Solid electrolyte, preparation method thereof and solid-state battery

Abstract

The invention relates to the technical field of batteries, in particular to a solid electrolyte, a preparation method thereof and a solid-state battery. A solid state electrolyte includes: a matrix including a halide electrolyte; the lithium ion battery comprises a substrate and a coating layer, the coating layer coats at least part of the surface of the substrate, the coating layer comprises a lithium element, a fluorine element, an oxygen element, a boron element and an M element, and the M element comprises at least one of Al, Nb, Ta or Zr. The preparation method of the solid electrolyte comprises the following steps: mixing a plurality of halide electrolyte synthesis raw materials in an inert atmosphere to obtain a precursor; mixing the precursor with fluoride and boride to obtain a mixture; and heating the mixture to obtain the solid electrolyte. The air stability of the halide electrolyte can be improved, the ionic conductivity of the electrolyte is ensured, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a solid electrolyte, a preparation method thereof, and a solid-state battery. Background Art

[0002] In recent years, lithium-ion batteries have seen rapid development in areas such as portable electronic devices and electric vehicles. Compared to traditional lithium-ion batteries, solid-state batteries, due to the absence of internal electrolytes and the use of non-flammable solid electrolytes, can avoid safety hazards such as electrolyte leakage. Therefore, all-solid-state batteries have attracted widespread attention from researchers due to their superior safety performance and high energy density.

[0003] Currently, the main solid electrolytes studied in solid-state batteries include polymers, oxides, sulfides, and halides. Among them, halide electrolytes have good mechanical properties, ionic conductivity, and a high electrochemical window, and are considered to be one of the most promising electrolyte materials. However, halide electrolytes easily absorb moisture in the air. Due to their poor air stability, their application in solid-state batteries is affected.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a solid-state electrolyte, a preparation method thereof, and a solid-state battery. While improving the air stability of the solid-state electrolyte, the present invention can also reduce the significant decrease in ionic conductivity, thereby improving the battery's cycling performance.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] According to one aspect of the present application, an embodiment of the present application provides a solid electrolyte, comprising:

[0008] a substrate comprising a halide electrolyte; and

[0009] A coating layer is coated on at least a portion of the surface of the substrate, and the coating layer includes lithium, fluorine, oxygen, boron and M elements, and the M element includes at least one of Al, Nb, Ta or Zr.

[0010] In addition, the solid electrolyte according to the present application may also have the following additional technical features:

[0011] In some embodiments, the halide electrolyte has the general chemical formula LiM a OX b ;

[0012] wherein M comprises at least one of Al, Nb, Ta or Zr;

[0013] X includes at least one of Cl, Br or F;

[0014] 0≤a≤1, 3≤b≤4.

[0015] In some embodiments, the coating layer has diffraction peaks at positions where the diffraction angle 2θ values ​​are 30.6°±0.5°, 35°±0.5°, and 38.67°±0.5°, respectively, in an X-ray diffraction (XRD) spectrum.

[0016] In some embodiments, the coating layer has a spectrum peak at a binding energy position of 191.8±0.5 eV and a spectrum peak in a binding energy range of 682 to 689 eV in an X-ray photoelectron spectroscopy (XPS) graph.

[0017] In some embodiments, the coating layer has a thickness of ≤500 nm.

[0018] In some embodiments, the coating layer accounts for 0.1% to 20% by mass in the solid electrolyte.

[0019] In some embodiments, it can be detected by energy dispersive X-ray spectroscopy (EDS) that the surface of the halide electrolyte, ie, the coating layer, contains lithium, fluorine, oxygen, boron, and M elements.

[0020] According to another aspect of the present application, an embodiment of the present application provides a method for preparing the solid electrolyte as described above, the method comprising the following steps:

[0021] In an inert atmosphere, a plurality of halide electrolyte synthesis raw materials are mixed to obtain a precursor;

[0022] mixing the precursor with a fluoride and a boride to obtain a mixture;

[0023] The mixture is subjected to a heating treatment to obtain a solid electrolyte.

[0024] In some embodiments, the heating treatment temperature is 70° C. to 350° C., and the heating time is 1 hour to 6 hours.

[0025] In some embodiments, the heat treatment atmosphere includes at least one of nitrogen, oxygen, argon, helium, or neon.

[0026] In some embodiments, the mass of the fluoride and boride is 0.1% to 20% of the halide electrolyte.

[0027] In some embodiments, the fluoride and boride include one or both of LiODFB or LiBF4;

[0028] The fluoride further comprises one or more of NH4F, LiFSI or LiTFSI.

[0029] In some embodiments, the multiple halide electrolyte synthesis raw materials include compounds containing M and X, and lithium compounds containing oxygen elements, wherein M includes at least one of Al, Nb, Ta or Zr, and X includes at least one of Cl, Br or F.

[0030] In some embodiments, the mixing method of the plurality of halide electrolyte synthesis raw materials includes ball milling.

[0031] In some embodiments, the precursor is mixed with the fluoride and the boride by ball milling.

[0032] According to another aspect of the present application, an embodiment of the present application provides a solid-state battery, which includes the solid-state electrolyte as described above or the solid-state electrolyte prepared according to the above method.

[0033] In some embodiments, the solid-state battery includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane, wherein one or more of the positive electrode sheet, the negative electrode sheet, and the solid electrolyte membrane includes the above-mentioned solid electrolyte.

[0034] In some embodiments, the positive electrode sheet includes the above-mentioned solid electrolyte.

