Solid electrolyte, lithium secondary battery including the same, and Methods thereof

Abstract

The present invention relates to a lithium secondary battery, wherein the lithium secondary battery comprises a first electrode, a second electrode spaced apart from the first electrode, and a solid electrolyte disposed between the first electrode and the second electrode. The solid electrolyte comprises a fiber comprising polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol, and a plurality of sulfide particles. The fiber is in contact with at least some of the sulfide particles.

Description

Technology Field

[0001] The present invention relates to a lithium secondary battery, and more specifically, to a solid electrolyte and a lithium secondary battery containing the same. Background Technology

[0002] Secondary batteries may include lithium batteries. Recently, the applicability of lithium batteries has been expanding. For example, lithium batteries are widely used as power sources for electric vehicles (EVs) and energy storage systems (ESS). Increasing the flame retardant content may lead to cost and performance issues.

[0003] The electrolyte in a lithium battery may include a liquid electrolyte or a solid electrolyte. In the case of liquid electrolytes, flammability and combustibility issues can compromise the stability of lithium secondary batteries. Various studies are being conducted to address this. [Published Patent Application No. 10-2023-0058153] The problem to be solved

[0004] The technical problem that the present invention aims to solve is to provide a solid electrolyte and a secondary battery with improved thermal stability and enhanced electrochemical properties. means of solving the problem

[0005] A lithium secondary battery according to some embodiments of the present invention may include a first electrode, a second electrode spaced apart from the first electrode, and a solid electrolyte disposed between the first electrode and the second electrode. The solid electrolyte may include a fiber comprising polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol, and a plurality of sulfide particles. The fiber may come into contact with at least some of the sulfide particles.

[0006] According to some embodiments, the fiber may have a thickness of 5 μm or less.

[0007] According to some embodiments, the solid electrolyte may have a thickness of 10 μm or more and 99 μm or less.

[0008] According to some embodiments, the sulfide may include LPSCl sulfide.

[0009] According to some embodiments, the weight of the polytetrafluoroethylene may be 0.1 wt% to 2 wt% of the weight of the solid electrolyte.

[0010] According to some embodiments, the fiber may have one or more shapes among a straight shape, a curved shape, and a curved shape having a split portion.

[0011] According to some embodiments, at least one of the first electrode and the second electrode may include particles identical to the sulfide particles included in the solid electrolyte.

[0012] According to some embodiments, the polytetrafluoroethylene may have a number average molecular weight of 10,000 kg / mol to 15,000 kg / mol.

[0013] According to some embodiments, the weight of the sulfide particles may be 98 wt% to 99.9 wt% of the weight of the solid electrolyte.

[0014] According to some embodiments, the polytetrafluoroethylene may have a number average molecular weight of 12,895 kg / mol.

[0015] A method for manufacturing a lithium secondary battery according to some embodiments of the present invention may include preparing a first electrode, preparing a second electrode, preparing a solid electrolyte, and placing the solid electrolyte between the first electrode and the second electrode. Preparing the solid electrolyte may include preparing a plurality of sulfide particles, preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol, mixing the polytetrafluoroethylene and the plurality of sulfide particles to prepare a mixture, thermally grinding the mixture to prepare a dough, and thermally pressing the dough to prepare a solid electrolyte.

[0016] According to some embodiments, in preparing the mixture, the weight ratio of the polytetrafluoroethylene to the sulfide particles may be 0.1:99.9 to 2:98.

[0017] According to some embodiments, in preparing the polytetrafluoroethylene, the number average molecular weight of the polytetrafluoroethylene may be 10,000 kg / mol to 15,000 kg / mol.

[0018] According to some embodiments, in preparing the plurality of sulfide particles, the plurality of sulfide particles may include LPSCl sulfide.

[0019] According to some embodiments, the dough may be manufactured at 60°C to 140°C.

[0020] According to some embodiments, the thermal grinding treatment in manufacturing the dough may be performed for a time of 100 to 400 seconds.

[0021] According to some embodiments, in manufacturing the solid electrolyte, the hot-pressing treatment may be a unidirectional hot-pressing treatment.

[0022] According to some embodiments, in manufacturing the solid electrolyte, the hot-pressure treatment may be performed at 60°C to 140°C.

[0023] According to some embodiments, in manufacturing the solid electrolyte, the hot-pressing treatment may be performed using a plurality of press rolls.

