A solid electrolyte material, its preparation method and application

Abstract

This invention relates to a solid electrolyte material, its preparation method, and its applications. In the solid electrolyte material of this invention, the content of Li gradually decreases along the direction from the center to the surface, while the content of La and Zr gradually increases. This invention prepares a solid electrolyte material with a novel structure through the non-uniform distribution of at least three elements—lithium, lanthanum, and zirconium—in the solid electrolyte material. This structure can fully utilize the high ionic conductivity and improve the surface stability of the material.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a solid electrolyte material for lithium-ion batteries with a concentration gradient distribution and its preparation method, as well as a solid electrolyte membrane and battery. Background Technology

[0002] Lithium-ion batteries are currently widely used in consumer electronics, electric vehicles, and large-scale energy storage. However, lithium-ion batteries using organic electrolytes still suffer from problems such as continuous growth of the solid electrolyte interphase (SEI) film, dissolution of transition metals, electrolyte oxidation, and high-temperature failure. Gradually replacing organic electrolytes with solid electrolytes to form semi-solid, quasi-solid, and solid batteries can further improve battery energy density while ensuring battery safety.

[0003] The development of solid electrolyte materials is particularly important for quasi-solid-state, semi-solid-state, and all-solid-state batteries. Currently, solid electrolytes include LiPON, perovskite, NASICON, sulfide, and garnet types. Compared to other solid electrolytes, garnet-type solid electrolytes have advantages such as stability with lithium metal, high lithium-ion conductivity (up to 1 mS / cm at room temperature), and a wide electrochemical window (0-5V). However, these electrolytes are relatively sensitive to air and readily react with water vapor and carbon dioxide to form Li₂CO₃ impurities with low lithium-ion conductivity, significantly limiting their application as lithium-ion conductors in the electrolyte interlayer and positive and negative electrode plates. Summary of the Invention

[0004] The problem the invention aims to solve

[0005] Garnet-type solid electrolytes typically exhibit poor stability in air, readily reacting with CO2 and water to form Li2CO3, thus affecting the material's ionic conductivity. The purpose of this invention is to provide a solid electrolyte material, specifically a lithium-ion electrolyte material with a concentration gradient structure, to further improve the lithium-ion conductivity and air stability of solid electrolyte materials.

[0006] This invention also provides a method for preparing solid electrolyte materials with a concentration gradient structure via coprecipitation. By controlling the content of lithium salt, zirconium salt, and lanthanum salt during the coprecipitation reaction, gradually decreasing the lithium salt content and increasing the zirconium salt content, this invention achieves a distribution of metal ion concentration variations. This not only allows for controllable coprecipitated crystal morphology but also facilitates large-scale production. Furthermore, the metal ion concentration can be arbitrarily adjusted according to design, making operation convenient.

[0007] Solution for solving the problem

[0008] As described below, this invention proposes a solid electrolyte material with improved ionic conductivity and air stability, and also proposes a method for preparing this solid electrolyte material, which is easy to scale up and operate, making the application of solid electrolyte materials more widespread.

[0009] [1] A solid electrolyte material in which the elemental content of Li gradually decreases and the elemental content of La and Zr gradually increases along the direction from the center to the surface of the solid electrolyte material.

[0010] [2] According to [1], the solid electrolyte material has the chemical composition of p(Li 7- x La3Zr 2-x A x O 12 )·q(La2Zr2O7), or p(Li 7-m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein, A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, and along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases;

[0011] The chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2-x A x O 12 When )·q(La2Zr2O7), the elemental content of A gradually decreases along the direction from the center to the surface of the solid electrolyte material.

[0012] [3] The solid electrolyte material according to [1] or [2], wherein the particle size D50 of the solid electrolyte material is 5 to 10 μm, preferably 6 to 8 μm.

[0013] [4] The solid electrolyte material according to any one of [1]-[3], wherein the elemental content of Li decreases in a concentration gradient and the elemental content of La and Zr increases in a gradient.

[0014] [5] The solid electrolyte material according to any one of [2]-[4], wherein the elemental content of A decreases in a gradient.

[0015] [6] The solid electrolyte material according to any one of [2]-[5], wherein at the center of the solid electrolyte material, p=1 and q=0;

[0016] On the surface of the solid electrolyte material, p = 0, q = 1.

[0017] [7] The solid electrolyte material according to any one of [1]-[6], wherein the solid electrolyte material has a spherical or near-spherical shape and an average sphericity of 0.8 to 1, preferably 0.9 to 1.

[0018] [8] A method for preparing a solid electrolyte material, characterized in that the preparation method includes:

[0019] Step S1 involves co-precipitating a solution containing lithium salt, zirconium salt, and lanthanum salt, gradually reducing the lithium salt content and increasing the zirconium salt content during the reaction to obtain a solid electrolyte precursor.

[0020] Step S2 involves heat-treating the solid electrolyte precursor obtained in step S1 to obtain the solid electrolyte material.

[0021] In this process, along the direction from the center to the surface of the solid electrolyte material, the elemental content of Li gradually decreases, while the elemental contents of La and Zr gradually increase.

[0022] [9] According to the preparation method described in [8], the content of lanthanum salt in the coprecipitation reaction remains unchanged or gradually increases, preferably the content of lanthanum salt remains unchanged.

[0023]

[10] According to the preparation method described in [8] or [9], in the process of coprecipitation reaction, salt A is added and the content of salt A is gradually reduced during the reaction, wherein salt A includes at least one of tantalum salt, niobium salt, tungsten salt or molybdenum salt.

[0024]

[11] The preparation method according to any one of [8]-

[10] , wherein the chemical composition of the solid electrolyte material is p(Li 7-x La3Zr 2-x A x O 12 )·q(La2Zr2O7), or p(Li 7-m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein, A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, and along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases.

[0025]

[12] According to the preparation method described in

[11] , during the co-precipitation reaction, the lithium salt content gradually decreases to 0, and the content of the A salt also gradually decreases to 0;

[0026] Preferably, on the surface of the solid electrolyte material, p = 0 and q = 1.

[0027]

[13] The preparation method according to any one of [8]-

[12] , wherein in step S1, a coprecipitation reaction is carried out by adding an alkaline solution to adjust the pH to 8-12;

[0028] The coprecipitation reaction is carried out at a temperature of 45–80°C for 4–10 hours.

[0029] The coprecipitation reaction is carried out under stirring at a speed of 80–400 rpm.

[0030]

[14] According to any one of [8]-

[13] , after step S1 and before step S2, the reaction solution containing the solid electrolyte precursor obtained after the co-precipitation reaction in step S1 is aged, filtered, washed and dried to obtain a solid electrolyte precursor with a spherical or near-spherical shape.

[0031]

[15] According to the preparation method described in

[14] , the aging temperature is 45 to 80°C, the time is 4 to 6 hours, and the rotation speed of the reaction solution is 80 to 400 rpm when the reaction is carried out under stirring.

