Nonwoven fabric reinforcing solid electrolyte sheet, all-solid battery, and manufacturing method of the nonwoven fabric reinforcing solid electrolyte sheet

Abstract

To provide a nonwoven fabric reinforcing solid electrolyte sheet which can be thinned, which has high tensile strength even when thinned, and which further has high thermal stability; an all-solid battery that uses such a nonwoven fabric reinforcing solid electrolyte sheet; and a manufacturing method of the nonwoven fabric reinforcing solid electrolyte sheet.SOLUTION: A nonwoven fabric reinforcing solid electrolyte sheet 1 includes: a double-layer nonwoven base material 10; a solid polymer 40; and a lithium salt 50 dispersed in the solid polymer 40. The double-layer nonwoven base material 10 includes: a microfiber layer 20 including microfibers 22 containing polyethylene terephthalate; and a nanofiber layer 30 formed on one surface of the microfiber layer 20 and including nanofibers 32 of polyvinylidene fluoride. The solid polymer is housed in gaps formed in the double-layer nonwoven base material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a nonwoven fabric-reinforced solid electrolyte sheet, an all-solid battery, and a method for manufacturing a nonwoven fabric-reinforced solid electrolyte sheet.

Background Art

[0002] Lithium-ion batteries are widely used as main energy storage devices such as personal computers, smartphones, wrist-type activity monitors, and further grid energy storage devices and electric vehicles. Conventionally, organic liquid electrolytes have been used as electrolytes for lithium-ion batteries. However, since organic liquid electrolytes are harmful to the human body, it is necessary to take all precautions to prevent leakage. There are also problems such as dendrite formation on the anode and short circuits due to side reactions. Therefore, all-solid lithium batteries using solid electrolytes have been studied as electrolytes to replace organic liquid electrolytes.

[0003] As solid electrolytes, solid polymer electrolytes such as polyoxyethylene (POE) are known. Solid polymer electrolytes have the advantages of high flexibility, easy manufacturing, and low interfacial resistance with electrodes compared to thick and brittle solid ceramic electrolytes. Patent Document 1 describes a solid polymer electrolyte containing a polymer compound having a polyoxyethylene chain and a lithium salt, and a solid polymer electrolyte containing a lithium salt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the solid polymer electrolyte described in Patent Document 1 is as thick as 100 to 1000 μm. In order to meet the requirements of high volumetric energy density and long cycle life required for lithium-ion batteries, a thin and uniform-thickness solid polymer electrolyte is necessary. However, there is a problem that it is not easy to manufacture a thin and uniform-thickness solid polymer electrolyte.

[0006] By reducing the thickness of the solid polymer electrolyte, the mechanical properties tend to be impaired. That is, by reducing the thickness of the solid polymer electrolyte, the tensile strength of the solid electrolyte sheet decreases, and the thermal stability is also lost.

[0007] An object of the present invention is to provide a nonwoven fabric-reinforced solid electrolyte sheet that can be made thin, has high tensile strength even when thinned, and further has high thermal stability, to provide an all-solid-state battery using such a nonwoven fabric-reinforced solid electrolyte sheet, and to provide a method for manufacturing such a nonwoven fabric-reinforced solid electrolyte sheet.

Means for Solving the Problems

[0008] [1] The nonwoven fabric-reinforced solid electrolyte sheet of this application example is a nonwoven fabric solid electrolyte sheet comprising a two-layer nonwoven fabric base material, a solid polymer, and a lithium salt dispersed in the solid polymer, wherein the two-layer nonwoven fabric base material includes a microfiber layer having microfibers containing polyethylene terephthalate, and a nanofiber layer formed on one surface of the microfiber layer and having nanofibers containing polyvinylidene fluoride, and the solid polymer is accommodated in voids formed in the two-layer nonwoven fabric base material.

[0009] [2] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the microfibers preferably contain two types of polyesters having different melting points, and at least one of the two types of polyesters is the polyethylene terephthalate.

[0010] [3] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the microfibers include microfibers containing stretched polyethylene terephthalate and non-stretched polyethylene terephthalate, and / or microfibers having a core-sheath structure, wherein the core contains the polyethylene terephthalate and the sheath contains an ester having a melting point lower than that of the polyethylene terephthalate. The nonwoven fabric-reinforced solid electrolyte sheet is characterized by this.

[0011] [4] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the microfibers preferably have an average diameter of 1 μm to 20 μm, and the nanofibers preferably have an average diameter of 50 nm to 300 nm.

[0012] [5] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the two-layer nonwoven fabric base material has pores, and the average pore diameter of the pores is preferably 0.1 μm or more and less than 3 μm.

