Powder for highly stable oxide-based solid electrolytes, highly stable oxide-based solid electrolytes containing the same, and methods for producing the same.

Abstract

To efficiently obtain a sintered body with excellent sinterability and structural stability while achieving high ionic conductivity and low electronic conductivity in a solid electrolyte. [Solution] The present invention aims to provide an oxide-based solid electrolyte powder that can produce a sintered body with high sinterability, structural stability, and high density without using a mother powder (mo powder), and a method for producing the same. Furthermore, the present invention aims to provide a technology that can efficiently manufacture solid electrolyte sintered bodies possessing both high ionic conductivity and interfacial stability with lithium.

Description

[Technical Field]

[0001] The present invention relates to a powder for solid electrolytes, a solid electrolyte containing the same, and a method for producing the same, more specifically, to a garnet-based Li7La3Zr2O as the solid electrolyte. 12 This invention relates to a powder for solid electrolytes that contains (LLZ) and has a sol-gel coating layer containing a Li-Al-O compound on its surface, and which can be sintered without using mother powder, as well as a solid electrolyte containing the same, and a method for producing the same. [Background technology]

[0002] Lithium-ion batteries (LIBs) are widely used in electric vehicles, energy storage devices, and portable electronic devices due to their high energy density and long lifespan. While these lithium-ion batteries generally use liquid electrolytes, safety concerns such as leakage, ignition, and explosion have been raised. Therefore, research into all-solid-state batteries (ASSBs) using solid electrolytes is actively progressing.

[0003] Solid electrolytes require not only excellent electrical conductivity and lithium-ion conductivity, but also high chemical and thermal stability, as well as interfacial stability with the negative and positive electrode materials. One solid electrolyte that satisfies these conditions is Li7La3Zr2O, which has a garnet structure. 12 (LLZ) is available. This material exhibits high lithium-ion conductivity and excellent chemical stability, and provides particularly excellent electrical properties and stability as an oxide-based solid electrolyte.

[0004] However, the manufacturing process of solid electrolytes using LLZ generally exhibits low sinterability, requiring the addition of mother powder or prolonged heat treatment at high temperatures to obtain a high-density sintered body. These manufacturing conditions lead to increased process costs and decreased productivity, as well as potential problems such as structural collapse and performance degradation due to the volatilization of lithium components.

[0005] Therefore, there is a need to develop powders for solid electrolytes that can ensure sinterability without using mopowder. To this end, research is underway to improve sinterability and ensure structural stability by coating the surface of solid electrolytes with Li-Al-O compounds through a sol-gel process. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the problem that the present invention aims to solve is to overcome the problems of the prior art described above and to provide an oxide-based solid electrolyte powder having high sinterability, excellent structural stability and high density without using a master powder, and to provide a highly stable oxide-based solid electrolyte powder containing this, a sintered body formed by sintering this powder, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present invention provides a powder and an oxide-based solid electrolyte powder having a coating layer containing a Li-Al-O compound formed on the surface of the powder.

[0008] In one embodiment of the present invention, the powder may be an oxide-based solid electrolyte powder that does not contain a Li-Al-O compound.

[0009] In one embodiment of the present invention, the powder is garnet-based Li7La3Zr2O 12 (LLZ) or Ta-doped Li 6.4 La3Zr 1.4 Ta 0.6 O12 It may be any of the (LLZT) powders.

[0010] In one embodiment of the present invention, the coating layer may be coated by a sol-gel method with a content of 0.5 wt% to 5.0 wt% with respect to the powder.

[0011] The present invention provides a method for producing an oxide-based solid electrolyte sintered body, including a step of coating a powder with a material containing a Li-Al-O compound, and a step of sintering the coated powder without using a mother powder.

[0012] In one embodiment of the present invention, the coating step may be performed using a sol-gel solution containing a lithium precursor and an aluminum precursor.