[0032]

[16] The preparation method according to any one of [8]-

[15] , wherein the heat treatment in step S2 includes a first heat treatment and a second heat treatment;

[0033] Preferably, the temperature of the first heat treatment is 600–950°C, and the time is 2–10 hours;

[0034] Preferably, the temperature of the second heat treatment is 900–1200°C, and the time is 4–12 hours.

[0035]

[17] The preparation method according to any one of [8]-

[16] , wherein the lithium salt is one or more selected from lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate, and lithium acetate; the zirconium salt is one or more selected from zirconium carbonate, zirconium nitrate, zirconium oxynitrate, zirconium chloride, zirconium sulfate, and zirconium acetate; and the lanthanum salt is one or more selected from lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate.

[0036]

[18] The preparation method according to any one of [8]-

[17] , wherein the A salt is a tantalum salt, preferably, the tantalum salt is one or more selected from tantalum acetate, tantalum chloride, and tantalum oxalate.

[0037]

[19] The preparation method according to any one of [8]-

[18] , wherein the reduction and / or increase of the content of lithium salt and / or zirconium salt and lanthanum salt is carried out by controlling the flow rates of lithium salt, zirconium salt and lanthanum salt;

[0038] Preferably, the flow rate of the solution of lithium salt, zirconium salt and lanthanum salt is controlled at 5-150 mL / h, more preferably 20-100 mL / h.

[0039]

[20] A solid electrolyte membrane, characterized in that the solid electrolyte membrane comprises a solid electrolyte material according to any one of [1]-[7] and / or a solid electrolyte material obtained by any one of the preparation methods according to [8]-

[10] .

[0040]

[21] A battery characterized in that it comprises a solid electrolyte membrane according to

[20] .

[0041] The effects of the invention

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] In the product obtained by this invention, at least three elements—lithium, lanthanum, and zirconium—are distributed in a concentration gradient within the particles of the solid electrolyte material. The resulting solid electrolyte material, with a novel structure, can fully utilize the properties of Li… 6.5 La3Zr 1.5 Ta 0.5 O 12 (LLZTO) or Li7La3Zr2O 12 The high ionic conductivity of garnet-type solid electrolytes such as LLZO can also improve the surface stability of the material. Furthermore, the solid electrolyte material with a gradient of elemental concentration in this invention can achieve a La2Zr2O7 surface layer through this concentration gradient. This thin La2Zr2O7 layer enhances the surface stability of the material. La2Zr2O7 also possesses a high lithium-ion transference number, excellent high-temperature thermal stability, and a certain lithium-ion conductivity, which not only facilitates lithium-ion transport but also inhibits transition metal migration, effectively enhancing the structural reversibility of the material and improving its high-temperature performance. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the elemental concentration gradient distribution of the lithium lanthanum zirconium tantalum oxide solid electrolyte material prepared in Example 1;

[0046] Figure 2 This is the XRD pattern of the lithium lanthanum zirconium tantalum oxide solid electrolyte material prepared in Example 1;

[0047] Figure 3 This is an EIS comparison chart of Example 1 and Comparative Example 1. Detailed Implementation

[0048] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0049] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0050] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0051] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0052] The term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or apparatus.

[0053] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," or "implementation" refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0054] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0055] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 20 to 40°C.

[0056] <First Aspect>

[0057] A first aspect of the present invention provides a solid electrolyte material in which the elemental content of Li gradually decreases and the elemental contents of La and Zr gradually increase along the direction from the center to the surface of the solid electrolyte material.

[0058] In this invention, the Li element content in the solid electrolyte material gradually decreases along the direction from the center to the surface. This prevents the solid electrolyte from reacting with carbon dioxide and water in the air to form lithium carbonate or lithium hydroxide, which would otherwise reduce the material's conductivity. Simultaneously, the gradient structure with gradually decreasing Li element content ensures a consistent overall concentration of mobile lithium ions, maintaining the material's ion conduction performance and guaranteeing the conductivity of the solid electrolyte. The gradually increasing La and Zr element contents complement the gradually decreasing Li element content, ensuring the final solid electrolyte material has a stable structure.

[0059] It should be noted that in the solid electrolyte material of the present invention, the elemental content of Li gradually decreases and the elemental content of La and Zr gradually increases along the direction from the center to the surface of the solid electrolyte material. Here, "content" refers to the atomic percentage and / or mass percentage of Li, La and Zr at the same level or at the same position at the same distance from the center.

[0060] In some preferred embodiments, the chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2- x A x O 12 )·q(La2Zr2O7), or p(Li 7-m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, and along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases. Preferably, 0≤x≤1, 0≤m≤1, 0≤n≤0.5.

[0061] Preferably, the chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2-x Ax O 12 When q(La₂Zr₂O₇) is used, the content of A gradually decreases along the direction from the center to the surface of the solid electrolyte material. In a specific embodiment, the elemental content of A decreases in a gradient.

[0062] In this invention, the gradient structure of the solid electrolyte material is achieved by adjusting the content of lithium, lanthanum, and zirconium elements, or lithium, lanthanum, zirconium, and alumina elements, from the inside out of the material. The solid electrolyte material as a whole can be regarded as Li 7-x La3Zr 2-x A x O 12 A mixture of lanthanum zirconate (La₂Zr₂O₇) and Li 7-m La3Zr 2+n O 12 A mixture of (LLZO) and lanthanum zirconate, preferably a molecular-level mixture. Within the particles that form the smallest structural component of the solid electrolyte material, the elemental content of Li or Li, A is decreased, while the elemental content of La and Zr is increased, along the direction from the center to the surface of the solid electrolyte material; that is, the Li content is gradually decreased from the inside out. 7-x La3Zr 2-x A x O 12 Increasing the content of LLZO (p) or lanthanum zirconate (q) can simultaneously improve the stability and ionic conductivity of garnet-type solid electrolytes.

[0063] Furthermore, at the center of the solid electrolyte material, p = 1, q = 0, and the center is Li. 7-x La3Zr 2-x A x O 12 Or LLZO; as the Li content in the solid electrolyte material gradually decreases and the La and Zr contents gradually increase, the Li content or the elemental content of Li and A in the outermost layer is 0. At this time, on the surface of the solid electrolyte material, p=0, q=1, and a thin layer of lanthanum zirconate is formed on the surface of the garnet-type solid electrolyte.

[0064] Lanthanum zirconate (La2Zr2O7), as the outermost layer of garnet-type solid electrolyte, firstly, synergistically forms an elemental concentration gradient distribution structure with the garnet-type solid electrolyte. The content of lanthanum zirconate gradually increases from the inside to the outside, which improves the air stability of the solid electrolyte material while ensuring ionic conductivity. It also forms an in-situ coating on the outermost layer. This in-situ coating structure brought about by the concentration gradient has better bonding force and a more stable material structure compared with conventional coating layers.

