Iron-based lithium lanthanum zirconate solid electrolyte, its preparation method and lithium battery

Abstract

This invention relates to an iron-based lithium lanthanum zirconate solid electrolyte, its preparation method, and a lithium battery. The iron-based lithium lanthanum zirconate solid electrolyte of this invention has a cubic lithium-rich garnet structure with space group , and its chemical formula is Li. 7‑3x La 3‑y Zr 2‑z Fe x O 12 (where 0)

Description

Technical Field

[0001] This invention relates to the technical field of solid electrolytes for all-solid-state and semi-solid-state high-performance lithium batteries (e.g., lithium-ion batteries, lithium-air batteries, and lithium-sulfur batteries, etc., electrochemical energy storage systems), and in particular to a method for preparing high-performance iron-based lithium lanthanum zirconate (LLZFO) precursors using a modified sol-gel method and for preparing high-performance (e.g., high density, high lithium-ion transport number, ultra-high current, and ultra-long lifetime) solid electrolyte powders and / or bulk materials using a compression molding and sintering process. Background Technology

[0002] To achieve the goal of lithium-ion battery energy density exceeding 500Wh / kg, in line with the technology roadmap for lithium-ion batteries, it is urgent to explore or discover new battery systems and key materials (such as high-performance positive and negative electrode materials and solid-state electrolytes) to break through the "physical ceiling" of existing technical indicators. All- / semi-solid-state lithium-ion batteries (using metallic lithium as the negative electrode and solid-state electrolytes instead of traditional liquid electrolytes, broadening the choice of positive electrode materials and allowing the use of high-voltage positive electrodes), all- / semi-solid-state lithium-sulfur batteries (solving the solubility problem of polysulfides), and all- / semi-solid-state lithium-air batteries (eliminating the problem of electrolyte volatilization) may become excellent strategies to break through existing technological bottlenecks. On the other hand, a significant increase in battery energy will inevitably significantly reduce the safety of the device, especially with the reintroduction of metallic lithium as the negative electrode (dendritic short-circuit problem during cycling), making its safety hazards more severe and intractable. The use of solid-state electrolytes is expected to fundamentally solve or greatly alleviate the safety problems of high-energy-density batteries.

[0003] Considering the feasibility of its application in high-performance all / semi-solid-state lithium batteries (including lithium-ion batteries, lithium-air batteries, and lithium-sulfur batteries) and the safety of its devices, cubic lithium-rich garnet-type lithium lanthanum zirconate (Li7La3Zr2O) is introduced. 12 Solid-state electrolytes (LLZO) are an ideal strategy. Compared to other electrolyte systems, this electrolyte offers advantages such as excellent thermal stability, good chemical / electrochemical compatibility (antioxidant, less prone to reaction with lithium), and high decomposition voltage (up to 6V). Similar to iridium-stabilized zirconium oxide oxygen ion solid-state electrolytes, cubic LLZO is thermodynamically unstable at room temperature and requires bulk doping to stabilize; otherwise, it easily transforms into the thermodynamically stable tetragonal phase with lower lithium-ion conductivity. Furthermore, research shows that the space group of the cubic phase product changes depending on the type of dopant ion, and more importantly, the apparent lithium-ion conductivity corresponding to different space groups also varies. Generally, higher symmetry corresponds to higher apparent lithium-ion conductivity. For example, bulk doping with Nb... 5+ Ta 5+and Mg 2+ After plasma treatment, the resulting cubic LLZO belongs to Space group; Al-doped 3+ Ga 3+ and Fe 3+ After plasma treatment, the resulting LLZO belongs to a class with higher symmetry and higher apparent lithium-ion conductivity. Space group. However, to date, more in-depth and extensive research on cubic lithium-rich garnet-type LLZO has mainly focused on... Space groups are the main component, and the mainstream solid electrolyte is mainly Li. 6.5 La3Zr 1.5 Ta 0.5 O 12 Primarily. And targeting Fe... 3+ Research on doped LLZO (hereinafter referred to as "iron-based LLZO solid electrolyte", abbreviated as LLZFO) is relatively scarce, especially in terms of its electrochemical performance.

[0004] In practical applications, the main problem with LLZO electrolytes is the low apparent lithium-ion conductivity of bulk materials (generally around 10 at room temperature). -4 The S / cm ratio is on the order of magnitude, and can be increased by an order of magnitude to 10 when heated to 60℃. -3 The fracture failure surface (on the order of S / cm) exhibits several issues, including: distinct grain boundaries (the grain boundaries are not dense enough, and the fracture failure mode mainly presents as grain boundary fracture characteristics); insufficient density (only electrolyte bulk materials obtained by hot pressing, plasma sintering, and flash sintering have relatively high density); large contact angles of molten lithium metal and LLZO, making them difficult to spread evenly; and high interfacial resistance between the solid electrolyte and electrode. These problems obviously affect its electrochemical performance and have more or less restricted its large-scale application in all-solid-state and semi-solid-state batteries.

[0005] To address the aforementioned issues, researchers worldwide have conducted extensive research and exploratory work on composition design, density enhancement, and electrolyte / electrode interface modification. To improve the apparent lithium-ion conductivity of solid electrolyte bulk materials, bulk doping with equivalent or heterovalent ions is performed at Li, La, and / or Zr sites. After doping, the apparent lithium-ion conductivity at room temperature can reach 10⁻⁶. -4 The S / cm order of magnitude can be increased to 10 at 60℃. -3The density is on the order of S / cm. To improve the density of the electrolyte bulk, sintering aids such as Li₂O, Li₃BO₃, La₂Zr₂O₇, SiO₂, and CaO are introduced during the sintering process, and even hot-pressing sintering is employed. After hot-pressing sintering, the relative density of the electrolyte bulk can be increased to 99%. To improve the grain boundary characteristics of the electrolyte bulk, innovative sintering methods are introduced, such as ultra-fast high-temperature sintering, to improve the apparent conductivity of lithium ions. To improve the wettability of molten lithium metal with the electrolyte and effectively reduce the interfacial resistance, lithium metal is alloyed with tin, sodium, or graphite, or a flexible graphite transition layer is introduced between the lithium metal anode and LLZO, or carbon is deposited on the electrolyte surface. After LiNa alloying, the interfacial resistance of the lithium metal anode / electrolyte decreases significantly, reaching 18.98 Ω / cm. 2 @60℃; Using a candle combustion method, carbon is deposited at the interface between lithium metal and the electrolyte, reducing the interface resistance to 52Ω / cm. 2 @60℃. In addition, in order to effectively reduce the interfacial resistance between the electrolyte and the positive electrode, a flexible transition or buffer layer (such as polyethylene oxide PEO-based or gel electrolyte) can be introduced between the electrolyte and the positive electrode, or a small amount of electrolyte or ionic liquid can be directly added between the electrolyte and the positive electrode to fill the gap and achieve a solid-solid "soft landing". By reducing the interfacial resistance, the utilization rate of the electrode material can be improved.

[0006] However, regardless of the modification strategy employed, the assembled all-solid-state or semi-solid-state lithium-ion batteries and lithium-symmetric batteries can only operate stably at relatively low current densities, and their electrochemical performance is far inferior to existing battery systems primarily using organic electrolytes. A semi-solid-state battery constructed by introducing a buffer layer P(VDF-HFP)-based gel at the interface between the lithium iron phosphate cathode and the LLZO electrolyte, followed by the addition of 10 μL of electrolyte, can stably cycle at a current density of 0.5C (85 mA / g). A lithium-symmetric battery assembled from an LLZO electrolyte obtained using ultrafast high-temperature sintering technology exhibits a maximum limiting current density of approximately 3.2 mA / cm² at room temperature. 2 (When the lithium layer thickness exceeds 100 μm), it can achieve 0.2 mA / cm at room temperature. 2 It can cycle stably for more than 400 hours at a current density. Therefore, if we want to further improve the electrochemical performance (especially the high current performance) of all-solid-state and semi-solid-state lithium batteries, developing high-performance solid electrolytes is likely to be a good breakthrough.