[0013] [6] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the solid polymer preferably contains at least one selected from the group consisting of polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polycarbonate, polysiloxane, starch, sugar, fiber, polyvinyl alcohol, polyphosphazene, and polystyrene.

[0014] [7] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the solid polymer preferably contains polyethylene oxide.

[0015] [8] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, the lithium salt preferably contains at least one selected from the group consisting of LiTFSI, LiPF 6 , LiN(CF 3 SO 2 ) 2 , Li(CF 3 SO 2 ) 3 C, LiN(SOCFCF), and LiB(CO).

[0016] [9] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, it is preferable that the mass ratio of the solid polymer to the lithium salt is 4:1 to 26:1.

[0017]

[10] In the nonwoven fabric-reinforced solid electrolyte sheet of this application example, it is preferable that the two-layer nonwoven fabric base material has a tensile strength that suppresses the growth of lithium dendrites.

[0018]

[11] The all-solid potential of this application example includes the above-mentioned nonwoven fabric-reinforced solid electrolyte sheet, a cathode electrode, and an anode electrode.

[0019]

[12] The method for manufacturing the nonwoven fabric-reinforced solid electrolyte sheet of the present invention includes a step of forming a microfiber layer having microfibers containing polyethylene terephthalate, and applying a solution containing polyvinylidene fluoride to one surface of the microfiber layer by an electrospinning method to form a nanofiber layer having nanofibers containing polyvinylidene fluoride to obtain a two-layer nonwoven fabric base material, and a casting step of casting a solid electrolyte in which a lithium salt is dispersed from the side of the microfiber layer of the two-layer nonwoven fabric base material.

[0020]

[12] In the method for manufacturing the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, a step of forming a microfiber layer having microfibers containing polyethylene terephthalate, a step of applying a solution containing polyvinylidene fluoride to one surface of the microfiber layer by an electrospinning method to form a nanofiber layer having nanofibers containing polyvinylidene fluoride to obtain a two-layer nonwoven fabric base material, a casting step of casting a solid electrolyte in which a lithium salt is dispersed from the side of the microfiber layer of the two-layer nonwoven fabric base material, and a hot pressing step of hot pressing the two-layer nonwoven fabric base material on which the solid electrolyte is cast to accommodate the solid electrolyte in the voids formed in the microfiber layer.

[0021]

[13] In the method for manufacturing the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, the hot press step is preferably a step of pressing the two-layer nonwoven fabric base material at a temperature range of 80°C to 120°C and a pressure range of 20 MPa to 30 MPa for 10 seconds to 120 seconds.

Advantages of the Invention

[0022] According to the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, the nonwoven fabric-reinforced solid electrolyte sheet includes a two-layer nonwoven fabric base material, a solid polymer, and a lithium salt dispersed in the solid polymer. Thereby, it becomes possible to make the solid electrolyte sheet thinner. As a result, when used as the solid electrolyte sheet of a solid battery, it is possible to achieve a high volumetric energy density.

[0023] Further, the nonwoven fabric-reinforced solid electrolyte sheet of the present invention includes a microfiber layer having microfibers containing polyethylene terephthalate, and a nanofiber layer formed on one surface of the microfiber layer and having nanofibers containing polyvinylidene fluoride. Since the microfiber layer and the nanofiber layer are firmly joined, even when the nonwoven fabric-reinforced solid electrolyte sheet is thinned, it has high tensile strength (mechanical stability) and thermal stability. A nonwoven fabric-reinforced solid electrolyte sheet having high tensile strength facilitates the manufacture of a highly reliable all-solid-state battery and can prevent structural failures or losses. Also, from a chemical perspective, increasing the tensile strength of the nonwoven fabric-reinforced solid electrolyte sheet can also enhance the resistance to redox environments. The tensile strength of the nonwoven fabric-reinforced solid electrolyte sheet is also effective in suppressing the formation of dendrites.

[0024] That is, according to one aspect of the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, it is possible to provide a nonwoven fabric-reinforced solid electrolyte sheet that can be thinned, has high tensile strength even when thinned, and further has high thermal stability, to provide an all-solid-state battery using such a nonwoven fabric-reinforced solid electrolyte sheet, and to provide a method for manufacturing such a nonwoven fabric-reinforced solid electrolyte sheet.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Mode for Carrying Out the Invention

[0026] Hereinafter, the non-woven fabric reinforced solid electrolyte sheet and the method for manufacturing the non-woven fabric reinforced solid electrolyte sheet according to the present invention will be described. The embodiments described below do not limit the invention according to the claims. Also, not all of the various elements and combinations thereof described in the embodiments are essential to the present invention.