[0065] Secondly, lanthanum zirconate can suppress side reactions between solid electrolyte materials and air, effectively improving the air stability of garnet-type solid electrolytes. When lanthanum zirconate is used as the outermost layer, the overall performance of the material is close to that of garnet-type solid electrolytes, and it also has high ionic conductivity, which can improve the surface stability and ionic conductivity of the material. Meanwhile, La₂Zr₂O₇ is a high-temperature superconducting coating material with high ionic conductivity, strong oxidation resistance, and excellent high-temperature thermal stability, without undergoing a phase transition at 1600℃. Furthermore, it has the advantages of low thermal conductivity and good thermal insulation, making it an ideal choice as a protective layer material.

[0066] Finally, the outermost layer of lanthanum zirconate not only effectively improves the surface stability of the material, but also hinders the side reactions between the electrolyte and the surface transition metal during electrochemical reactions, suppresses the corrosion of active materials by HF generated during electrolyte hydrolysis, and slows down the increase rate of interfacial charge transfer resistance and surface polarization during electrochemical cycling, so that the material exhibits better thermal stability and cycling stability, and can reduce the risk of short circuits during battery cycling.

[0067] In conventional garnet-type solid electrolytes, a high lithium content in the outer layers easily leads to reactions with carbon dioxide and water in the air to form lithium carbonate, resulting in a decrease in material conductivity. Therefore, it is desirable for the core to have a higher lithium content, with the outer layers containing less lithium. By gradually decreasing the Li content along the direction from the center to the surface of the solid electrolyte material, while gradually increasing the La and Zr contents, especially with a concentration gradient of decreasing Li content and increasing La and Zr contents, the solid electrolyte material obtained in this invention ensures that the overall concentration of mobile lithium ions is not too low, thus not affecting the material's ion conduction performance.

[0068] Therefore, in some preferred embodiments, the content of Li in the solid electrolyte material obtained by the present invention decreases in a concentration gradient, while the contents of La and Zr increase in a concentration gradient.

[0069] In some preferred embodiments, A is tantalum (Ta). When tantalum is used to dope lithium lanthanum zirconium oxide (LLZO), tantalum doping can more effectively improve the lithium-ion conductivity of LLZO. More specifically, along the direction from the center to the surface of the solid electrolyte material, the content of lithium and tantalum decreases in a concentration gradient, while the content of lanthanum and zirconium increases in a concentration gradient. Therefore, the solid electrolyte material obtained by this invention can effectively enhance the structural reversibility of the material and improve its high-temperature performance. Furthermore, the solid electrolyte material obtained by this invention facilitates lithium-ion transport and suppresses transition metal migration, thus ensuring the overall ion conductivity of the material.

[0070] In some preferred embodiments, the thickness of the La2Zr2O7 layer (i.e., the outermost La2Zr2O7 layer) when p=0 and q=1 is 10–20 nm, preferably 10–15 nm. For example, the thickness of the La2Zr2O7 layer can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, or 20 nm. If the thickness of the La2Zr2O7 layer exceeds 20 nm, the coating layer is relatively thick, which may hinder the diffusion of lithium insertion / extraction, affecting the ionic conductivity of the material and limiting its practical applications. If the thickness of the La2Zr2O7 layer is less than 10 nm, the La2Zr2O7 layer is too thin and may have uneven coating, making it easy for lithium carbonate to form on the material surface, failing to function as a protective layer and affecting the ionic conductivity of the solid electrolyte material.

[0071] In some preferred embodiments, the particle size D50 of the solid electrolyte material is 5–10 μm, preferably 6–8 μm. For example, the particle size D50 of the solid electrolyte material can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, etc.

[0072] Furthermore, in some preferred embodiments, the solid electrolyte material has a spherical or near-spherical shape with an average sphericity of 0.8 to 1, preferably 0.9 to 1. By making the solid electrolyte material spherical or near-spherical, the particle size of the solid electrolyte material can be made smaller and more uniform, thereby improving the density.

[0073] <Second aspect>

[0074] A second aspect of the present invention provides a method for preparing a solid electrolyte material. The method includes:

[0075] Step S1 involves co-precipitating a solution containing lithium salt, zirconium salt, and lanthanum salt, gradually reducing the lithium salt content and increasing the zirconium salt content during the reaction to obtain a solid electrolyte precursor.

[0076] Step S2 involves heat-treating the solid electrolyte precursor obtained in step S1 to obtain the solid electrolyte material.

[0077] In this process, along the direction from the center to the surface of the solid electrolyte material, the elemental content of Li gradually decreases, while the elemental contents of La and Zr gradually increase.

[0078] This invention prepares solid electrolyte materials with varying elemental concentrations via a crystallization co-precipitation method. On one hand, the preparation method yields micron-sized powder materials with uniform chemical composition, small particle size, and uniform distribution. These powders exhibit high density and good ionic conductivity after heat treatment. On the other hand, the Li content gradually decreases from the center to the surface of the solid electrolyte material. This prevents the reaction of the solid electrolyte with carbon dioxide and water in the air to form lithium carbonate or lithium hydroxide, which would otherwise reduce the material's conductivity. Simultaneously, the gradient structure of gradually decreasing Li content ensures a consistent overall concentration of mobile lithium ions, maintaining the material's ionic conductivity and guaranteeing the overall conductivity of the solid electrolyte. The gradually increasing La and Zr content complements the gradually decreasing Li content, ensuring the final solid electrolyte material has a stable structure.

[0079] In a further preferred embodiment, salt A is added during the coprecipitation reaction, and the content of salt A is gradually reduced during the reaction. Salt A includes at least one selected from tantalum salt, niobium salt, tungsten salt, or molybdenum salt. In a specific embodiment, salt A is a tantalum salt, preferably one or more selected from tantalum acetate, tantalum chloride, and tantalum oxalate.

[0080] In one embodiment, the chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2-x A x O 12 )·q(La2Zr2O7), or p(Li 7-m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein, A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases.

[0081] In one embodiment, during the co-precipitation reaction, the lithium salt content gradually decreases to 0, and the content of salt A also gradually decreases to 0, so that the surface of the solid electrolyte has p=0 and q=1. At this time, the surface composition of the solid electrolyte material is lanthanum zirconate.

[0082] In the past, the preparation of solid electrolyte materials, especially garnet-type solid electrolytes, through sintering required a large amount of excess lithium salt. This resulted in residual lithium oxide on the surface of the garnet-type solid electrolyte, which easily formed lithium carbonate or lithium hydroxide upon contact with air, significantly increasing the surface impedance of the garnet-type solid electrolyte and hindering its application. However, when preparing garnet-type solid electrolytes with concentration gradients (more specifically LLZTO and / or LLZO) via co-precipitation, the gradually increasing lanthanum zirconate and the outermost lanthanum zirconate can suppress side reactions between the garnet-type solid electrolyte and air. At the same time, the overall performance of the material is close to that of garnet-type solid electrolytes (more specifically LLZTO and / or LLZO), and the ionic conductivity is also relatively high.

[0083] In some preferred embodiments, the lanthanum salt content remains constant or gradually increases during the coprecipitation reaction, preferably remaining constant. During the coprecipitation reaction, only the lithium salt content needs to be reduced and the zirconium salt content increased, without changing the lanthanum salt content, to form a solid electrolyte material with a concentration gradient distribution structure.

