Sulfide composite solid electrolyte and preparation method thereof, positive electrode sheet and solid-state battery

Abstract

The present application relates to a sulfide composite solid electrolyte, a preparation method thereof, a positive electrode sheet and a solid-state battery. The sulfide composite solid electrolyte comprises a doped argyrodite sulfide solid electrolyte and an M oxide coating layer; the doping elements in the doped argyrodite sulfide solid electrolyte include M and O, and the M includes Al, Mg or Zn; the chemical general formula of the doped argyrodite sulfide solid electrolyte is Li 7‑z+5x‑2y P 1‑x M x S 6‑y‑ z O y X z , and X includes Cl, Br or I. By co-doping the argyrodite sulfide solid electrolyte with metal M elements and O elements, and by adjusting the doping amount of the doping elements and cooperating with the M oxide coating layer, the structural stability and interface performance of the sulfide composite solid electrolyte are simultaneously improved, and the ionic conductivity, air stability and electrochemical window of the sulfide composite solid electrolyte are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to solid-state batteries, and more particularly to a sulfide composite solid electrolyte and its preparation method, a positive electrode sheet, and a solid-state battery. Background Technology

[0002] With the rapid development of lithium-ion batteries in electric vehicles, smart grids, and other fields, there is an urgent need to develop energy storage systems with higher energy density and safety performance. Solid-state lithium-ion batteries (SSDs) have become one of the most promising options. Solid electrolytes are a crucial component of SSDs. Augensterite-type sulfide solid electrolytes have been widely studied due to their advantages such as high room temperature conductivity, simple synthesis, high reproducibility, and relatively low cost compared to other sulfides. However, Augensterite-type sulfide solid electrolytes still face problems such as poor air stability, narrow electrochemical window, and high cost, which severely restrict their application in SSDs.

[0003] CN120413760A discloses an air-stable silver-germanium sulfide electrolyte and its preparation method, as well as an all-solid-state battery. By introducing small organic molecule segments, a hydrophobic protective layer is formed on the electrolyte surface through halogen bonds, improving the water resistance and stability of the silver-germanium sulfide electrolyte and ensuring its conductivity. However, this technical solution cannot simultaneously solve the problem of the narrow electrochemical window of the silver-germanium sulfide electrolyte, and the conductivity improvement effect is not ideal.

[0004] CN119275330A discloses an oxygen-doped sulfide electrolyte, its preparation method, and its application. The sulfide electrolyte has a uniform oxide coating layer on its surface and is doped with oxygen. The thickness of the oxide coating layer is 1 nm to 50 nm, and the oxygen content in the oxide-doped sulfide electrolyte exhibits a gradient distribution. This structure can improve the air stability of the sulfide electrolyte and, due to the small amount of doped oxygen, results in minimal loss of ionic conductivity. Simultaneously, this structure also ensures that the oxygen coating shell is not easily detached, further improving the air stability of the sulfide electrolyte. However, this approach only improves the air stability of the sulfide electrolyte and may even cause a loss of conductivity, without simultaneously improving conductivity.

[0005] CN117013061A discloses a modified sulfide electrolyte, its preparation method, and its application. This invention modifies the surface of a sulfide electrolyte of the sulfide type by coating it with a uniform layer of a suitable mixture of lithium fluoride and alumina on the surface of the high-conductivity sulfide electrolyte particles. This achieves a target electrolyte with both high ionic conductivity and high air stability and lithium stability. However, this invention does not address the narrow electrochemical window of sulfide electrolytes.

[0006] Therefore, it is of great significance to provide a technical solution that can simultaneously solve the problems of poor air stability, low conductivity, and narrow electrochemical window of sulfide electrolytes of silver-germanium sulfide. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a sulfide composite solid electrolyte, its preparation method, a cathode sheet, and a solid-state battery. This invention involves co-doping a silver-germanium sulfide-type solid electrolyte with metallic elements M and O. By controlling the doping amount of these elements and combining it with an M oxide coating layer, the structural stability and interfacial properties of the sulfide composite solid electrolyte are simultaneously improved, significantly enhancing its ionic conductivity, air stability, and electrochemical window.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a sulfide composite solid electrolyte, the sulfide composite solid electrolyte comprising a doped silver-germanium sulfide solid electrolyte and an M oxide coating layer disposed on its surface; the doping element in the doped silver-germanium sulfide solid electrolyte comprises metallic M and O, wherein the metallic M comprises any one or a combination of at least two of Al, Mg, or Zn; the chemical formula of the doped silver-germanium sulfide solid electrolyte is Li. 7-z+5x-2y P 1-x M x S 6-y-z O y X z X includes any one or at least two of Cl, Br or I, 0.01≤x≤0.2, 0.01≤y≤0.3, 0.9≤z≤1.5.