[0035] The implementation of the technical solution of the present invention has at least the following beneficial effects:

[0036] In an embodiment of the present application, a solid electrolyte is provided, wherein a coating layer is provided on the surface of the halide electrolyte. The coating layer includes a compound containing lithium, fluorine, oxygen, boron, and the element M. The coating layer can serve as a hydrophobic protective layer for the halide electrolyte. Thus, the hydrophobic protective layer (coating layer) on the surface of the halide electrolyte prevents direct contact between the halide electrolyte material and moisture in the air, inhibits the adsorption of water molecules on the halide electrolyte, reduces the decomposition of the electrolyte, and enhances the stability of the electrolyte to humid air.

[0037] The preparation method of the solid electrolyte provided by the present invention does not destroy the crystal structure of the halide electrolyte. Moreover, the added fluoride and boride can be decomposed in situ on the surface of the halide electrolyte to form a coating layer compound. The generated compound has a certain ionic conductivity, and the coating layer is relatively thin, which has very little effect on the ionic conductivity. That is, the present invention can improve the air stability of the halide electrolyte while ensuring the ionic conductivity of the electrolyte. In addition, the preparation method is simple and easy to implement and apply.

[0038] The solid electrolyte of the present invention, after being exposed to a dew point of -50°C, has reduced electrolyte decomposition products, a high ion conductivity retention rate, reduced corrosion to the current collector in the battery, and significantly improved cycle performance of the assembled all-solid-state battery.

[0039] Additional aspects and advantages of the present application will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the invention. DETAILED DESCRIPTION

[0040] The present application will be further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0041] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0042] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0043] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0044] Among solid-state electrolytes, halide solid electrolytes have high ionic conductivity, a wide electrochemical window, and good mechanical properties. However, halide electrolytes easily absorb water in the air, forming hydrates and further decomposing. This places strict requirements on the process conditions for the preparation of all-solid-state batteries, greatly hindering their application in solid-state batteries. Therefore, improving the chemical stability of halide solid electrolytes is crucial for industrial advancement and practicality. In other words, the poor air stability of halide electrolytes affects their application effect in solid-state batteries. To address these issues, methods commonly used in related technologies to enhance the chemical stability of halide solid electrolytes include: increasing chemical structural stability through element doping (e.g., Chem. Eng., 2023, 455, 140509); or, modifying the halide electrolyte material by coating the outer surface of the solid electrolyte with an inert material (e.g., Adv. Funct. Mater., 2022, 32, 2108805) to improve its chemical stability. However, these existing methods often result in a significant decrease in the ionic conductivity of the electrolyte material. Therefore, providing a practical method to effectively improve the chemical stability (e.g., air stability) of the solid electrolyte while minimizing the reduction in ionic conductivity is a technical problem that urgently needs to be solved.

[0045] Therefore, although the existing technology can improve the air stability of halide electrolyte materials by modifying them through element doping or surface coating with inert materials, these existing methods often lead to a significant decrease in the ionic conductivity of the electrolyte materials, that is, at the cost of a significant reduction in ionic conductivity.

[0046] Based on the above research, the inventors of this application have fully considered the characteristics of halide electrolyte materials, adopted a specific modification method, and introduced a specific type of coating layer on the surface of the halide electrolyte to improve the structural stability of the halide electrolyte, and the formation of the coating layer basically does not lead to a significant decrease in the ionic conductivity of the halide electrolyte. That is, the present invention can ensure the ionic conductivity of the electrolyte while improving the air stability of the halide electrolyte. During the preparation of the solid electrolyte, a compound is added to decompose in situ to generate a layer of coating material. A small amount of coating material not only does not cause a significant decrease in ionic conductivity, but also can significantly improve the air stability of the electrolyte, which is beneficial to improving the cycle performance of the battery. In view of this, the present application provides a solid electrolyte, a method for preparing a solid electrolyte, and a solid-state battery. The present application is described in detail below.

[0047] [Solid State Electrolyte]

[0048] In some embodiments, a solid electrolyte is provided, comprising:

[0049] a substrate comprising a halide electrolyte; and

[0050] The coating layer is coated on at least a portion of the surface of the substrate, and the coating layer includes lithium (Li), fluorine (F), oxygen (O), boron (B) and M element, and the M element includes at least one of Al (aluminum), Nb (niobium), Ta (tantalum) or Zr (zirconium).

[0051] In this application, the term "coating" is not limited to direct coating but also includes indirect coating. For example, when a coating layer coats a substrate, there may be no other structure between the coating layer and the outer surface of the substrate, or there may be one or more layers of other structures between the coating layer and the outer surface of the substrate. Preferably, there is no other structure between the coating layer and the outer surface of the substrate.

[0052] The coating layer is formed or coated on at least a portion of the surface of the substrate, which can protect or improve the substrate, i.e., the halide electrolyte. It can be used to prevent the halide electrolyte from direct contact with air, alleviate the problem of poor air stability of the halide electrolyte, reduce the decomposition of the halide electrolyte, and improve the structural stability of the solid electrolyte. The coating layer is formed or coated on at least a portion of the surface of the substrate, which means that the coating layer can completely encapsulate the substrate within the coating layer, or the coating layer can only coat a portion of the outer surface of the substrate; that is, the coating layer can completely coat the substrate, or it can coat a portion of the surface of the substrate, preferably completely coating the substrate.