[0024] A method for manufacturing a solid electrolyte for a lithium secondary battery according to some embodiments of the present invention may include preparing a plurality of sulfide particles, preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol, mixing the polytetrafluoroethylene and the plurality of sulfide particles to produce a mixture, thermally grinding the mixture to produce a dough, and thermally pressing the dough to produce a solid electrolyte. Effects of the invention

[0025] The solid electrolyte and secondary battery according to the present invention can have improved thermal stability and enhanced electrochemical properties. Brief explanation of the drawing

[0026] FIG. 1a is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention. FIG. 1b is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention. Figure 2 is an enlarged view of area A of Figures 1a and 1b. FIG. 3a is a flowchart of a method for manufacturing a solid electrolyte according to one embodiment of the present invention. FIG. 3b is a flowchart of a method for manufacturing a secondary battery according to one embodiment of the present invention. Figure 4a shows the polytetrafluoroethylene (PTFE) particles of Example 1-1. Figure 4b shows the SEM observation results of Example 1-1. Figure 4c shows polytetrafluoroethylene (PTFE) particles of Example 1-2. Figure 4d shows the SEM observation results of Example 1-2. Figure 4e shows polytetrafluoroethylene (PTFE) particles of Examples 1-3. Figure 4f shows the SEM observation results of Examples 1-3. Figure 4g shows polytetrafluoroethylene (PTFE) particles of Examples 1-4. Figure 4h shows the SEM observation results of Examples 1-4. Figure 4i shows polytetrafluoroethylene (PTFE) particles of Examples 1-5. Figure 4j shows the SEM observation results of Examples 1-5. Figure 5a shows the SEM observation results of Example 2-2. Figure 5b shows the SEM observation results of Examples 2-3. Figure 5c shows the SEM observation results of Examples 2-4. Figure 5d shows the SEM observation results of Examples 2-5. Figure 6a shows the experimental results of the degree of fibrillation according to the stress time (sec) of grinding under 100°C conditions for Examples 1-1 to 1-5. FIG. 6b shows the experimental results of the degree of fiberization according to the grinding temperature (Stress temperature, °C) under the condition of grinding for 240 seconds for Examples 1-1 to 1-5. Figure 7a shows the SEM observation results of Example 3-2. Figure 7b shows the SEM observation results of Examples 3-4. Figure 7c shows the SEM observation results of Examples 3-5. Figure 8a shows the visual observation results of the dough of Example 4-2. Figure 8b shows the visual observation results of Example 4-4 dough. Figure 8c shows the visual observation results of the dough of Examples 4-5. Figures 9a and 9b show the condition of Example 4-4 after applying maximum tensile stress. Figure 9c shows the state of the Example 4-4 dough when maximum tensile stress was applied, observed by SEM. Figures 10a and 10b show the condition of the diagrams of Examples 4-5 after applying maximum tensile stress. Figure 10c shows the condition of the dough of Examples 4-5 observed by SEM when maximum tensile stress was applied. Fig. 10d is an enlarged view of area B of Fig. 10c. Figure 11 shows the results of comparing the Stress-Strain curves of Example 4-4 and Example 4-5. FIG. 12 illustrates Example 5. FIG. 13a shows the thickness measurement results using a micrometer of Example 5. Figure 13b shows the thickness measurement results using a high-magnification SEM of Example 5. Figure 14a is the result of the S element EDS mapping of Example 5. Figure 14b is the result of the Cl element EDS mapping of Example 5. Figure 14c is the result of the P element EDS mapping of Example 5. Figure 15a shows the discharge capacity retention rate according to the number of charge / discharge cycles of Example 6. Figure 15b shows the Coulomb efficiency according to the number of charge / discharge cycles of Example 6. Specific details for implementing the invention

[0027] To fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention. In the attached drawings, the components are depicted enlarged from their actual size for convenience of explanation, and the proportions of each component may be exaggerated or reduced.

[0029] FIG. 1a is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention.

[0030] Referring to FIG. 1a, a lithium secondary battery (1a) according to an embodiment of the present invention may include a first current collector (110), a first electrode (120) on the first current collector (110), an electrolyte (230) on the first electrode (120), a second electrode (220) on the electrolyte (230), and a second current collector (210) on the second electrode (220).

[0031] A first current collector (110) may be provided. The first current collector (110) may include a metal. The first current collector (110) may include, for example, copper or aluminum. The first current collector (110) may have a thickness of, for example, 10 μm or less.

[0032] A first electrode (120) may be provided on a first current collector (110). The first electrode (120) may function as an anode. The first electrode (120) may include an anode active material, a conductive material, and a binder.

[0033] An electrolyte (230) may be placed on the first electrode (120). The electrolyte (230) may serve as a medium for transferring lithium ions between the first electrode (120) and the second electrode (220). The electrolyte (230) may be a solid electrolyte. The electrolyte (230) may be a sulfide-based solid electrolyte. The electrolyte (230) may be manufactured by a dry process. The electrolyte (230) may include sulfide and polytetrafluoroethylene (PTFE). The electrolyte (230) may have a thickness of 10 μm to 99 μm.