[0009] This invention involves co-doping a sulfide solid electrolyte with metallic M and O elements. By controlling the doping amount, the co-doping of metallic M and O elements works synergistically to improve the ionic conductivity and structural stability of the sulfide composite solid electrolyte. Combined with an M oxide coating layer, where the M element in the M oxide is of the same type as the metallic M element in the dopant, the interfacial defects between the core of the doped sulfide solid electrolyte and the M oxide coating layer are effectively reduced, further improving the structural stability and interfacial performance of the sulfide composite solid electrolyte. The synergistic effect of the doping elements and the M oxide coating layer significantly enhances the ionic conductivity, air stability, and electrochemical window of the sulfide composite solid electrolyte.

[0010] When the sulfide composite solid electrolyte provided by this invention is applied in a solid-state battery, the metal M element in the dopant element can undergo an alloying reaction with the lithium metal anode, significantly reducing the nucleation barrier of lithium ions and enhancing the diffusion kinetics of lithium ions on the surface and in the bulk phase, thereby improving the electrochemical performance of the solid-state battery.

[0011] Preferably, the sulfide composite solid electrolyte has an ionic conductivity of 3 mS / cm or higher at 25°C.

[0012] Preferably, the average particle size of the sulfide composite solid electrolyte is 5 μm to 20 μm.

[0013] Preferably, the mass of the M oxide coating layer accounts for 0.3wt% to 1wt% of the total mass of the sulfide composite solid electrolyte.

[0014] In a second aspect, the present invention provides a method for preparing a sulfide composite solid electrolyte as described in the first aspect, the method comprising: According to the formula, metal M, lithium oxide and elemental sulfur are first mixed and ball-milled to obtain a first mixture including lithium sulfide and M oxide; then the first mixture, P2S5 and LiX are mixed and ball-milled to obtain a second mixture; then the second mixture is sintered under an inert atmosphere to obtain the sulfide composite solid electrolyte.

[0015] This invention replaces the traditional Li2S precursor with low-cost raw materials such as lithium oxide, and constructs a uniform metal oxide / lithium sulfide composite precursor system through mechanochemical in-situ reaction, providing a more favorable reaction basis for subsequent ion co-doping, metal oxide coating and sulfide main phase formation; through the synergistic effect of metal M / oxygen co-doping and M oxide coating, the structural stability and interfacial properties of the sulfide composite solid electrolyte are improved simultaneously, so that the prepared sulfide composite solid electrolyte has excellent ionic conductivity, air stability and wide electrochemical stability window.

[0016] Preferably, the rotational speeds of the first ball mill and the second ball mill are each independently 400 rpm to 600 rpm.

[0017] Preferably, the time for the first ball milling and the second ball milling is each 6h to 10h independently.

[0018] Preferably, the ball-to-material ratio of the first ball mill and the second ball mill is independently (10~20):1.

[0019] Preferably, the sintering temperature is 450℃~550℃.

[0020] Preferably, the sintering time is 8h to 12h.

[0021] Preferably, the inert atmosphere includes nitrogen and / or an inert gas.

[0022] Preferably, the sintering heating rate is 1℃ / min to 3℃ / min.

[0023] Preferably, the metal M includes any one or a combination of at least two of aluminum, magnesium, or zinc.

[0024] Preferably, the LiX includes any one or a combination of at least two of LiCl, LiBr, or LiI.

[0025] Preferably, the ball milling is carried out under a vacuum or inert atmosphere, the inert atmosphere including nitrogen and / or an inert gas.

[0026] Thirdly, the present invention provides a positive electrode sheet, the material of which includes a positive electrode active material and a solid electrolyte, wherein the solid electrolyte includes a sulfide composite solid electrolyte as described in the first aspect.