[0013] In one embodiment of the present invention, the powder is garnet-based Li7La3Zr2O 12 (LLZ) or Li doped with Ta 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZT) powder.

[0014] In one embodiment of the present invention, the powder may not contain a Li-Al-O compound.

[0015] In one embodiment of the present invention, the manufacturing method may be directly sintered after the coating step without a separate crystallization step.

[0016] In one embodiment of the present invention, the sintering treatment may be performed at a temperature of 1000 °C to 1100 °C in an oxygen atmosphere.

[0017] In one embodiment of the present invention, the sintered sintered body may have a shrinkage rate increased by 15% or more and a relative density of 95% or more as compared with the case where the uncoated powder is sintered without a mother powder.

[0018] In one embodiment of the present invention, the sintered body may maintain a cubic phase without structural collapse and may not generate a secondary phase.

[0019] The present invention provides a core containing Ta-doped Li7La3Zr2O 12 (LLZT), and an oxide-based solid electrolyte sintered body containing a Li-Al-O compound distributed at the particle interface of the core, having a relative density of 95% or more and a cubic phase.

[0020] In one embodiment of the present invention, the oxide-based solid electrolyte sintered body may be included in a all-solid-state secondary battery.

Advantages of the Invention

[0021] According to the present invention, it is possible to provide a powder for an oxide-based solid electrolyte having high sinterability, excellent structural stability, and high density without using a mother powder. Furthermore, the solid electrolyte sintered body produced using the powder maintains a stable cubic phase without structural collapse and exhibits excellent properties such as lithium volatilization suppression, interface stability, high density, and high ionic conductivity. In addition, since a high-performance solid electrolyte sintered body can be manufactured only by coating a Li-Al-O compound by a sol-gel method without undergoing an additional crystallization process, simplification of the manufacturing process and cost reduction are possible. Also, compared with the conventional method of directly adding a mother powder, LiAlO2 powder, or Al2O3 powder, the structure and manufacturing method according to the present invention show a significant performance difference, and it has been confirmed that it is a highly practical technology.

Brief Description of the Drawings

[0022] [Figure 1] It is a flowchart showing the manufacturing process of an oxide-based solid electrolyte according to an embodiment of the present invention. [Figure 2] It is a photograph showing the appearance of a solid electrolyte pellet manufactured according to an example of the present invention. [Figure 3] It is a photograph showing the appearance of a solid electrolyte pellet manufactured according to a comparative example. [Figure 4]This is an image of LLZT powder coated with a sol-gel of a Li-Al-O compound before sintering. [Figure 5] This is an image of a sintered body (LAO@LLZT) obtained after sintering sol-gel coated LLZT powder without the mother powder. [Figure 6] This is an image of a solid electrolyte sintered body manufactured by large-area sintering. [Figure 7] This graph shows the measurement results of the density of the manufactured sintered body. [Figure 8] This graph shows a comparison of the relative densities of the manufactured sintered bodies. [Figure 9] This figure shows the results of XRD analysis of the sintered body. [Figure 10] This is a SEM image of the fracture surface of a sintered body. [Figure 11] This figure shows the elemental analysis results of the sintered body using ICP. [Figure 12] This figure shows the results of XPS analysis of the surface of a sintered body. [Figure 13] This figure shows the results of electrical conductivity measurements of a sintered body. [Figure 14] This graph shows a comparison of electrical conductivity with that of a comparative example. [Figure 15] This is a schematic diagram showing the manufacturing process of electrical conductivity test specimens. [Figure 16] This is a schematic diagram showing the manufacturing process of test specimens used for measuring interfacial resistance with lithium. [Figure 17] This figure shows the measurement results of the interfacial resistance between the sintered body and lithium. [Figure 18] This figure shows the measurement results for long-term stability and critical current density with lithium. [Figure 19] This image shows an LLZT sintered body with added LiAlO2 powder and a graph comparing its properties. [Figure 20] This image shows an LLZT sintered body with added Al2O3 powder and a graph comparing its properties. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0024] Before describing the present invention in detail, the terms and phrases used herein should not be interpreted as being unconditionally limited to their ordinary or dictionary meanings, but rather the inventors have appropriately defined and used the concepts of various terms in order to best describe their invention.