[0053] The solid electrolyte provided is a core-shell structure, in which the core can adopt a traditional halide electrolyte, and the outer shell or shell layer, i.e., the coating layer, includes a compound containing lithium (Li), fluorine (F), oxygen (O), boron (B), and M (denoted as compound A), which can play an excellent protective or improvement role on the core material of the halide electrolyte, especially can alleviate the problem of poor air stability of the halide electrolyte. The inventors of this application have fully considered the intrinsic defects of existing halide electrolytes, such as, halide electrolytes have poor stability in air, easily absorb moisture to form hydrates, resulting in crystal structure degradation; halide electrolytes after absorbing water degradation products gather fluid to produce strong corrosiveness; existing modification technology will lead to low ionic conductivity of halide electrolytes. By using a coating layer containing the above-mentioned compound A to modify and coat it, a core-shell structure is formed, which improves the air stability of the halide electrolyte to a certain extent, improves the structural stability of the solid electrolyte, and can ensure the ionic conductivity of the solid electrolyte, thereby helping to improve the cycle performance of the battery. In detail:

[0054] In the present application, the coating layer formed on the surface of the halide electrolyte includes a compound A, which contains lithium (Li), fluorine (F), oxygen (O), boron (B), and M elements, and the M element includes at least one of Al, Nb, Ta, or Zr; wherein, during the preparation process of the solid electrolyte, fluoride and boride are added, and the added fluoride and boride are decomposed in situ on the surface of the halide electrolyte by heating to form compound A. Thus, the present invention fully utilizes the characteristics of fluoride and boride that are easily decomposed or melted by heating, so that a layer of protective layer with a hydrophobic effect is generated in situ on the surface of the halide electrolyte, that is, a coating layer. The coating layer can also be called a hydrophobic protective layer. It is formed on the surface of the halide electrolyte, which can prevent the halide electrolyte material from directly contacting with moisture in the air, inhibit the adsorption of water molecules on the halide electrolyte, reduce the decomposition of the electrolyte, and enhance the stability of the electrolyte to wet air, that is, effectively improve the stability of the halide electrolyte to air.

[0055] At the same time, the solid electrolyte of the present invention adopts a low-temperature heat treatment method during the preparation process, which will not destroy the crystal structure of the halide electrolyte. Moreover, the added fluoride and boride can decompose in situ on the surface of the halide electrolyte to form compound A, and the generated compound A has a certain ionic conductivity and the thin coating layer has very little effect on the ionic conductivity, that is, it does not significantly reduce the ionic conductivity. Therefore, compared with the prior art method of introducing an inert coating layer without ionic conductivity on the surface of the halide electrolyte, which will cause a sharp drop in ionic conductivity, the present invention can improve the air stability of the halide electrolyte while ensuring the ionic conductivity of the electrolyte.

[0056] The solid electrolyte of the present invention is a surface-modified halide electrolyte material. After exposure to a dew point of -50°C, the decomposition products of the solid electrolyte are reduced, the ion conductivity retention rate is high, the corrosion to the current collector in the battery is weakened, and the cycle performance of the assembled all-solid-state battery is significantly improved.

[0057] In some embodiments, the halide electrolyte has the general chemical formula LiM a OX b ; Wherein, M includes any one or more combinations of Al (aluminum), Nb (niobium), Ta (tantalum) or Zr (zirconium); X includes at least one of Cl (chlorine), Br (bromine) or F (fluorine); 0≤a≤1, 3≤b≤4.

[0058] Preferably, M includes one or more of Al (aluminum), Nb (niobium), Ta (tantalum) or Zr (zirconium).

[0059] Preferably, 0<a≤1, 3≤b≤4.

[0060] In the core-shell solid electrolyte of the present application, the matrix adopts a halide electrolyte, and the general chemical formula of the halide electrolyte is LiM a OX b wherein M comprises one or more of Al, Nb, Ta, or Zr, and X comprises one or more of Cl, Br, or F; and the coating layer comprises a compound A containing lithium, fluorine, oxygen, boron, and M. In this solid electrolyte, the M element in the halide electrolyte and the M element in the coating layer can be consistent.

[0061] In the above-mentioned compound A of lithium, fluorine, oxygen, boron, and M element, fluorine and boron can be derived from fluorides and borides added during the preparation process, that is, fluorine and boron are mainly provided by fluorides and borides, while lithium, oxygen, and M can be mainly derived from the surface of the halide electrolyte, or lithium can also be derived from fluorides and borides. The specific structural formula of the compound A is not limited in the examples of this application.

[0062] In some embodiments, it can be detected by energy dispersive X-ray spectroscopy (EDS) that the surface of the halide electrolyte, ie, the coating layer, contains lithium, fluorine, oxygen, boron, and M elements.

[0063] In some embodiments, the coating layer (compound A) has diffraction peaks at diffraction angles 2θ of 30.6°±0.5°, 35°±0.5°, and 38.67°±0.5° in its X-ray diffraction (XRD) spectrum.

[0064] In the present application, compound A has diffraction peaks at diffraction angles 2θ = 30.6°±0.5°, 35°±0.5°, and 38.67°±0.5° in an X-ray diffraction spectrum measured using a CuKα1 X-ray diffractometer (XRD).

[0065] X-ray diffraction analysis patterns are well known in the art and can be measured using methods known in the art. For example, the X-ray diffraction analysis pattern of compound A can be measured using CuKα1 radiation with reference to JIS K 0131-1996, General Rules for X-ray Diffraction Analysis Methods.

[0066] In some embodiments, the coating layer (compound A) has a peak at a binding energy position of 191.8±0.5 eV and a peak in a binding energy range of 682 to 689 eV in an X-ray photoelectron spectroscopy (XPS) graph.

[0067] In the present application, compound A has peaks at 191.8±0.5 eV and 682 to 689 eV in an X-ray photoelectron spectroscopy (XPS) spectrum.

[0068] The X-ray photoelectron spectroscopy (XPS) spectrum measurement is well known in the art and can be tested using methods known in the art.

[0069] In some embodiments, the thickness of the coating layer is ≤ 500 nm.

[0070] Preferably, in some embodiments, the thickness of the coating layer is ≤200 nm.

[0071] As an example, the thickness of the coating layer may be 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm or less than 10 nm, etc.

