Powder for high stability oxide-based solid electrolyte, high stability oxide-based solid electrolyte containing the same, and method for manufacturing the same

Abstract

An oxide-based solid electrolyte powder is provided, comprising: a powder; and a coating layer coated on the powder and comprising LiAlO2.

Description

Technology Field

[0001] The present invention relates to a powder for a highly stable oxide-based solid electrolyte, a highly stable oxide-based solid electrolyte containing the same, and a method for manufacturing the same. Background Technology

[0002] Conventional oxide-based solid electrolyte membrane manufacturing for secondary batteries has been carried out by creating a high-temperature environment (~1250 ℃ 12h) through long-term heat treatment. However, the high-temperature, long-term heat treatment process generally causes lithium volatilization in oxide-based solid electrolytes, which reduces the structural stability of the material. Furthermore, it causes changes in the surface composition of the electrolyte through reactions with carbon dioxide present in the atmosphere, leading to phase changes in the material or reduced conductivity due to decreased sinterability.

[0003] Therefore, when manufacturing a solid electrolyte membrane using general pressureless sintering, in order to prevent the collapse of the crystal structure due to lithium volatilization and to prevent the bending and fracture of the pellet due to uneven heat transfer, the pellet is placed between mother powder (also called bed powder or covering powder) composed of a solid electrolyte synthesized in a cubic phase and sintering is carried out.

[0004] Since the method involves uniformly covering the bottom with mother powder to a thickness approximately twice that of the pellet, placing the pellet on top, and then covering it with mother powder of the same thickness, the high consumption of electrolyte powder contributes to the increase in costs for electrolyte membrane manufacturing. Consequently, methods such as hot pressing (HP), spark plasma sintering (SPS), and ultrafast high-temperature sintering (UHS) utilizing pressure or high-speed sintering technology are being attempted; however, these methods are difficult to apply to tape casting due to the high cost of equipment, the impossibility of mass production and scaling up, and the difficulty of application to tape casting. The problem to be solved

[0005] Accordingly, the problem to be solved by the present invention is to provide a powder for an oxide-based solid electrolyte having high sinterability and structural stability without using a mother powder, a highly stable oxide-based solid electrolyte containing the same, and a method for manufacturing the same. means of solving the problem

[0006] In order to solve the above problem, the present invention provides a powder for oxide-based solid electrolytes, wherein

[0007] The present invention provides a powder for an oxide-based solid electrolyte comprising a powder; and a coating layer coated on the powder and comprising LiAlO2.

[0008] In one embodiment of the present invention, the coating layer is coated in a sol-gel manner.

[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 O 12 It is one of the (LLZT) powders.

[0010] In one embodiment of the present invention, the powder for the oxide-based solid electrolyte does not have crystallinity.

[0011] The present invention also provides a method for manufacturing an oxide-based solid electrolyte sintered body, comprising the steps of: coating a solid electrolyte powder with a LiAlO2 material; and heat-treating or sintering the solid electrolyte powder coated with the LiAlO2 material, wherein the mother powder is not used in the step of sintering.

[0012] In one embodiment of the present invention, the powder for the solid electrolyte is Garnet-based Li7La3Zr2O 12 (LLZ) and Ta-doped Li 6.4 La3Zr 1.4 Ta 0.6 O12 (LLZT) is powder.

[0013] In one embodiment of the present invention, the method for manufacturing a solid electrolyte further includes the step of forming the powder into a pellet shape prior to the step of heat treatment or sintering treatment in the heat treatment furnace.

[0014] In one embodiment of the present invention, the method for manufacturing a solid electrolyte comprises the steps of: coating a powder for a solid electrolyte with a LiAlO2 material and then stacking the powder for a solid electrolyte in the form of a film; and heat treating or sintering the stacked powder for a solid electrolyte, thereby forming a solid electrolyte structure in the form of a film.

[0015] In one embodiment of the present invention, the method for manufacturing the solid electrolyte involves sintering the powder for the solid electrolyte immediately after the step of coating it with a LiAlO2 material, without a separate crystallization process.

[0016] The present invention also provides a solid electrolyte prepared by heat treating or sintering the aforementioned oxide-based solid electrolyte powder.