[0027] 1. Non-woven fabric reinforced solid electrolyte sheet (Embodiment 1) 1-1. Overall configuration FIG. 1 is a diagram showing the nonwoven fabric-reinforced solid electrolyte sheet 1 according to Embodiment 1. FIG. 1(a) is a schematic view of the nonwoven fabric-reinforced solid electrolyte sheet 1 according to Embodiment 1. FIG. 1(b) is an electron micrograph of the nonwoven fabric-reinforced solid electrolyte sheet 1 taken from the surface of the microfiber layer 20, FIG. 1(c) is an electron micrograph of the nonwoven fabric-reinforced solid electrolyte sheet 1 taken from the surface of the nanofiber layer 30, and FIG. 1(d) is an electron micrograph of the cross-section of the nonwoven fabric-reinforced solid electrolyte sheet 1. Observation of the surface and cross-section of the nonwoven fabric-reinforced solid electrolyte sheet 1 was performed using a scanning electron microscope (SEM) JSM-60 of JEOL Ltd.

[0028] As shown in FIG. 1(a), the nonwoven fabric-reinforced solid electrolyte sheet includes a two-layer nonwoven fabric base material 10, a solid polymer 40, and a lithium salt 50 dispersed in the solid polymer 40. More specifically, the two-layer nonwoven fabric base material 10 has a microfiber layer 20 having microfibers 22 containing polyethylene terephthalate (PET), and a nanofiber layer 30 having nanofibers 32 containing polyvinylidene fluoride (PVDF).

[0029] In the two-layer nonwoven fabric base material 10, voids are formed between the microfibers 22 and between the nanofibers 32. The solid polymer 40 and the lithium salt 50 are accommodated in the above-described voids.

[0030] 1-2. Two-Layer Nonwoven Fabric Base Material FIG. 2 is a diagram showing the two-layer nonwoven fabric base material 10 constituting the nonwoven fabric-reinforced solid electrolyte sheet 1 according to Embodiment 1. FIG. 2(a) is a schematic view of the two-layer nonwoven fabric base material 10 according to Embodiment 1. FIG. 2(b) is an electron micrograph of the cross-section of the two-layer nonwoven fabric base material 10.

[0031] As shown in FIG. 2(a), the two-layer nonwoven fabric base material 10 has a microfiber layer 20 and a nanofiber layer 30 formed on one surface of the microfiber layer 20.

[0032] 1-2-1. Microfiber Layer The microfiber layer 20 has microfibers 22 mainly composed of polyethylene terephthalate (PET). Here, polyethylene terephthalate (PET) is a polyester obtained by the dehydration condensation of ethylene glycol and terephthalic acid. In this specification, the "main component" refers to a component that occupies more than half of the weight of the object (such as fibers). Also, in this specification, "mainly containing" a certain fiber means that the majority of the fibers are that certain fiber.

[0033] The microfibers 22 preferably contain two types of polyesters having different melting points. When the microfibers 22 contain two types of polyesters having different melting points, at least one of the two types of polyesters is polyethylene terephthalate (PET).

[0034] A polyester is a polymer obtained by the dehydration condensation of a polyalcohol and a polyvalent carboxylic acid. A polyester can be used without particular limitation as long as it is a polymer having an ester bond in the main chain, and includes polyethylene terephthalate (PET). Also, the polyester may be a modified polyester. Examples of polyesters include polyethylene glycol (PEG), a polyester obtained from a mixture of isophthalic acid and terephthalic acid and ethylene glycol, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and the like.

[0035] As an example of the microfibers 22 containing two types of polyesters having different melting points, a case where it contains stretched polyethylene terephthalate (PET) and non-stretched polyethylene terephthalate (PET) can be mentioned.

[0036] In this case, the melting point of the drawn polyethylene terephthalate (PET) is higher than that of the undrawn polyethylene terephthalate (PET). As a result, the undrawn polyethylene terephthalate (PET) functions as a binder, and the nanofibers 32 forming the nanofiber layer 30 can be firmly joined to the microfiber layer 20. Consequently, the ionic conductivity of the nonwoven fabric reinforced solid electrolyte sheet 1 can be enhanced.

[0037] As another example in which the microfibers 22 contain two types of polyesters having different melting points, the case where the microfibers 22 have a core-sheath structure having a core portion and a sheath portion, the core portion is polyethylene terephthalate (PET), and the sheath portion is an amorphous polyester having a melting point lower than that of polyethylene terephthalate (PET) can be cited.

[0038] In the microfibers 22, the low-melting-point polyester constituting the sheath portion functions as a binder, and the nanofibers 32 forming the nanofiber layer 30 can be firmly joined to the microfiber layer 20. As a result, the ionic conductivity of the nonwoven fabric reinforced solid electrolyte sheet 1 can be enhanced. On the other hand, since the core portion of the microfibers 22 is polyethylene terephthalate (PET), the tensile strength of the nonwoven fabric reinforced solid electrolyte sheet 1 can be made strong.