[0027] Fourthly, the present invention provides a solid-state battery, the solid-state battery comprising a positive electrode and a solid electrolyte layer; the solid electrolyte layer is made of a sulfide composite solid electrolyte as described in the first aspect; and / or, the positive electrode comprises a positive electrode as described in the third aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention improves the structural stability and interfacial properties of sulfide composite solid electrolyte by co-doping the sulfide solid electrolyte with metal M and O elements and combining it with M oxide coating layer. The sulfide composite solid electrolyte provided has excellent ionic conductivity, air stability and wide electrochemical stability window.

[0029] (2) This invention uses low-cost raw materials such as lithium oxide to replace traditional Li2S precursors and achieves low-cost preparation of sulfide composite solid electrolyte with excellent ionic conductivity, air stability and wide electrochemical stability window through mechanochemical in-situ reaction, without involving complicated preparation process.

[0030] (3) When the sulfide composite solid electrolyte provided by the present invention is applied in a solid battery, the metal M element in the doping element can undergo an alloying reaction with the lithium metal anode, significantly reducing the nucleation barrier of lithium ions and enhancing the diffusion kinetics of lithium ions on the surface and in the bulk phase, thereby improving the electrochemical performance of the solid battery. Detailed Implementation

[0031] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0032] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0033] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0034] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0035] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0036] In one specific embodiment, the present invention provides a sulfide composite solid electrolyte, the sulfide composite solid electrolyte comprising a doped silver-germanium sulfide solid electrolyte and an M oxide coating layer disposed on its surface; the doping element in the doped silver-germanium sulfide solid electrolyte comprises metallic M and O, wherein the metallic M comprises any one or a combination of at least two of Al, Mg, or Zn; the chemical formula of the doped silver-germanium sulfide solid electrolyte is Li. 7-z+5x-2y P 1-x M x S 6-y-z O y X z X includes any one or at least two of Cl, Br or I, 0.01≤x≤0.2, 0.01≤y≤0.3, 0.9≤z≤1.5, for example z can be 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0037] This invention involves co-doping a sulfide solid electrolyte with metallic M and O elements. The synergistic effect of the co-doping of metallic M and O elements improves the ionic conductivity and structural stability of the sulfide composite solid electrolyte. Combined with an M oxide coating layer, where the M element in the M oxide is of the same type as the metallic M element in the dopant, the interfacial defects between the core of the doped sulfide solid electrolyte and the M oxide coating layer are effectively reduced. This further improves the structural stability and interfacial performance of the sulfide composite solid electrolyte. The synergistic effect of the dopant elements and the M oxide coating layer significantly enhances the ionic conductivity, air stability, and electrochemical window of the sulfide composite solid electrolyte.

[0038] This invention regulates the doping amounts of metal M and O elements, where the doping amount of metal M is set to 0.01≤x≤0.2, for example, x can be 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2, and the doping amount of O is set to 0.01≤y≤0.3, for example, y can be 0.01, 0.02, 0.05, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28 or 0.3. Doping amounts of metal M and O within the above ranges facilitate synergistic effects, improving the structural stability and ionic conductivity of the sulfide composite solid electrolyte, and effectively enhancing the electrochemical stability window.

[0039] When the sulfide composite solid electrolyte provided by this invention is applied in a solid-state battery, the metal M element in the dopant element can undergo an alloying reaction with the lithium metal anode, significantly reducing the nucleation barrier of lithium ions and enhancing the diffusion kinetics of lithium ions on the surface and in the bulk phase, thereby improving the electrochemical performance of the solid-state battery.

[0040] In some embodiments, the sulfide composite solid electrolyte has an ionic conductivity of 3 mS / cm or higher at 25°C, for example, it can be 3 mS / cm, 3.2 mS / cm, 3.4 mS / cm, 3.6 mS / cm, 3.8 mS / cm, 4 mS / cm, 4.2 mS / cm, 4.4 mS / cm, 4.6 mS / cm, 4.8 mS / cm, 5 mS / cm, 5.2 mS / cm, 5.4 mS / cm, 5.6 mS / cm, 5.8 mS / cm, or 6 mS / cm.

[0041] In some embodiments, the average particle size of the sulfide composite solid electrolyte is 5 μm to 20 μm, for example, it can be 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm.