[0072] In the present application, the thickness of the coating layer in the solid electrolyte can be measured using methods known in the art, for example, by transmission electron microscopy (TEM).

[0073] The thickness of the coating layer can be adjusted according to the size of the substrate core. The appropriate thickness of the coating layer can not only ensure that the solid electrolyte has good processing performance, but also avoid the thickness being too thick and the excessive coating material affecting the ionic conductivity and other properties of the solid electrolyte, or it can also avoid the thickness being too thin to effectively exert the modification effect of the coating layer.

[0074] In some embodiments, the coating layer accounts for 0.1% to 20% by mass of the solid electrolyte.

[0075] Preferably, in some embodiments, the coating layer accounts for 0.5% to 10% by mass in the solid electrolyte.

[0076] As an example, the mass proportion of the coating layer in the solid electrolyte can be any point value among 0.1%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 18%, 20%, or a range value between any two of them.

[0077] By controlling the content of the coating layer within the above range, the excellent protection or improvement effect of the coating layer on the core material of the halide electrolyte can be effectively exerted, and the excessive content of the coating layer can be avoided to affect the ionic conductivity and other properties of the solid electrolyte.

[0078] Therefore, the solid electrolyte provided by the present invention is a surface-modified halide electrolyte material, which can avoid direct contact between the halide electrolyte and moisture in the air, inhibit the decomposition of the solid electrolyte surface, and be assembled into an all-solid-state battery at a dew point of -50°C, thereby significantly improving the cycle performance of the solid-state battery.

[0079] [Method for preparing solid electrolyte]

[0080] Accordingly, in some embodiments, the present application provides a method for preparing a solid electrolyte, the method comprising the following steps:

[0081] In an inert atmosphere, a plurality of halide electrolyte synthesis raw materials are mixed to obtain a precursor;

[0082] mixing the precursor with a fluoride and a boride to obtain a mixture;

[0083] The mixture is heated to obtain a solid electrolyte.

[0084] Preferably, the heating treatment is a low-temperature heating treatment, and the temperature of the low-temperature heating treatment is preferably ≤350°C.

[0085] The method provided by the present invention can first fully mix the raw materials for synthesizing the halide electrolyte to obtain a precursor, add fluoride and boride to the precursor, and then mix them by a wet or dry method to achieve full contact between the raw materials; and heat at a low temperature to decompose the added fluoride and boride in situ on the surface of the halide electrolyte to form compound A, that is, to form a coating layer on the surface of the halide electrolyte.

[0086] The coating formed by this method, namely the hydrophobic protective layer compound A, on the surface of the halide electrolyte prevents direct contact between the halide electrolyte material and moisture in the air, inhibits the adsorption of water molecules on the halide electrolyte, reduces electrolyte decomposition, and enhances the electrolyte's stability to humid air. After exposure to a dew point of -50°C, the solid electrolyte decomposition products are reduced, the ionic conductivity retention rate is high, the corrosion to the current collector in the battery is reduced, and the cycle performance of the assembled all-solid-state battery is significantly improved.

[0087] The preparation method provided by the embodiment of the present invention has a simple process, is easy to operate, has strong feasibility, and is easy to realize industrial application; in particular, the low-temperature heat treatment method used in this method will not destroy the crystal structure of the halide electrolyte, thereby ensuring the ionic conductivity of the solid electrolyte.

[0088] It should be understood that all the features and advantages described above for the “solid-state electrolyte” are also applicable to the “method for preparing the solid-state electrolyte” and will not be described in detail here.

[0089] In some specific embodiments, the method for preparing the solid electrolyte specifically includes the following steps (a) to (c):

[0090] (a) Preparation of precursor.

[0091] In step (a), preparing the precursor specifically includes: in an inert atmosphere, fully mixing and reacting a plurality of halide electrolyte synthesis raw materials by a dry method or a wet method to obtain the precursor.

[0092] In step (a), the multiple halide electrolyte synthesis raw materials can be fully mixed and reacted by a dry method, or can be fully mixed and reacted by a wet method.

[0093] Optionally, the method of mixing multiple halide electrolyte synthesis raw materials includes ball milling.

[0094] Optionally, the ball milling speed is 500 rpm to 2000 rpm, preferably 600 rpm to 1000 rpm, and the ball milling time is 1 hour to 5 hours, preferably 2 hours to 4 hours. For example, the ball milling time can be 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, etc., and the ball milling speed is 500 rpm, 600 rpm, 700 rpm, 800 rpm, 1000 rpm, 2000 rpm, etc.

[0095] It should be understood that the specific mixing method of the above-mentioned multiple halide electrolyte synthesis raw materials can adopt the conventional operation method in the field, and the specific operating conditions can also be selectively adjusted according to actual needs, which is not limited.

[0096] Optionally, the inert atmosphere may be a common inert gas atmosphere such as nitrogen, helium, argon, neon, etc.

[0097] In some embodiments, in step (a), the multiple halide electrolyte synthesis raw materials include compounds containing M and X, and a lithium compound containing an oxygen element, wherein M includes at least one of Al, Nb, Ta, or Zr, and X includes at least one of Cl, Br, or F.

[0098] According to the chemical formula of halide electrolyte LiM a OX b ; M includes at least one of Al, Nb, Ta or Zr; X includes at least one of Cl, Br or F; 0≤a≤1, 3≤b≤4, and the compound containing M and X can be selected accordingly, and the ratio or dosage of the compound containing M and X and the lithium compound containing oxygen element can also be calculated and added according to the required halide electrolyte chemical formula, and there is no limitation on this.

[0099] Optionally, the lithium compound containing oxygen elements may be one or more of LiOH, LiOH(H2O), Li2O, and Li2CO3.

[0100] (b) Preparing a mixture.