[0039] The average diameter of the microfibers 22 is preferably in the range of 1.0 μm to 20.0 μm, and more preferably in the range of 2.0 μm to 5.0 μm. When the average diameter of the microfibers 22 is equal to or greater than the lower limit of the above numerical values, the mechanical strength of the microfiber layer 20, and further of the nonwoven fabric reinforced solid electrolyte sheet 1, can be increased. Also, when the average diameter of the microfibers 22 is equal to or less than the upper limit of the above numerical values, the microfiber layer 20 can be made thinner.

[0040] The average fiber length of the microfibers 22 is, for example, 4 mm.

[0041] Further, the basis weight of the microfibers 22 in the microfiber layer 20 is, for example, 7 g / m 2 ~60 g / m 2 .

[0042] FIG. 3 shows the analysis results of the two-layer nonwoven fabric base material 10 constituting the nonwoven fabric-reinforced solid electrolyte sheet 1 according to Embodiment 1. FIG. 3(a) is an electron micrograph showing the surface state of the microfiber layer 20. FIG. 3(b) is a diagram showing the diameter distribution of the microfibers 22 contained in the microfiber layer 20. FIG. 3(c) is an electron micrograph showing the surface state of the nanofiber layer 30. FIG. 3(d) is a diagram showing the diameter distribution of the nanofibers 32 contained in the nanofiber layer 30.

[0043] As shown in FIGS. 3(a) and 3(b), it can be seen that the microfibers 22 having a diameter of 3.5 ± 0.8 μm are laminated in the microfiber layer. Further, there are gaps between the microfibers 22, and the gaps formed between the microfibers 22 are connected to form substantially voids (pores). Note that the electron micrograph shown in FIG. 3(a) is an electron micrograph when the basis weight of the polyethylene terephthalate (PET) microfibers 22 is 7 g / m 2 .

[0044] 1-2-2. Nanofiber layer The nanofiber layer 30 is formed on one surface of the microfiber layer 20. In FIG. 2, the nanofiber layer 30 is formed under the microfiber layer 20 in the figure.

[0045] The nanofiber layer 30 has nanofibers 32 containing polyvinylidene fluoride (PVDF). It is preferable that the weight of the polyvinylidene fluoride (PVDF) fibers in the nanofiber layer 30 occupies more than half of the weight of the nanofiber layer 30. More preferably, the nanofiber layer 30 is composed of the polyvinylidene fluoride (PVDF) nanofibers 32.

[0046] The microfiber layer 20 and the nanofiber layer 30 formed on one surface of the microfiber layer 20 are firmly joined. As a result, the nonwoven fabric reinforced solid electrolyte sheet 1 composed of the two-layer nonwoven fabric base material 10 will have high tensile strength (mechanical stability) and thermal stability. Since the nonwoven fabric reinforced solid electrolyte sheet 1 has high tensile strength and thermal stability, the formation of dendrites can be suppressed. Hereinafter, the effect of the tensile strength of the nonwoven fabric reinforced solid electrolyte sheet 1 in suppressing the formation of dendrites will be described.

[0047] FIG. 17 is a conceptual diagram shown to explain that the nonwoven fabric reinforced solid electrolyte sheet 1 according to Embodiment 1 suppresses the growth of Li dendrites in an all-solid-state battery. FIG. 17(a) is a conceptual diagram shown to explain the growth of dendrites in an all-solid-state battery using the nonwoven fabric reinforced solid electrolyte sheet 1 according to Embodiment 1, and FIG. 17(b) is a conceptual diagram shown to explain the growth of dendrites in an all-solid-state battery using a solid polymer composed of polyethylene oxide (PEO)-LiTFSI for reference.

[0048] In an all-solid-state battery using a solid polymer composed of polyethylene oxide (PEO)-LiTFSI, as shown in FIG. 17(b), dendrites 90 grow with the metallic lithium deposited on the anode electrode 82 as nuclei. The dendrites 90 penetrate through the solid electrolyte 86 and reach the cathode electrode 84. When the dendrites 90 reach the cathode electrode 84, a short circuit occurs.

[0049] On the other hand, in an all-solid-state battery using the nonwoven fabric reinforced solid electrolyte sheet 1 according to Embodiment 1, the microfiber layer 20 and the nanofiber layer 30 are firmly joined and have high tensile strength. Therefore, the growth of the dendrites 90 through the two-layer nonwoven fabric base material 10 can be suppressed. In addition, since the nonwoven fabric reinforced solid electrolyte sheet 1 is also excellent in thermal stability, the growth of the dendrites 90 can be suppressed even when the all-solid-state battery is used at high temperature.