[0034] The electrolyte (230) can be manufactured by a dry process. In the case of a dry process, a solid sulfide powder and a binder are used without a liquid organic solvent, so a process to remove the liquid organic solvent is not required, and thus the process can be simple. In the case of a dry process, it can be easy to manufacture into a thin film.

[0035] A second electrode (220) may be disposed on an electrolyte (230). The second electrode (220) may be spaced apart from the first electrode (120) with the electrolyte (230) in between. The electrolyte (220) may be disposed between the first electrode (120) and the second electrode (220). The second electrode (220) may function as an anode. The second electrode (220) may include an anode active material, a conductive material, and a binder.

[0036] A second current collector (210) may be provided on the second electrode (220). The second current collector (210) may include a metal. The second current collector (210) may include, for example, copper or aluminum. The second current collector (210) may have a thickness of, for example, 10 μm or less.

[0038] FIG. 1b is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention.

[0039] Referring to FIG. 1b, the lithium secondary battery (1b) according to an embodiment of the present invention is identical to FIG. 1a except that the second electrode (220a) is different. The following description will focus on the differences, excluding the parts that are identical to FIG. 1a.

[0040] Referring to FIG. 1b, the second electrode (220a) may be a composite electrode. The second electrode (220a) may be a composite electrode to which, for example, sulfide particles and fiber powder have been added. The sulfide particles of the second electrode (220) may, for example, include sulfide particles identical to those of the solid electrolyte. When the electrolyte (230) is a solid electrolyte in a solid state, it is often implemented as a composite electrode (220a). The composite electrode (220a) has the advantage of improving contact with the electrolyte (230).

[0042] FIG. 2 is a drawing for explaining a solid electrolyte according to an embodiment of the present invention, and is an enlarged view of area A of FIG. 1a and FIG. 1b.

[0043] Referring to FIG. 2, the electrolyte (230) may include sulfide particles (231) and fibers (232).

[0044] In one embodiment, the sulfide particles (231) may include LPSCl (Lithium Phosphorus Sulfur Chloride) sulfide. In one embodiment, the sulfide particles (231) may have a spherical shape. In the electrolyte (230), the weight of the sulfide particles (231) may be 98 wt% to 99.9 wt% of the weight of the electrolyte (230).

[0045] The fiber (232) may be a fiber (232, fibril). The fiber (232, fiber) may include polytetrafluoroethylene (PTFE). In the electrolyte (230), the weight of polytetrafluoroethylene may be 0.1 wt% to 2 wt% of the weight of the electrolyte (230). The number average molecular weight (Mn) of polytetrafluoroethylene may be 500 kg / mol to 20,000 kg / mol, 10,000 kg / mol to 15,000 kg / mol, or 12,895 kg / mol. The fiber (232) may be produced from polytetrafluoroethylene particles having an average particle size of 100 µm to 1,000 µm, or 500 µm. The fiber (232) may include a first fiber (2321), a second fiber (2322), and a third fiber (2323). The first fiber (2321) may have a curved shape. The second fiber (2322) may have a curved shape with a split portion. The third fiber (2323) may have a straight shape. The shape of the fiber (232) is not limited thereto.

[0046] The fiber (232) may be positioned between a plurality of sulfide particles (231). The fiber (232) may come into contact with the sulfide particles (231). The fiber (232) may wrap around at least a portion of the sulfide particles (231) or come into contact with at least a portion of the sulfide particles (231). The fiber (232) may have a thickness of 0.001 μm or more and 50 μm or less, 0.005 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, 0.05 μm or more and 1 μm or less, or 0.1 μm or more and 0.5 μm or less. The fiber (232) may have a thin thread shape.

[0048] FIG. 3a is a flowchart of a method for manufacturing a solid electrolyte according to one embodiment of the present invention.

[0049] Referring to FIG. 3a, a method (10) for manufacturing a solid electrolyte according to one embodiment of the present invention is provided. In this case, the solid electrolyte may be manufactured by a dry manufacturing process in which a liquid solvent is not used. The method (10) for manufacturing a solid electrolyte may include preparing a plurality of sulfide particles (S11), preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol (S12), mixing polytetrafluoroethylene with a plurality of sulfide particles to produce a mixture (S13), thermally grinding the mixture to produce a dough (S14), and thermally pressing the dough to produce a solid electrolyte (S15).

[0050] Preparing a plurality of sulfide particles (S11) may include preparing a plurality of LPSCl particles. Preparing a plurality of LPSCl particles may include preparing a plurality of Li6PS5Cl particles.

[0051] Preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol (S12) may include preparing polytetrafluoroethylene powder having a number average molecular weight of 500 kg / mol to 20,000 kg / mol. Preparing polytetrafluoroethylene powder having a number average molecular weight of 500 kg / mol to 20,000 kg / mol may include preparing particle polytetrafluoroethylene powder having a number average molecular weight of 500 kg / mol to 20,000 kg / mol and an average particle size of 100 µm to 1,000 µm.

