A method for preparing a solid electrolyte

Abstract

This invention discloses a method for preparing a solid electrolyte, comprising adding an excess of lithium precursor to a pre-prepared solid electrolyte preform, mixing it with a solvent, ball milling the mixture, and then drying it; molding the dried mixture; and then sintering the molded body in a sintering atmosphere containing an inert gas to obtain a solid electrolyte; wherein the prepared solid electrolyte is a tantalum-doped garnet-type solid electrolyte. The solid electrolyte prepared according to the method of this invention has high ionic conductivity, which can improve the performance of full cells and is beneficial for the commercial application of lithium metal solid-state batteries.

Description

Technical Field

[0001] This invention relates to a method for preparing a solid electrolyte. More specifically, it relates to a method for preparing a tantalum-doped garnet-type solid electrolyte with high lithium-ion conductivity, as well as the solid electrolyte prepared by this method and a solid lithium metal battery containing the solid electrolyte. Background Technology

[0002] Lithium-ion batteries, with their advantages of long cycle life and high energy density, have become one of the most important energy storage devices in people's daily lives. In recent years, with the rapid development of electric vehicles, higher requirements have been placed on the energy density and safety performance of batteries. Solid-state lithium metal batteries use lithium metal as the negative electrode and a solid electrolyte instead of traditional separators and electrolytes, which not only significantly improves the energy density of the battery but also significantly reduces the risk of spontaneous combustion and explosion.

[0003] Currently, common solid-state electrolytes include oxide solid-state electrolytes, sulfide solid-state electrolytes, composite solid-state electrolytes, and the emerging halide solid-state electrolytes. Among them, oxide solid-state electrolytes have been studied the longest and have the highest probability of commercialization. For example, research shows that garnet-type LLZO solid-state electrolytes (Li7La3Zr2O) are promising candidates for commercialization. 12 After doping with Ta, the conductivity of lithium ions can be greatly improved, so the research on tantalum-doped LLZTO solid electrolytes is more extensive.

[0004] The preparation of LLZTO still faces many challenges in current technologies, such as low ceramic sheet density and low ionic conductivity. Currently, the lithium-ion conductivity of LLZTO obtained by atmospheric pressure sintering is around 0.5 mS / cm, which is still low for commercial use in lithium batteries and far from the theoretical value. To meet commercial standards, the lithium-ion conductivity of the electrolyte needs to be further improved, ideally to above 0.8 mS / cm.

[0005] Therefore, designing a method to sinter LLZTO solid electrolyte with higher ionic conductivity is crucial for the commercial application of lithium metal solid-state batteries. Summary of the Invention

[0006] The technical problem to be solved by this invention is the low lithium-ion conductivity of ceramic sheets in the current air-sintered LLZTO solid electrolyte.

[0007] To solve the above technical problems, the present invention provides a method for preparing a high-conductivity solid electrolyte ceramic sheet. This method uses simple cold pressing and sintering, and prepares the solid electrolyte ceramic sheet by controlling lithium excess and sintering atmosphere environment. The preparation process is simple, which is conducive to industrial production and application. When sintering in a protective atmosphere containing an inert gas, oxygen vacancies can be generated in the solid electrolyte, thereby improving the ionic conductivity of the ceramic sheet.

[0008] The first aspect of the present invention provides a method for preparing a solid electrolyte, comprising the following steps:

[0009] (1) Adding a precursor of excessive lithium element to a pre-prepared solid electrolyte blank, mixing with a solvent and then performing ball milling treatment, and then drying;

[0010] (2) Shaping the mixture obtained in step (1);

[0011] (3) Sintering the shaped body obtained in step (2) in a sintering atmosphere containing an inert gas to obtain a solid electrolyte, wherein

[0012] the solid electrolyte is a tantalum-doped garnet-type solid electrolyte.

[0013] In some specific embodiments, the chemical formula of the tantalum-doped garnet-type solid electrolyte prepared according to the method of the present invention is Li 7-x La3Zr 2-x Ta x O 12 , where 0 < x ≤ 1, preferably 0.5 ≤ x ≤ 0.6.

[0014] In some specific embodiments, the sintering atmosphere in step (3) contains an inert gas of at least 50% by volume, preferably at least 80% by volume, more preferably at least 95% by volume. In the present invention, the inert gas is selected from helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xn), etc.

[0015] In some specific embodiments, the inert gas in the sintering atmosphere contains argon, preferably the inert gas consists of argon.