[0042] In this invention, an M oxide coating layer is provided on the surface of the doped silver-germanium sulfide solid electrolyte. The M oxide coating layer is the same as the metal M element in the doping element, which helps to reduce the interfacial impedance between the doped silver-germanium sulfide solid electrolyte and the M oxide coating layer and reduce interfacial defects. An appropriate mass ratio of the M oxide coating layer can improve the structural stability and air stability of the sulfide composite solid electrolyte without increasing the impedance.

[0043] In some embodiments, the mass of the M oxide coating layer accounts for 0.3wt% to 1wt% of the total mass of the sulfide composite solid electrolyte, for example, it can be 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%.

[0044] In another specific embodiment, the present invention provides a method for preparing a sulfide composite solid electrolyte as described in one of the foregoing specific embodiments, the preparation method comprising: According to the formula, metal M, lithium oxide and elemental sulfur are first mixed and ball-milled to obtain a first mixture including lithium sulfide and M oxide; then the first mixture, P2S5 and LiX are mixed and ball-milled to obtain a second mixture; then the second mixture is sintered under an inert atmosphere to obtain the sulfide composite solid electrolyte.

[0045] This invention replaces the traditional Li2S precursor with low-cost raw materials such as lithium oxide, and constructs a uniform metal oxide / lithium sulfide composite precursor system through mechanochemical in-situ reaction, providing a more favorable reaction basis for subsequent ion co-doping, metal oxide coating and sulfide main phase formation. Through the synergistic effect of metal M / oxygen co-doping and M oxide in-situ coating, the structural stability and interfacial properties of the sulfide composite solid electrolyte are improved simultaneously, resulting in the prepared sulfide composite solid electrolyte with excellent ionic conductivity, air stability and a wide electrochemical stability window.

[0046] In this invention, the rotation speed of the first ball mill affects the degree of reaction between metal M, lithium oxide and elemental sulfur. A suitable first ball mill rotation speed is conducive to the full reaction of metal M, lithium oxide and elemental sulfur, and the formation of a uniform metal oxide / lithium sulfide composite precursor system.

[0047] In some embodiments, the rotational speeds of the first ball mill and the second ball mill are each independently 400 rpm to 600 rpm, for example, 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm.

[0048] In some implementations, the time for the first ball milling and the second ball milling is independently 6h to 10h, for example, it can be 6h, 7h, 8h, 9h or 10h.

[0049] In some embodiments, the ball-to-material ratio of the first and second ball mills is independently (10~20):1, for example, it can be 10:1, 12:1, 14:1, 16:1, 18:1 or 20:1. In this invention, the ball-to-material ratio refers to the mass ratio of grinding balls to material.

[0050] In this invention, the sintering temperature affects the degree of reaction of the sulfide composite solid electrolyte. A suitable sintering temperature can not only successfully synthesize the sulfide solid electrolyte, but also achieve the doping of the metal M element in the sulfide solid electrolyte, thereby obtaining a sulfide composite solid electrolyte with excellent performance.

[0051] In some embodiments, the sintering temperature is 450°C to 550°C, for example, it can be 450°C, 470°C, 490°C, 500°C, 510°C, 530°C or 550°C.

[0052] In some embodiments, the sintering time is 8h to 12h, for example, it can be 8h, 9h, 10h, 11h or 12h.

[0053] In some embodiments, the inert atmosphere includes nitrogen and / or an inert gas.

[0054] In some embodiments, the heating rate of the sintering is 1℃ / min to 3℃ / min, for example, it can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min.

[0055] In some embodiments, the metal M includes any one or a combination of at least two of aluminum, magnesium, or zinc.

[0056] In some embodiments, the LiX includes any one or a combination of at least two of LiCl, LiBr, or LiI.

[0057] In some embodiments, the ball milling is carried out under a vacuum or inert atmosphere, the inert atmosphere including nitrogen and / or an inert gas.

[0058] In this invention, the inert gas includes argon and / or helium.

[0059] In yet another embodiment, the present invention provides a positive electrode sheet, the material of which includes a positive electrode active material and a solid electrolyte, the solid electrolyte including a sulfide composite solid electrolyte as described in the preceding embodiment.

[0060] In this invention, the type of positive electrode active material is not particularly limited. For example, the positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, or lithium-rich manganese-based positive electrode material.

[0061] In another specific embodiment, the present invention provides a solid-state battery, the solid-state battery comprising a positive electrode and a solid electrolyte layer; the solid electrolyte layer is made of a sulfide composite solid electrolyte as described in the preceding specific embodiment; and / or, the positive electrode comprises a positive electrode as described in yet another specific embodiment.