[0007] As mentioned earlier, the most researched and applied is LLZO electrolytes with space group characteristics are targeted at those with higher symmetry and... Studies on cubic LLZO with space group 1 are relatively scarce (limited to research on structure, lithium-ion conductivity, and activation energy). Clearly, it receives insufficient attention. The apparent lithium-ion conductivity and electrochemical performance of solid electrolytes are closely related to the densification degree of their grain boundaries. Generally, grain boundary densification helps reduce lithium-ion transport losses at grain boundaries (lithium-ion conduction at grain boundaries is only about 1 / 3 to 1 / 2 of that within the grain), thus playing a positive role in improving the electrochemical performance of the electrolyte. Existing studies have shown that iron-doped LLZO electrolytes prepared by solid-state methods have high apparent lithium-ion conductivity, reaching 1.38 × 10⁻⁶. -3 The S / cm@RT ratio is high, but the grain size is relatively large (few grain boundaries per unit area), which is not conducive to improving the cycle life of solid-state and semi-solid-state batteries (non-patent literature 1). An iron-doped electrolyte prepared by the sol-gel method using water as a solvent has relatively dense grain boundaries, and its apparent lithium-ion conductivity can reach 1.82 × 10⁻⁶. -3 S / cm@RT (Non-Patent Literature 2). Therefore, designing and optimizing the composition, grain boundaries, and preparation process of iron-based LLZO solid electrolytes is expected to yield high-performance electrolyte materials, thereby laying a solid foundation and opening up new avenues for the development of high-performance solid-state batteries.

[0008] References

[0009] Non-patent literature 1: Chem. Mater. 2016, 28, 5943-5951

[0010] Non-patent literature 2: Journal of the Electrochemical Society, 166(3)A5403-A5409(2019) Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Currently, there are two main methods for preparing iron-doped LLZO solid electrolytes: solid-state reaction and sol-gel methods using water as a solvent. The solid-state reaction method (which involves ball milling and mixing raw materials, followed by heat treatment, calcination, and sintering after molding) has the advantages of simple synthesis, fewer controllable factors, and easy acquisition of target products with stoichiometric ratios. However, its disadvantages include a large particle size (>100 μm) of the resulting product, making it highly susceptible to the influence of the raw material particle size itself. Uniform bulk doping is difficult to achieve, and second phases or impurities are easily generated at grain boundaries, leading to insufficient grain density. Clearly, these problems will adversely affect the physicochemical properties of the electrolyte material, especially when applied to high-performance solid-state battery devices, significantly reducing their cycle stability and lifespan. In contrast, the sol-gel method allows for bulk doping at the atomic scale, resulting in products with higher purity, better uniformity, and denser grain boundaries. It is also more suitable for designing and modulating composition and grain boundary properties, making this method more conducive to the preparation of high-performance solid electrolytes.

[0013] However, the main problems with the preparation of LLZO solid electrolyte using the sol-gel method are as follows: (1) The raw materials available are mostly deliquescent or their water of crystallization is difficult to identify, making it difficult to adjust the product composition and prepare pure phase LLZO, which presents certain technical barriers. (2) The solvent used is limited, mainly using aqueous solutions (deionized water or nitric acid) as solvents. Although iron-doped LLZO with high apparent lithium-ion conductivity can be prepared using deionized water as a solvent (compared to using nitric acid as a solvent), the purity and quality of water are easily affected by the environment (e.g., the dissolution of gases such as carbon dioxide in the air will affect the quality of water, leading to batch instability of product performance). More importantly, the purity or quality of water is difficult to detect, presenting certain technical uncertainties. (3) The preparation process is more complex and refined than the solid-phase method. The traditional solvent removal process (e.g., vacuum or forced-air drying) is time-consuming, and the product composition is easily affected by the drying process. For example, when using deionized water as a solvent, the reaction needs to be carried out at 40°C, aged at 120°C, and dried overnight at 250°C. Clearly, this increases the complexity of the process.

[0014] Solution for solving the problem

[0015] In view of the above situation, the present invention adopts the concept of "self-assembled framework", uses organic acids as self-assembled framework units, and self-assembles and synthesizes by means of chemical bonds formed by functional groups such as hydroxyl groups and carboxyl groups contained in the organic acid structure and metal ions. Specifically, a method for preparing a high-performance lithium-rich garnet-type lanthanum zirconate lithium solid electrolyte is proposed, which uses an organic reagent as a solvent at room temperature and adopts an improved sol-gel method to prepare a precursor of the high-performance iron-based lanthanum zirconate lithium solid electrolyte, and is prepared by processes such as pre-sintering, crushing, calcining, pressing into shape, and high-temperature sintering. First, without using a sintering aid, a high-performance lithium-rich garnet-type lanthanum zirconate lithium solid electrolyte can be prepared by a simple die pressing sintering process. Adopting a hot pressing sintering method, a plasma sintering method, a flash sintering process or introducing a granulation process in the forming process can further improve its performance index. Secondly, technologies such as vacuum distillation, rotary evaporation, supercritical extraction or freeze drying are creatively introduced into the desolvation process, which can not only ensure the uniformity of the product components, but also greatly improve the production efficiency. This process is also conducive to the later recycling of solvents, reducing environmental pollution and saving costs.

[0016] 1. Specifically, the present invention provides an iron-based lanthanum zirconate lithium solid electrolyte, which has a cubic-phase lithium-rich garnet-type structure and has space group, and its chemical formula is expressed as: Li 7-3x La 3-y Zr 2-z Fe x O 12 , where 0 < x ≤ 0.7, -0.4 ≤ y ≤ 0.4, -0.3 ≤ z ≤ 0.3, and 3y + 4z = 0,

[0017] its relative density is not less than 92%, and the cross section of fracture failure basically shows the characteristics of grain fracture rather than grain boundary fracture.

[0018] 2. The iron-based lanthanum zirconate lithium solid electrolyte according to item 1 above has no segregation of iron elements at the grain boundaries; and / or, there is no lithium carbonate on its surface or the cross section of fracture failure; and / or, its bulk phase does not contain aluminum elements; and / or, at room temperature, the lithium ion conductivity is between 3.7×10 -4 ~3.7×10 -2 S / cm; and / or, at room temperature, the electronic conductivity is between 1.0×10 -7 ~7.3×10 -10 S / cm; and / or, at room temperature, the limiting current density of the lithium-tin symmetric battery (LiSn|LLZFO|LiSn) is not less than 200 mA / cm 2 ; and / or, at room temperature, the lithium-tin symmetric battery (LiSn|LLZFO|LiSn) at 0.5 mA / cm 2 ~110 mA / cm 2It can stably cycle for more than 5,500 hours, preferably more than 6,000 hours, at a current density, and the overpotential is not higher than 0.2V, preferably not higher than 0.1V.

[0019] 3. A calcined feedstock for an iron-based lithium lanthanum zirconate solid electrolyte, exhibiting a three-dimensional antler-like or coral-like morphology, with the longest end measuring 2-100 μm.

[0020] The main phase of the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte is a tetragonal phase, a cubic phase, or a mixture of both.

[0021] Optionally, the composition of the calcined feedstock of the iron-based lithium lanthanum zirconate solid electrolyte, in addition to the main phase, includes one or more of lanthanum zirconate, lanthanum ferrite, lithium zirconate, lithium carbonate, zirconium oxide, lanthanum oxide, iron oxide, lithium lanthanum oxide, lithium ferrite, and lithium oxide.

[0022] The calcined material of the iron-based lithium lanthanum zirconate solid electrolyte is first pre-pressed into a blank, and then sintered, preferably by embedded powder sintering, to obtain the iron-based lithium lanthanum zirconate solid electrolyte described in 1 or 2 above.

[0023] 4. A method for preparing an iron-based lithium lanthanum zirconate solid electrolyte according to 1 or 2 above, the method comprising the following steps:

[0024] Preparation of precursor sol: At room temperature, sol E containing lanthanum salt, zirconium salt, lithium salt, iron salt and organic acid chelating agent is formed in the presence of non-aqueous solvent;

[0025] Preparation of dry gel: At room temperature, the sol E is allowed to stand and age to form a wet gel; the non-aqueous solvent contained in the sol E is removed by rotary evaporation, vacuum distillation, supercritical extraction or freeze drying to obtain the dry gel of the iron-based lithium lanthanum zirconate solid electrolyte precursor.