[0017] The present invention also provides an all-solid-state secondary battery comprising the solid electrolyte described above. Effects of the invention

[0018] The present invention provides a solid electrolyte powder comprising a Li-Al-O compound (LiAlO2), which is a material capable of imparting sinterability and structural stability, as a coating layer component. As a result, a solid electrolyte membrane can be manufactured using a pressureless sintering method without using a mother powder. In one embodiment of the present invention, the coating layer of the solid electrolyte powder is coated using a sol-gel method, and by proceeding with a sintering process using the coated solid electrolyte powder, structural stability of the solid electrolyte membrane can be maintained without using a mother powder, and a high-density electrolyte membrane can be manufactured with high sinterability that prevents bending and breakage. Furthermore, it was confirmed that multiple membranes can be manufactured using a heat treatment furnace and that the pellet size can be increased. Accordingly, mass production and scaling up of the electrolyte membrane are possible, thereby enabling the production of large oxide-based solid batteries with high energy density. Brief explanation of the drawing

[0019] FIG. 1 is a step diagram of a solid electrolyte manufacturing process according to an embodiment and a comparative example of the present invention. Figures 2 and 3 are images of solid electrolyte pellets prepared according to an example and a comparative example of the present invention. Figures 4 and 5 are images of solid electrolytes before and after sintering. Figure 4 is an image of LLZT powder coated with a Li-Al-O compound in a sol-gel coating before sintering without a mother powder, and Figure 5 is an image of a sintered body (LAO@LLZT) of LLZT powder coated with a Li-Al-O compound in a sol-gel coating after sintering without a mother powder. Figure 6 is an image of a solid electrolyte sintered body manufactured by large-area sintering treatment. Figures 7 and 8 are graphs comparing the measured density and relative density of the manufactured solid electrolyte sintered body with those of a comparative example, respectively. Figure 9 shows the XRD analysis results to confirm the stable cubic phase of the manufactured solid electrolyte sintered body. Figure 10 shows the results of observing the fracture surface of the manufactured solid electrolyte sintered body using SEM. Figures 11 and 12 are the electrical conductivity measurement results of the manufactured solid electrolyte sintered body and a graph comparing the electrical conductivity between the case using mother powder and the solid electrolyte sintered body according to the present invention. Figures 13 and 14 are the ion conductivity measurement results and comparison graphs of the manufactured solid electrolyte sintered body. Specific details for implementing the invention

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0021] Before describing the invention in detail, the terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, and the inventor of the invention may appropriately define and use the concepts of various terms to best describe his invention.

[0022] Furthermore, it should be understood that these terms or words should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0023] In other words, the terms used in this specification are used merely to describe preferred embodiments of the invention and are not intended to specifically limit the content of the invention.

[0024] It should be noted that these terms are defined in consideration of the various possibilities of the present invention.

[0025] Additionally, in this specification, singular expressions may include plural expressions unless the context clearly indicates a different meaning.

[0026] In addition, you should be aware that even if it is expressed in the plural, it may contain a singular meaning.

[0027] Throughout this specification, where it is stated that a component "includes" another component, unless specifically stated otherwise, this may mean that it does not exclude any other component but may include any other component.

[0028] Furthermore, in cases where it is stated that a component "exists inside or is installed in connection with" another component, this component may be installed in direct connection with or in contact with the other component.

[0029] In addition, they may be installed spaced apart at a certain distance, and in the case where they are installed spaced apart at a certain distance, there may be a third component or means for fixing or connecting the component to another component.

[0030] Meanwhile, it should be noted that the description of the third component or means mentioned above may be omitted.

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

[0032] Likewise, other expressions describing the relationship between each component, such as “between” and “right between”, or “adjacent to” and “directly adjacent to”, should be interpreted as having the same intent.

[0033] In addition, terms such as “one side,” “other side,” “one side,” “other side,” “first,” “second,” etc., in this specification are used to ensure that one component can be clearly distinguished from another component.

[0034] However, it should be noted that the meaning of the component is not used restrictively by such terminology.

[0035] In addition, positional terms such as "top," "bottom," "left," and "right" used in this specification should be understood as indicating the relative position of the corresponding component in the drawing.

[0036] Furthermore, unless an absolute location is specified regarding their positions, terms related to these locations should not be understood as referring to absolute locations.

[0037] Furthermore, in the specification of the present invention, terms such as “…part,” “…unit,” “module,” and “device,” if used, refer to a unit capable of handling one or more functions or operations.