[0062] In this invention, the solid-state battery further includes a negative electrode sheet, the material of which includes lithium metal and / or lithium alloy. For example, the lithium alloy includes any one of lithium indium alloy, lithium tin alloy, lithium aluminum alloy, or lithium magnesium alloy.

[0063] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0064] Example 1 This embodiment provides a sulfide composite solid electrolyte, which includes Li 6.3 P 0.9 Mg 0.1 S 4.9 O 0.1 Cl sulfide solid electrolyte and an in-situ formed MgO coating layer on its surface, wherein the mass of the MgO coating layer accounts for 0.6 wt% of the total mass of the sulfide composite solid electrolyte; the average particle size of the sulfide composite solid electrolyte is 12 μm.

[0065] The preparation method of the sulfide composite solid electrolyte includes: (1) Mix metallic Mg, lithium oxide and elemental sulfur according to the ratio, add grinding balls, the ball-to-material ratio is 15:1, set the ball milling speed to 500 rpm, and perform the first ball milling for 8 hours to obtain the first mixture of lithium sulfide and MgO. (2) According to the ratio, the relative content of Li2S and MgO in the first mixture is controlled by an air classifier, and then mixed with P2S5 and LiCl for a second ball milling. The parameters of the second ball milling are the same as those of the first ball milling to obtain the second mixture. Then, under a nitrogen atmosphere, the temperature is raised to 500°C at a heating rate of 1°C / min, and the second mixture is sintered for 10h to obtain the sulfide composite solid electrolyte.

[0066] Example 2 This embodiment provides a sulfide composite solid electrolyte, which includes Li 6.13 P 0.99 Zn 0.01 S 5.09 O 0.01 Cl 0.9 The sulfide solid electrolyte and the ZnO coating layer formed in situ on its surface, wherein the mass of the ZnO coating layer accounts for 0.3 wt% of the total mass of the sulfide composite solid electrolyte; the average particle size of the sulfide composite solid electrolyte is 5 μm.

[0067] The preparation method of the sulfide composite solid electrolyte includes: (1) According to the ratio, metal Zn, lithium oxide and elemental sulfur were mixed, and grinding balls were added. The ball-to-material ratio was 10:1. The ball milling speed was set to 600 rpm, and the first ball milling was carried out for 6 hours to obtain the first mixture of lithium sulfide and ZnO. (2) According to the ratio, the relative content of Li2S and ZnO in the first mixture is controlled by an air classifier, and then mixed with P2S5 and LiCl for a second ball milling. The parameters of the second ball milling are the same as those of the first ball milling to obtain the second mixture. Then, under a nitrogen atmosphere, the temperature is raised to 550°C at a heating rate of 2°C / min, and the second mixture is sintered for 12 hours to obtain the sulfide composite solid electrolyte.

[0068] Example 3 This embodiment provides a sulfide composite solid electrolyte, which includes Li 5.9 P 0.8 Al 0.2 S 4.2 O 0.3 Cl 1.5 The sulfide solid electrolyte and the Al2O3 coating layer formed in situ on its surface, wherein the mass of the Al2O3 coating layer accounts for 1 wt% of the total mass of the sulfide composite solid electrolyte; the average particle size of the sulfide composite solid electrolyte is 20 μm.

[0069] The preparation method of the sulfide composite solid electrolyte includes: (1) According to the ratio, metal Al, lithium oxide and elemental sulfur were mixed, and grinding balls were added. The ball-to-material ratio was 20:1. The ball milling speed was set to 400 rpm, and the first ball milling was carried out for 6 hours to obtain the first mixture of lithium sulfide and Al2O3. (2) According to the ratio, the relative content of Li2S and Al2O3 in the first mixture is controlled by an air classifier, and then mixed with P2S5 and LiCl for a second ball milling. The parameters of the second ball milling are the same as those of the first ball milling to obtain the second mixture. Then, under an argon atmosphere, the temperature is raised to 450°C at a heating rate of 3°C / min, and the second mixture is sintered for 8 hours to obtain the sulfide composite solid electrolyte.

[0070] Example 4 This embodiment provides a sulfide composite solid electrolyte, except that the mass of the MgO coating layer accounts for 0.25 wt% of the total mass of the sulfide composite solid electrolyte, and all other aspects are the same as in Example 1.