[0050] In Fig. 17(a), spaces are depicted between the anode electrode 82 and the two-layer nonwoven fabric substrate 10, between the two-layer nonwoven fabric substrate 10 and the cathode electrode 84, and in Fig. 17(b), between the anode electrode 82 and the solid electrolyte 86, and between the solid electrolyte 86 and the cathode electrode 84. These spaces are drawn for clarity and do not necessarily exist in all-solid-state batteries.

[0051] That is, since the nanofiber layer 30 is composed of nanofibers 32 with a small average diameter, voids are arranged in the nanofiber layer 30, and the voids are arranged at a high density. By forming such a nanofiber layer 30 on one surface of the microfiber layer 20, it is possible to obtain a nonwoven fabric-reinforced solid electrolyte sheet 1 that has excellent mechanical properties and can suppress the growth of lithium dendrites from the anode electrode 82.

[0052] The average diameter of the nanofibers 32 is preferably in the range of 50 nm to 300 nm, and more preferably in the range of 75 nm to 145 nm. When the average diameter of the nanofibers 32 is below the upper limit of the above numerical values, a high porosity can be realized. Also, when the average diameter of the nanofibers 32 is above the lower limit of the above numerical values, the mechanical strength of the nanofiber layer 30 can be ensured, and high productivity can be realized.

[0053] The basis weight of the nanofibers 32 in the nanofiber layer 30 is, for example, 1 g / m 2 ~3 g / m 2 .

[0054] The average diameter of the nanofibers 32 can be adjusted by adjusting the inner diameter of the capillary tip 112 (see Fig. 7) that discharges a solution of polyvinylidene fluoride (PVDF), which is the material, when manufacturing the nanofibers 32 by, for example, the electrospinning method (electrostatic spinning method). The electrospinning method will be described later.

[0055] In a preferred embodiment 1, as shown in FIGS. 3(c) and 3(d), it can be seen that nanofibers 32 with a diameter of 110.6 ± 31 μm are laminated. Also, each nanofiber 32 is interconnected to show a three-dimensional fiber structure. There are gaps between the nanofibers 32, and the gaps formed between the nanofibers 32 are connected to substantially form pores. Note that the electron micrograph shown in FIG. 3(c) is an electron micrograph when the basis weight of the polyvinylidene fluoride (PVDF) nanofibers 32 is 1 g / m 2 This is an electron micrograph at this time.

[0056] The two-layer nonwoven fabric substrate 10 preferably has a porosity of 60% to 70%. By the numerical range of the porosity being equal to or higher than the lower limit of the above numerical range, more solid polymer 40 and lithium salt 50 can be stored in the voids, and the ionic conductivity of the nonwoven fabric-reinforced solid electrolyte sheet 1 can be made sufficiently high. Also, by the numerical range of the porosity being equal to or lower than the upper limit of the above numerical range, the mechanical strength of the nonwoven fabric-reinforced solid electrolyte sheet 1 can be increased.

[0057] Note that the porosity can be calculated by performing a test of immersing the sample in n-butanol at room temperature for 10 minutes. That is, the porosity (%) can be obtained by the formula P = ((Ww - Wd) / ρbV)×100, where P is the porosity, Ww is the mass of the sample before immersion, Wd is the mass of the sample after immersion, ρb is the density of n-butanol, and V is the volume of the sample.

[0058] The nanofiber layer 30 preferably has a high porosity by laminating the nanofibers 32 densely.

[0059] 1 - 3. Solid polymer Examples of the solid polymer 40 include polyethers such as polyethylene oxide and polypropylene oxide. In addition to the above-mentioned polyethers, the solid polymer 40 may contain polymethyl methacrylate, polycarbonate, polysiloxane, starch, sugar, fiber, polyvinyl alcohol, polyphosphazene, and polystyrene. The solid polymer 40 may be crosslinked.

[0060] Among them, the solid polymer 40 is preferably polyethylene oxide. Since polyethylene oxide has high flexibility of the molecular chain, it can easily enter the voids formed in the two-layer nonwoven fabric substrate 10 and can be accommodated in the voids of the two-layer nonwoven fabric substrate 10. Furthermore, polyethylene oxide has a low glass transition temperature and excellent solubility of the lithium salt 50. For these reasons, polyethylene oxide can be suitably used as the solid polymer 40.