[0052] The process of preparing a mixture by mixing polytetrafluoroethylene and a plurality of sulfide particles (S13) may include preparing a mixture by mixing polytetrafluoroethylene and a plurality of sulfide particles in a weight ratio of 0.1:99.9 to 2:98. As a mixing method, various methods that apply high energy, such as mixing using a magnetic bar, planetary mixer, planetary ball milling, ultrasonic process, homogenizer, and centrifugal mixer, may be utilized. As an example, the process of preparing a mixture (S13) may include preparing a mixture through a mixer.

[0053] Manufacturing dough by thermal grinding the mixture (S14) may include manufacturing dough by thermal grinding the mixture at 60°C to 140°C, 70°C to 130°C, 80°C to 120°C, 90°C to 110°C, or 100°C. Manufacturing dough by thermal grinding the mixture (S14) may include carrying out the grinding process using a mortar and pestle. As an example, manufacturing dough by thermal grinding the mixture (S14) may include carrying out the grinding process dry (i.e., without adding a liquid solvent). As an example, manufacturing dough by thermal grinding the mixture (S14) may include manufacturing dough by thermal grinding the mixture for 100 seconds to 400 seconds, and as an example, manufacturing dough by thermal grinding the mixture for 240 seconds.

[0054] Manufacturing a solid electrolyte by hot-pressing the dough (S15) may include pushing the dough into the empty space between a plurality of press rolls rotating at a temperature of 60°C to 140°C, 70°C to 130°C, 80°C to 120°C, 90°C to 110°C, or 100°C. Manufacturing a solid electrolyte by hot-pressing the dough (S15) may include reducing the empty space between the press rolls and pushing the dough into the empty space two or more times. Manufacturing a solid electrolyte by hot-pressing the dough (S15) may include pushing the dough into the empty space between the press rolls with a size of 100 μm, pushing the dough into the empty space between the press rolls with a size of 75 μm, pushing the dough into the empty space between the press rolls with a size of 50 μm, and pushing the dough into the empty space between the press rolls with a size of 30 μm.

[0056] FIG. 3b is a flowchart of a method for manufacturing a secondary battery according to one embodiment of the present invention.

[0057] Referring to FIG. 3b, a method (20) for manufacturing a secondary battery according to one embodiment of the present invention is provided. The method (20) for manufacturing a secondary battery may include preparing a first electrode (S21), preparing a second electrode (S22), preparing a solid electrolyte (S23), and placing the solid electrolyte between the first electrode and the second electrode (S24). Preparing the solid electrolyte (S23) is the same as the process of FIG. 3a.

[0058] In preparing the first electrode (S21), the first electrode may include, for example, preparing a negative electrode comprising an alloy of lithium (Li) and indium (In). In preparing the second electrode (S22), the second electrode may include, for example, preparing a positive electrode comprising a lithium cobalt oxide (LCO) positive electrode material.

[0060] Examples and experimental examples are presented below. The examples and experimental examples are broadly divided into [Polytetrafluoroethylene (PTFE) Particle Experiments], [Mixture Experiments of Polytetrafluoroethylene (PTFE) and Sulfide], and [Solid Electrolyte Experiments].

[0062] [Polytetrafluoroethylene (PTFE) Particle Experiment]

[0063] <Experiment> Selection of PTFE

[0064] <Example 1> Selection of PTFE molecular weight

[0065] Polytetrafluoroethylene (PTFE) particles of Examples 1-1 to 1-5 presented in [Table 1] below were selected. Fig. 4a shows the polytetrafluoroethylene (PTFE) particles of Example 1-1, and Fig. 4b shows the SEM observation results of Example 1-1. Fig. 4c shows the polytetrafluoroethylene (PTFE) particles of Example 1-2, and Fig. 4d shows the SEM observation results of Example 1-2. Fig. 4e shows the polytetrafluoroethylene (PTFE) particles of Example 1-3, and Fig. 4f shows the SEM observation results of Example 1-3. Fig. 4g shows the polytetrafluoroethylene (PTFE) particles of Example 1-4, and Fig. 4h shows the SEM observation results of Example 1-4. Fig. 4i shows the polytetrafluoroethylene (PTFE) particles of Example 1-5, and Fig. 4j shows the SEM observation results of Example 1-5.

[0066] Average particle diameter (㎛) Number average molecular weight (kg / mol) Example 1-1 2 19 Examples 1-2 10 25 Examples 1-3 20 2294 Examples 1-4 800 2372 Examples 1-5 500 12895

[0068] <Example 2> Preparation of tensile test samples under room temperature conditions

[0069] Examples 2-1 to 2-5, which are cylindrical samples, were prepared by pressing each particle of Examples 1-1 to 1-5 under room temperature conditions.