[0071] The preparation method of the sulfide composite solid electrolyte is exactly the same as that in Example 1, except that after the first mixture is prepared in step (1), the relative contents of Li2S and MgO in the first mixture are controlled by an air classifier to meet the ratio.

[0072] Example 5 This embodiment provides a sulfide composite solid electrolyte, except that the mass of the MgO coating layer accounts for 1.05 wt% of the total mass of the sulfide composite solid electrolyte, and all other aspects are the same as in Example 1.

[0073] The preparation method of the sulfide composite solid electrolyte is exactly the same as that in Example 1, except that after the first mixture is prepared in step (1), the relative contents of Li2S and MgO in the first mixture are controlled by an air classifier to meet the ratio.

[0074] Example 6 This embodiment provides a sulfide composite solid electrolyte. Except for the ball milling speed of 300 rpm during the preparation of the sulfide composite solid electrolyte, everything else is the same as in Example 1.

[0075] Example 7 This embodiment provides a sulfide composite solid electrolyte. Except for the ball milling speed of 700 rpm during the preparation of the sulfide composite solid electrolyte, everything else is the same as in Example 1.

[0076] Example 8 This embodiment provides a sulfide composite solid electrolyte, except that the sintering temperature is 400℃ during the preparation of the sulfide composite solid electrolyte, all other aspects are the same as in Example 1.

[0077] Example 9 This embodiment provides a sulfide composite solid electrolyte, except that the sintering temperature is 600°C during the preparation of the sulfide composite solid electrolyte, all other aspects are the same as in Example 1.

[0078] Comparative Example 1 This comparative example provides a Li6PS5Cl sulfide solid electrolyte. The preparation method of the Li6PS5Cl sulfide solid electrolyte is the same as that in Example 1, except that after step (1), the first mixture is separated by an air classifier to obtain alumina and lithium sulfide, and in step (2), the separated lithium sulfide is used to replace the first mixture.

[0079] Comparative Example 2 This comparative example provides a sulfide composite solid electrolyte, except that the sulfide composite solid electrolyte includes Li 5.84 P 0.992 Mg 0.008 S 4.9 O 0.008 The Cl sulfide solid electrolyte and the MgO coating layer formed in situ on its surface, i.e., the doping amount of Mg and O is reduced to 0.008, are otherwise the same as in Example 1.

[0080] The preparation method of the sulfide composite solid electrolyte is the same as in Example 1, except that after the first mixture is prepared in step (1), the relative content of Li2S and MgO in the first mixture is controlled by an air classifier, and the amount of P2S5 added is increased adaptively to meet the ratio.

[0081] Comparative Example 3 This comparative example provides a sulfide composite solid electrolyte, except that the sulfide composite solid electrolyte includes Li 6.9 P 0.78 Mg 0.32 S 4.9 O 0.32 The Cl sulfide solid electrolyte and the MgO coating layer formed in situ on its surface, i.e. the Mg doping amount is increased to 0.32, are otherwise the same as in Example 1. The preparation method of the sulfide composite solid electrolyte is the same as in Example 1, except that after the first mixture is prepared in step (1), the relative contents of Li2S and MgO in the first mixture are controlled by an air classifier, and the amount of P2S5 added is appropriately reduced to meet the ratio.

[0082] Comparative Example 4 This comparative example provides a sulfide composite solid electrolyte, which is the same as that in Example 1 except that it does not contain doping elements; The preparation method of the sulfide composite solid electrolyte is the same as that of Comparative Example 1, except that after step (2) the Li6PS5Cl sulfide solid electrolyte and the separated MgO are ball-milled and mixed at a mass ratio of 99.6:0.4.

[0083] Comparative Example 5 This comparative example provides a Li 6.3 P 0.9 Mg 0.1 S 4.9 O 0.1 The Cl sulfide solid electrolyte is the same as in Example 1, except that it does not have an MgO coating layer; The Li 6.3 P 0.9 Mg 0.1 S 4.9 O 0.1 The preparation method of Cl sulfide solid electrolyte is as follows: (1) After the first mixture is prepared, the gas stream separates out MgO in an amount equal to that of the coating layer to meet the ratio. The rest is the same as in Example 1.

