Solid electrolytes and batteries that use them

Abstract

The present invention provides a solid electrolyte that simultaneously possesses good flexibility, good mechanical strength, and high ionic conductivity, as well as a lithium-ion battery comprising the solid electrolyte that exhibits excellent mechanical performance, high ionic conductivity, high electrochemical stability, and excellent cycle stability. [Solution] The present invention provides a solid electrolyte for lithium-ion batteries. The solid electrolyte comprises a garnet-type solid electrolyte and a polymer filler, the polymer filler being dispersed within the garnet-type solid electrolyte. The garnet-type solid electrolyte does not contain lithium carbonate, and the content of the garnet-type solid electrolyte is 60 wt% or more based on the total weight of the garnet-type solid electrolyte and the polymer filler.

Description

[Technical Field]

[0001] The present invention provides a solid electrolyte for lithium-ion batteries, particularly a solid electrolyte comprising a garnet-type solid electrolyte and a polymer filler in a specific ratio. The present invention also provides a lithium-ion solid battery comprising a solid electrolyte. [Background technology]

[0002] To address global warming and climate change, energy conservation and carbon dioxide reduction have become top priorities worldwide. Among these, improving energy storage efficiency is a crucial challenge in achieving energy savings. Lithium-ion batteries are one of the most widely used energy storage systems. Conventional lithium-ion batteries utilize liquid electrolytes, however, such electrolytes pose several safety risks, including leakage, internal short circuits due to dendritic lithium penetrating the separator, and the risk of explosion. Consequently, recent research on lithium-ion batteries has focused on the development of solid electrolytes. Garnet-type solid electrolytes possess high mechanical strength and high ionic conductivity (approximately 10%). -3 S / cm~10 -4 Its high chemical stability (S / cm) makes it one of the most promising solid electrolytes.

[0003] However, all-solid garnet-type ceramic electrolyte sheets are inherently brittle and difficult to mold. They are prone to cracking under pressure during processing, significantly limiting their practical applications. In addition, garnet-type solid electrolytes tend to react with carbon dioxide (CO2) and water (H2O) present in the air, forming a passive layer of lithium carbonate (Li2CO3) on their surface. This passive layer increases the interfacial impedance between the all-solid garnet-type ceramic electrolyte sheet and the lithium metal. [Overview of the Initiative]

[0004] In view of the above technical problems, the present invention provides a solid electrolyte combining a garnet-type solid electrolyte without lithium carbonate and a polymer filler. The solid electrolyte of the present invention simultaneously has good flexibility, good mechanical strength, and high ionic conductivity. The solid electrolyte of the present invention is particularly suitable for use in lithium-ion batteries. The lithium-ion battery provided in this specification exhibits excellent mechanical performance, high ionic conductivity, high electrochemical stability, and excellent cycle stability.

[0005] Therefore, an object of the present invention is to provide a solid electrolyte comprising a garnet-type solid electrolyte and a polymer filler, the polymer filler being dispersed within the garnet-type solid electrolyte, the garnet-type solid electrolyte being free of or lithium carbonate-free, and the content of the garnet-type solid electrolyte being 60 wt% or more based on the total weight of the garnet-type solid electrolyte and the polymer filler.

[0006] In one embodiment of the present invention, the garnet-type solid electrolyte is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO), Li 6.4 La3Zr2Al 0.2 O 12 (LLZAO), Li 6.4 La3Zr2Ga 0.2 O 12 (LLZGO), Li 6.25 Al 0.20 La3Zr 1.85 Nb 0.15 O 12 (LALZNO), and combinations thereof.

[0007] In one embodiment of the present invention, the garnet-type solid electrolyte is provided by garnet-type solid electrolyte ceramic powder without lithium carbonate. The above ceramic powder has an average particle size of less than 100 μm.

[0008] In one embodiment of the present invention, the polymer filler is made of a material selected from the group consisting of polytetrafluoroethylene (PTFE), poly(ethylene oxide) (PEO), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), and combinations thereof.

[0009] In one embodiment of the present invention, based on the total weight of the garnet-type solid electrolyte and the polymer filler, the content of the polymer filler ranges from 0.1 wt% to less than 40 wt%, preferably from 0.1 wt% to less than 10 wt%, more preferably from 0.1 wt% to less than 5 wt%.