[0026] Preparation of calcined material: The dry gel is pre-calcined, pulverized and calcined to obtain the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte;

[0027] Preparation of solid electrolyte bulk material: The calcined material of the iron-based lithium lanthanum zirconate solid electrolyte is first pre-pressed into a blank, and then sintered, preferably by embedded powder sintering, to obtain the bulk material of the iron-based lithium lanthanum zirconate solid electrolyte.

[0028] Optionally, the solid electrolyte powder is prepared by crushing the bulk of the iron-based lithium lanthanum zirconate solid electrolyte to obtain the powder of the iron-based lithium lanthanum zirconate solid electrolyte; or, the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte is sintered to obtain the powder of the iron-based lithium lanthanum zirconate solid electrolyte.

[0029] 5. The preparation method of the iron-based lithium lanthanum zirconate solid electrolyte according to 4 above, wherein the preparation of the sol E includes the following steps:

[0030] Lanthanum salt and zirconium salt are dissolved or dispersed in a first non-aqueous solvent to form solution A, sol A, or suspension A; lithium salt and iron salt are dissolved or dispersed in a second non-aqueous solvent to form solution B, sol B, or suspension B; wherein the first non-aqueous solvent and the second non-aqueous solvent may be the same or different.

[0031] Then, an organic acid chelating agent is added to the mixture of solution A, sol A, or suspension A with solution B, sol B, or suspension B to form sol E;

[0032] or

[0033] An organic acid chelating agent is added to the solution A, sol A, or suspension A to form solution C, sol C, or suspension C accordingly; optionally, an organic acid chelating agent is added to the solution B, sol B, or suspension B to form solution D, sol D, or suspension D accordingly.

[0034] Then, solution B, sol B, or suspension B is mixed with solution C, sol C, or suspension C to form sol E; or, solution A, sol A, or suspension A is mixed with solution D, sol D, or suspension D to form sol E; or, solution C, sol C, or suspension C is mixed with solution D, sol D, or suspension D to form sol E.

[0035] 6. The preparation method of the iron-based lithium lanthanum zirconate solid electrolyte according to 4 or 5 above, wherein the organic acid chelating agent is one or more selected from lauric acid, citric acid, oxalic acid, ascorbic acid, acetic acid, sulfonic acid, tartaric acid, and salicylic acid; and / or, the first non-aqueous solvent and the second non-aqueous solvent are each one or more selected from propanol, isopropanol, acetone, ethanol, ethylene glycol, n-hexane, isooctane, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide; and / Or, the molar ratio of the organic acid to the metal ion is (0.5~10.0):1; and / or, the lithium salt is in excess of 0-30 wt.%; and / or, the concentration of the sol E is 0.01~20 mol / L; and / or, the pre-calcination temperature is 200~600℃, and the holding time is 1~30h; and / or, the calcination temperature is 600~1000℃, and the holding time is 5~60h; and / or, the calcination atmosphere is air, oxygen, vacuum, or inert gas.

[0036] 7. The preparation method of the iron-based lithium lanthanum zirconate solid electrolyte according to any one of 4-6 above, wherein the pre-pressing is carried out by isostatic pressing at a pressure of 2-700 MPa; and / or, the embedded powder includes one or more of lithium carbonate, lanthanum zirconate, lithium zirconate, lithium lanthanum oxide, lithium ferrite, lanthanum ferrite, lithium oxide, zirconium oxide, lanthanum oxide, iron oxide, calcined material of the iron-based lithium lanthanum zirconate solid electrolyte, and iron-based lithium lanthanum zirconate solid electrolyte powder; and / or, the sintering includes non-hot pressing sintering, hot pressing sintering, plasma sintering, or flash sintering, and no sintering aid is used; and / or, the sintering temperature in the preparation of the solid electrolyte block and the sintering temperature when preparing the iron-based lithium lanthanum zirconate solid electrolyte powder from the calcined material are 1100-1400°C, the holding time is 1-30 h, and the sintering atmosphere is air, oxygen, vacuum, or inert gas.

[0037] 8. The preparation method of the iron-based lithium lanthanum zirconate solid electrolyte according to any one of 4-7 above, wherein the precursor, pre-burned material, calcined material, green embryo, bulk and powder of the iron-based lithium lanthanum zirconate solid electrolyte are all stored in a dry, carbon dioxide-free inert or weakly reducing atmosphere; the inert or weakly reducing gas is argon, nitrogen or argon-hydrogen mixture.

[0038] 9. A solid-state or semi-solid-state lithium battery, comprising a lithium-ion battery, a lithium-air battery, and a lithium-sulfur battery, characterized in that the battery's electrodes, electrolyte, or separator comprises one or more of the bulk or powder form of the iron-based lithium lanthanum zirconate solid electrolyte according to 1 or 2 above, and the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte according to 3 above, or comprises one or more of the bulk, powder, and calcined material of the iron-based lithium lanthanum zirconate solid electrolyte prepared according to any one of the preparation methods described in 4-8 above.

[0039] 10. The all-solid-state or semi-solid-state lithium battery according to claim 9 above, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a lithium-rich manganese-based positive electrode material or a covalent organic framework (COF) compound, and the electrolyte comprises one or more of the bulk or powder form of the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2 above and the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte according to claim 3 above, or comprises one or more of the bulk, powder, and calcined material of the iron-based lithium lanthanum zirconate solid electrolyte prepared according to any one of the preparation methods described in claims 4-8 above.

[0040] The effects of the invention

[0041] The advantages of the iron-based LLZO solid electrolyte and its preparation method of the present invention are as follows.

[0042] 1) The iron-doped LLZO solid electrolyte bulk of the present invention has high density, good grain boundary quality (the fracture failure section mainly exhibits grain fracture characteristics), and no obvious glass phase and impurity segregation. Its electrochemical performance is excellent, namely high lithium-ion conductivity, low electronic conductivity, good cycle stability, and excellent rate performance.

[0043] 2) The preparation method of the iron-based LLZO solid electrolyte of the present invention is simple, has few control factors, and has a high yield. The use of vacuum distillation, rotary evaporation or supercritical extraction technology greatly reduces the desolvation time and is also conducive to the recycling of solvent in the later stage.

[0044] 3) Using non-aqueous solvents, the product is less affected by the quality of the solvent, and the quality of iron-based LLZO solid electrolyte powder, the composition of electrolyte blocks and grain boundary characteristics can be effectively controlled.

[0045] 4) No sintering aids are used in the preparation of the electrolyte in this invention, which reduces the introduction of impurities.

[0046] 5) The calcined material generated during the electrolyte preparation process of the present invention can be used as an intermediate product for preparing iron-based LLZO solid electrolyte bulk material or as an intermediate product for directly preparing iron-based LLZO solid electrolyte powder. Attached Figure Description

[0047] Figure 1 The image shows the XRD pattern of the calcined iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0048] Figure 2 This is a SEM image of the calcined iron-based lithium lanthanum zirconate solid electrolyte from Example 1.

[0049] Figure 3 This is the XRD pattern of the sintered bulk iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0050] Figure 4 This is a SEM image of the cross-section of the sintered block of the iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0051] Figure 5 This is a cross-sectional EDS energy spectrum of the sintered block of the iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0052] Figure 6 This is the electrochemical AC impedance spectrum of the sintered bulk iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0053] Figure 7 The results are the limiting current test results of a lithium symmetric battery containing the sintered block of iron-based lithium zirconate solid electrolyte from Example 1.

[0054] Figure 8 The results are the limiting current density test results of a lithium symmetric battery containing the sintered block of iron-based lithium lanthanum zirconate solid electrolyte from Example 2.

[0055] Figure 9 The results are the cycle stability test results of a lithium symmetric battery containing the sintered block of iron-based lithium lanthanum zirconate solid electrolyte from Example 3.

[0056] Figure 10 The image shows the surface and cross-section of the iron-based lithium lanthanum zirconate solid electrolyte in Example 1.

[0057] Figure 11 This is the EDS spectrum of the cross section of the iron-based lithium lanthanum zirconate solid electrolyte in Comparative Example 1.

[0058] Figure 12 The images show the cross-section and surface of the iron-based lithium lanthanum zirconate solid electrolyte in Comparative Example 2.