[0016] In some specific embodiments, the sintering atmosphere in step (3) further contains one or more gases selected from hydrogen, nitrogen, oxygen, and carbon dioxide.

[0017] In some particularly preferred embodiments, the sintering atmosphere in step (3) consists of an inert gas, preferably consisting of argon.

[0018] In some specific embodiments, in step (1), the excess ratio of the number of moles of lithium precursor added relative to the molar content of lithium in the solid electrolyte is greater than or equal to 30%, preferably greater than or equal to 40%.

[0019] In some specific embodiments, in step (2), the molding is carried out by cold pressing at a pressure of 15 to 20 MPa.

[0020] In some specific embodiments, in step (3), the sintering temperature is 1000-1500℃, preferably 1050-1200℃, and more preferably 1100-1150℃.

[0021] In some specific embodiments, the preparation method of the solid electrolyte preform used in step (1) includes the following steps:

[0022] (a1) Based on the chemical composition of the solid electrolyte, the precursors of each element and the precursor of optional excess lithium element are mixed with solvent and then ball-milled and then dried.

[0023] (a2) The mixture obtained in step (a1) is pre-calcined to obtain the solid electrolyte preform.

[0024] In some specific embodiments, the precursors of each element can be oxides, hydroxides, or salts of the corresponding element. In some preferred embodiments, the precursors of each element include lithium sources, lanthanum sources, zirconium sources, and tantalum sources; preferably, the precursors of each element include LiOH·H2O, La2O3, ZrO2, and Ta2O5.

[0025] In some specific embodiments, the excess ratio of the lithium element precursor in step (a1) is 1% to 20%, preferably 5% to 15%.

[0026] In some specific embodiments, the pre-firing temperature in step (a2) is lower than the sintering temperature in step (3). Specifically, the pre-firing temperature is 700–1000°C, preferably 800–900°C.

[0027] A second aspect of the present invention provides a solid electrolyte prepared by the preparation method of the first aspect of the present invention.

[0028] In some specific embodiments, the solid electrolyte of the present invention is a tantalum-doped garnet-type solid electrolyte, preferably with the chemical formula Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 .

[0029] In some specific embodiments, the ionic conductivity of the solid electrolyte of the present invention is greater than or equal to 0.8 mS / cm, preferably greater than or equal to 1.0 mS / cm.

[0030] The third aspect of the present invention provides the application of the solid electrolyte of the second aspect of the present invention in solid lithium metal batteries.

[0031] A fourth aspect of the present invention provides a solid-state lithium metal battery, which includes the solid electrolyte described in the second aspect of the present invention.

[0032] Beneficial effects of the invention

[0033] This invention achieves a high ionic conductivity (e.g., greater than 1 × 10⁻⁶) in solid electrolyte ceramic sheets by controlling the excess lithium molar ratio during sintering and sintering under a protective atmosphere containing an inert gas (e.g., argon). -3 S / cm), which is 2-5 times higher than that of conventional air sintering (approximately 1-5 × 10⁻⁵). -4 Higher lithium-ion conductivity (S / cm) can improve the performance of the entire battery, such as better cycle performance, higher capacity retention, higher charge-discharge efficiency, and the ability to perform greater charge-discharge rates. Attached Figure Description

[0034] Figure 1 Exemplary optical images of solid electrolyte LLZTO ceramic sheets prepared under different sintering atmospheres in Example 5 of the present invention are shown. The sintering atmospheres from left to right are: (A) air; (B) nitrogen; (C) oxygen; (D) argon + hydrogen; (E) argon + oxygen; (F) argon.

[0035] Figure 2 Exemplary impedance test diagrams of solid electrolytes prepared according to embodiments and comparative examples of the present invention are shown. The circular markings on the left represent LLZTO ceramic sheets sintered in air; the triangular markings on the right represent LLZTO ceramic sheets sintered in argon.

[0036] Figure 3 Optical images of LLZTO ceramic sheets sintered under different lithium excess conditions in Example 4 of the present invention are shown. (A) shows sintering in argon gas, and (B) shows sintering in air. The lithium excess ratios from left to right are 10%, 20%, 30%, and 40%, respectively.

[0037] Figure 4 The XRD pattern of a solid electrolyte LLZTO ceramic sheet prepared according to an embodiment of the present invention is shown. The preparation conditions were sintering in argon atmosphere with a lithium excess of 40%.