[0010] Another object of the present invention is to provide a lithium-ion battery comprising a positive electrode, a negative electrode, and the above solid electrolyte.

[0011] In one embodiment of the present invention, the positive electrode is made of a material selected from the group consisting of LiFePO4 (LFP), LiCoO2 (LCO), lithium nickel cobalt aluminum oxide (NCA), and lithium nickel cobalt manganese oxide (NCM).

[0012] In one embodiment of the present invention, the negative electrode is made of a material selected from the group consisting of lithium metal, lithium indium alloy, lithium aluminum alloy, silicon lithium alloy, and combinations thereof.

[0013] In one embodiment of the present invention, the lithium-ion battery further comprises an ionic liquid between the positive electrode and the solid electrolyte and between the negative electrode and the solid electrolyte, and the ionic liquid contains a lithium salt.

[0014] In one embodiment of the present invention, the lithium salt is selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, and combinations thereof.

[0015] To further clarify the above-mentioned objectives, technical features, and advantages of the present invention, the present invention will be described in detail below with reference to several embodiments. [Brief explanation of the drawing]

[0016] [Figure 1] These are the Raman spectra of the garnet-type solid electrolyte ceramic powders of Example 1 and Comparative Example 1. [Figure 2] This is a photograph of the solid electrolyte from Example 1. [Figure 3] This is an electron microscope image of the solid electrolyte from Example 1. [Figure 4] This is the thermogravimetric analysis curve of the solid electrolyte in Example 1. [Figure 5] Figure 5 shows the impedance analysis results for the symmetrical batteries of Example 1 and Comparative Example 1. [Figure 6] The voltage-time profiles of the symmetrical batteries in Example 1 and Comparative Example 1 are shown. [Figure 7] The impedance analysis results for the lithium-ion batteries of Example 1 and Comparative Example 1 are shown. [Figure 8] These are graphs of the initial charge and discharge curves of lithium-ion batteries for Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0017] Several embodiments of the present invention will be described in detail below. However, the present invention can be carried out in various embodiments and is not limited to the embodiments described herein.

[0018] Unless otherwise specified, expressions such as "a" or "the" in this specification and the claims shall include both singular and plural forms.

[0019] Unless otherwise specified, the term “positive electrode” as used herein and in the appended claims refers to the cathode during battery discharge, and the term “negative electrode” as used herein and in the appended claims refers to the anode during battery discharge.

[0020] Unless otherwise specified, the unit of weight-average molecular weight (Mw) as used herein and in the appended claims is "dalton".

[0021] As used herein, the term "ionic liquid" refers to ionic compounds in liquid form, particularly compounds that exhibit lithium ion mobility enhancement properties and are capable of dissolving lithium salts.

[0022] As used herein, the term "polymer-in-ceramic (PIC)" refers to a composite material of polymer and ceramic, where the ceramic content is greater than 50 wt% based on the total weight of the composite material, i.e., the polymer content is less than 50 wt%.

[0023] The advantage of the present invention over the prior art lies in the fact that a polymer-in-ceramic solid electrolyte is formed by adding a relatively small amount of polymer filler to a garnet-type solid electrolyte. This approach provides a solid electrolyte that combines excellent flexibility, mechanical strength, and high ionic conductivity. The solid electrolyte can be applied to lithium-ion batteries, resulting in lithium-ion batteries that exhibit excellent mechanical performance, high ionic conductivity, high electrochemical stability, and excellent cycle stability. Further details regarding the solid electrolyte and its applications are described in detail below.

[0024] 1.Solid electrolyte

[0025] The solid electrolyte of the present invention comprises a garnet-type solid electrolyte and a polymer filler, wherein the polymer filler is dispersed within the garnet-type solid electrolyte.

[0026] 1.1. Garnet-type solid electrolytes

[0027] Garnet-type solid electrolytes are a type of oxide-type electrolyte, with Li7La3Zr2O being a typical example. 12It has (LLZO). Generally, garnet-type solid electrolytes exist in a metastable cubic phase at high temperatures and a stable tetragonal phase at low temperatures / room temperature. In the tetragonal phase, the lithium moieties are completely (100%) occupied, whereas the cubic phase contains lithium vacancies, so the ionic conductivity of tetragonal garnet is two orders of magnitude lower than that of cubic garnet. One way to stabilize cubic garnet is to add Li + One method is to replace it by directly doping, thereby creating lithium vacancies. Another method is to replace it with Zr 4+ This involves substituting with high-value ions, thereby stabilizing the cubic phase garnet, 10 -3 A high ionic conductivity close to S / cm can be achieved. In one embodiment of the present invention, the garnet-type solid electrolyte is selected from the group consisting of LLZTO, LLZAO, LLZGO, and LALZNO. The above garnet-type solid electrolytes can be used alone or in any combination. In the attached example, LLZTO is used.