[0071] <Results of Tensile Test and SEM Observation Experiment for Example 2>

[0072] For Example 2, a tensile test, specifically a stress-strain test, was performed. After the tensile test, an SEM observation test was performed.

[0073] [Table 2] shows the SEM observation results after the tensile test for Examples 2-1 to 2-5. Fig. 5a shows the SEM observation results after the tensile test of Example 2-2. Fig. 5b shows the SEM observation results after the tensile test of Example 2-3. Fig. 5c shows the SEM observation results after the tensile test of Example 2-4. Fig. 5d shows the SEM observation results after the tensile test of Example 2-5.

[0074] Fiber observation results Example 2-1 Not observed Example 2-2 Not observed Examples 2-3 Observed Examples 2-4 Observed Examples 2-5 (The largest number of fibers) was observed

[0075] Referring to Table 2 and Figures 5a to 5d, in the case of Examples 2-1 and 2-2, with number average molecular weights (kg / mol) of 19 and 25 kg / mol, respectively, no thread-like fine fibers were observed around the cracks even when tensile stress was applied at room temperature. On the other hand, in the case of Examples 2-3, 2-4, and 2-5, with number average molecular weights (kg / mol) of 2,294, 2,372, and 12,895, respectively, it was confirmed that fibers were observed.

[0076] The formation of fibers observed in Examples 2-3, 2-4, and 2-5 indicates that polytetrafluoroethylene (PTFE) effectively performs the role of a binder that binds particles within a solid electrolyte. In particular, it was confirmed that polytetrafluoroethylene (PTFE) particles with a number average molecular weight (kg / mol) in Example 2-5 perform the role of a binder best.

[0078] As a result of the tensile test, a graph of tensile stress (σ) according to tensile strain (ε) of each example was obtained. Subsequently, the maximum tensile stress and toughness values ​​were calculated.

[0079] [Table 3] shows the tensile test results for Example 2.

[0080] Maximum tensile stress (MPa) Toughness (J / m 3 ) Example 2-2 0.3 7.6ⅹ10 2 Examples 2-3 0.7 2.1ⅹ10 4 Examples 2-4 0.7 2.1ⅹ10 4 Examples 2-5 0.7 3.0ⅹ10 4

[0081] Experimental results for Example 2, for Examples 2-3 to 2-5, maximum tensile stress (MPa) and toughness (J / m 3 It was confirmed that the effect as a binder was also excellent due to its outstanding performance.

[0083] The following experiment was conducted to determine the optimal process conditions for PTFE fiberization.

[0085] <Experiment> Experiment to Verify Optimal PTFE Fiberization Process Conditions

[0086] Experiment to Verify Optimal Mechanical Grinding Time

[0087] Measurement of degree of fiberization according to mechanical grinding time under 100℃ conditions

[0088] Using each particle of Examples 1-1 to 1-5, the degree of fibrillation according to the stress time (sec) applied during grinding under 100°C conditions was tested. The results of the experiment are shown in Fig. 6a.

[0089] Referring to the experimental graph for samples 1-3 to 1-5 in Fig. 6a, it was confirmed that the degree of fibrillation gradually increased when grinding up to 240 seconds, but reached saturation when grinding for more than 240 seconds. Based on this, it was confirmed that under 100°C conditions, grinding for 240 seconds is the optimal condition that satisfies both process cost and degree of fibrillation.

[0091] Experiment to Verify Optimal Grinding Temperature

[0092] Measurement of the degree of fiberization according to changing temperature under 240-second grinding conditions

[0093] Using each particle of Examples 1-1 to 1-5, the degree of fiberization according to the grinding temperature (Stress temperature, °C) was tested under the condition of grinding for 240 seconds. The results of the experiment are shown in Fig. 6b.

[0094] Referring to the experimental graph for samples 1-3 to 1-5 in Fig. 6b, the experimental results confirmed that at temperatures below 100°C, the degree of fiberization increased as the stress temperature increased. In particular, for sample 1-5 with a molecular weight of 12,895 kg / mol, it was confirmed that the degree of fiberization saturates from a temperature of 70°C or higher, and for samples 1-3 and 1-4 with molecular weights of 2,294 and 2,372 kg / mol, respectively, it was confirmed that a temperature condition of 100°C showed a sufficient degree of fiberization to manufacture the binder.

[0096] A fiber manufacturing experiment was conducted with fiber manufacturing conditions of a stress temperature of 100℃ and a grinding time of 240 seconds.

[0098] <Example 3> Fiber preparation under conditions of 100℃ and a grinding time of 240 seconds

[0099] Fibers of Examples 3-1 to 3-5 were prepared by grinding each particle of Examples 1-1 to 1-5 at 100°C for 240 seconds.