[0084] In some preferred embodiments, in step S1, the coprecipitation reaction is carried out with the addition of an alkaline solution to adjust the pH to 8-12.

[0085] The present invention does not limit the specific type of alkaline solution, such as ammonia and / or sodium carbonate, preferably ammonia, which has moderate alkalinity, a wide range of applications, and does not introduce impurity ions.

[0086] In some preferred embodiments, in step S1, ammonia is added to adjust the pH of the coprecipitation reaction solution to 8-12, the temperature of the coprecipitation reaction is 45-80°C, the time of the coprecipitation reaction is 4-8 hours, and the rotation speed of the coprecipitation reaction is 80-400 rpm when carried out with stirring.

[0087] In this invention, there are no particular limitations on the raw materials for the metal salts. For Li salts, La salts, Zr salts, and optionally A salts as doping compounds, carbonates, nitrates, acetates, halides, etc., can be used. From the perspective of ease of obtaining raw materials and cost, one or more of, for example, lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate, and lithium acetate are preferred. For La salts, one or more of, lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate can be used. For Zr salts, one or more of, zirconium carbonate, zirconium nitrate, zirconium oxynitrate, zirconium chloride, zirconium sulfate, and zirconium acetate can be used.

[0088] In some preferred embodiments, in step S1, the concentrations of each metal salt solution are the same, ranging from 1 to 2.0 mol / L; the concentration of the alkaline solution is 2 to 8 mol / L. It should be noted that the same concentration of the metal salt solutions here refers to the same concentration of the initial solutions added during feeding. When a co-precipitation reaction is carried out, if the feeding rates and flow rates of each metal salt solution are different, the proportion of metal ions in the metal salt solutions participating in the reaction will vary.

[0089] In one specific embodiment, when the solid electrolyte center is Li 7-x La3Zr 2-x Ta x O 12 In the preparation of LLZTO precursor with lanthanum zirconate as the surface, the molar ratio of lithium, tantalum, and zirconium in the inner layer of the LLZTO precursor, which serves as a solid electrolyte precursor, is 6.5:0.5:1.5 at the center. Then, from the inside to the surface, the addition rate (flow rate) of lithium, tantalum, and zirconium salt solutions is adjusted. The addition rate of lithium salt is gradually reduced, while the addition rate of zirconium salt is gradually increased, while the addition rate of lanthanum salt remains constant. This allows the concentration of lithium and tantalum elements to gradually decrease and the concentration of zirconium elements to gradually increase during the growth process of the inner layer of the LLZTO precursor, starting from the center. All three elements, lithium, tantalum, and zirconium, exhibit a concentration gradient distribution in the LLZTO precursor. Finally, the addition of lithium and tantalum elements reaches 0, and the molar ratio of zirconium to lanthanum is 1:1. After reacting for a period of time in this stage, the feeding is stopped, resulting in an outermost coating layer of lanthanum zirconate. By controlling the reaction conditions after the addition of lithium and tantalum elements is zero, the lanthanum zirconate coating layer is made neither too thin nor too thick, thus obtaining a lanthanum zirconate coating that does not negatively affect the lithium-ion conductivity of the garnet-type solid electrolyte.

[0090] In this invention, zirconium lanthanum hydroxide is generated when the amount of lithium and tantalum added is 0. During the subsequent heat treatment process, zirconium lanthanum hydroxide will generate lanthanum zirconate. As the outermost layer, lanthanum zirconate can ensure the stability and ionic conductivity of the solid electrolyte material. Moreover, this co-precipitation method of gradually reducing the lithium salt content makes the material generated in an integrated manner from the center to the surface. Compared with directly coating the lanthanum zirconate layer, the interfacial bonding force is stronger and the overall structure of the solid electrolyte is more stable.

[0091] This invention prepares Li 6.5-x La3Zr 1.5+z+y Ta 0.5-y O 12 The key is to control the ratio of Li, Ta, and Zr elements in the crystal grains. This is achieved by controlling the addition rates of lithium salt, tantalum salt, and zirconium salt solutions; that is, controlling the flow rates to control the ratios when the concentration of the metal salt solutions is constant. The Li in the above solutions... + La3+ Zr 2+ Ta 5+ With OH - The ionic reaction forms the necessary precursor precipitate. The material prepared by this invention ensures both high ionic conductivity and good air stability.

[0092] In one embodiment, the reduction and / or increase of the lithium salt content and / or the zirconium and lanthanum salt content are achieved by controlling the flow rates of the lithium salt, zirconium salt, and lanthanum salt; preferably, the flow rates of the lithium salt, zirconium salt, and lanthanum salt solutions are controlled at 5-150 mL / h, more preferably 8-100 mL / h. In a more preferred embodiment, the flow rates of the lithium salt, zirconium salt, and lanthanum salt solutions are controlled at 10-80 mL / h, more preferably 10-50 mL / h.

[0093] In a preferred embodiment, the flow rates of the lithium salt, zirconium salt, and lanthanum salt solutions are controlled by gradually increasing or decreasing the flow rate. In a further preferred embodiment, the flow rates of the lithium salt and zirconium salt solutions can be controlled by gradually increasing or decreasing the flow rate while maintaining the flow rate of the lanthanum salt solution. For example, while maintaining the flow rate of the lanthanum salt solution, the flow rate of the lithium salt solution can be reduced by 10 mL / h first, then reduced by 30 mL / h, and the flow rate of the zirconium salt solution can be increased by 3 mL / h first, then increased by 5 mL / h, and so on.

[0094] In one embodiment, after step S1 and before step S2, the reaction solution containing the solid electrolyte precursor obtained after the co-precipitation reaction in step S1 is further aged, filtered, washed, and dried. Specifically, the aging temperature is 45–80°C, the time is 4–6 hours, and the rotation speed of the reaction solution during stirring is 80–400 rpm.

[0095] In step S2, the heat treatment includes a first heat treatment and a second heat treatment.

[0096] In one embodiment, the temperature of the first heat treatment is 600–950°C and the time is 2–10 hours; in another embodiment, the temperature of the second heat treatment is 900–1200°C and the time is 4–12 hours.

[0097] In this invention, as the temperature and time of heat treatment increase, solid particles combine with each other, grains grow, and voids (pores) and grain boundaries gradually decrease. Through material transfer, the overall volume shrinks and the density increases, eventually becoming a rigid polycrystalline sintered body. However, excessively high temperatures will promote secondary crystallization, which will deteriorate the material properties. Therefore, from the perspective of obtaining the best performance of the solid electrolyte material, the heat treatment conditions within the range of this invention can be appropriately selected.