[0028] Garnet-type solid electrolytes tend to react with carbon dioxide and water present in the air, forming lithium carbonate (Li2CO3) on their surface. Studies have shown that the presence of lithium carbonate results in a high interfacial impedance between the garnet-type solid electrolyte and the lithium metal, which reduces ionic conductivity and thus adversely affects the performance of lithium-ion batteries. Therefore, one of the technical features of the present invention is that the garnet-type solid electrolyte does not contain lithium carbonate.

[0029] X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), and Raman spectroscopy are commonly used techniques for elemental analysis of ceramic materials. Of these, Raman spectroscopy can detect the elemental composition of the sample surface to a depth of approximately 0.1 μm and has a low detection limit, reaching down to 0.1 ppm. Therefore, in this specification, a Raman spectroscopy is used to confirm that the garnet-type solid electrolyte does not contain lithium carbonate. A laser light source with a wavelength of 532 nm and a laser output of 10 mW is used for surface analysis of the garnet-type solid electrolyte. The absence of a lithium carbonate signal in the resulting Raman spectrum confirmed the absence of lithium carbonate. Since lithium carbonate is produced by the reaction of the surface of the garnet-type solid electrolyte with carbon dioxide and water, the absence of lithium carbonate on the surface of the garnet-type solid electrolyte indicates that the garnet-type solid electrolyte does not contain lithium carbonate. Therefore, Raman spectroscopy can be used to confirm that the lithium carbonate content in the garnet-type solid electrolyte used in this invention is either 0 or less than 0.1 ppm. In the attached example, the Raman spectrometer used is the DXR Raman Microscope, available from Thermo Fisher Scientific.

[0030] A lithium carbonate-free (or lithium carbonate-free) garnet-type solid electrolyte is obtained by acid washing a garnet-type solid electrolyte. First, a garnet-type solid electrolyte ceramic powder is added to an organic solvent, and then an aqueous solution of a strong acid is added to obtain an initial mixed solution. The initial mixed solution is subjected to ultrasonic vibration, and then an appropriate amount of ultrapure water is added to prevent the surface of the garnet-type solid electrolyte ceramic powder from being corroded by excessive strong acid. The initial mixed solution subjected to ultrasonic vibration is then placed in a centrifuge and centrifuged. The precipitate obtained after centrifugation is a lithium carbonate-free garnet-type solid electrolyte ceramic powder. Examples of organic solvents include, but are not limited to, ethanol, isopropanol, and acetone. The above organic solvents can be used alone or in any combination. Examples of aqueous solutions of strong acids include, but are not limited to, aqueous solutions of hydrochloric acid, sulfuric acid, and nitric acid. The above aqueous solutions of strong acids can be used alone or in any combination. The concentration of the aqueous solution of the strong acid may range from 0.1 M to 2.0 M. For example, the concentration of an aqueous solution of a strong acid may be within the range of 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M, or 2.0M, or any two values ​​between the values ​​listed herein.

[0031] In one embodiment of the present invention, the content of the garnet-type solid electrolyte is 60 wt% or more, based on the total weight of the garnet-type solid electrolyte and polymer filler, and more specifically, the content of the garnet-type solid electrolyte is in the range of 60 wt% to 99 wt%. For example, based on the total weight of the garnet-type solid electrolyte and polymer filler, the content of the garnet-type solid electrolyte is 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 7 The content of the garnet-type solid electrolyte may be within the range of 8wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, or 99wt%, or any two of the values ​​listed herein. From the viewpoint of having better mechanical performance, ionic conductivity, electrochemical stability, and cycle stability in lithium-ion batteries, the content of the garnet-type solid electrolyte is preferably in the range of 90wt% to 99wt%, and more preferably in the range of 95wt% to 99wt%, based on the total weight of the garnet-type solid electrolyte and polymer filler. For example, based on the total weight of the garnet-type solid electrolyte and polymer filler 4, the content of the garnet-type solid electrolyte may be 95.0 wt%, 95.5 wt%, 96.0 wt%, 96.5 wt%, 97.0 wt%, or 97.5 wt%, or within the range of any two values ​​listed herein.

