; The second particle has a particle size of 3μm to 20μm.

9. The method according to claim 6 or 7, characterized in that, The process of mixing and grinding lithium sulfide and phosphorus sulfide to obtain an amorphous mixture includes: Lithium sulfide and phosphorus sulfide in a molar ratio of (3~3.2):1 were placed in an inert gas atmosphere and mechanically mixed and ground to obtain the amorphous mixture. The inert gas includes at least one of argon, nitrogen, and neon.

10. The method according to claim 6 or 7, characterized in that, In the first heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 240~320℃, and the holding time is 0.5~8h.

11. The method according to claim 6 or 7, characterized in that, The refining process includes at least one of mechanical grinding, ball milling, sand milling, or air jet milling.

12. The method according to claim 6 or 7, characterized in that, The phosphorus sulfide includes at least one of P2S3, P2S5, P4S4, P4S7, P4S9 and P4S6. and / or; The lithium halide salt includes at least one of LiCl, LiBr, LiI, and LiF.

13. The method according to claim 6 or 7, characterized in that, The molar ratio of lithium sulfide to phosphorus sulfide in the first mixture is (3~3.2):1; and / or; The molar ratio of lithium sulfide to the lithium halide salt in the second mixture is (0.176~0.19):1; And / or, The molar ratio of the first mixture to the second mixture is 1:(1.9~2.1).

14. The method according to claim 6 or 7, characterized in that, The process of obtaining a sulfide solid electrolyte based on the first mixture and the second mixture includes: The first mixture is mixed with the second mixture to obtain a third mixture; The third mixture is subjected to a second heat treatment to obtain a sintered body; The sintered body is crushed and sieved to obtain the sulfide solid electrolyte.

15. The method according to claim 14, characterized in that, In the second heat treatment, the heating rate is 0.5~10℃ / min, the temperature is 400~560℃, and the holding time is 2~24h.

16. An all-solid-state 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 5, and / or a sulfide solid electrolyte prepared by the method described in any one of claims 6 to 15.

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