[0098] This invention, by separately preparing the required metal salt solutions and simultaneously adding at least three metal salts through controlled crystallization co-precipitation technology, achieves a concentration gradient effect in the elemental distribution of the material, facilitating the control of the uniform distribution of metal ion concentrations within the crystal at a predetermined ratio. By controlling the reaction conditions of the crystallization co-precipitation technology, including the reaction temperature and pH value within appropriate ranges, and adjusting the addition rate (flow rate) of the metal salt ions, a gradient distribution of at least three metal ions (Li, La, and Zr, or Li, La, Zr, and A) can be achieved. This not only allows for controllable crystal morphology but also facilitates large-scale production. Furthermore, the metal ion concentration can be arbitrarily adjusted according to design, simplifying operation. Uniform distribution of metal ions within the crystal can be achieved simply by adjusting the dropping rate of at least two metal ion solutions (Li and Zr, or Li, Zr, and A), without requiring other methods. This also facilitates the formation of an outermost layer containing lanthanum zirconate hydroxide on the surface of a solid electrolyte containing Li, La, Zr hydroxide and / or Li, La, Zr, and A hydroxide, which forms the outermost layer of lanthanum zirconate during subsequent heat treatment solid-phase reactions.

[0099] <Third aspect>

[0100] A third aspect of the present invention provides a solid electrolyte membrane comprising the solid electrolyte material as described above and / or a solid electrolyte material obtained by the preparation method as described above. Further, a third aspect of the present invention provides a battery comprising the solid electrolyte membrane described above.

[0101] Because the solid electrolyte material of the present invention has high ionic conductivity and excellent air stability, the solid electrolyte membrane and battery containing the solid electrolyte material of the present invention have high energy density and good safety performance.

[0102] Example

[0103] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0104] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0105] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0106] Example 1

[0107] In Example 1, a lithium-lanthanum-zirconium-tantalum-oxygen solid electrolyte material with a concentration gradient distribution of lithium, lanthanum, tantalum, and zirconium was prepared. The chemical composition of the solid electrolyte material is p(Li 6.5 La3Zr 1.5 Ta 0.5 O 12 )·q(La₂Zr₂O₇)(p+q=1, 0≤p≤1, 0≤q≤1), the center of the solid electrolyte is Li. 6.5 La3Zr 1.5 Ta 0.5 O 12 The surface is La₂Zr₂O₇, and along the direction from the center to the surface of the solid electrolyte material, the contents of Li and Ta gradually decrease, while the contents of La and Zr gradually increase, i.e., p gradually decreases and q gradually increases. At the center, p=1 and q=0, while at the surface, p=0 and q=1. The particle size D50 of the solid electrolyte material is 8-10 μm, and the morphology is spherical.

[0108] The specific preparation method in this embodiment includes the following steps:

[0109] (1) Raw material preparation and reaction process: Prepare 2 mol / L lithium nitrate solution, 2 mol / L lanthanum nitrate solution, 2 mol / L zirconium oxynitrate solution, 1 mol / L tantalum oxalate solution and 6 mol / L ammonia solution respectively.

[0110] First, lithium nitrate solution, tantalum oxalate solution, zirconium oxynitrate solution, and lanthanum nitrate solution were added to the co-precipitation reactor at flow rates of 78 mL / h, 10 mL / h, 15 mL / h, and 30 mL / h, respectively. Simultaneously, the flow rate of ammonia water was adjusted to control the pH of the ammonia reaction system to 9.5 ± 0.2. The total addition time was 1 h. Then, a concentration gradient structure was formed by controlling the flow rates of each solution. In this embodiment, the gradient structure prepared from the center to the surface was 0.9 (Li) 6.5 La3Zr 1.5 Ta 0.5 O 12 )·0.1(La2Zr2O7), 0.8(Li 6.5 La3Zr 1.5 Ta 0.5 O 12 )·0.2(La2Zr2O7), 0.7(Li 6.5 La3Zr 1.5 Ta 0.5 O 12 )·0.3(La2Zr2O7),...0.1(Li 6.5 La3Zr 1.5 Ta 0.5 O12 0.9(La₂Zr₂O₇), La₂Zr₂O₇. After the core preparation process is completed, adjust the flow rate of the added solution, for example, to prepare 0.9(Li₂Zr₂O₇). 6.5 La3Zr 1.5 Ta 0.5 O 12 When preparing 0.1 (La₂Zr₂O₇), the lithium addition flow rate was reduced to 70.19 mL / h, the tantalum addition flow rate was reduced to 9 mL / h, the zirconium addition flow rate was increased to 16.5 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h, with an injection time of 0.5 h; ... to prepare 0.6 (Li₂Zr₂O₇) 6.5 La3Zr 1.5 Ta 0.5 O 12 When preparing 0.3 (La₂Zr₂O₇), the lithium addition flow rate was reduced to 46.8 mL / h, the tantalum addition flow rate was reduced to 5.99 mL / h, the zirconium addition flow rate was increased to 20 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h, with an injection time of 0.5 h; ... to prepare 0.3 (Li₂Zr₂O₇) 6.5 La3Zr 1.5 Ta 0.5 O 12 When preparing the outermost La₂Zr₂O₇ layer, the lithium addition flow rate was reduced to 23.39 mL / h, the tantalum addition flow rate was reduced to 2.99 mL / h, the zirconium addition flow rate was increased to 25.49 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h. The injection time was 0.5 h. ... When preparing the outermost La₂Zr₂O₇ layer, the lithium addition flow rate was reduced to 0 mL / h, the tantalum addition flow rate was reduced to 0 mL / h, the zirconium addition flow rate was increased to 30 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h. The injection time was 0.5 h. Throughout the reaction, the reactor atmosphere was air, the reaction temperature was set to 50 °C, and the stirring speed was set to 180 rpm.

[0111] (2) After that, the solution temperature was maintained at 50°C, the stirring speed was 180 rpm, the solution was aged for 4 hours, filtered, washed, and dried at 100°C for 2 hours to obtain spherical precursor particles.

[0112] (3) The above precursor particles are placed in an alumina crucible and placed in a muffle furnace. The temperature is increased to 950°C at a rate of 3°C / min, and the mixture is pre-fired in air for 6 hours for the first heat treatment. Then, the temperature is increased to 1175°C and sintered for another 6 hours for the second heat treatment.

[0113] The resulting product was then crushed and sieved to obtain lithium lanthanum zirconium tantalum oxide powder (lithium lanthanum zirconium tantalum oxide solid electrolyte material) with an average particle size of 8-10 μm and a concentration distribution.

[0114] (4) Performance testing:

[0115] ①XRD testing: The obtained powder was subjected to XRD to analyze the crystal form and phase composition of the sample. The test conditions were: scanning range of 10-80°, step size of 0.02°, and scanning speed of 4° / min.

[0116] ②EIS test:

[0117] Impedance value: The impedance value of the lithium lanthanum zirconium tantalum oxide powder with concentration gradient distribution was determined by AC impedance testing method. First, the lithium lanthanum zirconium tantalum oxide powder was placed in a φ17mm mold and pressed into a pellet under a pressure of 200MPa. Then, the pellet was placed in the Chenhua electrochemical workstation to test the AC impedance. The frequency was set to 0.1~10MPa and the amplitude was 5mV.