[0038] Figure 5SEM images of the solid electrolyte LLZTO ceramic sheets prepared according to the embodiments and comparative examples of the present invention are shown. (A) and (B) are surface SEM images, and (C) and (D) are cross-sectional SEM images. The preparation conditions are sintering in argon. In (A) and (C), the lithium excess is 40%, and in (B) and (D), the lithium excess is 10%. Detailed Description of the Invention

[0039] The present invention will be further described below by way of specific embodiments. Unless otherwise defined, the terms used herein have the same meaning as commonly understood by those of ordinary skill in the art. The numerical limits or ranges stated herein include endpoints and specifically include all values and sub-ranges within the numerical limits or ranges.

[0040] The first aspect of the present invention provides a method for preparing a solid electrolyte, comprising the following steps:

[0041] (1) Adding an excessive precursor of lithium element to a pre-prepared solid electrolyte blank, mixing with a solvent, followed by ball milling and then drying;

[0042] (2) Shaping the mixture obtained in step (1);

[0043] (3) Sintering the shaped body obtained in step (2) in a sintering atmosphere containing an inert gas to obtain a solid electrolyte, wherein

[0044] the solid electrolyte is a tantalum-doped garnet-type solid electrolyte.

[0045] In some specific embodiments of the present invention, the chemical formula of the tantalum-doped garnet-type solid electrolyte prepared according to the method of the present invention is Li 7-x La3Zr 2-x Ta x O 12 , where 0 < x ≤ 1, preferably 0.5 ≤ x ≤ 0.6.

[0046] In some particularly preferred embodiments, the chemical formula of the tantalum-doped garnet-type solid electrolyte prepared according to the method of the present invention is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 .

[0047] In some specific embodiments of the present invention, the sintering atmosphere in step (3) contains at least 50% by volume of inert gas, preferably at least 80% by volume, and more preferably at least 95% by volume. In the present invention, inert gas refers to the gaseous element corresponding to Group 0 elements in the periodic table, including helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xn), etc. Inert gases have very low chemical reactivity and can be used as protective gases under high-temperature conditions. Under the preparation conditions of the present invention, they essentially do not react with the solid electrolyte of the present invention or any of its precursors or intermediates, thus avoiding potential side reactions during the preparation process and ensuring that the prepared solid electrolyte has an ideal crystal structure.

[0048] In some specific embodiments of the present invention, the inert gas in the sintering atmosphere comprises argon, and preferably the inert gas is composed of argon. The expression "composed of argon" means that the argon used is commercially available industrial or laboratory argon with a purity greater than 99%, greater than 99.9%, or greater than 99.99%, but may still contain unavoidable impurities.

[0049] In some specific embodiments of the present invention, the sintering atmosphere in step (3) further includes one or more gases selected from hydrogen, nitrogen, oxygen, and carbon dioxide. The content of the gases other than the aforementioned inert gases in the sintering atmosphere is less than or equal to 50% by volume, preferably less than or equal to 20% by volume, and more preferably less than or equal to 5% by volume.

[0050] In the preparation method of the solid electrolyte of the present invention, an excess of lithium source is required. In the context of the present invention, "excess" means that the molar number of lithium precursors added during the preparation process is greater than the molar content of lithium in the solid electrolyte calculated based on the chemical composition of the solid electrolyte according to the molar number of other elemental precursors (e.g., lanthanum source, zirconium source, tantalum source, etc.). For example, the chemical formula of the tantalum-doped garnet-type solid electrolyte prepared by the present invention is Li. 7-x La3Zr 2-x Ta x O 12 If the molar ratio of lithium, lanthanum, zirconium, and tantalum elements in the lithium source, lanthanum source, zirconium source, and tantalum source is Li:La:Zr:Ta=M:3:2-x:x, then the molar ratio of lithium element in the lithium source, M, is greater than 7-x; the excess percentage is calculated as (M-(7-x)) / (7-x).

[0051] In some particularly preferred embodiments, the sintering atmosphere in step (3) consists of an inert gas, preferably argon. That is, the sintering atmosphere does not contain any gas other than an inert gas.

[0052] In some specific embodiments of the present invention, in step (1), the excess proportion of the number of moles of lithium precursor added relative to the molar content of lithium in the solid electrolyte is greater than or equal to 30%, preferably greater than or equal to 40%. According to research based on the present invention, providing an excess lithium source not only compensates for the volatilization of lithium components during high-temperature sintering, but also, when the excess lithium source is greater than or equal to 30%, preferably greater than or equal to 40%, further improves the ionic conductivity of the prepared solid electrolyte.