[0059] Figure 13 This is a comparison of the electrochemical AC impedance spectra of the iron-based lithium lanthanum zirconate solid electrolytes in Example 3 and Comparative Example 2. Detailed Implementation

[0060] The following describes embodiments of the present invention, but the invention is not limited thereto. The present invention is not limited to the configurations described below; various modifications can be made within the scope of the claims. Embodiments and examples obtained by appropriately combining the disclosed technical means in different embodiments and examples are also included within the technical scope of the present invention. Furthermore, all documents described in this specification are incorporated herein by reference.

[0061] Unless otherwise defined, the technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0062] 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.

[0063] Unless otherwise stated, in this instruction manual, "more" in "multiple", "multi-variety", "multiple", etc., means a value of 2 or more.

[0064] In this specification, the terms "substantially" or "truly" mean that the difference is less than 5%, or less than 3%, or less than 1% compared to the relevant perfect or theoretical standard.

[0065] Unless otherwise specified, "%" in this instruction manual refers to the percentage content by mass.

[0066] In this instruction manual, if terms such as "room temperature" or "normal temperature" appear, the temperature is generally between 10-35℃.

[0067] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0068] In this specification, "optional" or "optionally" means that the event or situation described below may or may not occur, and the description includes both the scenario in which the event occurs and the scenario in which the event does not occur.

[0069] In this specification, the word "comprising" and any variations thereof are intended to cover 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 process, method, product, or apparatus.

[0070] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., 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.

[0071] <First Aspect>

[0072] In a first aspect of the invention, a powder or bulk form of an iron-based lithium lanthanum zirconate solid electrolyte is provided. The iron-based lithium lanthanum zirconate solid electrolyte of the present invention is a cubic phase lithium-rich garnet type with a crystal structure symmetry of [missing information]. That is, it has Space group. The iron-based lithium lanthanum zirconate solid electrolyte of the present invention is represented by the following formula: Li 7-3x La 3-y Zr 2-z Fe x O 12, where 0 < x ≤ 0.7, preferably 0 < x ≤ 0.5, more preferably 0.1 ≤ x ≤ 0.4. For example, x can be 0.15, 0.20, 0.25, 0.30, 0.35, 0.45, 0.55, 0.6, 0.65, etc. where -0.4 ≤ y ≤ 0.4, -0.3 ≤ z ≤ 0.3 and 3y + 4z = 0. For example, y can be -0.4, -0.3, -0.2, -0.1, -0.05, -0.02, -0.01, 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, etc., and z can be -0.4, -0.3, -0.2, -0.1, -0.05, -0.02, -0.01, 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, etc.

[0073] The calcined material of the iron-based lanthanum lithium zirconate solid electrolyte of the present invention presents a three-dimensional antler-like or coral-like morphology, and the longest end is about 2 - 100 μm, preferably 3 - 50 μm, more preferably 3 - 20 μm. The main phase of the calcined material is a tetragonal phase, a cubic phase or a mixed phase of both. Optionally, in addition to the main phase, the calcined material further includes one or more of lanthanum zirconate, lanthanum ferrate, lithium zirconate, lithium carbonate, zirconia, lanthanum oxide, iron oxide, lithium lanthanate, lithium ferrate, lithium oxide.

[0074] The iron-based lanthanum lithium zirconate solid electrolyte block of the present invention is formed by pre-pressing the above-mentioned calcined material into a green body and then sintering (powder-embedded sintering or direct sintering without powder embedding). It does not contain a sintering aid and the relative density is not less than 92%, preferably not less than 94%. For example, it can be 93%, 95%, 96%, 97%, etc. The cross-section of the fractured failure of the block mainly shows grain fracture characteristics rather than grain boundary fracture characteristics. If the pressing and forming process introduces a granulation process, it will be more beneficial to the performance of the electrolyte (such as relative density, electrochemical performance). As described above, the grain fracture characteristics indicate that the grain boundaries of the prepared electrolyte are dense, which is very beneficial to reducing the loss of lithium ion transmission at the grain boundaries.

[0075] The bulk phase of the iron-based lanthanum lithium zirconate solid electrolyte block of the present invention does not contain aluminum element, there is no segregation of iron element at the grain boundaries, and there is no lithium carbonate on its surface or cross-section (i.e., the cross-section of the fractured failure). That is, the components in the electrolyte of the present invention are pure, and there is no obvious glass phase and impurity segregation. Good grain boundaries are very beneficial to improving the cycle stability of the device.

[0076] In some embodiments of the present invention, the apparent lithium ion conductivity of the iron-based lanthanum lithium zirconate solid electrolyte block at room temperature is between 3.7×10 -4 ~3.7×10 -2 S / cm, preferably 1.0×10 -3 ~3.7×10 -2S / cm. At room temperature, the electronic conductivity of the bulk material is not less than 10. -7 ~10 -10 The value is on the order of S / cm, specifically 1.0 × 10⁻⁶. -7 ~7.3×10 -10 S / cm, preferably 1.0×10 -7 ~7.3×10 -9 S / cm. At room temperature, the limiting current density of the lithium-tin symmetric cell (LiSn|LLZFO|LiSn) composed of the bulk components is not less than 200 mA / cm. 2 At room temperature, the lithium-tin symmetric cell (LiSn|LLZFO|LiSn) achieves a current of 0.5 mA / cm². 2 ~110mA / cm 2 It can stably cycle for more than 5,500 hours, preferably more than 6,000 hours, such as 5,800h, 6,100h, 6,200h, 6,300h, 6,400h, 6,500h, etc., at a current density, and the overpotential is not higher than 0.2V, preferably not higher than 0.1V.

[0077] As can be seen from the above, the iron-based lithium lanthanum zirconate solid electrolyte block of the present invention does not contain sintering aids, and the resulting electrolyte block has the characteristics of high density and dense and clean grain boundaries. Therefore, it has high lithium-ion conductivity, low electronic conductivity, and excellent cycle stability.

[0078] <Second aspect>

[0079] In a second aspect of the invention, a method for preparing the iron-based lithium lanthanum zirconate solid electrolyte described in the first aspect of the invention is provided.

[0080] The preparation method of the iron-based lithium lanthanum zirconate solid electrolyte of the present invention includes the following steps: preparation of precursor sol, preparation of dry gel, preparation of pre-calcined and calcined materials, preparation of solid electrolyte bulk material, and optionally preparation of solid electrolyte powder. The following provides a detailed description of each step.

[0081] Preparation steps of precursor sol

[0082] The precursor sol (hereinafter also referred to as "solvent E") is a sol E containing lanthanum salt, zirconium salt, lithium salt, iron salt and organic acid chelating agent. Its preparation steps are the steps of forming sol E containing lanthanum salt, zirconium salt, lithium salt, iron salt and organic acid chelating agent at room temperature in the presence of a non-aqueous solvent.

[0083] More specifically, the preparation of sol E includes the following steps:

[0084] Lanthanum salt and zirconium salt are dissolved or dispersed in a first non-aqueous solvent to form solution A, sol A, or suspension A, and lithium salt and iron salt are dissolved or dispersed in a second non-aqueous solvent to form solution B, sol B, or suspension B, wherein the first non-aqueous solvent and the second non-aqueous solvent may be the same or different.

[0085] An organic acid chelating agent is added to a mixture of solution A, sol A, or suspension A with solution B, sol B, or suspension B to form sol E;

[0086] or

[0087] An organic acid chelating agent is added to the solution A, sol A, or suspension A to form solution C, sol C, or suspension C accordingly; optionally, an organic acid chelating agent is added to the solution B, sol B, or suspension B to form solution D, sol D, or suspension D accordingly.

[0088] Then, solution B, sol B, or suspension B is mixed with solution C, sol C, or suspension C to form sol E; or, solution A, sol A, or suspension A is mixed with solution D, sol D, or suspension D to form sol E; or, solution C, sol C, or suspension C is mixed with solution D, sol D, or suspension D to form sol E.

[0089] The phrase "mixing solution B, sol B, or suspension B with solution C, sol C, or suspension C" means that any one of solution B, sol B, or suspension B can be mixed with any one of solution C, sol C, or suspension C. Similarly, "mixing solution A, sol A, or suspension A with solution D, sol D, or suspension D" and "mixing solution C, sol C, or suspension C with solution D, sol D, or suspension D" have the same meaning.