[0118] Lithium-ion conductivity: The impedance value and lithium-ion conductivity of the obtained lithium lanthanum zirconium tantalum oxide powder were calculated using a fitting method. The fitting software used was Zview 2.

[0119] Ionic conductivity σ = h / RA

[0120] Where: h - sample thickness (cm);

[0121] R - Sample impedance (Ω);

[0122] A - Cross-sectional area of ​​the sample circle (cm²) 2 )

[0123] After cleaning the ceramic sheet, its mass and volume can be measured to calculate its density. The ratio of bulk density to theoretical density is the density.

[0124] Bulk density

[0125] Ceramic sheet density

[0126] (Where m is the mass of the ceramic sheet; v is the volume of the ceramic sheet; ρ0 is the theoretical density of the ceramic sheet)

[0127] (5) The prepared material with concentration gradient was placed in the air for 48 hours and then subjected to EIS testing to compare it with the material that was not exposed to air.

[0128] Figure 1 This diagram illustrates the elemental concentration gradient distribution of the prepared lithium-lanthanum-zirconium-tantalum-oxygen solid electrolyte material, with the central portion (core) being Li. 6.5 La3Zr 1.5 Ta 0.5 O 12Subsequently, the concentration gradient changes, with the lithium and tantalum content gradually decreasing, and the transition layer is p(Li) 6.5 La3Zr 1.5 Ta 0.5 O 12 )·q(La2Zr2O7), with the outermost layer being La2Zr2O7.

[0129] Figure 2 The image shows the XRD pattern of the prepared lithium lanthanum zirconium tantalum oxide solid electrolyte material. The image indicates that the material possesses Li... 6.5 La3Zr 1.5 Ta 0.5 O 12 The two phases, La2Zr2O7 and La2Zr2O7, are consistent with the design structure.

[0130] Figure 3 The comparison chart of EIS results shows that the ionic conductivity of the concentration gradient material decreased only slightly after being placed in the air for 2 days, indicating that the outermost La2Zr2O7 layer can play an isolating role and reduce the reaction of lithium lanthanum zirconium oxide solid electrolyte with water and carbon dioxide in the air.

[0131] Example 2

[0132] In Example 2, a lithium-lanthanum-zirconium-niobium-oxygen solid electrolyte material with a concentration gradient distribution of lithium, lanthanum, niobium, and zirconium was prepared. The chemical composition of the solid electrolyte material is p(Li 6.5 La3Zr 1.5 Nb 0.5 O 12 )·q(La₂Zr₂O₇)(p+q=1, 0≤p≤1, 0≤q≤1), the center of the solid electrolyte is Li. 6.5 La3Zr 1.5 Nb 0.5 O 12 The surface is La₂Zr₂O₇, and along the direction from the center to the surface of the solid electrolyte material, the contents of Li and Nb gradually decrease, while the contents of La and Zr gradually increase, i.e., p gradually decreases and q gradually increases. At the center, p=1 and q=0, while at the surface, p=0 and q=1. The particle size D50 of the solid electrolyte material is 8-10 μm, and the morphology is spherical.

[0133] The specific preparation method in this embodiment includes the following steps:

[0134] (1) Raw material preparation and reaction process: Prepare 2 mol / L lithium nitrate solution, 2 mol / L lanthanum nitrate solution, 2 mol / L zirconium oxynitrate solution, 1 mol / L niobium oxalate solution and 6 mol / L ammonia solution respectively.

[0135] First, lithium nitrate solution, niobium oxalate solution, zirconium oxynitrate solution, and lanthanum nitrate solution were added to the co-precipitation reactor at flow rates of 78 mL / h, 10 mL / h, 15 mL / h, and 30 mL / h, respectively, for a reaction time of 1 h. Simultaneously, the flow rate of ammonia water was adjusted to control the pH of the ammonia reaction system to 9.5 ± 0.2. Then, a concentration gradient structure was formed by controlling the flow rate of each solution. In this embodiment, the gradient structure prepared from the center to the surface was 0.9 (Li... 6.5 La3Zr 1.5 Nb 0.5 O 12 )·0.1(La2Zr2O7), 0.8(Li 6.5 La3Zr 1.5 Nb 0.5 O 12 )·0.2(La2Zr2O7), 0.7(Li 6.5 La3Zr 1.5 Nb 0.5 O 12 )·0.3(La2Zr2O7),...0.1(Li 6.5 La3Zr 1.5 Nb 0.5 O 12 0.9(La₂Zr₂O₇), La₂Zr₂O₇. After the core preparation process is completed, adjust the flow rate of the added solution, for example, to prepare 0.9(Li₂Zr₂O₇). 6.5 La3Zr 1.5 Nb 0.5 O 12 When preparing 0.1 (La₂Zr₂O₇), the lithium addition flow rate was reduced to 70.19 mL / h, the tantalum addition flow rate was reduced to 9 mL / h, the zirconium addition flow rate was increased to 16.5 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h, with an injection time of 0.5 h; ... to prepare 0.6 (Li₂Zr₂O₇) 6.5 La3Zr 1.5 Nb 0.5 O 12 When preparing 0.3 (La₂Zr₂O₇), the lithium addition flow rate was reduced to 46.8 mL / h, the tantalum addition flow rate was reduced to 5.99 mL / h, the zirconium addition flow rate was increased to 20 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h, with an injection time of 0.5 h; ... to prepare 0.3 (Li₂Zr₂O₇) 6.5 La3Zr 1.5 Nb 0.5 O 12When preparing the outermost La₂Zr₂O₇ layer, the lithium addition flow rate was reduced to 23.39 mL / h, the tantalum addition flow rate was reduced to 2.99 mL / h, the zirconium addition flow rate was increased to 25.49 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h. The injection time was 0.5 h. ... When preparing the outermost La₂Zr₂O₇ layer, the lithium addition flow rate was reduced to 0 mL / h, the tantalum addition flow rate was reduced to 0 mL / h, the zirconium addition flow rate was increased to 30 mL / h, and the lanthanum addition flow rate was kept constant at 30 mL / h. The injection time was 0.5 h. Throughout the reaction, the reactor atmosphere was air, the reaction temperature was set to 50 °C, and the stirring speed was set to 180 rpm.

[0136] (2) After that, the solution temperature was maintained at 50°C, the stirring speed was 180 rpm, the solution was aged for 4 hours, filtered, washed, and dried at 100°C for 2 hours to obtain spherical precursor particles.

[0137] (3) The above precursor particles are placed in an alumina crucible and placed in a muffle furnace. The temperature is increased to 950°C at a rate of 3°C / min, and the mixture is pre-fired in air for 6 hours for the first heat treatment. Then, the temperature is increased to 1175°C and sintered for another 6 hours for the second heat treatment.

[0138] The resulting product was then crushed and sieved to obtain lithium lanthanum zirconium niobium oxygen powder (lithium lanthanum zirconium niobium oxygen solid electrolyte material) with a particle size of 8-10 μm and a concentration distribution.