[0053] In some specific embodiments of the present invention, in step (2), the forming is performed by cold pressing at a pressure of 15-20 MPa. For example, the ball-milled and dried powder can be placed in a circular mold with a diameter of 15 mm and pressed into a sheet under a pressure of 15-20 MPa to obtain a shaped disc.

[0054] In some specific embodiments of the present invention, in step (3), the sintering temperature is 1000-1500℃, preferably 1050-1200℃, and more preferably 1100-1150℃. In some specific embodiments of the present invention, in step (3), the heating rate is 5-20℃ / min, preferably 10℃ / min; and the sintering time is 6-24 hours, preferably 12 hours.

[0055] In some specific embodiments of the present invention, the method for preparing the solid electrolyte preform used in step (1) includes the following steps:

[0056] (a1) Based on the chemical composition of the solid electrolyte, the precursors of each element and the precursor of optional excess lithium element are mixed with solvent and then ball-milled and then dried.

[0057] (a2) The mixture obtained in step (a1) is pre-calcined to obtain the solid electrolyte preform.

[0058] In some specific embodiments of the present invention, the precursors of each element can be oxides, hydroxides, or salts (e.g., nitrates) of the corresponding element. For example, lithium hydroxide monohydrate (LiOH·H2O) can be used as a lithium source, La2O3 can be used as a lanthanum source, and ZrO2 can be used as a zirconium source. Ta2O5 can be used as a tantalum source. The precursors can be pretreated according to the actual situation. For example, when using La2O3, it needs to be calcined at above 900°C for more than 12 hours in advance to remove moisture. In some preferred embodiments, the precursors of each element include LiOH·H2O, La2O3, ZrO2, and Ta2O5.

[0059] In some specific embodiments of the present invention, the excess proportion of the lithium precursor in step (a1) is 1% to 20%, preferably 5% to 15%. In the preparation of the solid electrolyte preform, the definition of excess lithium is the same as above, that is, the molar number of lithium precursor added in step (a1) is greater than the molar content of lithium in the solid electrolyte preform calculated based on the chemical composition of the solid electrolyte according to the molar number of other element precursors (e.g., lanthanum source, zirconium source, tantalum source, etc.).

[0060] In some specific embodiments of the present invention, the pre-firing temperature in step (a2) is lower than the sintering temperature in step (3). Specifically, the pre-firing temperature in step (a2) is 700–1000°C, preferably 800–900°C. In some specific embodiments of the present invention, the heating rate in step (2a) is 5–20°C / min, preferably 10°C / min; the pre-firing time is 6–24 hours, preferably 12 hours. There are no particular limitations on the atmosphere used in the pre-firing process; air can be used for ease of operation and cost reduction.

[0061] In addition, in some specific embodiments of the present invention, in the two ball milling steps (step (a1) and step (1)), the solid-liquid ratio of the solid (i.e., the precursor or preform) to the solvent can be 1:1 to 5, the ball-to-material ratio can be 1:1 to 10, the ball milling time can be 1 to 24 hours, the drying temperature can be 50 to 200°C, and the drying time can be 2 to 24 hours. Furthermore, the solvent can be isopropanol.

[0062] In one exemplary embodiment of the present invention, the chemical formula is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The preparation method of the solid electrolyte includes the following steps:

[0063] (a1) Based on the chemical composition of the solid electrolyte and with a lithium source in excess of 10%, the precursors of each element were mixed with the solvent in a molar ratio of LiOH·H2O:La2O3:ZrO2:Ta2O5 = 7.04:1.5:1.4:0.3 and then ball-milled and dried.

[0064] (a2) The mixture obtained in step (a1) is pre-calcined at 900°C to obtain a solid electrolyte preform;

[0065] (1) Add a lithium precursor LiOH·H2O with a molar excess of 40% to the solid electrolyte preform prepared in step (a2), mix with solvent and then ball mill, followed by drying;

[0066] (2) Cold press the mixture obtained in step (1);

[0067] (3) Sinter the formed body obtained in step (2) in an argon sintering atmosphere to obtain a solid electrolyte with the chemical formula Li 6.4 La3Zr 1.4 Ta 0.6 O 12 .