[0101] SEM observation experiment results for <Example 3>

[0102] For Example 3, it was confirmed whether the fiber was manufactured well through SEM observation. [Table 4] shows the results of the SEM observation experiment for Example 3. Fig. 7a shows the SEM observation results of Example 3-2. Fig. 7b shows the SEM observation results of Example 3-4. Fig. 7c shows the SEM observation results of Example 3-5.

[0103] Fiber observation results Example 3-1 Not observed Example 3-2 Not observed Example 3-3 Observed Examples 3-4 Observed Examples 3-5 (The largest number of fibers) was observed

[0104] Referring to Table 4 and Figures 7a to 7c, it was confirmed that, similar to the SEM observation results for Example 2 described above, fibers were not produced in the case of Examples 3-1 and 3-2, but fibers were produced in the case of Examples 3-3 to 3-5.

[0106] <Tensile test results for Example 3>

[0107] A tensile test was conducted on Example 3 using the same method as the tensile test for Example 2 described above. [Table 5] shows the results of the tensile test for Example 3.

[0108] Maximum tensile stress (MPa) Toughness (J / m 3 ) Examples 3-4 1.8 8.1ⅹ10 4 Examples 3-5 1.9 2.1ⅹ10 5

[0109] By referring to [Table 3] and [Table 5] together, it can be confirmed that PTFE tensile test samples with increased maximum tensile stress (MPa) and toughness (J / m3) can be produced when ground for 240 seconds under 100℃ conditions.

[0111] The aforementioned experimental results are from fiber manufacturing experiments using only PTFE particles. To test the physical properties of the mixture when PTFE particles and LPSCl-based sulfide particles are mixed, the dough produced during the solid electrolyte manufacturing process was tested as a sample as follows.

[0113] [Experiment on a mixture of polytetrafluoroethylene (PTFE) and sulfides]

[0114] <Example 4> Preparation of Hard Dough under conditions of 100℃ and 240 seconds grinding time

[0115] Each particle of Examples 1-2, 1-4, and 1-5 was mixed with Li6PS5Cl sulfide particles in a weight ratio of 2:98. The mixture was then ground at 100°C for 240 seconds, and the dough for Examples 4-2, 4-4, and 4-5 was visually inspected to see if it was prepared.

[0116] In this specification, the term "dough" may refer to a state in which adhesive force is formed between the constituent components. Although there is no adhesive force in the powder state, PTFE can perform an adhesive function due to fiberization. As a result, adhesive force is formed with the sulfide particles, and a dough can be formed.

[0118] Figure 8a shows the visual observation results for Example 4-2 prepared based on the particles of Example 1-2. Figure 8b shows the visual observation results for Example 4-4 prepared based on the particles of Example 1-4. Figure 8c shows the visual observation results for Example 4-5 prepared based on the particles of Example 1-5.

[0119] Experimental results showed that in the case of Fig. 8a, which was prepared based on the particles of Example 1-2, no dough was produced and the powder remained in its original state. In the case of Figs. 8b and 8c, which were prepared based on the particles of Example 1-4 and Example 1-5, it was confirmed that dough was produced.

[0120] In the case of Figs. 8b and 8c, PTFE with number average molecular weights of 2,372 kg / mol and 12,895 kg / mol, respectively, effectively performs the role of a binder for binding Li6PS5Cl particles, resulting in adhesion to the Li6PS5Cl particles and the formation of a dough. In particular, in the case of Fig. 8c, a dough is formed over a larger area than in Fig. 8b, and since the most active fiberization occurs, it was confirmed that it performs the role of a binder most effectively.

[0122] <Tensile test results for Example 4>

[0123] Tensile tests were performed on the doughs of Examples 4-4 and 4-5, which were manufactured. Tensile tests were conducted in the same manner as the tensile test for Example 2 described above. In addition, the state after applying the maximum tensile stress was observed visually. Furthermore, the state when the maximum tensile stress was applied was observed using SEM.

[0124] Figures 9a and 9b show the condition of the Example 4-4 dough after applying the maximum tensile stress. Figure 9c shows the condition of the Example 4-4 dough when the maximum tensile stress is applied, observed via SEM. Figures 10a and 10b show the condition of the Example 4-5 dough after applying the maximum tensile stress. Figure 10c shows the condition of the Example 4-5 dough when the maximum tensile stress is applied, observed via SEM. Figure 10d is an enlarged view of area B in Figure 10c. Figure 11 shows the results of comparing the Stress-Strain curves of the Example 4-4 dough and the Example 4-5 dough.

[0126] Referring to FIGS. 9a, 9b, 10a, and 10b together, in the case of the dough of Example 4-4, fracture occurs when the maximum tensile stress is applied, whereas in the case of the dough of Example 4-5, only partial torn occurs first when the maximum tensile stress is applied, and fracture does not occur.