[0139] (4) EIS test:

[0140] Impedance value: The impedance value of the lithium lanthanum zirconium niobium oxygen powder with concentration gradient distribution was determined by AC impedance testing method. First, the lithium lanthanum zirconium niobium oxygen powder was placed in a φ17mm mold and pressed into a pellet under a pressure of 200MPa. Then, the pellet was placed in the Chenhua electrochemical workstation to test the AC impedance. The frequency was set to 0.1~10MPa and the amplitude was 5mV.

[0141] Lithium-ion conductivity: The impedance value and lithium-ion conductivity of the obtained lithium lanthanum zirconium niobium oxygen powder were calculated using a fitting method. The fitting software used was Zview 2.

[0142] Comparative Example 1

[0143] This comparative example prepared a lithium lanthanum zirconium oxide solid electrolyte material, comprising a lithium lanthanum zirconium tantalum oxide core and a lanthanum zirconate coating layer on the surface of the lithium lanthanum zirconium tantalum oxide core. The molecular formula of the lithium lanthanum zirconium oxide solid electrolyte material is Li. 6.5 La3Zr 1.5 Ta 0.5 O 12(LLZTO), with a lanthanum zirconate coating of La2Zr2O7. The solid electrolyte material has a particle size D50 of 8-10 μm and a morphology of near-spherical.

[0144] The specific preparation method in this embodiment includes the following steps:

[0145] (1) Raw material preparation and reaction process: Prepare 2 mol / L lithium nitrate solution, 2 mol / L lanthanum nitrate solution, 2 mol / L zirconium oxynitrate solution, 1 mol / L tantalum oxalate solution and 6 mol / L ammonia solution respectively.

[0146] Lithium nitrate solution, tantalum oxalate solution, zirconium oxynitrate solution, and lanthanum nitrate solution were added to the coprecipitation reactor at flow rates of 78 mL / h, 10 mL / h, 15 mL / h, and 30 mL / h, respectively, for a total reaction time of 5.5 h. The pH of the ammonia reaction system was maintained at 9.5 ± 0.2 by adjusting the flow rates of each solution. Then, the outermost La₂Zr₂O₇ layer was prepared by adjusting the flow rates of lithium and tantalum to 0 mL / h, increasing the flow rate of zirconium to 30 mL / h, and keeping the flow rate of lanthanum constant at 30 mL / h for 0.5 h. The reactor atmosphere was air throughout the reaction, the reaction temperature was set to 50 °C, and the stirring speed was set to 180 rpm.

[0147] (2) After that, the solution temperature was maintained at 50°C, the stirring speed was 180 rpm, the solution was aged for 4 hours, filtered, washed, and dried at 100°C for 2 hours to obtain spherical precursor particles.

[0148] (3) The above precursor particles are placed in an alumina crucible and placed in a muffle furnace. The temperature is increased to 950°C at a rate of 3°C / min, and the mixture is pre-fired in air for 6 hours for the first heat treatment. Then, the temperature is increased to 1175°C and sintered for another 6 hours for the second heat treatment.

[0149] The resulting product was then crushed and sieved to obtain lithium lanthanum zirconium tantalum oxide powder with a particle size of 8-10 μm and a lanthanum zirconate coating on the surface of the lithium lanthanum zirconium tantalum oxide core.

[0150] (4) EIS test:

[0151] Impedance value: The impedance value of the obtained lithium lanthanum zirconium tantalum oxide powder was determined by AC impedance testing. The lithium lanthanum zirconium tantalum oxide powder was first placed in a φ17mm mold and pressed into a pellet under a pressure of 200MPa. Then the pellet was placed in the Chenhua electrochemical workstation to test the AC impedance. The frequency was set to 0.1~10MPa and the amplitude was 5mV.

[0152] Lithium-ion conductivity: The impedance value and lithium-ion conductivity of the obtained lithium lanthanum zirconium tantalum oxide powder were calculated using a fitting method. The fitting software used was Zview 2.

[0153] (5) The prepared material with concentration gradient was placed in the air for 48 hours and then subjected to EIS testing to compare it with the material that was not exposed to air.

[0154] Comparative Example 2

[0155] This comparative example yielded a lithium lanthanum zirconium oxy-based solid electrolyte material. The molecular formula of the lithium lanthanum zirconium oxy-based solid electrolyte material is Li. 6.5 La3Zr 1.5 Ta 0.5 O 12 The particle size is 8-10 μm and the morphology is spherical.

[0156] The specific preparation method in this embodiment includes the following steps:

[0157] (1) Raw material preparation and reaction process: Prepare 2 mol / L lithium nitrate solution, 2 mol / L lanthanum nitrate solution, 2 mol / L zirconium oxynitrate solution, 1 mol / L tantalum oxalate solution and 6 mol / L ammonia solution respectively.

[0158] Lithium nitrate solution, tantalum oxalate solution, zirconium oxynitrate solution, and lanthanum nitrate solution were added to the co-precipitation reactor at flow rates of 78 mL / h, 10 mL / h, 15 mL / h, and 30 mL / h, respectively. The total reaction time was 6 h. The pH of the ammonia reaction system was controlled to be 9.5 ± 0.2 by adjusting the flow rate of ammonia water. The reactor atmosphere was air throughout the reaction process, the reaction temperature was set to 50℃, and the stirring speed was set to 180 rpm.

[0159] (2) After that, the solution temperature was maintained at 50°C, the stirring speed was 180 rpm, the solution was aged for 4 hours, filtered, washed, and dried at 100°C for 2 hours to obtain spherical precursor particles.

[0160] (3) The above precursor particles are placed in an alumina crucible and placed in a muffle furnace. The temperature is increased to 950°C at a rate of 3°C / min, and the mixture is pre-fired in air for 6 hours for the first heat treatment. Then, the temperature is increased to 1175°C and sintered for another 6 hours for the second heat treatment.

[0161] The resulting product was then crushed and sieved to obtain lithium lanthanum zirconium tantalum oxide powder with a particle size of 8-10 μm.

[0162] (4) EIS test:

[0163] Impedance value: The impedance value of the obtained lithium lanthanum zirconium tantalum oxide powder was determined by AC impedance testing. The lithium lanthanum zirconium tantalum oxide powder was first placed in a φ17mm mold and pressed into a pellet under a pressure of 200MPa. Then the pellet was placed in the Chenhua electrochemical workstation to test the AC impedance. The frequency was set to 0.1~10MPa and the amplitude was 5mV.

[0164] Lithium-ion conductivity: The impedance value and lithium-ion conductivity of the obtained lithium lanthanum zirconium tantalum oxide powder were calculated using a fitting method. The fitting software used was Zview 2.

[0165] (5) The prepared material was placed in the air for 48 hours and then subjected to EIS testing to compare it with the material that was not exposed to air.