[0068] The inventors' research found that in the preparation method of the solid electrolyte of the present invention, after first preparing the solid electrolyte blank and then performing secondary ball milling, the powder particle size can be made finer, the pressed and sintered LLZTO is denser, and the ionic conductivity is higher. After the first ball milling for preparing the blank and then low-temperature sintering, the main purpose is to form a phase of the powder to obtain the LLZTO phase. The 10% excess lithium source added in the first ball milling can supplement the loss of lithium when calcining the powder at 900 degrees. In this step, if the excess ratio of the lithium source is insufficient, the phase formation of the sintered LLZTO powder is poor, and the LLZTO phase cannot be fully formed, affecting the final solid electrolyte product; if the excess ratio of the lithium source is too large, more impurity phases will be introduced. The purpose of the second ball milling for preparing the solid electrolyte is to refine the impurity phases, coarse grains, and phases with low activity in the LLZTO phase of the solid electrolyte blank, improving the sintering activity of the subsequent ceramic sheets; and further adding an excess lithium source during the secondary ball milling can make the supplemented lithium hydroxide fully mixed with the phase powder to be reacted, which is beneficial to the full reaction during the secondary sintering. It is proved by SEM and XRD characterizations that when supplementing an excess lithium source with a molar ratio of 40% during the secondary ball milling and sintering, a solid electrolyte with large LLZTO grains, few grain boundaries, no pores, and no other impurity phases can be formed. ​​​​​​​​​​​​​​​​​​In some particularly preferred embodiments, the chemical formula of the tantalum-doped garnet-type solid electrolyte according to the present invention is Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 .

[0073] The solid electrolyte of the second aspect of the present invention has an ionic conductivity superior to that of prior art solid electrolytes. In some specific embodiments of the present invention, the ionic conductivity of the solid electrolyte of the present invention is greater than or equal to 0.8 mS / cm, preferably greater than or equal to 1.0 mS / cm.

[0074] The third aspect of the present invention provides the application of the solid electrolyte of the second aspect of the present invention in solid lithium metal batteries.

[0075] A fourth aspect of this invention provides a solid-state lithium metal battery. In some specific embodiments, the solid-state lithium metal battery of this invention includes the solid electrolyte described in the second aspect of this invention. There are no particular limitations on the materials and preparation methods for other parts of the lithium battery besides the solid electrolyte; conventional materials and preparation methods in the art can be used.

[0076] Example

[0077] The present invention will be described in detail below through embodiments, which are not intended to limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0078] Example 1: Preparation of LLZTO solid electrolyte preform

[0079] To prepare the chemical formula Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The following raw materials were weighed according to the stoichiometric ratio and with a lithium source excess of 10% in molar ratio for the LLZTO solid electrolyte: 3.3198 g of lithium hydroxide monohydrate (LiOH·H2O), 5.4948 g of lanthanum oxide (La2O3), 1.9396 g of zirconium oxide (ZrO2), and 1.4945 g of tantalum oxide (Ta2O5).

[0080] The weighed precursor powders of each element were placed in a zirconia ball mill jar, and 9-10 mL of isopropanol and 50 g of zirconia ball milling beads were added. The mixture was wet-milled at 500 rpm for 3 hours until homogeneous to obtain a mixed powder. The mixed powder was then placed in an oven and dried at 80°C to completely remove the solvent isopropanol.

[0081] The powder was placed in a muffle furnace for pre-calcination. The temperature was increased from 50°C to 900°C at a heating rate of 10°C / min and held for 12 hours. Then, the temperature was reduced to 500°C at a cooling rate of 10°C / min and allowed to cool naturally to room temperature before being removed to obtain the pre-calcined LLZTO solid electrolyte preform.

[0082] Unless otherwise specified, the LLZTO solid electrolyte preform prepared above will be used as the starting material in the subsequent embodiments for the preparation of LLZTO solid electrolyte.

[0083] Example 2 Preparation of LLZTO solid electrolyte

[0084] Weigh 10g of pre-calcined LLZTO solid electrolyte preform, and weigh lithium hydroxide monohydrate (LiOH·H2O) according to the required Li excess molar ratio. Place the mixture in a zirconia ball mill jar, add 8-10mL of isopropanol and 50g of zirconia ball milling beads, and wet ball mill at 500rpm for 8 hours to obtain a homogeneous powder. Then place the above mixed powder in an oven and dry it at 80℃ to completely remove the solvent isopropanol.