[0025] Furthermore, these terms and phrases must be interpreted in a way that is consistent with the technical concept of the present invention.

[0026] In other words, the terms used herein are used to describe preferred embodiments of the present invention and are not intended to specifically limit the scope of the invention.

[0027] It should be understood that these terms are defined in consideration of the diverse possibilities of the present invention.

[0028] Furthermore, in this specification, even if a word is expressed in the singular form, it shall be interpreted as including the plural form unless the context clearly indicates a different meaning. Conversely, it should be understood that even if a word is expressed in the plural form, it may still include the meaning of the singular form.

[0029] Furthermore, throughout this specification, where it is stated that a component “includes” another component, unless otherwise stated, it means that the component may further include the other component rather than excluding it.

[0030] In addition, when a component is described as being "located inside" or "connected to" another component, it may be installed in direct connection or contact with the other component, or it may be installed at a certain distance apart. In the latter case, there may be a third component or means for fixing or connecting the component to the other component. Note that the description of the third component or means may be omitted.

[0031] On the other hand, if it is stated that one component is "directly connected" or "in direct contact" with another component, it should be understood that there is no third component or means.

[0032] Furthermore, other expressions describing the relationships between constituent elements, such as "between" and "immediately adjacent," or "adjacent to" and "directly adjacent to," should be interpreted in the same sense.

[0033] Furthermore, while terms such as "one side," "the other side," "one side," "the other side," "first," and "second" are used in this specification to clearly distinguish one component from another, their meanings are not limited.

[0034] Furthermore, when using position-related terms such as "up," "down," "left," and "right," it should be understood that these terms indicate the relative position of the component on the drawing, and not its absolute position.

[0035] Furthermore, it should be understood that in the specification of this invention, terms such as "~part," "~machine," "module," and "device," when used, mean a unit capable of processing one or more functions or operations, which may consist of hardware, software, or a combination of both.

[0036] The size, position, connection relationships, etc., of each component constituting the present invention shown in the attached drawings may be exaggerated, reduced, or omitted in order to clearly convey the concept of the present invention or for the sake of explanatory convenience, and therefore their proportions and scales may not be strictly accurate.

[0037] In describing the present invention, detailed explanations of configurations that may unnecessarily obscure the gist of the invention, such as those relating to known technologies, may be omitted below. This invention relates to a new powder for solid electrolytes, obtained by directly coating the powder surface with a Li-Al-O compound using a sol-gel method, in order to solve the sintering problems in conventional oxide-based solid electrolytes. This makes it possible to manufacture high-density solid electrolytes using a sintering process that does not require pressure, without using a mother powder, which is a factor in increasing costs.

[0038] Here, "Li-Al-O compound" is a general term for compounds containing lithium (Li), aluminum (Al), and oxygen (O). The coating layer is formed on the powder surface and plays a role in suppressing the volatilization of lithium during the sintering process and increasing the bonding force between particles to maximize sinterability. According to embodiments of the present invention, the compound may be LiAlO2 or Li5AlO4, but is not limited thereto, and is a concept that includes all oxides of various compositions that can be formed from lithium and aluminum precursors.

[0039] The technical feature of the present invention lies in the fact that the Li-Al-O compound is not simply added as a powder, but is directly formed as a "coating layer" on the powder surface. In comparative examples where LiAlO2 or Al2O3 powder was simply added, problems such as the sintered body breaking down or the crystallinity collapsing occurred when sintering was performed without a mother powder. In contrast, only when the coating layer was formed by the sol-gel method according to the present invention was it possible to produce a high-density electrolyte membrane that was structurally stable and free from bending or fracture, even without a mother powder.