[0166] Table 1 Density and Ionic Conductivity

[0167]

[0168] As can be seen from the results in Table 1, the ionic conductivity of the prepared lithium lanthanum zirconium tantalum oxide solid electrolyte with a concentration gradient structure can also reach 8.7 × 10⁻⁶. -4 The ionic conductivity of the sample was significantly higher than that of Comparative Example 2 after 48 hours of exposure to air (S / cm), indicating that this structure can improve the surface stability of the material. Furthermore, the ionic conductivity was also higher than that of Comparative Example 1 after exposure. This is likely because the material structure formed by this concentration gradient transition is more stable. The core-shell structure formed in the comparative example has a large difference between its internal and external components, making it prone to core-shell separation. Consequently, the surface stability of the material is not as good as that of the lithium lanthanum zirconium tantalum oxygen solid electrolyte with a concentration gradient structure in Example 1. Therefore, the ionic conductivity decreases accordingly when exposed to air for a long time.

[0169] Industrial availability

[0170] The lithium lanthanum zirconium oxide solid electrolyte prepared by this invention can fully utilize the high ionic conductivity of lithium lanthanum zirconium oxide while improving the surface stability of the material through the outermost La2Zr2O7 layer. La2Zr2O7 also possesses a high lithium-ion transference number, excellent high-temperature thermal stability, and a certain lithium-ion conductivity, which not only facilitates lithium-ion transport but also inhibits transition metal migration, effectively enhancing the structural reversibility of the material and improving its high-temperature performance. Furthermore, the preparation method of this invention is simple, has a high yield, and is very suitable for large-scale industrial production.

[0171] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0172] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from its principles and spirit.

[0173] Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A solid electrolyte material, characterized in that, Along the direction from the center to the surface of the solid electrolyte material, the elemental content of Li gradually decreases, while the elemental contents of La and Zr gradually increase. The chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2-x A x O 12 )·q(La2Zr2O7), or p(Li 7- m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein, A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, and along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases.

2. The solid electrolyte material according to claim 1, wherein the chemical composition of the solid electrolyte material is p(Li) 7- x La3Zr 2-x A x O 12 When )·q(La2Zr2O7), the elemental content of A gradually decreases along the direction from the center to the surface of the solid electrolyte material.

3. The solid electrolyte material according to claim 1 or 2, wherein the particle size D50 of the solid electrolyte material is 5~10 μm.

4. The solid electrolyte material according to claim 1 or 2, wherein the elemental content of Li decreases in a gradient, and the elemental contents of La and Zr increase in a gradient.

5. The solid electrolyte material according to claim 1 or 2, wherein the elemental content of A decreases in a gradient.

6. The solid electrolyte material according to claim 1 or 2, wherein at the center of the solid electrolyte material, p=1 and q=0; On the surface of the solid electrolyte material, p=0, q=1.

7. The solid electrolyte material according to claim 1 or 2, wherein the solid electrolyte material has a spherical or near-spherical shape and an average sphericity of 0.8 to 1.

8. A method for preparing a solid electrolyte material, characterized in that, The preparation method includes: Step S1 involves co-precipitating a solution containing lithium salt, zirconium salt, and lanthanum salt, gradually reducing the lithium salt content and increasing the zirconium salt content during the reaction to obtain a solid electrolyte precursor. Step S2 involves heat-treating the solid electrolyte precursor obtained in step S1 to obtain the solid electrolyte material. In this process, along the direction from the center to the surface of the solid electrolyte material, the content of Li gradually decreases, while the content of La and Zr gradually increases. The chemical composition of the solid electrolyte material is p(Li) 7-x La3Zr 2-x A x O 12 )·q(La2Zr2O7), or p(Li 7- m La3Zr 2+n O 12 )·q(La2Zr2O7); wherein, A includes at least one of Ta, Nb, W or Mo, 0≤x<2, 0≤m<7, 0≤n≤1, p+q=1, 0≤p≤1, 0≤q≤1, and along the direction from the center to the surface of the solid electrolyte material, p gradually decreases and q gradually increases.

9. The preparation method according to claim 8, wherein the content of lanthanum salt in the coprecipitation reaction remains unchanged or gradually increases.

10. The preparation method according to claim 8 or 9, wherein during the co-precipitation reaction, salt A is added and the content of salt A is gradually reduced during the reaction, wherein salt A includes at least one of tantalum salt, niobium salt, tungsten salt or molybdenum salt.

11. The preparation method according to claim 10, wherein during the co-precipitation reaction, the lithium salt content gradually decreases to 0, and the content of the A salt also gradually decreases to 0.

12. The preparation method according to claim 8 or 9, wherein on the surface of the solid electrolyte material, p=0 and q=1.

13. The preparation method according to claim 8 or 9, wherein in step S1, the coprecipitation reaction is carried out while adding an alkaline solution to adjust the pH to 8-12; The coprecipitation reaction is carried out at a temperature of 45-80°C for 4-10 hours. The coprecipitation reaction is carried out under stirring at a speed of 80-400 rpm.

14. The preparation method according to claim 8 or 9, wherein after step S1 and before step S2, the reaction solution containing the solid electrolyte precursor obtained after the co-precipitation reaction in step S1 is further aged, filtered, washed, and dried to obtain a solid electrolyte precursor having a spherical or near-spherical shape.

15. The preparation method according to claim 14, wherein the aging temperature is 45~80℃, the time is 4~6 hours, and the rotation speed of the reaction solution during stirring is 80~400 rpm.

16. The preparation method according to claim 8 or 9, wherein the heat treatment in step S2 includes a first heat treatment and a second heat treatment.

17. The preparation method according to claim 16, wherein, The temperature of the first heat treatment is 600~950℃, and the time is 2~10 hours; The second heat treatment is performed at a temperature of 900~1200℃ for 4~12 hours.

18. The preparation method according to claim 8 or 9, wherein the lithium salt is one or more selected from lithium carbonate, lithium nitrate, lithium chloride, lithium sulfate, and lithium acetate; the zirconium salt is one or more selected from zirconium carbonate, zirconium nitrate, zirconium oxynitrate, zirconium chloride, zirconium sulfate, and zirconium acetate; and the lanthanum salt is one or more selected from lanthanum nitrate, lanthanum chloride, lanthanum sulfate, and lanthanum acetate.

19. The preparation method according to claim 10, wherein the A salt is a tantalum salt.

20. The preparation method according to claim 19, wherein the tantalum salt is one or more selected from tantalum acetate, tantalum chloride, and tantalum oxalate.

21. The preparation method according to claim 8 or 9, wherein the reduction and / or increase of the lithium salt content and / or the zirconium salt and lanthanum salt content are carried out by controlling the flow rates of the lithium salt, zirconium salt and lanthanum salt.

22. The preparation method according to claim 21, wherein the flow rate of the solution of lithium salt, zirconium salt and lanthanum salt is controlled to be 5-150 mL / h.

23. A solid electrolyte membrane, characterized in that, The solid electrolyte membrane comprises the solid electrolyte material according to any one of claims 1-7 and / or the solid electrolyte material obtained by the preparation method according to any one of claims 8-22.

24. A battery, characterized in that, It includes the solid electrolyte membrane according to claim 23.

Images