[0032] 1.2. Polymer Fillers

[0033] The solid electrolyte of the present invention has polymer fillers added, which improves the flexibility and mechanical strength of the solid electrolyte, thereby improving its processability.

[0034] Examples of polymer filler materials include, but are not limited to, PTFE, PEO, PAN, and PMMA. These materials can be used alone or in any combination. In the attached example, PTFE filler is used.

[0035] The polymer filler material may have a weight-average molecular weight (Mw) in the range of 300,000 to 1,000,000. For example, the Mw of the polymer filler material may be 300,000, 310,000, 320,000, 330,000, 340,000, 350,000, 360,000, 370,000, 380,000, 390,000, 400,000, 410,000, 420,000, 430,000, 440,000, 450,000, 460,000. ,470000,480000,490000,500000,510000,520000,530000,540000,550000,560000,570000,580000,590000,600000,610000,620000,630000,640000,650000,66000 0, 670000, 680000, 690000, 700000, 710000, 720000, 730000, 740000, 750000, 760000, 770000, 780000, 790000, 800000, 810000, 820000, 830000, 840000, 850000, 860 It may be 000, 870000, 880000, 890000, 900000, 910000, 920000, 930000, 940000, 950000, 960000, 970000, 980000, 990000, or 1000000, or within the range of any two of the values ​​listed herein.

[0036] In the solid electrolyte of the present invention, the polymer filler content may range from 0.1 wt% to less than 40.0 wt%, based on the total weight of the garnet-type solid electrolyte and the polymer filler. For example, based on the total weight of the garnet-type solid electrolyte and the polymer filler, the polymer filler content may be 0.1 wt%, 0.5 wt%, 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, 7.0 wt%, 8.0 wt%, 9.0 wt%, 10.0 wt%, 11.0 wt%, 12.0 wt%, 13.0 wt%, 14.0 wt%, 15.0 wt%, 16.0 wt%, 17.0 wt%, 18.0 wt%, 19.0 wt%. t%, 20.0wt%, 21.0wt%, 22.0wt%, 23.0wt%, 24.0wt%, 25.0wt%, 26.0wt%, 27.0wt%, 28.0wt%, 29.0wt%, 30.0wt%, 31.0wt%, 32.0wt%, 33.0wt%, 34.0wt%, 35.0wt%, 36.0wt%, 37.0wt%, 38.0wt%, 39.0wt%, or 40.0wt%, or within the range of any two values ​​specified herein. In the solid electrolyte of the present invention, the preferred content of polymer filler, based on the total weight of the garnet-type solid electrolyte and polymer filler, is 1.0 wt% to less than 10.0 wt%, more specifically 1.0 wt% to less than 5.0 wt%, for example, 2.5 wt%. When the polymer filler content is within the above preferred range, the solid electrolyte of the present invention can have good flexibility and mechanical strength while maintaining good ionic conductivity. Furthermore, it can reduce the interfacial contact impedance between the solid electrolyte and electrodes of a lithium-ion battery, and can effectively improve the mechanical performance and cycle performance of the lithium-ion battery.

[0037] 1.3. Preparation of Solid Electrolytes

[0038] The method for preparing the solid electrolyte of the present invention is not particularly limited. In one embodiment of the present invention, a mixture is obtained by uniformly mixing a lithium carbonate-free garnet-type solid electrolyte ceramic powder and a polymer filler, and the mixture is pressed to prepare the solid electrolyte. The particle size of the lithium carbonate-free garnet-type solid electrolyte ceramic powder can be changed as needed, and the average particle size of the lithium carbonate-free garnet-type solid electrolyte ceramic powder is preferably less than 100 μm. For example, the average particle size of the lithium carbonate-free garnet-type solid electrolyte ceramic powder may be 95 μm, 90 μm, 85 μm, 80 μm, 75 μm, 70 μm, 65 μm, 60 μm, 55 μm, 50 μm, 45 μm, 40 μm, 35 μm, 30 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm, or 1 μm, or within the range of two values ​​listed herein.