[0038] You should be aware that this can be implemented in hardware, software, or a combination of hardware and software.

[0039] In the drawings attached to this specification, the size, position, connection relationships, etc., of each component constituting the present invention may be described in a partially exaggerated, reduced, or omitted manner for the convenience of explanation or to sufficiently clearly convey the concept of the present invention, and therefore, the proportions or scale may not be strictly accurate.

[0040] In addition, in describing the present invention below, detailed descriptions of components that are deemed to unnecessarily obscure the essence of the invention, such as known technologies including prior art, may be omitted.

[0041] To solve the aforementioned problems, the present invention provides a powder for a solid electrolyte comprising a Li-Al-O compound (LiAlO2), which is a material capable of imparting sinterability and structural stability, as a coating layer component. As a result, a solid electrolyte membrane can be manufactured using a pressureless sintering method without using a mother powder.

[0042] In one embodiment of the present invention, the coating layer of the solid electrolyte powder is coated using a sol-gel method, and by performing heat treatment or sintering treatment with the coated solid electrolyte powder, it is possible to manufacture a high-density electrolyte membrane that maintains structural stability of the solid electrolyte membrane without using a mother powder and prevents bending and breakage due to high sinterability.

[0043] In addition, it was confirmed that multiple membranes can be manufactured through a heat treatment furnace and that the pellet size can be increased, thereby enabling mass production and scaling up of electrolyte membranes, which in turn enables the production of large oxide-based solid batteries with high energy density.

[0045] The present invention will be explained in more detail through the following examples and experimental examples. However, the scope of the present invention is not limited thereto.

[0047] Examples

[0048] FIG. 1 is a step diagram of a solid electrolyte manufacturing process according to an embodiment and a comparative example of the present invention.

[0049] Referring to Fig. 1, Solid electrolyte powder (Garnet-based Li synthesized in cubic form) 7 La 3 Zr 2 O 12 (LLZ) system, Ta-doped Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZT) powder as a solid electrolyte powder The comparative example was prepared by a sintering process without a separate sol-gel coating, Example 1 was prepared by a sintering process without a crystallization step after sol-gel coating, and Example 2 was prepared by a sintering process after crystallization following sol-gel coating.

[0050] Each process condition is as shown in Fig. 1.

[0051] In addition, the naming of the specimens used in this embodiment is as follows.

[0052]

[0053] When using the mother powder, which is the conventional solid electrolyte sintering manufacturing method, the specimen name is written as LLZT-MP by attaching MP, which is an abbreviation for mother powder.

[0054] When using coated solid electrolyte powder, it is expressed by adding @, and if the coating material is a Li-Al-O compound, it is expressed as LAO, and if it is an Al-O compound, as AO, etc. If a heat treatment process is included after sol-gel coating, it is expressed by adding H-.

[0055] The process described based on the examples is as follows.

[0057] Examples

[0058] Process :

[0059] ① Garnet-based Ta-doped Li7La3Zr2O synthesized in cubic phase 12 Prepare the (LLZT) electrolyte powder.

[0060] ② Solid Electrolyte Surface Coating: The sol-gel solution for solid electrolyte coating is prepared by adding precursors to IPA according to the type and ratio of the desired compound.

[0061] That is, for the Li-Al-O compound coating according to the embodiment of the present invention, Li-ethoxide and Al-ethoxide were used as precursors, and for the comparative example Li-O, only Li-ethoxide was used, and for Al-O, only Al-ethoxide was used.

[0062] In one embodiment of the present invention, a sol-gel solution was prepared so that 2 wt.% LiAlO2, Al2O3, and Li2O could be formed in the solid electrolyte. The solid electrolyte was added to the prepared sol-gel solution and mixed.

[0063] The mixing and sol-gel process is carried out by rotating a magnetic bar on a hot plate at 120°C for 6 to 12 hours at 120 rpm or higher to remove IPA and coat the surface of the solid electrolyte. The solid electrolyte surface crystallization treatment, which is the path of Example 2, is carried out by heat treatment at 500°C for 6 hours to produce a powder for the solid electrolyte.