[0090] It should be noted that the main reason for mixing zirconium salt with lanthanum salt and lithium salt with iron salt is to facilitate the preparation of lithium-site doping of iron ions. However, this does not mean that such mixing is the only option.

[0091] In this invention, examples of lanthanum salts may include one or more of lanthanum nitrate, lanthanum chloride, lanthanum acetate, lanthanum carbonate, lanthanum hydroxide, lanthanum oxide, lanthanum acetylacetone, lanthanum isopropoxide, and lanthanum fluoride.

[0092] In this invention, examples of zirconium salts may include one or more of zirconium oxychloride, zirconium tetrachloride, zirconium oxynitrate, zirconium nitrate, zirconium acetate, zirconium isopropoxide, lithium zirconate, zirconium ethoxylate, and ammonium zirconium carbonate.

[0093] In this invention, examples of lithium salts may include one or more of lithium carbonate, lithium acetate, lithium hydroxide, lithium chloride, lithium oxalate, lithium oxide, lithium fluoride, and lithium perchlorate.

[0094] In this invention, examples of iron salts may include one or more of ferric chloride, ferrous chloride, ferric nitrate, ferrous nitrate, ferric oxalate, ferrous oxalate, and ferric citrate.

[0095] As mentioned above, this invention draws on the concept of "self-assembly", uses organic acid chelating agents as framework units and organic solvents as solvents, and achieves effective bonding between the hydroxyl and carboxyl functional groups contained in the organic acid and metal ions through self-assembly reaction, thereby obtaining a highly dense iron-doped LLZO electrolyte with dense and clean grain boundaries.

[0096] In this invention, one or more of the following organic acid chelating agents can be used: lauric acid, citric acid, oxalic acid, ascorbic acid, acetic acid, sulfonic acid, tartaric acid, and salicylic acid. Citric acid and ascorbic acid are particularly preferred because they contain a greater number of hydroxyl or carboxyl groups, resulting in more effective bonding between the hydroxyl and carboxyl functional groups and the metal ions. This leads to a more compact and cleaner LLZO electrolyte with denser grain boundaries.

[0097] In sol E, the molar ratio of organic acid to metal ions can be (0.5–10.0):1, preferably (0.5–7.0):1, more preferably (0.5–5):1, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5.5:1, 6:1, 6.5:1, etc. The metal ions are zirconium, lanthanum, lithium, and iron ions. If the amount of organic acid is too small, it is difficult to effectively bond with the metal ions, which may result in the inability to obtain a highly dense LLZO electrolyte with clean grain boundaries. If the amount of organic acid is too large, it will cause the pre-calcined material to be too loose.

[0098] In some embodiments of the present invention, lithium is typically required in excess because some lithium is lost during calcination and subsequent sintering. In this invention, the lithium salt may be in excess of 0-30 wt.%, preferably 5-30 wt.%. Excessive lithium may result in an inability to obtain a dense and clean LLZO electrolyte with clear grain boundaries.

[0099] In some embodiments of the present invention, the theoretical ratio of zirconium to lanthanum should be 1:1.5 according to stoichiometry. However, in actual preparation of electrolytes, considering that the selected zirconium salt and / or lanthanum salt is hygroscopic and its water content is difficult to control, or that the crystal water content of the selected zirconium salt and lanthanum salt is unclear, the actual stoichiometric ratio of zirconium to lanthanum can be slightly adjusted.

[0100] In this invention, unless otherwise specified, the molar ratios of other elements are approximately the theoretical stoichiometric ratios.

[0101] In embodiments of the present invention, examples of the first non-aqueous solvent and the second non-aqueous solvent are each one or more of propanol, isopropanol, acetone, ethanol, ethylene glycol, n-hexane, isooctane, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide. As described above, the first non-aqueous solvent and the second non-aqueous solvent may be the same or different.

[0102] Furthermore, in embodiments of the present invention, the concentration of sol E can be 0.01–20 mol / L. When the sol concentration is greater than 20 mol / L, there is a risk of resulting in larger particle sizes of the obtained electrolyte; when the sol concentration is less than 0.01 mol / L, the resulting particle size is smaller, but this may lead to a lower yield. In the present invention, the concentration of sol E is preferably 0.01–10 mol / L, more preferably 0.01–5 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 6 mol / L, 8 mol / L, etc.

[0103] Dry gel preparation steps

[0104] The sol E prepared in the above steps is allowed to stand and age at room temperature to form a wet gel. Then, the non-aqueous solvent contained in the sol E is removed by rotary evaporation, vacuum distillation, supercritical extraction, or freeze drying to obtain a dry gel of the iron-based lithium lanthanum zirconate solid electrolyte precursor.

[0105] As mentioned earlier, current methods for preparing LLZO solid electrolytes using the sol-gel method employ traditional solvent removal processes such as vacuum or forced-air drying, which are time-consuming and the product composition is easily affected by the drying process. This invention, for the first time, introduces vacuum distillation, rotary evaporation, freeze-drying, or supercritical fluid extraction into the solvent removal process. This significantly reduces solvent removal time to improve production efficiency, greatly ensures the uniformity of the product composition, and facilitates subsequent solvent recycling.

[0106] Preparation steps of pre-burned and calcined feedstocks

[0107] The dry gel obtained in the above steps is pre-calcined and pulverized to obtain a pre-calcined material, which is then calcined to obtain an iron-based lithium lanthanum zirconate solid electrolyte, Li. 7-3x La 3-y Zr 2-z Fe x O 12 Calcination feedstock.

[0108] In some embodiments of the present invention, the pre-firing temperature can be 200–600°C, preferably 300–500°C, and the holding time can be 1–30 h, preferably 1–10 h. The calcination temperature can be 600–1000°C, preferably 700–900°C, and the holding time can be 5–60 h, preferably 5–30 h. The calcination atmosphere can be air, oxygen, vacuum, or an inert gas.

[0109] Solid electrolyte bulk preparation steps

[0110] After obtaining the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte, the raw material can be optionally further prepared according to actual needs. In this invention, the term "bulk" includes not only blocky shapes but also sheet-like shapes.

[0111] In this step, the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte prepared in the above steps is sintered using a molding sintering technique to obtain the iron-based lithium lanthanum zirconate solid electrolyte Li. 7-3x La 3-y Zr 2-z Fe x O 12 The block.

[0112] In an embodiment of the present invention, the molding and sintering technology involves pre-pressing the obtained electrolyte powder into a blank, and then sintering the electrolyte blank by means of sintering.

[0113] Pre-pressing can be carried out using methods such as isostatic pressing. When isostatic pressing is used, the pressure is 2-700 MPa, preferably 2-500 MPa, and more preferably 2-100 MPa.

[0114] In this invention, sintering is preferably performed using embedded powder sintering. In some embodiments of this invention, the embedded powder is selected from, but is not limited to, one or more of lithium carbonate, lanthanum zirconate, lithium zirconate, lithium lanthanum oxide, lithium ferrite, lanthanum ferrite, lithium oxide, lanthanum oxide, zirconium oxide, iron oxide, the prepared electrolyte calcined material, and the sintered material of the prepared electrolyte. In the art, "embedded powder" is sometimes also referred to as "embedded master powder," "embedded material," etc. Therefore, in this invention, "embedded powder" has the same meaning as "embedded master powder," "embedded material," etc.

[0115] In some embodiments of the present invention, sintering may include non-hot-pressing sintering, hot-pressing sintering, plasma sintering, or flash sintering. The sintering temperature may be 1100–1400°C, preferably 1100–1300°C, and the holding time is 1–30 h, preferably 5–25 h, more preferably 5–20 h. The sintering atmosphere is air, oxygen, vacuum, or an inert gas.

[0116] The method of this invention does not require the addition of sintering aids, thus resulting in a product with high purity and a simple, easy-to-produce process. Of course, sintering aids can also be used. Adding a granulation step to the molding process will also improve performance, but it will increase the number of process steps.

[0117] Preparation of optional solid electrolyte powder

[0118] In some embodiments of the present invention, the bulk of the iron-based lithium lanthanum zirconate solid electrolyte can be crushed after preparation to obtain powder of the iron-based lithium lanthanum zirconate solid electrolyte.