[0039] 2. Lithium-ion batteries

[0040] The solid electrolyte of the present invention is particularly suitable for lithium-ion batteries. Accordingly, the present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode, and the above-mentioned solid electrolyte, wherein the solid electrolyte is disposed between the positive electrode and the negative electrode.

[0041] In this invention, the negative electrode of a lithium-ion battery may be made from a material selected from lithium metal, lithium indium alloy, lithium aluminum alloy, and silicon lithium alloy. The above materials for making the negative electrode may be used alone or in any combination. In the attached examples, the material of the negative electrode is lithium.

[0042] In this invention, the positive electrode of a lithium-ion battery may be made from a material selected from LFP, single lithium cathode material, binary lithium cathode material, and ternary lithium cathode material. Examples of single lithium cathode materials include, but are not limited to, LCO, lithium nickel oxide, and lithium manganese oxide. Examples of binary lithium cathode materials include, but are not limited to, lithium nickel cobalt oxide, LNMO (lithium nickel manganese oxide), and lithium manganese cobalt oxide. Examples of ternary lithium cathode materials include, but are not limited to, NCA and NCM. In one embodiment of the present invention, the positive electrode is made from a material selected from the group consisting of LFP, LCO, NCA, and NCM. An example of NCA is LiNi 0.8 Co 0.15 Al 0.05 O2, LiLiLi 0.8 Co 0.18 Al 0.02 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2 is one example, but it is not limited to these. An example of NCM is LiNi 0.33 Co 0.33 Mn 0.33 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), and LiNi 0.8 Co 0.1 Mn 0.1 It contains O2 (NCM811). In the attached example, the positive electrode material is LFP.

[0043] The lithium-ion battery of the present invention may further include an ionic liquid between the positive electrode and the solid electrolyte, and between the negative electrode and the solid electrolyte, thereby further improving the interfacial stability between the positive electrode and the solid electrolyte, and between the negative electrode and the solid electrolyte, and reducing the interfacial impedance. The ionic liquid contains a lithium salt. The ionic liquid containing a lithium salt can increase the mobility of lithium ions, thereby improving ionic conductivity and enhancing the battery's cycle performance. In one embodiment of the present invention, examples of lithium salts contained in the ionic liquid include, but are not limited to, LiTFSI, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3. The above lithium salts may be used alone or in any combination. Examples of organic solvents that may be used to form the ionic liquid include, but are not limited to, triethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and propylene glycol dimethyl ether. The above organic solvents may be used alone or in any combination. In the attached example, the ionic liquid containing lithium salt is a LiTFSI-containing TEGDME solution. While we do not wish to be limited to any particular theory, it is thought that ionic liquids containing lithium salt can form a stable lithium ion transfer interface and reduce interfacial impedance. In addition, ionic liquids containing lithium salt can mitigate harmful side reactions, improve electrode performance, and prevent performance degradation in the short term. [Examples]

[0044] 3. Examples

[0045] 3.1. Preparation and Testing of Solid Electrolytes

[0046] (Preparation of LLZTO powder that does not contain lithium carbonate)

[0047] 1g of Li 6.4 La3Zr 1.4 Ta0.6 O 12 (LLZTO) powder was prepared and subjected to surface analysis using a Raman spectrometer (model: DXR Raman Microscope, available from Thermo Fisher Scientific) with a laser light source of 532 nm and a laser output of 10 mW. The results are shown in Figure 1 and are labeled "Before Acid Treatment". As shown in Figure 1, the LLZTO powder that has not been acid-treated shows a lithium carbonate signal in Raman spectroscopy, indicating that the LLZTO powder contains lithium carbonate.

[0048] The LLZTO powder was then subjected to acid treatment. First, 1 g of LLZTO powder (i.e., LLZTO powder containing lithium carbonate) was added to a mixed solvent containing 1 mL of ethanol and 3 mL of isopropanol, and the mixture was uniformly stirred to form a well-mixed dispersion. Next, 12 mL of 1 M hydrochloric acid was mixed into this dispersion to obtain an initial mixed solution. The initial mixed solution was then placed in an ultrasonic generator and subjected to ultrasonic vibration for 60 seconds. Next, 10 mL of ultrapure water was added to dilute the hydrochloric acid. The diluted mixed solution was then placed in a centrifuge and subjected to centrifugation at a rotation speed of 8000 rpm for 10 minutes. The precipitate obtained after centrifugation was LLZTO powder that did not contain lithium carbonate.