[0061] 1-4. Lithium Salt Examples of the lithium salt 50 include LiTFSI (lithium bis(trifluoromethane)sulfonimide), LiPF 6 (lithium hexafluorophosphate), LiN(CF 3 SO 2 ) 2 (lithium bis(trifluoromethanesulfonylimide), Li(CF 3 SO 2 ) 3 C (lithium tris(trifluoromethylsulfonylmethide), LiN(SOCFCF), LiB(CO), and mixtures thereof, etc. can be mentioned.

[0062] The mass ratio of the solid polymer 40 to the lithium salt 50 is preferably 4:1 to 26:1. When the mass ratio of the solid polymer 40 to the lithium salt 50 is within the above numerical range, the viscosity of the solid polymer in which the lithium salt is dispersed can be made appropriate, and in the subsequent processes such as casting when manufacturing the nonwoven fabric-reinforced solid electrolyte sheet 1, the manufacturing can be made easy.

[0063] Furthermore, in addition to the solid polymer 40 and the lithium salt 50, it may contain oxides, ceramics, sulfides, plasticizers, etc. By including the above-mentioned oxides, etc., the ionic conductivity of the non-woven fabric reinforced solid electrolyte sheet 1 can be improved.

[0064] Examples of oxides include silica (SiO 2 ), alumina (Al 2 O 3 ), titanium oxide (TiO 2 ), barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), lithium niobate (LiNbO 3 ), carbon nanotubes, carbon quantum dots, etc.

[0065] Examples of ceramics include zeolite, Li 7 La 3 Zr 2 O 12 (LLZO), Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO), etc.

[0066] Examples of sulfides include Li 10 GeP 2 S 12 (LGPS), Li 10 SnP 2 S12(LSPS), Li 6.25 PS 5.25 C 10.25 , Li 2 S-P 2 S 5 ), etc.

[0067] Examples of plasticizers include polyethylene glycol, polyethylene, etc.

[0068] 1-5. Non-woven fabric reinforced solid electrolyte sheet As can be seen from FIGS. 1(b) and 1(c), the surfaces of the nonwoven fabric reinforced solid electrolyte sheet 1 on the microfiber layer 20 side and on the nanofiber layer 30 side are formed smoothly. This is because after casting the solid polymer 40 and the lithium salt 50, a hot press is performed on the two-layer nonwoven fabric substrate 10 to eliminate the unevenness on the surfaces of the microfiber layer 20 side and the nanofiber layer 30 side and make them smooth. By making the surfaces of the microfiber layer 20 side and the nanofiber layer 30 side smooth surfaces, good contact with the electrodes can be obtained.

[0069] The thickness of the nonwoven fabric reinforced solid electrolyte sheet 1 is preferably 80 μm or less, more preferably 40 μm or less, and even more preferably 25 μm or less. By the thickness of the nonwoven fabric reinforced solid electrolyte sheet 1 being within the above numerical range, it is possible to contribute to the reduction of the volume of the solid battery. Note that the thickness of the nonwoven fabric reinforced solid electrolyte sheet 1 according to Embodiment 1 is about 23 μm.

[0070] 2. Evaluation, Analysis 2-1. Thermogravimetric Analysis of the Two-Layer Nonwoven Fabric Substrate FIG. 4 is a diagram shown to explain the analysis results by thermogravimetric analysis (TGA) of the two-layer nonwoven fabric substrate 10 according to Embodiment 1. In FIG. 4, the horizontal axis of the graph indicates temperature (unit: °C), and the vertical axis indicates weight (unit: %). For the thermogravimetric analysis, a thermoanalyzer Thermo plus TG 8200 manufactured by Rigaku Corporation was used.

[0071] As shown in FIG. 4, for the two-layer nonwoven fabric substrate 10, only a slight weight loss due to the evaporation of adsorbed water was observed up to 350 °C, indicating that it is stable. On the other hand, between 350 °C and 450 °C, a weight loss due to the decomposition of the two-layer nonwoven fabric substrate 10 occurred. From the above results, it was confirmed that the two-layer nonwoven fabric substrate 10 can maintain its structure stably at temperatures up to 350 °C.

[0072] 2-2. Pore Size Distribution of the Two-Layer Nonwoven Fabric Substrate As described above, in the microfiber layer 20 of the two-layer nonwoven fabric base material 10 according to Embodiment 1, there are gaps between the microfibers 22, and the gaps formed between the microfibers 22 are connected to form substantially voids (holes). Also, in the nanofiber layer 30, there are gaps between the nanofibers 32, and the gaps formed between the nanofibers 32 are connected to form substantially voids (holes).

[0073] The pore diameters of the holes formed in the microfiber layer and the holes formed in the nanofiber layer are preferably 0.1 μm or more and less than 3 μm, and more preferably 0.2 μm or more and 1 μm or less.