[0084] Performance testing: Air stability test: The sulfide solid electrolyte powder obtained in the above examples and comparative examples was placed in a mold with a diameter of 10 mm and cold-pressed into sheets under a pressure of 300 MPa. The sheets were then placed in a sealed container with a volume of 10 L in an air atmosphere with a dew point of -40 °C for 2 hours. The H2S concentration in the sealed container was detected using a hydrogen sulfide gas sensor to evaluate the air stability of the sulfide solid electrolyte. The test results are shown in Table 1.

[0085] Ionic conductivity testing: The sulfide solid electrolyte powder obtained in the above examples and comparative examples was placed between two stainless steel blocking electrodes and pressed into a symmetrical mold battery under a pressure of 500 MPa. Subsequently, the electrochemical impedance spectroscopy (EIS) method was used for testing at 25°C, with a frequency range of 10 MHz to 0.1 Hz and an AC disturbance voltage of 10 mV. The impedance values ​​obtained from the tests were combined with the sample thickness and area, and the formula... The ionic conductivity was calculated, where σ is the ionic conductivity, L is the sample thickness, R is the impedance value, and A is the electrode contact area. The test results are shown in Table 1.

[0086] Electrochemical window testing: The sulfide solid electrolytes obtained in the above examples and comparative examples were mixed with conductive carbon fibers at a certain mass ratio and pressed into working electrodes. A lithium metal sheet was used as the counter electrode, and a test battery was assembled. After applying a pressure of 10 MPa to both sides of the electrode and sealing it, linear sweep voltammetry (LSV) was used for testing. The scan range was from open-circuit voltage to 5 V (vs. Li / Li). + The scan rate was 0.1 mV / s. -1 The oxidation decomposition voltage was determined based on the potential corresponding to a significant increase in oxidation current, in order to evaluate the electrochemical stability window of the material. The test results are shown in Table 1.

[0087] Solid-state battery performance testing: The sulfide solid electrolytes provided in all the above embodiments and comparative examples were assembled with NCM811 composite cathodes and lithium indium alloy anodes to form all-solid-state batteries, and electrochemical performance was tested by holding the battery under pressure (10MPa) with a steel kit. The NCM811 composite cathode consists of NCM811 cathode material in a mass ratio of 90:6:4, the sulfide solid electrolytes provided in all the above embodiments and comparative examples, and conductive carbon black.

[0088] First, at 25℃ and within a voltage range of 2.5V to 4.4V, the 0.1C discharge specific capacity was tested by charging and discharging at a rate of 0.1C. Then, the 0.1C charge-discharge cycle was repeated 100 times to test the cycle capacity retention rate. The cycle capacity retention rate = discharge specific capacity of the 100th cycle / discharge specific capacity of the first cycle × 100%. The test results are shown in Table 1.

[0089] Table 1 Based on the test results of Examples 1 to 9 and Comparative Example 1 in Table 1, this invention improves the structural stability and interfacial properties of the sulfide composite solid electrolyte by co-doping it with metal M and O elements and using an M oxide coating layer. This significantly enhances the ionic conductivity, air stability, and electrochemical window of the sulfide composite solid electrolyte. The high electrochemical window enables the application of the sulfide composite solid electrolyte in higher voltage cathode material scenarios.

[0090] Based on the test results of Examples 1, 4, and 5, in sulfide composite solid electrolytes, a suitable mass ratio of the M oxide coating layer can improve the structural stability and air stability of the sulfide composite solid electrolyte without significantly sacrificing ionic conductivity. If the mass ratio of the M oxide coating layer is too small, sufficient physical isolation cannot be formed, resulting in poor air stability, manifested as an increase in hydrogen sulfide concentration; while if the mass ratio of the M oxide coating layer is too large, it not only hinders the transport of lithium ions and electrons, leading to a decrease in electrochemical performance, but also hinders the improvement of the energy density of solid-state batteries.

[0091] According to the test results of Examples 1, 6 and 7, when the rotation speed of the first ball mill deviates from the appropriate range, it will not be conducive to the full reaction of metal M, lithium oxide and elemental sulfur, and a uniform metal oxide / lithium sulfide composite precursor system cannot be formed. This results in unsatisfactory subsequent doping and coating effects, poor performance improvement of sulfide composite solid electrolyte, and deterioration of the electrical performance of solid battery.