[0040] Furthermore, it was confirmed that it is possible to increase the pellet size by manufacturing multiple membranes using a heating furnace. This enables mass production and scaling up of electrolyte membranes, making it possible to produce large-scale, high-energy-density oxide-based all-solid-state batteries.

[0041] The present invention will be described in more detail below through examples and experimental cases. However, the scope of the present invention is not limited thereto.

[0042] Examples

[0043] In one embodiment of the present invention, a garnet-based Li7La3Zr2O synthesized in the cubic phase is used as the powder for the solid electrolyte. 12 (LLZ) type with Ta-doped Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZT) powder was prepared.

[0044] In Example 1, sintering was performed at 1100 degrees Celsius for 10 hours under an oxygen atmosphere without crystallization treatment after sol-gel coating. In Example 2, sintering was performed under the same conditions as in Example 1 after crystallization treatment following sol-gel coating. In Comparative Example 1, the sintering was performed under the same conditions without sol-gel coating.

[0045] Comparative Examples 2 and 3 involved adding 1.2 wt.% of AO and LAO to the powder, respectively, and then performing sintering under the same conditions, one case using a master powder (MP) and the other not using one (bare). The process conditions are as shown in Figure 1.

[0046] Furthermore, the names of the samples used in this example are as follows: [ka]

[0047] When naming a test specimen using the conventional solid electrolyte sintering manufacturing method with mother powder, the abbreviation "MP" for "mother powder" is added, resulting in the name "LLZT-MP".

[0048] When using solid electrolyte powder with added compounds, a "+" sign should be added, and the added substance should be indicated as "LAO" if it is a Li-Al-O compound, "AO" if it is an Al-O compound, and so on.

[0049] When using coated solid electrolyte powder, it should be indicated with "@", and if the coating material is a Li-Al-O compound, it should be indicated with "LAO", and if it is an Al-O compound, it should be indicated with "AO", etc. Furthermore, if a heat treatment step is included after sol-gel coating, it should be indicated with "H-".

[0050] The steps described based on the examples are as follows:

[0051] (Process)

[0052] (1) Li7La3Zr2O, a garnet-based compound synthesized in the cubic phase and doped with Ta. 12 Prepare the (LLZT) electrolyte powder.

[0053] (2) Coating of solid electrolyte surface: The sol-gel solution used for coating the solid electrolyte is prepared by adding precursors to IPA according to the type and ratio of the target compound. In other words, the Li-Al-O compound coating according to the examples of the present invention uses Li-ethoxide and Al-ethoxide as precursors, while in the comparative example of Li-O, only Li-ethoxide is used, and in the case of Al-O, only Al-ethoxide is used. In one example of the present invention, a sol-gel solution was prepared so that 2 wt.% of LiAlO2, Al2O3, and Li2O were formed in the solid electrolyte, and the solid electrolyte was added to the prepared sol-gel solution and mixed. The mixing and sol-gel process was carried out on a hot plate while rotating a magnetic bar, and the coating was applied to the solid electrolyte surface while removing IPA at 120 rpm or more for 6 to 12 hours at 120°C. The crystallization treatment of the solid electrolyte surface, which is the route of Example 2, was performed by heat treatment at 500°C for 6 hours to produce a powder for the solid electrolyte.

[0054] (3) Sintering of solid electrolyte: In the sintering process, without using mother powder, approximately 1 g of electrolyte powder was first placed into the mold and molded into a pellet shape by applying pressure of 3 to 4 tons with a hydraulic press. Various sizes were tested to enable sintering of pellets with diameters ranging from 10 to 65 mm. Sintering was carried out using alumina, magnesium oxide, or platinum crucibles, and sintering was performed at 1000 to 1100°C for 10 hours while supplying high-purity O2 gas (99.995%) at a rate of 300 cc / min or more. In this process, as described above, the sintering process was carried out without using mother powder.