[0049] LLZTO powder subjected to acid treatment was subjected to surface analysis using a DXR Raman microscope with a 532 nm laser light source and a 10 mW laser output. The results are also shown in Figure 1 and are labeled "After Acid Treatment". As shown in Figure 1, the LLZTO powder subjected to acid treatment did not show a lithium carbonate signal in Raman spectroscopy, indicating that the LLZTO powder subjected to acid treatment does not contain lithium carbonate.

[0050] (Example 1) Preparation of the solid electrolyte of the present invention

[0051] The solid electrolyte sheet of Example 1 was prepared as follows: 1 g (97.5 wt%) of LLZTO powder, which does not contain lithium carbonate, was subjected to acid treatment in a glove box where both water and oxygen levels were less than 1 ppm. This powder was then uniformly mixed with 0.026 g (2.5 wt%) of PTFE powder in a mortar using a solvent-free method to obtain a mixture. The mixture was then placed in a mold and hot-pressed onto a ceramic sheet by uniaxial pressure using a CrushIR 15-ton digital press (model number: 181-1100, available from PIKE Technologies). The hot-pressing conditions were a hot-pressing temperature of 100°C, a hot-pressing pressure of 200 MPa, and a hot-pressing time of 10 minutes. The ceramic sheet was cut into thin circular sheets with a diameter of 12 mm and a thickness of 200 μm, thereby obtaining the solid electrolyte sheet of Example 1.

[0052] A photograph of the ceramic sheet shown above was taken with a camera, as shown in Figure 2. A cross-sectional view of the ceramic sheet was taken using a scanning electron microscope (model number: JSM-6510, available from JEOL), as shown in Figure 3.

[0053] (Comparative Example 1) Preparation of a solid electrolyte not belonging to the present invention

[0054] The preparation procedure of Example 1 was repeated to prepare the solid electrolyte sheet of Comparative Example 1, except that the LLZTO powder subjected to acid treatment was replaced with LLZTO powder containing lithium carbonate that had not been acid-treated.

[0055] (Thermogravimetric analysis of solid electrolytes)

[0056] The solid electrolyte sheets of Example 1 and Comparative Example 1 were analyzed using a thermogravimetric analyzer (model number: STA 8122, available from Rigaku), and the results are shown in Figure 4. The test conditions for the thermogravimetric analyzer were as follows: Argon was introduced at a flow rate of 10 mL / min to create an argon atmosphere, and the temperature was raised from room temperature to 900°C at a heating rate of 5°C / min.

[0057] As shown in Figure 4, after the PTFE decomposes at 400°C, the amount of garnet-type solid electrolyte ceramic powder in both Example 1 and Comparative Example 1 is over 90 wt%. However, when the temperature rises to 800°C, the weight loss of the solid electrolyte sheet (represented as w / Li2CO3) in Comparative Example 1 can be observed to be greater than that of the solid electrolyte sheet (represented as w / o / Li2CO3) in Example 1. This is because lithium carbonate begins to decompose at temperatures between 500°C and 800°C.

[0058] (Preparation and testing of symmetrical batteries)

[0059] Symmetrical batteries of Example 1 and Comparative Example 1 were prepared using the solid electrolyte sheets of Example 1 and Comparative Example 1, respectively. The following materials were prepared in advance: a button cell housing, a lithium metal sheet with a diameter of 10 mm and a thickness of 0.025 mm as an electrode sheet, and an ionic liquid containing lithium salt at a concentration of 1 M. The 1 M lithium salt-containing ionic liquid was obtained by dissolving LiTFSI as a lithium salt in TEGDME.

[0060] The symmetrical battery was assembled in a glove box containing both water and oxygen concentrations of less than 1 ppm. First, the bottom cover of the button cell was placed, then the lithium metal sheet (electrode sheet), and then 5 μL of 1 M lithium salt-containing ionic liquid was added onto the electrode sheet. Subsequently, the solid electrolyte sheet of Example 1 or Comparative Example 1 was placed on top, and 5 μL of 1 M lithium salt-containing ionic liquid was added onto the solid electrolyte sheet. Finally, the lithium metal sheet (electrode sheet) and the top cover of the button cell were sequentially placed to obtain a laminate. The laminate was pressed under a pressure of 40 MPa using a button cell tablet to obtain the symmetrical batteries of Example 1 and Comparative Example 1.