[0064] ③ Solid Electrolyte Sintering: For the sintering process, approximately 1 g of electrolyte powder was first placed into a mold without a mother powder, and then pressed with a hydraulic press at a pressure of 3 to 4 tons to produce green pellets. Experiments were conducted with various pellet sizes ranging from Ø10 to 20 to allow for sintering in diverse sizes. Sintering was performed using alumina, magnesium oxide, or platinum crucibles. Sintering was carried out at 1000 to 1100 ℃ for 10 hours while injecting high-purity O2 gas (99.995%) at a rate of over 300 cc / min. As mentioned above, the sintering process was performed without using a separate mother powder.

[0065] However, in addition to this, the above-mentioned powder can be laminated onto a substrate and subjected to heat treatment or sintering treatment to manufacture a solid electrolyte structure in the form of a sheet (including both thin films and thick films).

[0067] Comparative example

[0068] In the case of the comparative example, the sintered body was prepared in the same manner as the example, excluding step ②.

[0070] Experimental Example

[0071] Figures 2 and 3 are images of solid electrolyte pellets prepared according to an example and a comparative example of the present invention.

[0072] Referring to Figures 2 and 3, in the case of (c) LAO@LLZT sintered body in Figure 2, the shrinkage rate is high at 21% even when manufactured by heat treatment or sintering without using mother powder, and it can be confirmed in the side image of Figure 3 that it was manufactured by sintering without warping.

[0073] In addition, since the shrinkage rate of the conventional sintering method (a)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. Furthermore, in the case of (d)AO@LLZT and (e)LO@LLZT coated with Al-O and Li-O compounds instead of Li-Al-O compounds, fracture and breakage of the sintered body occur.

[0074] From the above results, it can be confirmed that even with the same compound, the sinterability is low, as fracture and breakage of the sintered body occur in the case of (fh)H-XO@LLZT including a crystallization treatment process.

[0075] Therefore, compared to conventional sintering methods, using solid electrolyte powder coated with a Li-Al-O compound exhibits high sinterability without the need for a mother powder, thereby reducing the costs of precursors and solid electrolytes used in the mother powder. Furthermore, excellent sinterability is achieved solely through sol-gel coating without the need for additional crystallization treatment, allowing for savings in process costs.

[0076] Figures 4 and 5 are images of solid electrolytes before and after sintering. Figure 4 is an image of LLZT powder coated with a Li-Al-O compound in a sol-gel coating before sintering without a mother powder, and Figure 5 is an image of a sintered body (LAO@LLZT) of LLZT powder coated with a Li-Al-O compound in a sol-gel coating after sintering without a mother powder.

[0077] Referring to Figures 4 and 5, it can be seen that LLZT powder coated with a sol-gel of a Li-Al-O compound has sufficient uniform moldability even when sintered without a mother powder.

[0078] Figure 6 is an image of a solid electrolyte sintered body manufactured by large-area sintering treatment.

[0079] Referring to Fig. 6, it can be seen that mass production and the manufacture of large-area sintered bodies are possible by using solid electrolyte powder coated with a Li-Al-O compound and performing a sintering process.

[0080] Figures 7 and 8 are graphs comparing the measured density and relative density of the manufactured solid electrolyte sintered body with those of a comparative example, respectively.

[0081] Referring to Figures 7 and 8, it can be seen that the LAO@LLZT sintered body according to Example 1 has the highest density and exhibits a density higher than that of LLZT. In other words, when heat-treated using solid electrolyte powder coated with a Li-Al-O compound, it demonstrates high density along with high sinterability.

[0082] Figure 9 shows the XRD analysis results to confirm the stable cubic phase of the manufactured solid electrolyte sintered body.

[0083] Referring to Fig. 9, XRD analysis results of sintered bodies treated without using mother powder show that LAO@LLZT sintered bodies have a stable, complete cubic phase without structural collapse, whereas LLZT bodies have reduced structural stability and do not maintain a complete cubic phase, resulting in the formation of secondary phases such as Li2CO3. This demonstrates that when sintered using solid electrolyte powder coated with a Li-Al-O compound, structural stability is maintained.

[0084] Figure 10 shows the results of observing the fracture surface of the manufactured solid electrolyte sintered body using SEM.

[0085] Referring to Figure 10, the results of SEM cross-sectional observation of sintered bodies treated without using mother powder show that the LAO@LLZT sintered body is densely sintered without pores, whereas the LLZT body has a microstructure that is porous and not dense. This result once again confirms that sintering treatment using solid electrolyte powder coated with a Li-Al-O compound results in high sinterability.