[0119] In other embodiments of the present invention, the solid electrolyte powder can also be obtained by sintering the above-described calcined material. The sintering method and conditions here are the same as those in the "Solid Electrolyte Bulk Preparation Step" described above.

[0120] Furthermore, the precursors, pre-calcined materials, calcined materials, raw preforms, bulk materials, and powders of the iron-based lithium lanthanum zirconate solid electrolyte of this invention must be stored in a dry, carbon dioxide-free, inert or weakly reducing atmosphere replacement system. The inert or weakly reducing gas can be argon, nitrogen, or an argon-hydrogen mixture. The atmosphere replacement system may contain a gas adsorption reagent (mainly for adsorbing harmful gases such as carbon dioxide) and / or a drying reagent (mainly for dehumidification) to ensure a dry, inert or weakly protective atmosphere. The gas adsorption reagent can be sodium hydroxide or sodium carbonate, etc. The drying reagent can be 3A or 4A molecular sieves, etc.

[0121] <Third aspect>

[0122] A third aspect of the present invention provides an all-solid-state or semi-solid-state lithium battery, including a lithium-ion battery, a lithium-air battery, and a lithium-sulfur battery, wherein the electrode, electrolyte, or separator of the battery comprises one or more of the bulk, powder, and calcined material of the iron-based lithium lanthanum zirconate solid electrolyte of the first aspect, or comprises one or more of the bulk, powder, and calcined material of the iron-based lithium lanthanum zirconate solid electrolyte prepared by the preparation method of the second aspect.

[0123] In some preferred embodiments of the present invention, the all-solid-state or semi-solid-state lithium battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a lithium-rich manganese-based positive electrode material or a covalent organic framework (COF) compound, and the electrolyte includes one or more of the bulk, powder, and calcined materials of the iron-based lithium lanthanum zirconate solid electrolyte of the first aspect above, or includes one or more of the bulk, powder, and calcined materials of the iron-based lithium lanthanum zirconate solid electrolyte prepared by the preparation method of the second aspect above.

[0124] Example

[0125] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0126] The test method of the present invention is described below.

[0127] XRD testing

[0128] An X-ray powder diffractometer (Smartlab model) was used with Cu kα rays at a tube voltage of 45 kV and a tube current of 200 mA. Scanning was performed within the 2θ range of 10°–70°, with a step size of 0.01 and a scanning speed of 2–5° / min.

[0129] Determination of relative density

[0130] The relative density of the samples was tested using a self-made device. The test principle was Archimedes' water displacement method, and anhydrous ethanol was used as the auxiliary liquid.

[0131] Microscopic morphology and cross-sectional morphology of the product and EDS energy dispersive spectroscopy determination

[0132] The morphology of the samples and their cross-sections was analyzed using a scanning electron microscope (SEM, instrument model HITACHI SU-70, operating voltage 5kV). Energy dispersive spectroscopy (EDS) was performed on the cross-sections to analyze their elemental composition and distribution. The cross-sections of the samples were those after fracture failure. To improve the conductivity of the samples and ensure clear images, the samples were sputter-coated with gold.

[0133] Electrochemical performance testing

[0134] The electronic conductivity of the samples was tested using the Wagner DC polarization method. The samples were assembled into an all-solid-state asymmetric LiSn|LLZFO|Au cell, and the electronic conductivity was measured using a Bio-logic SP-200 single-channel electrochemical workstation (France).

[0135] The lithium-ion conductivity of the samples was measured using electrochemical impedance spectroscopy. The samples were assembled into a LiSn|LLZFO|LiSn all-solid-state symmetric cell, and the electrochemical impedance spectroscopy of the samples was measured using a Bio-logic SP-200 single-channel electrochemical workstation (France). The conductivity was calculated by curve fitting using an equivalent circuit.

[0136] The electrochemical performance of the samples was evaluated using constant current charge-discharge testing. The samples were assembled into LiSn|LLZFO|LiSn all-solid-state symmetric batteries, and charge-discharge cycle life was tested at different constant current densities with a charge-discharge depth of 1 hour. The LAND CT2001 battery testing system was used to test their charge-discharge performance. The limiting current density test was conducted using a similar method on the same equipment. The difference was that the charge-discharge current density was gradually increased until the overpotential equaled 1V.

[0137] Although the samples are assembled as LiSn|LLZFO|Au and LiSn|LLZFO|LiSn batteries in this invention, it is not limited thereto. For example, all-solid-state asymmetric batteries can also use LiSn|LLZFO|Ag, etc.

[0138] Fourier Transform Infrared Spectroscopy (FTIR) Measurement

[0139] The lithium carbonate content in the samples was analyzed using a Thermo Fisher Nicolet 6700 Fourier transform infrared spectrometer. Specifically, the powdered sample was mixed and ground uniformly with spectroscopically pure KBr reagent, and then pressed into tablets under 10 kPa pressure to ensure high sample transparency. The test wavelength was selected from 500 to 4000 cm⁻¹. -1 .

[0140] Raman spectroscopy (Raman test)

[0141] The samples were analyzed using a LabRAM HR800 laser confocal Raman spectrometer manufactured by Horiba, with wavenumbers ranging from 500 to 3000 cm⁻¹. -1 A laser with a wavelength of 532nm was selected.

[0142] ICP-OES elemental analysis

[0143] The elemental composition of the samples was quantitatively analyzed using a Thermo Fisher ICAP 7000SERIES inductively coupled plasma atomic emission spectrometer. After thorough dissolution and digestion, the samples were diluted in volumetric flasks, and the elemental content was determined using standard samples.

[0144] Example 1:

[0145] (1) At room temperature, 2.58 g of zirconium nitrate (Zr(NO3)4·5H2O) and 3.90 g of lanthanum nitrate (La(NO3)3·6H2O) were dissolved in 200 mL of anhydrous ethanol at a molar ratio of 1:1.5 and stirred thoroughly until completely dissolved to form sol A.

[0146] (2) Disperse and dissolve 0.74g lithium carbonate (Li2CO3) and 0.243g ferric chloride (FeCl3·6H2O) in 100mL of anhydrous ethanol to form suspension B.

[0147] (3) Add 14.25g of citric acid to suspension B and stir until completely dissolved to form sol D.

[0148] (4) Mix sol A and sol D and stir evenly to form sol E with a concentration of 0.01 mol / L.

[0149] (5) After aging at room temperature, the gel is dried by rotary evaporation at 90°C (SY-2000 rotary evaporator, manufactured by Shanghai Yarong Biochemical Instrument Factory) to obtain a yellow iron-doped lithium lanthanum zirconate dry gel.

[0150] (6) The dried gel was placed in a muffle furnace and pre-calcined at 400°C for 5 hours. After grinding and crushing, it was placed back into a tube furnace and calcined at 800°C for 15 hours in a dry air atmosphere. The iron-doped calcined material (i.e., powder) was obtained. After gas replacement, it was sealed in a dry, carbon dioxide-free argon atmosphere.

[0151] (7) Using isostatic pressing technology, the calcined material is pressed into sheets under a pressure of 20 MPa. After embedding powder (a mixture of lithium carbonate and calcined material is used), the sheet is sintered at 1300℃ for 5 hours without the use of sintering aids to obtain iron-doped lithium lanthanum zirconate solid electrolyte sheets. After gas replacement, the sheets are sealed in dry, carbon dioxide-free nitrogen.

[0152] (8) After polishing, an iron-doped lithium lanthanum zirconate solid electrolyte block is obtained.

[0153] The elemental composition of the iron-doped lithium lanthanum zirconate solid electrolyte bulk obtained in this embodiment was determined by ICP-OES. The results were as follows: Li: 6.23; Fe: 0.33; Zr: 2.01; La: 2.98. Among them, the Fe doping amount was approximately 0.3%.

[0154] from Figure 1 It can be concluded that the calcined material of the obtained iron-doped lithium lanthanum zirconate solid electrolyte is tetragonal. From... Figure 3 It can be concluded that the obtained iron-doped lithium lanthanum zirconate solid electrolyte has a cubic lithium-rich garnet structure, possessing... Space group. From Figure 2 As can be seen from the results, the morphology of the obtained iron-doped lithium lanthanum zirconate solid electrolyte calcined material is a three-dimensional antler-like morphology, with the longest end being 2-100 μm.