[0061] The impedance of the symmetrical batteries in Example 1 and Comparative Example 1 was measured at room temperature using a modular potentiostat / galvanostat (Autolab PGSTAT302N) over an AC frequency range of 0.1 Hz to 10 Hz. 7The measurement was performed with the frequency set to Hz, and the results are shown in Figure 5. As can be seen from Figure 5, the impedance of the symmetrical battery of Example 1 (represented as w / o / Li2CO3) is significantly lower than that of the symmetrical battery of Comparative Example 1 (represented as w / Li2CO3). This indicates that a solid electrolyte that does not contain lithium carbonate can effectively reduce the interfacial impedance between the solid electrolyte and the electrode, resulting in a stable interface. In other words, the distribution of lithium ions in the symmetrical battery is uniform, and the electrode interface remains stable.

[0062] In addition, 0.05mAh / cm² 2 The symmetric batteries of Example 1 and Comparative Example 1 were cycle-tested at the specified current density and room temperature, and the results are shown in Figure 6. As can be seen in Figure 6, the symmetric battery of Example 1 (represented as w / o / Li2CO3) maintained cycle stability for over 700 hours at room temperature. In contrast, the symmetric battery of Comparative Example 1 (represented as w / Li2CO3) maintained cycle stability for only about 100 hours. This indicates that a solid electrolyte without lithium carbonate can effectively reduce the interfacial impedance between the solid electrolyte and the electrode, thereby improving the cycle life of the lithium-ion battery.

[0063] 3.2. Preparation and Testing of Lithium-ion Batteries

[0064] First, LFP as the active material for the positive electrode, conductive carbon KS6 as the carbon source, and poly(vinylidene fluoride) (PVDF) as the binder were placed in a mortar in a weight ratio of 75:20:5 and stirred for 20 minutes. Next, 2.0 mL of N-methyl-2-pyrrolidone (NMP) was added to the mortar as a solvent, and the mixture was stirred uniformly to obtain a slurry. Then, the slurry was coated onto aluminum foil to form a layer approximately 150 μm thick, and the coated aluminum foil was dried in a vacuum oven at 100°C for 12 hours to remove the solvent. Next, the dried film formed from the slurry was peeled off the aluminum foil and cut into circular positive electrode sheets with a diameter of 8 mm and a thickness of 100 μm.

[0065] Furthermore, a lithium metal sheet with a diameter of 8 mm and a thickness of 0.025 mm was prepared as the negative electrode sheet.

[0066] Lithium-ion batteries of Example 1 and Comparative Example 1 were prepared using the solid electrolyte sheets of Example 1 and Comparative Example 1, respectively. The following materials, a housing for the button cell, and an ionic liquid containing a 1M lithium salt were prepared in advance. The 1M lithium salt-containing ionic liquid was obtained by dissolving LiTFSI as the lithium salt in TEGDME. The lithium-ion batteries were assembled in a glove box where both water and oxygen levels were less than 1 ppm. First, the bottom cover of the button cell was placed, then the positive electrode sheet was placed, and 5 μL of the 1M lithium salt-containing ionic liquid was added onto the positive electrode sheet. Then, the solid electrolyte sheet of Example 1 or Comparative Example 1 was placed on top, and 5 μL of the 1M lithium salt-containing ionic liquid was added onto the solid electrolyte sheet. Finally, the negative electrode sheet and the top cover of the button cell were placed sequentially to form a laminate. The laminate was pressed under a pressure of 40 MPa using a button cell tablet press to obtain the lithium-ion batteries of Example 1 and Comparative Example 1.

[0067] The impedance of the lithium-ion batteries in Example 1 and Comparative Example 1 was measured at room temperature using a modular potentiostat / galvanostat (Autolab PGSTAT302N) over an AC frequency range of 0.1 Hz to 10 Hz. 7 The measurement was performed with the frequency set to Hz, and the results are shown in Figure 7. As can be seen from Figure 7, the sum of the bulk impedance and interface impedance of the lithium-ion battery of Comparative Example 1 (represented as w / Li2CO3) is a maximum of 10783Ω, while the sum of the bulk impedance and interface impedance of the lithium-ion battery of Example 1 (represented as w / o / Li2CO3) is only about 787Ω. Furthermore, as shown in the enlarged upper left portion of Figure 7, the bulk impedance of the lithium-ion battery of Comparative Example 1 in the high-frequency range is also greater than that of the lithium-ion battery of Example 1. This indicates that a solid electrolyte that does not contain lithium carbonate can effectively reduce the interface impedance between the solid electrolyte and the electrode.