[0085] 1.1g of dried powder was weighed and placed in a circular mold with a diameter of 15mm. The molded disc was pressed under a pressure of 15-20MPa to obtain a shaped disc. Then, using a crucible as a carrier, the shaped disc was placed in a muffle furnace. Under the appropriate sintering atmosphere, the temperature was increased from 50℃ to 1150℃ at a heating rate of 10℃ / min and held for 12h. After that, the temperature was decreased to 500℃ at a cooling rate of 5℃ / min and then allowed to cool naturally to room temperature to obtain the LLZTO solid electrolyte.

[0086] Example 3 Characterization of LLZTO solid electrolyte

[0087] After sintering, the LLZTO ceramic sheets are polished until smooth, then soaked in dilute hydrochloric acid for 30 seconds to remove impurities such as Li2CO3 and LiOH from the surface, and then placed in a glove box for later use.

[0088] The diameter and thickness of LLZTO ceramic sheets are measured using a micrometer.

[0089] To test the ionic conductivity of the LLZTO solid electrolyte, a layer of Ag was deposited on each side of the LLZTO electrolyte sheet using a thermal evaporation coating apparatus, forming an Ag / LLZTO / Ag blocking system, which was then encapsulated using a coin cell. AC impedance was measured using MetrohmAutolab at an AC voltage of 10 mV and a frequency of 1-10 MHz. After measuring the AC impedance of the solid electrolyte ceramic sheet, the ionic conductivity σ was calculated using the formula σ = L / RS, where L is the thickness of the ceramic sheet, R is the AC impedance of the ceramic sheet, and S is the area of ​​one side of the ceramic sheet.

[0090] In addition, XRD and SEM tests were performed on some LLZTO ceramic sheets.

[0091] The XRD testing instrument is the Rigaku MiniFlex from Japan, with a scanning angle of 10-60° and a scanning rate of 8° / minute.

[0092] The SEM instrument used was a Zeiss Sigma 300, which was used to directly test the sintered solid electrolyte. The tests included surface SEM and cross-sectional SEM.

[0093] Example 4: Effect of excess lithium molar ratio on the conductivity of LLZTO solid electrolyte

[0094] To determine the effects of different sintering conditions on parameters such as conductivity of LLZTO ceramic sheets, the conductivity of lithium ions in LLZTO ceramic sheets sintered under different excess lithium molar ratios was first investigated.

[0095] LLZTO solid electrolyte was prepared according to the method described in Example 2 above. The excess molar ratio of the newly added lithium source (LiOH·H2O) relative to the molar content of lithium in the LLZTO solid electrolyte preform was 10%, 20%, 30%, and 40%, respectively. Air and argon were used as the sintering atmosphere, respectively. After the LLZTO solid electrolyte was prepared, various parameters of the obtained LLZTO ceramic sheet were measured according to the method described in Example 3. The results are listed in Table 1.

[0096] Table 1. Parameters and conductivity of LLZTO ceramic sheets prepared under different lithium excess conditions.

[0097]

[0098]

[0099] Furthermore, optical images of LLZTO ceramic sheets sintered under the aforementioned different lithium excess conditions are shown in... Figure 3 As shown in the image. Figure 3 (A) From left to right: LLZTO solid electrolytes with lithium excess molar ratios of 10%, 20%, 30%, and 40% sintered in argon gas; Figure 3 (B) From left to right: LLZTO solid electrolytes sintered in air with lithium excess molar ratios of 10%, 20%, 30%, and 40%. Figure 3 As can be seen, the LLZTO solid electrolytes obtained after sintering are all regular-shaped discs. The LLZTO solid electrolyte sintered in argon is white in color, and its color does not change significantly with the increase of the lithium excess molar ratio. In contrast, the color of the LLZTO solid electrolyte sintered in argon gradually becomes yellower and darker with the increase of the lithium excess molar ratio, which can indirectly indicate the increase of impurities in the electrolyte.

[0100] By comparing the characterization data of solid electrolytes sintered in air and argon atmospheres, it was found that during argon sintering, the ionic conductivity of LLZTO ceramic sheets increased continuously with the increase of lithium excess ratio; the highest ionic conductivity was observed at a lithium excess ratio of 40%. However, during air sintering, even with an increase in the lithium excess ratio, the ionic conductivity of the LLZTO ceramic sheets remained at a low level and did not increase with the increase in lithium excess ratio. This is because excess lithium may undergo side reactions with the sintering atmosphere, generating impurities such as LiCO3, LiOH, and Li3N, which are incompatible with the LLZTO crystal structure, thus affecting the structure and ionic conductivity of the solid electrolyte.