[0128] From this, it was confirmed that in both Example 4-4 dough and Example 4-5 dough, the PTFE binder plays a role in fixing LPSCl sulfide particles, but in Example 4-5 dough, the PTFE binder performs the role of fixing LPSCl sulfide particles better than in Example 4-4 dough.

[0129] Referring to FIGS. 9c, FIGS. 10c, and FIGS. 10d together, it can be seen that in the case of Example 4-4 dough, although the PTFE was fiberized, some PTFE fibers were clumped together without wrapping around the LPSCl sulfide particles. On the other hand, in the case of Example 4-5 dough, it can be seen that the PTFE fibers did not clump together and wrapped around the LPSCl sulfide particles relatively uniformly.

[0130] Referring to Fig. 11, it was confirmed that in the case of Example 4-5, the maximum tensile stress was 7 times greater and the toughness was 30 times greater than in Example 4-4.

[0132] [Solid Electrolyte Experiment]

[0133] <Example 5>

[0134] Solid electrolyte experiments were conducted based on the particles of Examples 1-5, which had the best physical properties as a result of the dough manufacturing experiment. First, a mixture was prepared by mixing the particles of Examples 1-5 and Li6PS5Cl particles in a weight ratio of 0.5:99.5. Subsequently, the mixture was ground in a mixer at 100°C for 240 seconds to produce dough. The solid electrolyte of Example 5 was prepared by applying unidirectional hot-pressure treatment to the prepared dough.

[0135] A process of pushing dough into the empty space between two press rolls rotating at 100°C was carried out as a unidirectional hot-pressing process. At this time, in order to reduce the thickness of the dough, the process of pushing dough into the empty space was performed a total of 4 times while decreasing the size of the empty space in the order of 100 µm, 75 µm, 50 µm, and 30 µm.

[0137] Figure 12 illustrates Example 5 prepared. Referring to Figure 12, a solid electrolyte measuring 12 cm in width and 12 cm in length was prepared through a solid electrolyte preparation experiment. The solid electrolyte of Figure 12 can be cut and used as needed.

[0139] <Thickness measurement results using a micrometer>

[0140] The thickness of the manufactured Example 5 was measured using a micrometer. Figure 13a shows the results of the thickness measurement of Example 5 using a micrometer, and it was confirmed that it had a thickness of 18 μm.

[0142] <Thickness measurement results using high-magnification SEM>

[0143] The thickness of the prepared Example 5 was measured using a high-magnification SEM. Figure 13b shows the results of the thickness measurement of Example 5 using a high-magnification SEM, and it was confirmed that the experimental results matched the thickness measurement results using a micrometer, with a thickness of 18 μm.

[0145] <EDS 원소 매핑(mapping) 결과>

[0146] An EDS elemental mapping experiment was conducted using Example 5 as a sample. This was to verify whether the Li6PS5Cl particles were well dispersed within the solid electrolyte. EDS mapping was performed on the elements P, S, and Cl of Li6PS5Cl. Figure 14a shows the EDS mapping results for the S element of Example 5. Figure 14b shows the EDS mapping results for the Cl element of Example 5. Figure 14c shows the EDS mapping results for the P element of Example 5.

[0147] Referring to Figures 14a to 14c, it was confirmed that the S element, the Cl element, and the P element were well dispersed within the solid electrolyte, and not only was the solid electrolyte successfully manufactured, but the polytetrafluoroethylene (PTFE) particles of Examples 1-5 were also confirmed to successfully bind the Li6PS5Cl particles.

[0149] <Ion Conductivity Measurement Results>

[0150] Measurement experiments for electrical conductance (mS) and ionic conductivity (mS / cm) were conducted using Example 5 as a sample. [Table 6] shows the measurement results of electrical conductance (mS) and ionic conductivity (mS / cm) of Example 5.

[0151] Sample Electric conductance (mS) Ionic conductivity (mS / cm) Example 5 625 0.84

[0152] Experimental results confirmed that the solid electrolyte of Example 5 has electrical conductance and ionic conductivity values ​​that can be applied as a secondary battery.

[0154] <Lithium Secondary Battery Charge / Discharge Cycling Evaluation Results>

[0155] A lithium secondary battery of Example 6 was manufactured using Example 5 as a sample. A cathode containing an LCO (Lithium cobalt oxide) cathode material was used as the positive electrode, and a negative electrode containing an alloy of lithium (Li) and indium (In) was used as the negative electrode. A lithium secondary battery of Example 6 was manufactured by placing the solid electrolyte of Example 5 between the positive electrode and the negative electrode.