[0155] The resulting iron-doped lithium lanthanum zirconate solid electrolyte bulk was translucent, with a thickness of approximately 0.7 cm, a relative density of approximately 94%, and an electronic conductivity of 1.23 × 10⁻⁶ at room temperature. -7 S / cm ( Figure 6 The conductivity of lithium ions is 1×10⁻⁶. -3 The lithium-ion transference number is approximately 1, and the limiting current is 1.0 mA / cm. 2 ( Figure 7 ).

[0156] according to Figure 4 As shown, the grain boundaries of the obtained iron-doped lithium lanthanum zirconate solid electrolyte block are relatively dense and clean, and the interface shows obvious crystal fracture cracks, i.e. grain cracks, rather than obvious grain boundary cracks.

[0157] according to Figure 5 The results show that the iron-doped lithium lanthanum zirconate solid electrolyte bulk ( Figure 5 (a)) does not contain aluminum in its bulk phase. Figure 5 (b)), and there is no iron segregation at the grain boundaries. Figure 5 (c)). According to Raman spectra ( Figure 10 It can be seen that lithium carbonate is not present on the surface or cross-section of the iron-doped lithium lanthanum zirconate solid electrolyte block.

[0158] Example 2:

[0159] (1) At room temperature, 46.2 g of zirconium oxynitrate (ZrO(NO3)2·xH2O) and 94.8 g of lanthanum acetate (C6H9O6La·xH2O) were dissolved in 120 mL of isooctane to form sol A. Then, 105.1 g of ascorbic acid (C6H8O6) was added and stirred until completely dissolved to form sol C.

[0160] (2) Disperse and dissolve 34.9g of lithium hydroxide (LiOH·H2O) and 8.08g of ferric nitrate (Fe(NO3)3·9H2O) in 280mL of anhydrous ethanol to form sol B. Then add 176.52g of ascorbic acid and dissolve it completely to form sol D.

[0161] (3) Mix sol C and sol D and stir thoroughly to form sol E with a concentration of 0.25 mol / L.

[0162] (5) After aging at room temperature and vacuum distillation (using a self-made vacuum distillation device, the temperature is the specific fraction temperature), iron-doped lithium lanthanum zirconate dry gel is obtained.

[0163] (6) The dried gel was placed in a muffle furnace and pre-calcined at 350°C for 6 hours. After crushing, it was placed in a tube furnace and calcined at 900°C for 10 hours in air atmosphere to obtain calcined powder. After gas replacement, it was sealed in dry, carbon dioxide-free argon gas.

[0164] (7) The powder was pressed into sheets using isostatic pressing (pressure 50 MPa), and then sintered at 1250 °C (using a mixture of lithium carbonate and calcined material) for 10 h to obtain cubic iron-doped lanthanum zirconate solid electrolyte sheets. After gas replacement, the sheets were sealed in a dry, carbon dioxide-free argon-hydrogen mixture.

[0165] (8) After polishing, an iron-doped lithium lanthanum zirconate solid electrolyte bulk material is obtained. The Fe doping amount is approximately 0.2%.

[0166] The resulting electrolyte mass had a thickness of 0.7 cm, a relative density of 95%, and a lithium-ion conductivity of 3.8 × 10⁻⁶ at room temperature. -3 S / cm. The limiting current density is 200 mA / cm. 2 The above can reach 250mA / cm 2 ,like Figure 8 As shown.

[0167] Example 3:

[0168] (1) At room temperature, 12.2g of zirconium acetate (C8H) was placed... 12 16.0 g of lanthanum chloride (LaCl3·7H2O) and 16.0 g of lanthanum chloride (LaCl3·7H2O) were dissolved in 100 mL of anhydrous ethanol to form sol A. Then, 29.232 g of citric acid (C6H8O7) was added and stirred until completely dissolved to form sol C.

[0169] (2) 3.49 g of ferrous oxalate (Fe2(C2O4)3·6H2O) and 12.78 g of lithium oxalate (C2O4Li) were dispersed in 200 mL of anhydrous ethanol to form sol B.

[0170] Mix sol C and sol B and stir until homogeneous to form sol E with a concentration of 0.06 mol / L.

[0171] After aging (at room temperature) and rotary evaporation at 90°C (SY-2000 rotary evaporator, Shanghai Yarong Biochemical) until dry, a yellow iron-doped lithium lanthanum zirconate dry gel was obtained.

[0172] The dried gel was placed in a muffle furnace and pre-calcined at 400°C for 5 hours. After grinding and crushing, it was placed back into a tube furnace and calcined at 850°C for 10 hours in a dry air or oxygen atmosphere. This yielded a cubic iron-doped lanthanum lithium zirconate calcined material. After gas replacement, it was sealed in a dry, carbon dioxide-free argon atmosphere.

[0173] The calcined material was pressed into sheets using cold isostatic pressing (pressure 2 MPa), then embedded with lithium carbonate powder, and sintered at 1200℃ for 12 h to obtain a cubic iron-doped lithium zirconate solid electrolyte sheet. The Fe doping amount is approximately 0.4%.

[0174] like Figure 9 As shown, at room temperature, this sample can achieve a current of 0.5 mA / cm. 2 ( Figure 9 (a) and 110 mA / cm 2 ( Figure 9 (b) It can operate stably for more than 6000 hours (up to 6300 hours) without short circuit at current density.

[0175] After gas replacement, it is sealed in dry, carbon dioxide-free argon gas. (The argon gas used needs to be dried by a self-made gas drying system containing gas adsorption and drying reagents such as 3A and 4A molecular sieves, sodium hydroxide, and sodium carbonate).

[0176] Comparative Example 1:

[0177] (1) At room temperature, 2.58 g of zirconium nitrate (Zr(NO3)4·5H2O) and 3.90 g of lanthanum nitrate (La(NO3)3·6H2O) were dissolved in 200 mL of anhydrous ethanol and stirred until completely dissolved to form sol A.

[0178] (2) Disperse and dissolve 1.55g lithium carbonate and 0.64g ferric chloride in 100mL anhydrous ethanol to form suspension B.

[0179] (3) Add 5.04g of citric acid to suspension B and stir until completely dissolved to form sol C.

[0180] (4) Mix sol A and sol C and stir evenly to form sol E with a concentration of 0.01 mol / L.

[0181] (5) After aging (at room temperature) and rotary evaporation at 90°C (SY-2000 rotary evaporator, Shanghai Yarong Biochemical) until dry, a yellow iron-doped lithium lanthanum zirconate dry gel is obtained.

[0182] (6) The dried gel was placed in a muffle furnace and pre-calcined at 400°C for 5 hours. After grinding and crushing, it was placed back into a tube furnace and calcined at 800°C for 15 hours in a dry air or oxygen atmosphere. Iron-doped cubic lithium lanthanum zirconate solid electrolyte powder was obtained. After gas replacement, it was sealed in a dry, carbon dioxide-free argon atmosphere.

[0183] The bulk preparation steps are the same as in Example 1. The Fe doping amount is approximately 0.79.

[0184] like Figure 11 As shown, EDS analysis of the samples revealed that when the iron doping amount x exceeds 0.7, iron-containing phases precipitate at the grain boundaries in the obtained samples.

[0185] Comparative Example 2:

[0186] (1) At room temperature, 12.2g of zirconium acetate (C8H) was placed... 12 16.0 g of lanthanum chloride (LaCl3·7H2O) and 16.0 g of lanthanum chloride (LaCl3·7H2O) were dissolved in 100 mL of anhydrous ethanol to form sol A. Then, 29.232 g of citric acid (C6H8O7) was added and stirred until completely dissolved to form sol C.

[0187] (2) 3.49 g of ferrous oxalate (Fe2(C2O4)3·6H2O) and 14.38 g of lithium oxalate (C2O4Li) were dispersed in 200 mL of anhydrous ethanol to form sol B.

[0188] Mix sol C and sol B and stir until homogeneous to form sol E with a concentration of 0.06 mol / L.

[0189] After aging (at room temperature) and rotary evaporation at 90°C (SY-2000 rotary evaporator, Shanghai Yarong Biochemical) until dry, a yellow iron-doped lithium lanthanum zirconate dry gel was obtained.