[0101] like Figure 4 The XRD pattern shows that the LLZTO solid electrolyte sintered in argon with a lithium excess of 40% exhibits characteristic peaks of the LLZTO crystalline phase, indicating the formation of a Li₂O₃ solid electrolyte. 6.4 La3Zr 1.4 Ta 0.6 O 12 The LLZTO solid electrolyte was observed. The XRD pattern showed no characteristic peaks other than the LLZTO phase, indicating that there were essentially no other impurity phases in the solid electrolyte, and that the excess lithium precursor did not affect the crystal structure of the solid electrolyte.

[0102] like Figure 5 As shown in the SEM images, compared to a 10% Li excess ratio, the synthesized LLZTO crystals with a 40% Li excess ratio are larger, have fewer grain boundaries, and are free of pores, indicating that they are essentially free of impurities. However, when the Li excess ratio is low, the loss due to lithium source volatilization results in insufficient Li in the sintered solid electrolyte, which may affect the crystal structure.

[0103] Further experiments by the inventors showed that if the excess Li ratio was increased further, the amount of lithium-containing impurity phases (such as LiOH·H₂O, LiOH, Li₂O, etc.) in the sintered LLZTO ceramic sheet would increase, and the ionic conductivity would decrease. Therefore, in this invention, the most preferred excess Li ratio is 40%.

[0104] Example 5: Effect of sintering atmosphere on the conductivity of LLZTO solid electrolyte

[0105] To further determine the effects of different sintering atmospheres on parameters such as the conductivity of LLZTO ceramic sheets, the lithium-ion conductivity of LLZTO ceramic sheets sintered in different sintering atmospheres was investigated under the condition of a 40% lithium excess ratio.

[0106] LLZTO solid electrolytes were prepared according to the method described in Example 2 above. The excess molar ratio of the newly added lithium source (LiOH·H2O) relative to the molar content of lithium in the LLZTO solid electrolyte preform was 40%. The sintering atmospheres used were air, argon, nitrogen, oxygen, a mixture of argon (95 vol%) and hydrogen (5 vol%), and a mixture of argon (95 vol%) and oxygen (5 vol%). After the LLZTO solid electrolyte was prepared, the parameters of the obtained LLZTO ceramic sheets were measured according to the method described in Example 3. The results are listed in Table 2.

[0107] Table 2. Parameters and conductivity of LLZTO ceramic sheets prepared under different sintering atmospheres.

[0108]

[0109]

[0110] Furthermore, optical images of LLZTO ceramic sheets sintered in the above different atmospheres are shown in... Figure 1 The diagram shows that the sintering atmospheres, in order, are: (A) air; (B) nitrogen; (C) oxygen; (D) argon + hydrogen; (E) argon + oxygen; (F) argon. From... Figure 1 As can be seen, the LLZTO solid electrolytes obtained after sintering are all regular-shaped discs, but there are some differences in color. The LLZTO solid electrolyte sintered in argon (F) is white; the LLZTO solid electrolyte sintered in argon and hydrogen (D) is basically white; the LLZTO solid electrolyte sintered in other atmospheres is darker and yellowish, which can indicate the increase of impurities in the electrolyte.

[0111] Figure 2 An exemplary impedance test diagram of LLZTO ceramic sheets sintered in air and argon is shown. The circular marking on the left indicates LLZTO ceramic sheets sintered in air, and the triangular marking on the right indicates LLZTO ceramic sheets sintered in argon.

[0112] Characterization data of solid electrolytes sintered under different atmospheres revealed that the ionic conductivity of LLZTO ceramic sheets sintered in an inert gas atmosphere, such as argon, was significantly better than that sintered in air. Furthermore, the ionic conductivity of LLZTO ceramic sheets sintered in pure nitrogen and pure oxygen atmospheres was similar to that sintered in air. This is because a larger amount of Li3N impurities may be generated in a nitrogen atmosphere, while a large amount of LiCO3, LiOH, and other impurities are generated in an oxygen atmosphere, affecting the density and ionic conductivity of LLZTO. When argon is mixed with a reducing gas such as hydrogen, the ionic conductivity of the resulting solid electrolyte is similar to that of a pure argon atmosphere. However, when argon is mixed with an oxidizing gas (oxygen), even with an oxygen content of only 5%, the ionic conductivity of the resulting solid electrolyte is significantly reduced. This indicates that argon and a trace reducing atmosphere promote the formation of LLZTO crystals and inhibit the formation of impurities such as LiCO3 and LiOH on the LLZTO surface. On the other hand, an oxidizing atmosphere (oxygen) promotes impurity formation and does not have an inhibitory effect.