[0156] Subsequently, charge-discharge cycling evaluation was conducted under 0.3C charge-discharge conditions using Example 6 as a sample. Coulomb efficiency (Column efficiency, %) and discharge capacity retention rate (Discharge retention rate, %) were measured. Figure 15a shows the Coulomb efficiency of Example 6 according to the number of charge-discharge cycles. Figure 15b shows the discharge capacity retention rate of Example 6 according to the number of charge-discharge cycles.

[0157] Referring to Fig. 15a, it can be seen that Example 6 exhibits high Coulomb efficiency. Referring to Fig. 15b, it was confirmed that it exhibits a high discharge capacity retention rate of 84% despite 150 cycles, indicating a discharge capacity retention rate that can be applied as a secondary battery.

[0159] Although embodiments of the present invention have been described above with reference to the attached drawings, the present invention may be implemented in other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 A lithium secondary battery comprising: a first electrode; a second electrode spaced apart from the first electrode; and a solid electrolyte disposed between the first electrode and the second electrode, wherein the solid electrolyte comprises: a fiber comprising polytetrafluoroethylene having a number average molecular weight of 2,000 kg / mol to 15,000 kg / mol; and a plurality of sulfide particles, wherein the fiber is in contact with at least some of the sulfide particles. Claim 2 In claim 1, the fiber is a lithium secondary battery having a thickness of 5 μm or less. Claim 3 In claim 1, the solid electrolyte is a lithium secondary battery having a thickness of 10㎛ or more and 99㎛ or less. Claim 4 In claim 1, the sulfide is a lithium secondary battery comprising LPSCl sulfide. Claim 5 A lithium secondary battery according to claim 1, wherein the weight of the polytetrafluoroethylene is 0.1 wt% to 2 wt% of the weight of the solid electrolyte. Claim 6 In claim 1, the fiber is a lithium secondary battery having one or more shapes among a straight shape, a curved shape, and a curved shape having a split portion. Claim 7 A lithium secondary battery according to claim 1, wherein at least one of the first electrode and the second electrode comprises particles identical to the sulfide particles included in the solid electrolyte. Claim 8 In claim 1, the polytetrafluoroethylene is a lithium secondary battery having a number average molecular weight of 10,000 kg / mol to 15,000 kg / mol. Claim 9 A lithium secondary battery according to claim 1, wherein the weight of the sulfide particles is 98 wt% to 99.9 wt% of the weight of the solid electrolyte. Claim 10 In claim 1, the polytetrafluoroethylene is a lithium secondary battery having a number average molecular weight of 12,895 kg / mol. Claim 11 A method for manufacturing a lithium secondary battery comprising: preparing a first electrode; preparing a second electrode; preparing a solid electrolyte; and placing the solid electrolyte between the first electrode and the second electrode, wherein preparing the solid electrolyte comprises: preparing a plurality of sulfide particles; preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol; mixing the polytetrafluoroethylene and the plurality of sulfide particles to produce a mixture; thermally grinding the mixture to produce a dough; and thermally pressing the dough to produce a solid electrolyte. Claim 12 A method for manufacturing a lithium secondary battery according to claim 11, wherein in preparing the mixture, the weight ratio of the polytetrafluoroethylene to the sulfide particles is 0.1:99.9 to 2:

98. Claim 13 A method for manufacturing a lithium secondary battery according to claim 11, wherein, in preparing the polytetrafluoroethylene, the number average molecular weight of the polytetrafluoroethylene is 10,000 kg / mol to 15,000 kg / mol. Claim 14 A method for manufacturing a lithium secondary battery according to claim 11, wherein, in preparing the plurality of sulfide particles, the plurality of sulfide particles include LPSCl sulfide. Claim 15 In claim 11, the method for manufacturing a lithium secondary battery is performed at 60°C to 140°C to manufacture the above dough. Claim 16 A method for manufacturing a lithium secondary battery according to claim 11, wherein the thermal grinding treatment in manufacturing the above dough is performed for a time of 100 to 400 seconds. Claim 17 A method for manufacturing a lithium secondary battery according to claim 11, wherein the hot-press treatment in manufacturing the solid electrolyte is a unidirectional hot-press treatment. Claim 18 A method for manufacturing a lithium secondary battery according to claim 11, wherein, in manufacturing the solid electrolyte, the hot-pressure treatment is performed at 60°C to 140°C. Claim 19 A method for manufacturing a lithium secondary battery according to claim 11, wherein the hot-pressing treatment in manufacturing the solid electrolyte is performed using a plurality of press rolls. Claim 20 A method for manufacturing a solid electrolyte for a lithium secondary battery, comprising: preparing a plurality of sulfide particles; preparing polytetrafluoroethylene having a number average molecular weight of 500 kg / mol to 20,000 kg / mol; mixing the polytetrafluoroethylene and the plurality of sulfide particles to produce a mixture; thermally grinding the mixture to produce a dough; and thermally pressing the dough to produce a solid electrolyte.

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