[0074] FIG. 5 is a diagram showing the pore size distribution of the two-layer nonwoven fabric base material 10 according to Embodiment 1. In FIG. 5, the horizontal axis of the graph indicates the pore diameter (unit: μm), and the vertical axis indicates the distribution (unit: number).

[0075] As shown in FIG. 5, the average pore diameter of the two-layer nonwoven fabric base material 10 is, for example, 0.38 μm. Note that the average pore diameter of the two-layer nonwoven fabric base material 10 can be adjusted by changing the structure of the microfiber layer 20 and the structure of the nanofiber layer 30.

[0076] 3. All-solid-state battery (Embodiment 2) The all-solid-state battery according to Embodiment 2 includes a nonwoven fabric-reinforced solid electrolyte sheet 1, an anode electrode 82, and a cathode electrode 84. Since the nonwoven fabric-reinforced solid electrolyte sheet 1 is the same as the nonwoven fabric-reinforced solid electrolyte sheet 1 according to Embodiment 1 described above, the description thereof is omitted. As the anode electrode 82 and the cathode electrode 84, the anode electrodes and cathode electrodes conventionally used in all-solid-state batteries can be used without particular limitation.

[0077] 4. Manufacturing method of nonwoven fabric-reinforced solid electrolyte sheet FIG. 6 is a flowchart shown to explain a method for manufacturing a nonwoven fabric-reinforced solid electrolyte sheet according to an embodiment. As shown in FIG. 6, the method for manufacturing a nonwoven fabric-reinforced solid electrolyte sheet according to the embodiment includes a nanofiber layer forming step S10, a casting step S20, and a hot press step S30.

[0078] The nanofiber layer forming step S10 is a step of forming a nanofiber layer 30 including nanofibers 32 of polyvinylidene fluoride (PVDF) by applying a spinning solution containing polyvinylidene fluoride (PVDF) to one surface of a microfiber layer 20 including microfibers of polyethylene terephthalate (PET).

[0079] Since the microfiber layer 20 is the same as the microfiber layer 20 in the nonwoven fabric-reinforced solid electrolyte sheet described above, detailed description is omitted. However, the microfiber layer 20 including microfibers of polyethylene terephthalate (PET) can be obtained as a nonwoven fabric including microfibers of polyethylene terephthalate (PET). In the method for manufacturing a nonwoven fabric-reinforced solid electrolyte sheet according to the embodiment, a nonwoven fabric including microfibers of polyethylene terephthalate (PET) obtained from Amami Special Paper Co., Ltd. was used.

[0080] In the nanofiber layer forming step S10, first, a spinning solution containing polyvinylidene fluoride (PVDF) as a main component of the solute is prepared.

[0081] The spinning solution preferably contains only polyvinylidene fluoride (PVDF) as a polymer component for forming nanofibers. Further, the spinning solution may contain, in addition to polyvinylidene fluoride (PVDF), a substance for assisting electrospinning, etc. For example, the spinning solution may contain 0.05 wt% to 0.5 wt% of tetrabutylammonium perchlorate (TBAP).

[0082] In the nanofiber layer forming step S10, a nanofiber layer 30 including nanofibers 32 of polyvinylidene fluoride (PVDF) can be formed by an electrospinning method (electrostatic spinning method).

[0083] FIG. 7 is a schematic diagram showing an electrospinning apparatus 100 that can be suitably used in the method for manufacturing the nonwoven fabric-reinforced solid electrolyte sheet 1 according to the embodiment. The electrospinning apparatus 100 includes a syringe 110 attached with a capillary tip 112, a collector 120, and a power supply device 130.

[0084] As the syringe 110, a 2 mL to 10 mL, for example, 5 mL plastic syringe can be used. As the capillary tip 112, one having an inner diameter of 0.4 mm to 0.8 mm, for example, 0.6 mm can be used.

[0085] As the collector 120, a grounded rotary drum collector is used. During spinning, it is preferable to cover the collector 120 with kitchen paper and aluminum foil.

[0086] As the power supply device 130, for example, Har-100*12 of Matsuida Precision Co., Ltd. can be used. For the electrical connection between the anode of the power supply device 130 and the spinning solution in the syringe 110, a copper wire 132 can be suitably used.

[0087] The applied voltage and the distance between the capillary tip 112 and the collector 120 (Tip to Corrector Distance: TCD) can be determined for each nanofiber to be spun. For example, when spinning nanofibers of polyvinylidene fluoride (PVDF), the applied voltage and TCD can be appropriately set in the ranges of 10 kV to 20 kV and 10 cm to 20 cm, respectively.