[0055] Furthermore, it is also possible to manufacture a sheet-shaped solid electrolyte structure (including thin films and thick films) by stacking the manufactured powders described above onto a substrate and performing a sintering process.

[0056] (Example of experiment)

[0057] Figures 2 and 3 are images of solid electrolyte pellets manufactured according to the examples and comparative examples of the present invention.

[0058] Referring to Figures 2 and 3, in the case of the (c)LAO@LLZT sintered body in Figure 2, despite being manufactured by sintering without using mother powder, the shrinkage rate is high at 21%, and the side view in Figure 3 confirms that a sintered body without warping has been obtained.

[0059] On the other hand, in (a) LLZT-bare, which was manufactured by sintering without using mother powder, cracks occurred, indicating that sufficient shrinkage was not achieved. Furthermore, it can be confirmed that there are many voids after sintering, indicating that it is not dense.

[0060] Furthermore, while the shrinkage rate of the conventional sintering method (b) LLZT-MP is 15%, it can be confirmed that the sinterability of the LAO@LLZT sintered body is superior to that of the conventional method. In addition, even in the case of (d) AO@LLZT and (e) LO@LLZT, which are coated with Al-O and Li-O compounds instead of Li-Al-O compounds, fracture and collapse occur in the sintered body.

[0061] From these results, it can be confirmed that even with the same compound, in the case of (fh)H-XO@LLZT which includes crystallization treatment, fracture and collapse of the sintered body occur, indicating low sinterability.

[0062] Therefore, compared to conventional sintering methods, using solid electrolyte powder coated with Li-Al-O compounds allows for high sinterability without the need for mother powder, thereby reducing the cost of precursors and solid electrolytes used in mother powder. Furthermore, it exhibits excellent sinterability with only sol-gel coating without the need for additional crystallization treatment, saving on process costs.

[0063] Figures 4 and 5 are images of the solid electrolyte before and after sintering. Figure 4 is an image of LLZT powder coated with a Li-Al-O compound in a sol-gel state, without mother powder, before sintering. Figure 5 is an image of the sintered body (LAO@LLZT) of the same powder after sintering.

[0064] Referring to Figures 4 and 5, it can be seen that LLZT powder coated with a Li-Al-O compound in a sol-gel configuration exhibits sufficiently uniform moldability even when sintered without a mother powder.

[0065] Figure 6 is an image of a solid electrolyte sintered body manufactured by a large-area sintering process.

[0066] Referring to "Figure 6," it can be confirmed that sintering using solid electrolyte powder coated with a Li-Al-O compound enables mass production and the manufacture of large-area sintered bodies.

[0067] Figures 7 and 8 are graphs comparing the density and relative density of the manufactured solid electrolyte sintered body with that of a comparative example.

[0068] Referring to Figures 7 and 8, it can be confirmed that the LAO@LLZT sintered body of Example 1 exhibits the highest density, which is higher than that of LLZT-bare. In other words, it is proven that when heat treatment is performed using solid electrolyte powder coated with a Li-Al-O compound, high sinterability and high density are achieved.

[0069] Figure 9 shows the results of XRD analysis to confirm the stable cubic phase of the manufactured solid electrolyte sintered body.

[0070] Referring to Figure 9, XRD analysis results of sintered bodies treated without using mother powder show that the LAO@LLZT sintered body has a stable, complete cubic phase without structural collapse, but the LLZT-bare body exhibits reduced structural stability, failing to maintain a complete cubic phase and resulting in the formation of a tetragonal phase. This demonstrates that structural stability is achieved when sintering is performed using solid electrolyte powder coated with a Li-Al-O compound.

[0071] Figure 10 shows the results of observing the fracture surface of the manufactured solid electrolyte sintered body using a scanning electron microscope (SEM).