[0190] The dried gel was placed in a muffle furnace and pre-calcined at 400°C for 5 hours. After grinding and crushing, it was placed back into a tube furnace and calcined at 850°C for 10 hours in a dry air or oxygen atmosphere. This yielded a cubic iron-doped lanthanum lithium zirconate calcined material. After gas replacement, it was sealed in a dry, carbon dioxide-free argon atmosphere.

[0191] The bulk material preparation steps are the same as in Example 3.

[0192] like Figure 12 As shown, Raman analysis of the sample surface and cross-section revealed the presence of a lithium carbonate phase. This is likely due to an excess of lithium oxalate.

[0193] Figure 13 A comparison of the electrochemical impedance spectroscopy (EIS) spectra of the solid electrolytes of Example 3 and Comparative Example 2 at room temperature is shown. It was found that, compared to Example 3, the presence of lithium carbonate on the surface and cross-section of the electrolyte in Comparative Example 2 resulted in a larger interfacial resistance.

[0194] 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. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A preparation method of an iron-based lithium lanthanum zirconate solid electrolyte, wherein the iron-based lithium lanthanum zirconate solid electrolyte has a cubic-phase lithium-rich garnet-type structure and has an I 3d space group, and its chemical formula is expressed as: Li 7-3x La 3-y Zr 2-z Fe x O 12 , where 0 < x ≤ 0.7, -0.4 ≤ y ≤ 0.4, -0.3 ≤ z ≤ 0.3, and 3y + 4z = 0, and its relative density is not lower than 92%, and the cross-section of fracture failure basically presents a grain fracture characteristic rather than a grain boundary fracture characteristic. The iron-based lithium lanthanum zirconate solid electrolyte described there is no iron segregation at the grain boundaries. Using the aforementioned iron-based lithium lanthanum zirconate solid electrolyte, a lithium-tin symmetric cell at room temperature ( The limiting current density is not less than 200 mA / cm². 2 , The preparation method includes the following steps: Preparation of precursor sol: At room temperature, sol E containing lanthanum salt, zirconium salt, lithium salt, iron salt and organic acid chelating agent is formed in the presence of non-aqueous solvent; Preparation of dry gel: At room temperature, the sol E is allowed to stand and age to form a wet gel; the non-aqueous solvent contained in the sol E is removed by rotary evaporation, vacuum distillation, supercritical extraction or freeze drying to obtain the dry gel of the iron-based lithium lanthanum zirconate solid electrolyte precursor. Preparation of calcined material: The dry gel is pre-calcined, pulverized and calcined to obtain the calcined material of the iron-based lithium lanthanum zirconate solid electrolyte; Preparation of solid electrolyte block: The calcined material of the iron-based lithium lanthanum zirconate solid electrolyte is first pre-pressed into a blank, and then sintered by embedding powder to obtain the block of iron-based lithium lanthanum zirconate solid electrolyte. The sol E is prepared by the following steps: Lanthanum salt and zirconium salt are dissolved or dispersed in a first non-aqueous solvent to form solution A or sol A, and lithium salt and iron salt are dissolved or dispersed in a second non-aqueous solvent to form solution B, sol B or suspension B, wherein the first non-aqueous solvent and the second non-aqueous solvent may be the same or different. An organic acid chelating agent is added to solution A or sol A to form solution C or sol C accordingly, and / or an organic acid chelating agent is added to solution B or sol B or suspension B to form solution D or sol D or suspension D accordingly; Then, solution B or sol B or suspension B is mixed with solution C or sol C to form sol E; or, solution A or sol A is mixed with solution D or sol D or suspension D to form sol E; or, solution C or sol C is mixed with solution D or sol D or suspension D to form sol E.

2. The method for preparing the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1, wherein the organic acid chelating agent is one or more of lauric acid, citric acid, oxalic acid, ascorbic acid, acetic acid, sulfonic acid, tartaric acid, and salicylic acid; and / or, the first non-aqueous solvent and the second non-aqueous solvent are each one or more of propanol, isopropanol, acetone, ethanol, ethylene glycol, n-hexane, isooctane, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide; and / or, the molar ratio of the organic acid to the metal ion is (0.5~10.0):1; and / or, the lithium salt is in excess at 0-30 wt.%; and / or, the concentration of the sol E is 0.01~20 mol / L; and / or, the pre-calcination temperature is 200~600 °C, and the holding time is 1~30 h; and / or, the calcination temperature is 600~1000 °C, and the holding time is 5~60 h. h; and / or, the calcination atmosphere is air, oxygen, vacuum, or an inert gas.

3. The method for preparing iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2, wherein the pre-pressing is carried out by isostatic pressing at a pressure of 2-700 MPa; and / or, the embedded powder comprises one or more of lithium carbonate, lanthanum zirconate, lithium zirconate, lithium lanthanum oxide, lithium ferrite, lanthanum ferrite, lithium oxide, zirconium oxide, lanthanum oxide, iron oxide, calcined material of the iron-based lithium lanthanum zirconate solid electrolyte, and iron-based lithium lanthanum zirconate solid electrolyte powder; and / or, the sintering comprises non-hot pressing sintering, hot pressing sintering, plasma sintering, or flash sintering, and without the use of sintering aids; and / or, the sintering temperature in the preparation of the solid electrolyte block and the sintering temperature when preparing the iron-based lithium lanthanum zirconate solid electrolyte powder from the calcined material is 1100-1400 °C, the holding time is 1-30 h, and the sintering atmosphere is air, oxygen, vacuum, or inert gas.

4. The method for preparing the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2, wherein the precursor, pre-calcined material, calcined material, raw material, bulk material and powder of the iron-based lithium lanthanum zirconate solid electrolyte are all stored in a dry, carbon dioxide-free inert or weakly reducing atmosphere; the inert or weakly reducing gas is argon, nitrogen or argon-hydrogen mixture.

5. The method for preparing the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2, wherein lithium carbonate is not present on the surface or at the fracture failure section of the iron-based lithium lanthanum zirconate solid electrolyte; and / or, the bulk phase of the iron-based lithium lanthanum zirconate solid electrolyte does not contain aluminum; and / or, the lithium-ion conductivity of the iron-based lithium lanthanum zirconate solid electrolyte at room temperature is between 3.7 × 10⁻⁶. -4 ~3.7×10 -2 The S / cm range; and / or, the electronic conductivity of the iron-based lithium lanthanum zirconate solid electrolyte at room temperature is between 1.0 × 10⁻⁶. -7 ~7.3×10 -10 Between S / cm; and / or, using the aforementioned iron-based lithium lanthanum zirconate solid electrolyte, lithium-tin symmetric cells at room temperature ( At 0.5 mA / cm 2 ~110 mA / cm 2 It can cycle stably for more than 5500 hours at a current density, and the overpotential is no higher than 0.2 V.

6. The method for preparing the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2, wherein the calcined material exhibits a three-dimensional antler-like or coral-like morphology, with the longest end being 2-100 μm, and The main phase of the calcined material is a tetragonal phase, a cubic phase, or a mixture of both.

7. The method for preparing the iron-based lithium lanthanum zirconate solid electrolyte according to claim 1 or 2, wherein, The preparation method further includes the following steps: Preparation of solid electrolyte powder: The bulk of the iron-based lithium lanthanum zirconate solid electrolyte is crushed to obtain the powder of the iron-based lithium lanthanum zirconate solid electrolyte.

8. A method for preparing an all-solid-state or semi-solid-state lithium battery, wherein the all-solid-state or semi-solid-state lithium battery includes lithium-ion batteries, lithium-air batteries, and lithium-sulfur batteries, wherein the electrodes, electrolytes, or separators of the battery contain bulk or powder form of an iron-based lithium lanthanum zirconate solid electrolyte. The preparation method includes preparing bulk or powder form of iron-based lithium lanthanum zirconate solid electrolyte by the preparation method according to any one of claims 1-7.

9. The method for preparing an all-solid-state or semi-solid-state lithium battery according to claim 8, wherein the all-solid-state or semi-solid-state lithium battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a lithium-rich manganese-based positive electrode material or a covalent organic framework (COF) compound.

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