[0086] Figures 11 and 12 show the results of measuring the electrical conductivity of the manufactured solid electrolyte sintered body and a graph comparing the electrical conductivity between the case using mother powder and the solid electrolyte sintered body according to the present invention. In this experimental example, the conductivity test specimen was prepared by mirror-polishing the solid electrolyte sintered body and depositing Au ion blocking electrodes with excellent electron conductivity on both sides, and the electrical conductivity was calculated using a formula by applying a constant voltage using the direct current (DC) polarization technique.

[0087] Referring to Figures 11 and 12, it can be confirmed that when heat-treated using solid electrolyte powder coated with a Li-Al-O compound, it has lower electrical conductivity compared to LLZT-MP, and Table 1 below shows the quantitative results.

[0088] [Table 1]

[0089]

[0090] Figures 13 and 14 are the ion conductivity measurement results and comparison graphs of the manufactured solid electrolyte sintered body.

[0091] The above electrical conductivity and ionic conductivity experiments were conducted to analyze the characteristics of solid electrolytes that require high ionic conductivity and low electronic conductivity. Conductivity test specimens were fabricated by mirror-polishing a solid electrolyte sintered body and depositing Au ion blocking electrodes with excellent electronic conductivity on both sides. Ionic conductivity is measured as impedance. After applying an AC voltage with an amplitude of 100 mV and a frequency range of 500 Hz to 3 MHz, the resistance of the bulk electrolyte was determined from the intersection point where the semicircle of the trajectory meets the real axis from the measured impedance, and the ionic conductivity was calculated using a formula.

[0092] Referring to Figures 13 and 14, it can be confirmed that solid electrolyte powder coated with a Li-Al-O compound exhibits higher ionic conductivity compared to LLZT-MP when subjected to sintering treatment. At room temperature, 10 -3 It exhibits a very high ionic conductivity of S / cm, and high ionic conductivity can be confirmed even at low temperatures. Table 2 below shows the quantitative results.

[0093] [Table 2]

[0094]

[0095] The above results indicate that solid electrolyte structures (pellets, sheets, thin films, etc.) with secured sinterability, high density, phase stability, ion conductivity, and productivity can be manufactured through heat treatment alone, without the need for a mother powder, by coating solid electrolyte particles with Li-Al-O compounds using the sol-gel method.

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 A method for manufacturing an oxide-based solid electrolyte sintered body, comprising the steps of: coating a solid electrolyte powder with a LiAlO2 material; and heat treating or sintering the solid electrolyte powder coated with the LiAlO2 material, wherein the mother powder is not used in the sintering step. Claim 6 In claim 5, the powder for the solid electrolyte is Garnet-based Li7La3Zr2O 12 (LLZ) and Ta-doped Li 6.4 La3Zr 1.4 Ta 0.6 O 12 A method for manufacturing an oxide-based solid electrolyte sintered body characterized by being (LLZT) powder. Claim 7 In claim 6, the method for manufacturing an oxide-based solid electrolyte sintered body is characterized by further including a step of forming the powder into a pellet shape prior to the step of heat treatment or sintering treatment in the heat treatment furnace. Claim 8 In claim 6, the method for manufacturing an oxide-based solid electrolyte sintered body comprises the steps of: coating a solid electrolyte powder with a LiAlO2 material and then stacking the solid electrolyte powder in a film form; and heat treating or sintering the stacked solid electrolyte powder, thereby forming a solid electrolyte structure in the form of a film. Claim 9 In claim 5, the method for manufacturing an oxide-based solid electrolyte sintered body is characterized by the step of coating the solid electrolyte powder with a LiAlO2 material, after which the sintering process is performed immediately without a separate crystallization process. Claim 10 A powder for an oxide-based solid electrolyte used in a method for manufacturing an oxide-based solid electrolyte sintered body according to any one of claims 5 to 9, comprising: a powder; and a powder for an oxide-based solid electrolyte comprising a coating layer coated on the powder and comprising LiAlO2, wherein the coating layer is coated by a sol-gel method, and the powder is Garnet-based Li7La3Zr2O 12 (LLZ) or Ta-doped Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Powder for oxide-based solid electrolytes characterized by being one of the (LLZT) powders. Claim 11 A solid electrolyte manufactured by heat-treating or sintering the oxide-based solid electrolyte powder according to Clause 10. Claim 12 All-solid-state secondary battery comprising a solid electrolyte according to Clause 11.

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