[0072] Referring to "Figure 10," SEM fracture surface observation of sintered bodies treated without mother powder shows that the LAO@LLZT sintered body is densely sintered without voids, while LLZT-bare is found to have many voids and a non-dense microstructure. This result reaffirms that sintering treatment using solid electrolyte powder coated with a Li-Al-O compound exhibits high sinterability.

[0073] Figure 11 shows the results of component analysis performed by ICP on each manufactured solid electrolyte sintered body.

[0074] Referring to "Figure 11," it can be confirmed that the LAO@LLZT sintered body of Example 1 shows the highest result, with no volatilization of the lithium component at high temperatures, and is superior to LLZT-bare. In other words, by heat treatment using solid electrolyte powder coated with a Li-Al-O compound, lithium volatilization is suppressed, demonstrating high sinterability and structural stability.

[0075] Figure 12 shows the results of XPS measurements of the surface of the manufactured solid electrolyte sintered body.

[0076] Referring to "Figure 12," it can be confirmed that aluminum components are detected in the (b)LAO@LLZT sintered body of Example 1, whereas they are not detected in (a)LLZT-MP. In other words, the high sinterability is demonstrated by the aluminum components distributed on the surface and inside when heat treatment is performed using a solid electrolyte powder coated with a Li-Al-O compound.

[0077] Figures 13 and 14 are comparative graphs of the electrical conductivity of the solid electrolyte sintered body according to the present invention, comparing the results of electrical conductivity measurements of the manufactured solid electrolyte sintered body with that of the case using mother powder. In this experimental example, conductivity test specimens were prepared by mirror-polishing the solid electrolyte sintered body and depositing Au ion-blocking electrodes with excellent electronic conductivity on both sides. Electrical conductivity was determined by applying a constant voltage using DC polarization (direct current polarization technique) and calculating it using a mathematical formula.

[0078] Referring to Figures 13 and 14, it can be confirmed that when solid electrolyte powder coated with a Li-Al-O compound is heat-treated, it exhibits lower electrical conductivity compared to LLZT-MP. Table 1 below shows the quantitative results. [Table 1]

[0079] Figures 15 and 16 show the ionic conductivity measurement results and comparison graphs of the manufactured solid electrolyte sintered bodies.

[0080] The electrical conductivity and ionic conductivity tests described above were conducted to analyze the properties of solid electrolytes that require high ionic conductivity and low electronic conductivity. Conductivity test specimens were prepared by mirror-polishing a solid electrolyte sintered body and depositing gold (Au) ion-blocking electrodes, which have excellent electronic conductivity, onto both sides. Ionic conductivity was measured by impedance. An AC voltage of 100 mV was applied, and the resistance of the bulk electrolyte was determined from the intersection of the semicircle with the real axis in the Nyquist plot of impedance measured in the frequency range of 500 Hz to 3 MHz. Ionic conductivity was then calculated using a formula based on this resistance.

[0081] As is clear from Figures 15 and 16, when solid electrolyte powder coated with a Li-Al-O compound is used for sintering, it can be confirmed that it exhibits higher ionic conductivity compared to LLZT-MP. At room temperature, 10 -3 It exhibits extremely high ionic conductivity of S / cm and maintains high ionic conductivity even in low-temperature environments. Quantitative results are shown in Table 2 below. [Table 2]

[0082] Figure 17 shows the measurement results of the interfacial resistance between the fabricated solid electrolyte sintered body and lithium.

[0083] The material was fabricated by deposition of lithium metal, and the interfacial resistance was measured by impedance. After applying an AC voltage with an amplitude of 100 mV and a frequency range of 500 Hz to 3 MHz, the interfacial resistance with lithium was determined from the point where the semicircle intersected the real axis in the measured impedance trajectory.

[0084] Referring to "Figure 17," it was confirmed that when a solid electrolyte powder coated with a Li-Al-O compound was used for heat treatment, the interfacial resistance with lithium was lower compared to LLZT-MP.

[0085] Figure 18 shows the long-term stability and critical current density measurements of the fabricated solid electrolyte sintered body at the lithium interface.