[0092] According to the test results of Examples 1, 8 and 9, the sintering temperature affects the composition of the sulfide composite solid electrolyte. If the sintering temperature is too low, the reaction between the first mixture, P2S5 and LiCl will be incomplete, resulting in a small amount of unreacted impurities. Furthermore, the diffusion kinetics of Mg and O elements in the sulfide solid electrolyte lattice will be insufficient, leading to uneven doping. Consequently, the performance improvement effect of the sulfide composite solid electrolyte will be worse, and the electrochemical performance of the solid battery will decrease.

[0093] Based on the test results of Examples 1 and Comparative Examples 2 to 5, if Li6PS5Cl is not simultaneously doped and coated, or if the doping amounts of metal M and O are not within an appropriate range, it is detrimental to achieving the optimal performance of the sulfide composite solid electrolyte. Simultaneous improvement of ionic conductivity, air stability, and electrochemical window cannot be achieved, and the electrochemical performance of the solid-state battery cannot be effectively enhanced. Furthermore, in Comparative Example 4, if magnesium oxide is directly used to ball-mill and coat the Li6PS5Cl sulfide solid electrolyte, a continuous coating layer cannot be formed, resulting in a significant decrease in coating effect and consequently, a deterioration in electrochemical performance.

[0094] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A sulfide composite solid electrolyte, characterized in that, The sulfide composite solid electrolyte includes a doped silver-germanium sulfide solid electrolyte and an M oxide coating layer disposed on its surface. The doping elements in the doped silver-germanium sulfide solid electrolyte include metal M and O, wherein the metal M includes any one or a combination of at least two of Al, Mg or Zn. The chemical formula of the doped silver-germanium sulfide solid electrolyte is Li 7-z+5x-2y P 1-x M x S 6-y-z O y X z X includes any one or at least two of Cl, Br or I, 0.01≤x≤0.2, 0.01≤y≤0.3, 0.9≤z≤1.

5.

2. The sulfide composite solid electrolyte as described in claim 1, characterized in that, The sulfide composite solid electrolyte has an ionic conductivity of over 3 mS / cm at 25°C. And / or, the average particle size of the sulfide composite solid electrolyte is 5 μm to 20 μm.

3. The sulfide composite solid electrolyte as described in claim 1, characterized in that, The mass of the M oxide coating layer accounts for 0.3wt% to 1wt% of the total mass of the sulfide composite solid electrolyte.

4. A method for preparing a sulfide composite solid electrolyte as described in any one of claims 1 to 3, characterized in that, The preparation method includes: According to the formula, metal M, lithium oxide and elemental sulfur are first mixed and ball-milled to obtain a first mixture including lithium sulfide and M oxide; then the first mixture, P2S5 and LiX are mixed and ball-milled to obtain a second mixture; then the second mixture is sintered under an inert atmosphere to obtain the sulfide composite solid electrolyte.

5. The preparation method according to claim 4, characterized in that, The rotational speeds of the first ball mill and the second ball mill are each independently 400 rpm to 600 rpm; And / or, the time for the first ball milling and the second ball milling is each independently 6h~10h; And / or, the ball-to-material ratio of the first ball mill and the second ball mill is independently (10~20):

1.

6. The preparation method according to claim 4, characterized in that, The sintering temperature is 450℃~550℃; And / or, the sintering time is 8h~12h; And / or, the inert atmosphere includes nitrogen and / or an inert gas; And / or, the sintering heating rate is 1℃ / min to 3℃ / min.

7. The preparation method according to claim 4, characterized in that, The metal M includes any one or a combination of at least two of the following: aluminum, magnesium, or zinc. And / or, the LiX includes any one or a combination of at least two of LiCl, LiBr, or LiI.

8. The preparation method according to claim 4, characterized in that, The ball milling is carried out under a vacuum or inert atmosphere, which includes nitrogen and / or an inert gas.

9. A positive electrode plate, characterized in that, The positive electrode sheet is made of a positive electrode active material and a solid electrolyte, wherein the solid electrolyte includes a sulfide composite solid electrolyte as described in any one of claims 1 to 3.

10. A solid-state battery, characterized in that, The solid-state battery includes a positive electrode and a solid electrolyte layer; The solid electrolyte layer is made of the sulfide composite solid electrolyte as described in any one of claims 1 to 3; And / or, the positive electrode includes the positive electrode as described in claim 9.

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