[0068] Furthermore, the lithium-ion batteries of Example 1 and Comparative Example 1 underwent their first charge-discharge cycles at a charge-discharge current of 0.1C and room temperature conditions, and the results are shown in Figure 8. As can be seen from Figure 8, the lithium-ion battery of Comparative Example 1 (represented as w / Li2CO3) failed to complete its first charge-discharge cycle, while the lithium-ion battery of Example 1 (represented as w / o / Li2CO3) successfully completed its first charge-discharge cycle, achieving an initial discharge capacity of 123.25 mAh / g. This indicates that a solid electrolyte without lithium carbonate can effectively reduce the interfacial impedance between the solid electrolyte and the electrode, maintain a stable interface, improve lithium-ion conductivity, and thereby improve the electrochemical properties of the lithium-ion battery.

[0069] The above examples are used to illustrate the principles and effectiveness of the present invention and to demonstrate its inventive features, and do not limit the scope of the invention. Those skilled in the art can make various modifications and substitutions based on the disclosures and suggestions of the present invention. Therefore, the scope of protection of the present invention is limited to that described in the appended claims.

Claims

1. A solid electrolyte for a lithium-ion battery comprising a garnet-type solid electrolyte and a polymer filler, wherein the polymer filler is dispersed within the garnet-type solid electrolyte, the garnet-type solid electrolyte does not contain lithium carbonate, and the content of the garnet-type solid electrolyte is 60 wt% or more based on the total weight of the garnet-type solid electrolyte and the polymer filler.

2. The garnet-type solid electrolyte is Li ６．４ La ３ Zr １．４ Ta ０．６ O １２ (LLZTO), Li ６．４ La ３ Zr ２ Al ０．２ O １２ (LLZAO), Li ６．４ La ３ Zr ２ Ga ０．２ O １２ (LLZGO), Li ６．２５ Al ０．２０ La ３ Zr １．８５ Nb ０．１５ O １２ The solid electrolyte according to claim 1, selected from the group consisting of (LALZNO) and combinations thereof.

3. The solid electrolyte according to claim 1, wherein the garnet-type solid electrolyte is provided by a garnet-type solid electrolyte ceramic powder that does not contain lithium carbonate.

4. The solid electrolyte according to claim 3, wherein the garnet-type solid electrolyte ceramic powder, which does not contain lithium carbonate, has an average particle size of less than 100 μm.

5. The solid electrolyte according to any one of claims 1 to 4, wherein the polymer filler is made from a material selected from the group consisting of polytetrafluoroethylene (PTFE), poly(ethylene oxide) (PEO), polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), and combinations thereof.

6. The solid electrolyte according to any one of claims 1 to 4, wherein the content of the polymer filler is in the range of 0.1 wt% to less than 40 wt%, based on the total weight of the garnet-type solid electrolyte and the polymer filler.

7. A lithium-ion battery comprising a positive electrode, a negative electrode, and a solid electrolyte according to any one of claims 1 to 4.

8. The positive electrode is LiFePO ４ (LFP), LiCoO ２ The lithium-ion battery according to claim 7, made from a material selected from the group consisting of (LCO), lithium nickel cobalt aluminum oxide (NCA), and lithium nickel cobalt manganese oxide (NCM).

9. The lithium-ion battery according to claim 7, wherein the negative electrode is made from a material selected from the group consisting of lithium metal, lithium indium alloy, lithium aluminum alloy, silicon lithium alloy, and combinations thereof.

10. The lithium-ion battery according to claim 7, further comprising an ionic liquid between the positive electrode and the solid electrolyte, and between the negative electrode and the solid electrolyte, wherein the ionic liquid contains a lithium salt.

11. The lithium salts mentioned above are lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPF ６ LiBF ４ LiClO ４ LiAsF ６ LiCF ３ SO ３ A lithium-ion battery according to claim 10, selected from the group consisting of, and combinations thereof.

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