[0086] The long-term stability and critical current density tests with the lithium interface described above were conducted to analyze the properties of solid electrolytes required for long-term cycling with lithium in a low-voltage range and for high critical current density characteristics with lithium. Test specimens for lithium interface stability and critical current density were prepared by mirror-polishing a solid electrolyte sintered body and then depositing lithium metal on both sides.

[0087] Long-term stability with lithium was evaluated by applying the same current density during discharge and charge cycles and measuring stability over voltage range and time. The critical current density with lithium was determined by increasing the current density over time during discharge and charge cycles and measuring the current density at which a short circuit occurred.

[0088] Referring to Figure 18, it was confirmed that (b) when a solid electrolyte powder coated with a Li-Al-O compound was used for sintering, (a) long-term stability with lithium was higher compared to LLZT-MP. The reading was 0.2 mA / cm² at room temperature. 2 When a very high current density was applied for an extended period, (b)LAO@LLZT was able to cycle stably for more than 3,500 hours without overvoltage in a lower voltage range compared to (a)LLZT-MP, confirming its long-term stability with lithium.

[0089] The critical current density with lithium is maintained up to a high current density of 2.5 mA / cm², compared to (c) LLZT-MP, where (d) LAO@LLZT is short-circuited at a low current density. 2 An extremely high critical current density was confirmed.

[0090] The above results demonstrate that by using the sol-gel method to coat solid electrolyte particles with a Li-Al-O compound, and proceeding solely through heat treatment without the use of a master powder, solid electrolyte structures (pellets, sheets, thin films, etc.) with sinterability, high density, phase stability, ionic conductivity, interfacial stability with lithium, and productivity can be manufactured.

[0091] Furthermore, the inventors confirmed that this remarkable effect appears only when LiAlO2 is used in the form of a sol-gel coating layer on the surface of a solid electrolyte powder. This is clearly differentiated from methods that simply add LiAlO2 powder or Al2O3 powder and sinter it.

[0092] Figure 19 shows the image and characteristic comparison graph of the LLZT sample with added LiAlO2 powder after sintering.

[0093] Referring to Figure 19, in the LLZT sample in which 1.2 wt.% of LiAlO2 powder was added to the solid electrolyte powder, the sinterability was low at 90% when the master powder was used (MP), but the sintered body was maintained, and some degree of crystallinity was also maintained. However, when the master powder was not used (bare), the sintered body broke down, and crystallinity collapsed along with low density. This indicates that when Li-Al-O compounds such as LiAlO2 are simply added in powder form, there are limitations to maintaining the sinterability of the solid electrolyte and ensuring structural stability in the absence of a master powder. Of particular note is that the sinterability was relatively low at 90% despite the additional material and process cost of the master powder (96.1% in Example 1).

[0094] Therefore, a sintered body according to one embodiment of the present invention has a structure in which a core is a powder formed by sintering LLZT particles, and a Li-Al-O compound is distributed at the interface (grain boundary) of the core particles.

[0095] Due to this structure, the sintered body of the present invention exhibits a high relative density of over 95%, specifically reaching 96.1%, even though it is manufactured without using a master powder. Furthermore, as confirmed by XRD analysis, it has the characteristic of suppressing lithium volatilization and completely maintaining a stable cubic phase without the collapse of the crystal structure.

[0096] Figure 20 shows the image and characteristic comparison graph of the LLZT sample with added Al2O3 powder after sintering.

[0097] Referring to "Figure 20," the LLZT sample with 1.2 wt.% Al2O3 powder added also exhibited phenomena such as sintering and a significant decrease in density and crystallinity when the mother powder was not used. This means that Al-O compounds do not exhibit the same excellent sinterability and structural stability as Li-Al-O compounds coated using the sol-gel method.