[0101] In step (b), preparing the mixture specifically includes: adding fluoride and boride to the precursor, mixing them by dry or wet method to fully contact each other, and obtaining a mixture.

[0102] In step (a), the precursor, the fluoride, and the boride may be fully mixed by a dry method or a wet method.

[0103] Optionally, the method of mixing the precursor with the fluoride and boride includes ball milling.

[0104] Optionally, the ball milling speed is 500 rpm to 2000 rpm, preferably 600 rpm to 1000 rpm, and the ball milling time is 0.5 h to 5 h, preferably 1 h to 3 h. For example, the ball milling time can be 0.5 h, 1 h, 1.5 h, 2 h, 3 h, 4 h, 5 h, etc., and the ball milling speed is 500 rpm, 600 rpm, 700 rpm, 800 rpm, 1000 rpm, 2000 rpm, etc.

[0105] In some embodiments, the fluoride and boride include one or both of LiODFB (lithium difluorooxalatoborate) or LiBF4 (lithium tetrafluoroborate);

[0106] The fluoride further includes one or more of NH4F (ammonium fluoride), LiFSI (lithium bis(fluorosulfonyl)imide) or LiTFSI (lithium bis(trifluoromethanesulfonyl)imide).

[0107] In the present application, the fluoride and boride may be one or more of NH4F, LiODFB, LiFSI, LiTFSI or LiBF4.

[0108] Among them, the fluoride is a fluorine-containing compound, which is a compound that can provide the fluorine (F) element. The fluoride can be one or more of NH4F, LiODFB, LiFSI, LiTFSI or LiBF4, that is, NH4F, LiODFB, LiFSI, LiTFSI or LiBF4 can all be used to provide the F element.

[0109] The boride is a compound containing boron and can provide the boron (B) element. The boride can be one or more of LiODFB and LiBF4.

[0110] It should be understood that LiODFB or LiBF4 can be used to provide both F and B. In practical applications, the selection of the above fluorides and borides is not limited as long as they can be used to provide F and B elements.

[0111] In some embodiments, the mass of the fluoride and boride is 0.1% to 20% of the halide electrolyte. As an example, the mass of the fluoride and boride is any one of 0.1%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 18%, 20% of the halide electrolyte, or a range therebetween.

[0112] (c) heating the mixture.

[0113] In step (c), the heating treatment of the mixture specifically includes: heating the mixture at a low temperature in an atmosphere of nitrogen, argon, oxygen or a mixed gas, wherein the fluoride and boride decompose or melt products during the heating process to form an in-situ coating layer on the electrolyte surface.

[0114] In some embodiments, in step (c), the atmosphere for the heat treatment includes but is not limited to at least one of nitrogen, oxygen, argon, helium, or neon.

[0115] In some embodiments, in step (c), the heating treatment is a low-temperature heating treatment. Optionally, the heating treatment temperature is 70°C to 350°C, and the heating time is 1 hour to 6 hours. As an example, the heating treatment temperature can be any one of 70°C, 80°C, 90°C, 100°C, 120°C, 150°C, 180°C, 200°C, 250°C, 300°C, and 350°C, or a range between any two thereof; the heating treatment time can be any one of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours, or a range between any two thereof.

[0116] By controlling the temperature of the heat treatment within the above range, damage to the crystal structure of the halide electrolyte can be avoided, and the fluoride and boride can be decomposed in situ on the surface of the halide electrolyte to form compound A. The generated compound A has a certain ionic conductivity and the thin coating layer has very little effect on the ionic conductivity, thereby ensuring the ionic conductivity of the solid electrolyte.

[0117] In some embodiments, the thickness of the coating layer is ≤500 nm. Preferably, the thickness of the coating layer is ≤200 nm.

[0118] Therefore, the embodiment of the present invention utilizes the property that fluorides and borides are easily decomposed or melted when heated, so that a protective layer with a hydrophobic effect, i.e., a coating layer, is generated in situ on the surface of the halide electrolyte. The coating layer on the surface of the solid electrolyte of the present invention can prevent the halide electrolyte material from directly contacting with moisture in the air, inhibit the adsorption of water molecules on the halide electrolyte, and effectively improve the stability of the halide electrolyte to air. After exposure to a dew point of -50°C, the decomposition products of the electrolyte are reduced, the ionic conductivity retention rate is high, the corrosion to the current collector in the battery is reduced, and the cycle performance of the assembled all-solid-state battery is significantly improved.

[0119] [Solid-state battery]

[0120] In some embodiments, the present application provides a solid-state battery, which includes the solid-state electrolyte as described above or a solid-state electrolyte prepared according to the aforementioned method.

[0121] Optionally, the solid-state battery can be an all-solid-state battery or a semi-solid-state battery, preferably an all-solid-state battery. More preferably, the solid-state battery is an all-solid-state lithium metal battery.

[0122] In some embodiments, the solid-state battery includes a positive electrode sheet, a negative electrode sheet, and a solid electrolyte membrane, wherein one or more of the positive electrode sheet, the negative electrode sheet, and the solid electrolyte membrane includes the solid electrolyte provided in any one of the above embodiments of the present application.

[0123] Preferably, the positive electrode sheet and / or the solid electrolyte membrane include the solid electrolyte provided in any one of the above embodiments of the present application. More preferably, the positive electrode sheet includes the solid electrolyte provided in any one of the above embodiments of the present application.

[0124] In some embodiments, in a solid-state battery, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces that oppose each other in its thickness direction, and the positive electrode film layer is disposed on the two opposing surfaces of the positive electrode current collector. It is understood that the positive electrode film layer can also be laminated and disposed on either of the two surfaces of the positive electrode current collector.