[0113] In summary, this invention enables the preparation of tantalum-doped garnet-type solid electrolytes with high ionic conductivity by sintering in a protective atmosphere containing inert gas and controlling the excess molar ratio of lithium during the sintering process, which is beneficial for the commercial application of lithium metal solid batteries.

[0114] The foregoing embodiments have described exemplary implementations of the present invention, but the present invention is not limited thereto. Those skilled in the art should understand that the above embodiments are merely illustrative, and the specific implementations and examples of the present invention should not be considered as limiting the scope of the present invention. Changes and modifications can be made to the implementations within the scope of the present invention, and such changes and modifications should fall within the protection scope of the present invention.

Claims

1. A method of preparing a solid-state electrolyte, characterized by, The production method comprises the following steps: (1) adding an excess amount of a lithium element precursor to a previously prepared solid electrolyte green material, mixing with a solvent, and then performing ball milling, followed by drying; (2) performing molding on the mixture obtained in step (1); (3) performing sintering on the molded body obtained in step (2) in a sintering atmosphere containing an inert gas to obtain a solid electrolyte, wherein in the step (1), the excess ratio of the number of moles of the lithium element precursor added to the molar content of lithium elements in the solid electrolyte is 30% to 40%; the sintering atmosphere in the step (3) contains an inert gas of 95% or more by volume; the inert gas consists of argon; and The solid-state electrolyte is a tantalum-doped garnet-type solid-state electrolyte, and a chemical formula of the tantalum-doped garnet-type solid-state electrolyte is Li 7-x La3Zr 2-x Ta x O 12 wherein 0.5≤x≤0.

6.

2. The production method according to claim 1, characterized by, the sintering atmosphere in the step (3) further contains one or more gases selected from hydrogen, nitrogen, oxygen, and carbon dioxide.

3. The production method according to claim 1, characterized by, In the step (2), molding is performed by cold pressing at a pressure of 15 to 20 MPa.

4. The method of claim 1, wherein, In the step (3), the sintering temperature is 1000 to 1500°C.

5. The preparation method according to claim 4, characterized in that, In the step (3), the sintering temperature is 1050 to 1200°C.

6. The preparation method according to claim 4, characterized in that, In the step (3), the sintering temperature is 1100 to 1150°C.

7. The production method according to any one of claims 1 to 6, characterized by, The production method of the solid electrolyte green material in the step (1) comprises the following steps: (a1) mixing each element precursor and optionally an excess amount of a lithium element precursor with a solvent, and then performing ball milling, followed by drying, according to the chemical composition of the solid electrolyte; (a2) performing pre-sintering on the mixture obtained in step (a1) to obtain the solid electrolyte green material.

8. The preparation method according to claim 7, characterized in that, The each element precursor includes LiOH·H2O, La2O3, ZrO2, and Ta2O5.

9. The preparation method according to claim 7, characterized in that, The excess ratio of the number of moles of the lithium element precursor in step (a1) is 1% to 20%.

10. The method of claim 9, wherein, The excess ratio of the number of moles of the lithium element precursor in step (a1) is 5% to 15%.

11. The preparation method according to claim 7, characterized in that, The pre-sintering temperature in the step (a2) is lower than the sintering temperature in the step (3).

12. The method of claim 11, wherein, The pre-sintering temperature in the step (a2) is 700 to 1000°C.

13. The preparation method according to claim 11, characterized in that, The pre-sintering temperature in the step (a2) is 800 to 900°C.

14. A solid state electrolyte, characterized in that, The solid electrolyte is produced by the production method according to any one of claims 1 to 13.

15. The solid-state electrolyte of claim 14, wherein, The ionic conductivity of the solid electrolyte is 0.8 mS / cm or more.

16. The solid-state electrolyte of claim 15, wherein, The ionic conductivity of the solid electrolyte is 1.0 mS / cm or more.

17. Use of the solid electrolyte according to any one of claims 14 to 16 in a solid-state lithium metal battery.

18. A solid-state lithium metal battery, characterized in that, The solid-state lithium metal battery includes the solid electrolyte according to any one of claims 14 to 16.

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