[0098] The comparison results in "Figure 19" and "Figure 20" above show a significant difference from the excellent sinterability, density, and structural stability of the (c)LAO@LLZT sample in "Figure 2" (LLZT powder sintered without a mother powder after being sol-gel coated with a Li-Al-O compound). This strongly supports the idea that coating the Li-Al-O compound by the sol-gel method and forming it only as a coating layer on the surface of the solid electrolyte powder is essential for producing a solid electrolyte sintered body without a mother powder, and is at the core of the technical features of the invention.

Claims

1. A powder for oxide-based solid electrolytes, powder; and A powder for oxide-based solid electrolytes, characterized in that a coating layer containing a Li-Al-O compound is formed on the surface of the solid electrolyte powder.

2. In the oxide-based solid electrolyte powder according to claim 1, A powder for oxide-based solid electrolytes, characterized in that the aforementioned powder does not contain a Li-Al-O compound.

3. In the oxide-based solid electrolyte powder according to claim 1, The powder is Garnet-based Li ７ La ３ Zr ２ O １２ (LLZ) or Li doped with Ta ６．４ La ３ Zr １．４ Ta ０．６ O １２ (LLZT) powder, and is characterized by being any one of the powders for an oxide solid electrolyte.

4. In the oxide-based solid electrolyte powder according to claim 1, The oxide-based solid electrolyte powder is characterized in that the coating layer containing the Li-Al-O compound is coated by a sol-gel method in an amount of 0.5% to 5.0% by weight relative to the oxide-based solid electrolyte powder.

5. A process of coating powder with a substance containing a Li-Al-O compound; The step includes sintering a powder coated with a substance containing the Li-Al-O compound; Herein, a method for producing an oxide-based solid electrolyte sintered body, characterized in that no master powder is used in the sintering process.

6. In the method for producing an oxide-based solid electrolyte sintered body according to claim 5, A method for producing an oxide-based solid electrolyte sintered body, characterized in that the coating step utilizes a sol-gel solution containing a lithium precursor and an aluminum precursor.

7. In the method for producing an oxide-based solid electrolyte sintered body according to claim 5, The aforementioned powder is Garnet-based Li ７ La ３ Zr ２ O １２ (LLZ) or Ta-doped Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ A method for producing an oxide-based solid electrolyte sintered body, characterized by being (LLZT) powder.

8. In the method for producing an oxide-based solid electrolyte sintered body according to claim 7, A method for producing an oxide-based solid electrolyte sintered body, characterized in that the powder does not contain a Li-Al-O compound.

9. In the method for producing an oxide-based solid electrolyte sintered body according to claim 8, A method for producing an oxide-based solid electrolyte sintered body, characterized in that, after the coating step, the body is directly subjected to a sintering process without undergoing a separate crystallization step.

10. In the method for producing an oxide-based solid electrolyte sintered body according to claim 9, A method for producing an oxide-based solid electrolyte sintered body, characterized in that the sintering process is carried out in an oxygen atmosphere at a temperature of 1000°C to 1100°C.

11. In the method for producing an oxide-based solid electrolyte sintered body according to claim 8, A method for producing an oxide-based solid electrolyte sintered body, characterized in that the sintered solid electrolyte sintered body exhibits a shrinkage rate of 15% or more compared to a case where uncoated powder is sintered without a master powder, and is formed with a relative density of 95% or more.

12. In the method for producing an oxide-based solid electrolyte sintered body according to claim 10, A method for producing an oxide-based solid electrolyte sintered body, characterized in that the sintered solid electrolyte sintered body maintains the cubic phase without structural collapse and does not generate a secondary phase.

13. An oxide-based solid electrolyte sintered body, Ta doped Li ７ La ３ Zr ２ O １２ Cores including (LLZT); and An oxide-based solid electrolyte sintered body characterized by containing a Li-Al-O compound distributed at the particle interface of the core, having a relative density of 95% or more, and possessing a cubic phase.

14. An all-solid-state secondary battery comprising an oxide-based solid electrolyte sintered body as described in claim 13.

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