[0125] The present application does not particularly limit the material of the positive electrode current collector, as long as it can achieve the purpose of the present application, and can be selected according to actual needs. For example, in some embodiments, the positive electrode current collector can be aluminum, nickel, stainless steel, iron, titanium or carbon, and has a foil or mesh shape. Of course, in other embodiments, a composite current collector (such as an aluminum-carbon composite current collector or a polymer and metal composite current collector) can also be used.

[0126] In some embodiments, in the positive electrode sheet, the positive electrode film layer includes a positive electrode active material, an electrolyte material, a conductive agent and a binder; wherein the electrolyte material is the solid electrolyte provided in any one of the above embodiments of the present application.

[0127] The present application adds electrolyte materials to the positive electrode film layer, which can enhance the lithium ion transport in electrodes such as the positive electrode.

[0128] The present invention does not particularly limit the type of positive electrode active material in the positive electrode film layer, as long as the purpose of the present application can be achieved. As an example, the positive electrode active material can be various positive electrode active materials known in the art, such as lithium cobaltate, lithium nickelate, lithium manganate, lithium cobalt manganate, lithium cobalt nickelate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, and lithium iron phosphate.

[0129] It should be noted that the present invention has no particular restrictions on the types of conductive agents and binders in the positive electrode film layer, as long as the purpose of this application can be achieved. As an example, the binder can be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), nitrile rubber (NBR), styrene butadiene latex (SBR), carboxymethyl cellulose (CMC), polyvinyl alcohol, polyacrylate, polyimide, and polyamide. The conductive agent can be one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNT), carbon nanofibers (CNF), and vapor grown carbon fibers (VGCF).

[0130] Optionally, in the positive electrode film layer, the mass ratio of the positive electrode active material, the electrolyte material, the conductive agent and the binder is (50-90): (1-50): (0.1-15): (0.1-15).

[0131] In some embodiments, in a solid-state battery, the negative electrode sheet includes a negative electrode material, which may be lithium-indium alloy, lithium metal, graphite (or other carbon-based materials), silicon (silicon-based materials), silicon-carbon negative electrode, or other various negative electrode materials known in the art.

[0132] Optionally, the thickness of the negative electrode material layer in the negative electrode sheet is 20 μm to 50 μm.

[0133] In some embodiments, in a solid-state battery, the solid electrolyte in the solid electrolyte membrane can be a halide electrolyte, a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte, or any other solid electrolyte material known in the art.

[0134] Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0135] In order to better understand the present invention, the specific implementation process of the present invention will be described in detail below in a specific implementation mode. The embodiments described below are exemplary and are only used to explain this application and are not to be construed as limiting this application. If specific techniques or conditions are not specified in the embodiments, they shall be carried out in accordance with the techniques or conditions described in the literature in this field or in accordance with the product specifications.

[0136] Example 1

[0137] The preparation of the solid electrolyte comprises the following steps:

[0138] (a) 2.10 g NbCl5 and 0.19 g LiOH, raw materials for halide electrolyte synthesis, were weighed and placed in a 100 mL ball mill. The mixture was ball milled at 700 rpm in an inert atmosphere for 2 h to allow the raw materials to fully mix and react to form a precursor.

[0139] (b) 0.05 g NH4F and 0.02 g LiODFB were added to the precursor and ball milled at 600 rpm for 2 h to form a mixture.

[0140] (c) The mixture is placed in a tube furnace and sintered (low-temperature heating treatment) in an argon atmosphere at 120°C for 1 hour, so that the decomposition products of NH4F and LiODFB form an in situ surface coating layer containing lithium, boron, oxygen, fluorine, and niobium on the surface of the halide electrolyte (LiNbOCl4).

[0141] Example 2

[0142] The preparation of the solid electrolyte comprises the following steps:

[0143] (a) 2.03 g TaCl5 and 0.14 g LiOH, raw materials for halide electrolyte synthesis, were weighed and placed in a 100 mL ball mill. The mixture was ball milled at 700 rpm in an inert atmosphere for 2 h to allow the raw materials to fully mix and react to form a precursor.

[0144] (b) 0.05 g NH4F, 0.02 g LiODFB, and 0.02 g LiTFSI were added to the precursor and ball milled at 750 rpm for 1 h to form a mixture.

[0145] (c) The mixture is placed in a tube furnace (or box furnace) and sintered (low-temperature heating treatment) in an argon atmosphere at a temperature of 300°C for 1 hour, so that the decomposition products of NH4F, LiODFB, and LiTFSI form an in situ surface coating layer containing lithium, boron, oxygen, fluorine, and tantalum elements on the surface of the halide electrolyte (LiTaOCl4).

[0146] Example 3

[0147] The preparation of the solid electrolyte comprises the following steps:

[0148] (a) The raw materials for halide electrolyte synthesis, 1.34 g NbCl₅, 0.77 g ZrCl₄, and 0.20 g LiOH, were weighed into a 100-mL ball mill and milled at 650 rpm in an inert atmosphere for 3 h to allow the raw materials to fully mix and react to form a precursor.

[0149] (b) 0.1 g NH4F and 0.05 g LiBF4 were added to the precursor and ball milled at 750 rpm for 1 h to form a mixture.

[0150] (c) The mixture was placed in a tube furnace and sintered (low temperature heating treatment) in an argon atmosphere at a temperature of 150°C for 2 h to allow the decomposition products of NH4F and LiBF4 to react with the halide electrolyte (LiNb 0.6 Zr 0.4 OCl 3.6 ) A surface coating layer containing lithium, boron, oxygen, fluorine, zirconium and niobium elements is in situ generated on the surface.

[0151] Example 4

[0152] The preparation of the solid electrolyte comprises the following steps:

[0153] (a) The raw materials for halide electrolyte synthesis, 1.23 g NbCl₅, 0.078 g NbF₅, 0.77 g ZrCl₄, and 0.20 g LiOH, were weighed into a 100-mL ball mill and milled at 650 rpm in an inert atmosphere for 3 h to allow the raw materials to fully mix and react to form a precursor.

[0154] (b) 0.05 g NH4F, 0.05 g LiODFB, and 0.045 g LiBF4 were added to the precursor and ball milled at 750 rpm for 1 h to form a mixture.

[0155] (c) The mixture was placed in a tube furnace and sintered (low temperature heating treatment) under an argon atmosphere at a temperature of 150°C for 2 h to allow the decomposition products of NH4F, LiODFB and LiBF4 to react with the halide electrolyte (LiNb 0.6 Zr 0.4 OCl 3.55 F 0.05 ) A surface coating layer containing lithium, boron, oxygen, fluorine, zirconium and niobium elements is in situ generated on the surface.

[0156] Example 5

[0157] The difference between Example 5 and Example 1 is that:

[0158] In step (c), the heating temperature is 70° C. and the heating time is 6 h.

[0159] The rest are the same as in Example 1.

[0160] Example 6

[0161] The difference between Example 6 and Example 2 is that:

[0162] In step (c), the heating temperature is 350° C. and the heating time is 1 h.

[0163] The rest are the same as in Example 2.

[0164] Comparative Example 1

[0165] The preparation of the solid electrolyte comprises the following steps:

[0166] Weigh 2.10 g NbCl5 and 0.19 g LiOH, raw materials for halide electrolyte synthesis, into a 100 mL ball mill jar and ball mill them at 700 rpm in an inert atmosphere for 2 h to allow the raw materials to fully mix and react to form a precursor. The precursor was then placed in a tubular furnace and sintered under an argon atmosphere at a temperature of 120°C for 1 h to obtain a solid electrolyte.

[0167] The main difference between Comparative Example 1 and Example 1 is that step (b) is eliminated.

[0168] Comparative Example 2

[0169] The preparation of the solid electrolyte comprises the following steps:

[0170] Weigh 2.03 g TaCl5 and 0.14 g LiOH, raw materials for halide electrolyte synthesis, into a 100 mL ball mill. Mill the mixture at 700 rpm in an inert atmosphere for 2 h to allow the raw materials to fully mix and react to form a precursor. The precursor is then placed in a tubular furnace and sintered under an argon atmosphere at 300 ° C for 1 h to obtain a solid electrolyte.

[0171] The main difference between Comparative Example 2 and Example 2 is that step (b) is eliminated.

[0172] Comparative Example 3

[0173] The preparation of the solid electrolyte comprises the following steps:

[0174] Weigh 1.34 g NbCl5, 0.77 g ZrCl4, and 0.20 g LiOH, raw materials for halide electrolyte synthesis, into a 100 mL ball mill and mill at 650 rpm for 3 h to fully mix the raw materials to form a precursor. The precursor is then placed in a tubular furnace and sintered under an argon atmosphere at 150°C for 2 h to obtain a solid electrolyte.

[0175] The main difference between Comparative Example 3 and Example 3 is that step (b) is eliminated.

[0176] Performance Testing

[0177] 1. The solid electrolytes obtained in the above embodiments and comparative examples were subjected to performance tests.

[0178] The solid electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were exposed to a dew point of -50°C for 10 min, 30 min, 60 min, and 120 min, respectively, and the changes in their ionic conductivities were tested.

[0179] This test is carried out in a low humidity room with a dew point of -50°C. The test specifically includes:

[0180] After the solid electrolyte was exposed in a low-humidity room at a dew point of -50°C for different times (10 minutes, 30 minutes, 60 minutes, and 120 minutes), 150 mg of powder was weighed and placed in a battery mold (10 mm inner diameter). A pressure of 100 MPa was applied, and the AC impedance was measured using an electrochemical workstation with an applied voltage of 20 mV over a frequency range of 1 Hz to 1 MHz. The ionic conductivity of the solid electrolyte after different exposure times was calculated, and the test results are shown in Table 1.

[0181] 2. The solid electrolytes obtained in the above examples and comparative examples were exposed for 30 minutes and then added to the lithium cobalt oxide composite positive electrode to form the positive electrode layer, the sulfide electrolyte was used as the electrolyte layer, and metallic lithium was used as the negative electrode to assemble an all-solid-state battery. Specifically:

[0182] (1) Preparation of positive electrode sheet:

[0183] Lithium cobalt oxide, a solid electrolyte exposed for 30 minutes, a conductive agent (VGCF), and a binder (PTFE) were mixed in a mass ratio of 80:20:2:0.6 to prepare a positive electrode membrane, which was then composited with stainless steel to form a positive electrode sheet, thus obtaining a positive electrode sheet.

[0184] (2) Using lithium metal negative electrode as the negative electrode sheet.

[0185] (3) Preparation of solid electrolyte membrane:

[0186] The sulfide electrolyte (Li 5.5PS 4.5 C 1.5 ) and a binder (PTFE) were fully mixed in a mass ratio of 100:0.6 to prepare a solid electrolyte membrane.

[0187] (4) Battery assembly:

[0188] A rolling machine is used to compound the metallic lithium negative electrode with the solid electrolyte membrane, and then composite it with the positive electrode (positive electrode sheet) to form an all-solid-state battery.

[0189] The assembled solid-state battery is then subjected to electrochemical performance tests, including:

[0190] 1) First charge and discharge test: The solid-state battery is charged and discharged at 0.1C constant current for one cycle at 25°C, with a charge and discharge cut-off voltage and voltage range of 2.7-4.3V.

[0191] 2) Rate test: The solid-state battery is charged and discharged at 0.2C, 0.5C, and 2C constant currents for 5 cycles at 25°C. The charge and discharge cut-off voltage and voltage range are 2.7-4.3V.

[0192] 3) Long-cycle test: The solid-state battery is subjected to 100 cycles of charge and discharge at 0.1C constant current at 25°C, with a charge and discharge cut-off voltage and a voltage range of 2.7-4.3V. Among them, the capacity retention rate after 100 cycles = capacity after 100 cycles / initial discharge specific capacity * 100%.

[0193] The test results are shown in Table 2 below.

[0194] Table 1 Air stability test of halide electrolyte in various embodiments and comparative examples

[0195]

[0196] As can be seen from Table 1, compared with Comparative Examples 1-3, the solid electrolytes prepared in Examples 1-6 of the present invention still have higher ionic conductivity after exposure for 2 hours, while the solid electrolytes of Comparative Examples 1-3 do not have a coating layer on the surface, and their ionic conductivity drops sharply after exposure for 2 hours.

[0197] In addition, compared with Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, the data in Table 1 show that the in-situ surface coating of fluoride and boride has little effect on the ionic conductivity of the electrolyte; the results of the air stability test of the coated halide electrolyte at a dew point of -50°C show that the surface coating significantly improves the ionic conductivity retention rate of the electrolyte, and the halide electrolyte still has a high ionic conductivity after exposure for 2 hours.

[0198] Table 2 Electrochemical performance test of solid-state batteries prepared in various embodiments and comparative examples

[0199]

[0200] As can be seen from Table 1, compared with Comparative Examples 1-3, the solid-state batteries prepared using the solid-state electrolytes of Examples 1-6 of the present invention have better first discharge specific capacity, first coulombic efficiency, rate performance and capacity retention rate during the charge and discharge process, thereby improving the cycle performance and rate performance of the battery.

[0201] In addition, when Example 1 is compared with Comparative Example 1, Example 2 with Comparative Example 2, and Example 3 with Comparative Example 3, the electrochemical performance data results in Table 2 show that the first discharge specific capacity and coulombic efficiency of the battery assembled with the modified halide electrolyte after exposure to a dew point of -50°C for 30 minutes are higher than those of the unmodified corresponding sample. Similarly, the capacity retention rate and rate performance of the battery are also better than those of the unmodified material.

[0202] In summary, the present invention utilizes fluoride and boride to in situ generate a hydrophobic electrolyte coating on the surface of the halide electrolyte. The chemical components in the modified layer can prevent direct contact between the halide electrolyte and water vapor in the air, thereby reducing the adsorption of water on the electrolyte surface. After exposure to a dew point of -50°C, the decomposition products of the electrolyte are reduced, the ionic conductivity retention rate is high, the corrosion to the current collector in the battery is reduced, and the cycle performance and rate performance of the assembled all-solid-state battery are significantly improved.

[0203] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0204] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0205] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0206] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0207] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A solid electrolyte, characterized in that The solid electrolyte comprises: a substrate comprising a halide electrolyte; and The coating layer is coated on at least a portion of the surface of the substrate, and the coating layer includes lithium, fluorine, oxygen, boron and M elements, and the M element includes at least one of Al, Nb, Ta or Zr.

2. The solid electrolyte according to claim 1, characterized in that The general chemical formula of the halide electrolyte is LiM a OX b ; Wherein, M includes at least one of Al, Nb, Ta or Zr; X includes at least one of Cl, Br or F; 0≤a≤1, 3≤b≤4.

3. The solid electrolyte according to claim 1, characterized in that The X-ray diffraction spectrum of the coating layer has diffraction peaks at diffraction angles 2θ of 30.6°±0.5°, 35°±0.5°, and 38.67°±0.5°, respectively.

4. The solid electrolyte according to claim 1, characterized in that In the X-ray photoelectron energy spectrum, the coating layer has a spectrum peak at a binding energy position of 191.8±0.5 eV and a spectrum peak in a binding energy range of 682 to 689 eV.

5. The solid electrolyte according to any one of claims 1 to 4, characterized in that The thickness of the coating layer is ≤500nm; And / or, the coating layer accounts for 0.1% to 20% by mass in the solid electrolyte.

6. The method for preparing a solid electrolyte according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: In an inert atmosphere, a plurality of halide electrolyte synthesis raw materials are mixed to obtain a precursor; mixing the precursor with a fluoride and a boride to obtain a mixture; The mixture is subjected to a heating treatment to obtain a solid electrolyte.

7. The method for preparing a solid electrolyte according to claim 6, characterized in that: The heating treatment temperature is 70°C to 350°C, and the heating time is 1h to 6h; And / or, the atmosphere of the heat treatment includes at least one of nitrogen, oxygen, argon, helium or neon.

8. The method for preparing a solid electrolyte according to claim 6, characterized in that: The mass of the fluoride and boride is 0.1% to 20% of the halide electrolyte; And / or, the fluoride and boride include one or both of LiODFB or LiBF4; The fluoride further comprises one or more of NH4F, LiFSI or LiTFSI.

9. The method for preparing a solid electrolyte according to any one of claims 6 to 8, characterized in that: The multiple halide electrolyte synthesis raw materials include compounds containing M and X, and lithium compounds containing oxygen elements, wherein M includes at least one of Al, Nb, Ta or Zr, and X includes at least one of Cl, Br or F; and / or, the method of mixing the plurality of halide electrolyte synthesis raw materials comprises ball milling; And / or, the precursor is mixed with the fluoride and the boride by ball milling.

10. A solid-state battery, characterized in that: The solid-state battery comprises the solid-state electrolyte according to any one of claims 1 to 5 or the solid-state electrolyte prepared by the method according to any one of claims 6 to 9.

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