[0088] Before proceeding to the next casting step S20, a gel of the solid polymer 40 / lithium salt 50 is prepared. The gel of the solid polymer 40 / lithium salt 50 is prepared by mixing the solid polymer 40 and the lithium salt 50 with a solvent at room temperature and stirring until a uniform and stable gel is formed. Examples of the solvent used for preparing the gel include a mixed solvent of DMF and acetone (DMF / acetone = 3 / 1 to 3 / 2 (v / v)).

[0089] FIG. 8 is a schematic diagram of a casting apparatus 200 that can be preferably used in the casting of the solid polymer 40. In the casting step S20, as shown in FIG. 8, a gel of the solid polymer 40 / lithium salt 50 is cast onto the two-layer nonwoven fabric substrate 10.

[0090] As shown in FIG. 8, the two-layer nonwoven fabric substrate 10 is placed on the glass plate 210, and the prepared solid polymer / lithium salt gel is cast onto the two-layer nonwoven fabric substrate 10. At this time, it is preferable to arrange the two-layer nonwoven fabric substrate 10 so that the nanofiber layer 30 is on the bottom and the microfiber layer 20 is on the top, and to cast the gel of the solid polymer 40 / lithium salt 50 from the surface of the microfiber layer 20.

[0091] In the casting step S20, by arranging the nanofiber layer 30 on the lower side of the two-layer nonwoven fabric substrate 10, the gel of the solid polymer 40 / lithium salt 50 can be stored in the voids formed in the microfiber layer 20 composed of the microfibers 22 of polyethylene terephthalate (PET), and it becomes possible to form the dense and thin nonwoven fabric-reinforced solid electrolyte sheet 1.

[0092] Examples of the casting method of the gel of the solid polymer 40 / lithium salt 50 include a slurry coating method and a doctor blade method, and the method is not particularly limited, but in terms of being able to uniformly distribute the gel of the solid polymer 40 / lithium salt 50, it is preferably by the doctor blade method.

[0093] By casting the gel of solid polymer 40 / lithium salt 50 multiple times using a doctor blade 220, the surface of the non-woven fabric reinforced solid electrolyte sheet 1 can be smoothed. Also, it can efficiently penetrate into the voids of the two-layer non-woven fabric substrate 10 of solid polymer 40 / lithium salt 50, and a uniform distribution of solid polymer 40 / lithium salt 50 in the two-layer non-woven fabric substrate 10 can be obtained.

[0094] The non-woven fabric reinforced solid electrolyte sheet 1 cast with the gel of solid polymer 40 / lithium salt 50 is placed in a vacuum oven and dried at 60°C for 24 hours.

[0095] In the hot press process S30, the microfiber layer 20 and the nanofiber layer 30 of the dried non-woven fabric reinforced solid electrolyte sheet 1 are pressed at a temperature range of 80°C to 120°C, a pressure range of 20 MPa to 30 MPa, and for 10 seconds to 120 seconds. Thereby, a dense, thin, smooth and uniform non-woven fabric reinforced solid electrolyte sheet 1 can be formed.

[0096] 5. Examples The present invention will be described below with reference to examples. Note that the present invention is not limited by these examples in any way.

[0097] 5-1. Preparation of Samples 5-1-1. Example 1 First, on one surface of the microfiber layer containing 6.9 g / m of polyethylene terephthalate (PET) microfibers, a nanofiber layer containing 2.0 g / m of polyvinylidene fluoride (PVDF) nanofibers was laminated to create a two-layer non-woven fabric substrate. Specifically, 6.9 g / m of polyethylene terephthalate (PET) microfibers 2 On one surface of the microfiber layer containing 6.9 g / m of polyethylene terephthalate (PET) microfibers, a nanofiber layer containing 2.0 g / m of polyvinylidene fluoride (PVDF) nanofibers was laminated to create a two-layer non-woven fabric substrate. 2 On one surface of the microfiber layer containing 6.9 g / m of polyethylene terephthalate (PET) microfibers, a nanofiber layer containing 2.0 g / m of polyvinylidene fluoride (PVDF) nanofibers was laminated to create a two-layer non-woven fabric substrate. Specifically, 6.9 g / m of polyethylene terephthalate (PET) microfibers 2A nonwoven fabric containing was prepared. Also, 3 g of polyvinylidene fluoride was dissolved in a mixed solvent of 15 ml of DMF / acetone (3 / 1) and dissolved at room temperature for 12 hours to prepare a spinning solution. The prepared spinning solution was filled into a plastic syringe 110 having a conductive tip at the tip. By the electrospinning method, nanofibers of polyvinylidene fluoride (PVDF) were deposited on the surface of a nonwoven fabric containing microfibers of polyethylene terephthalate (PET) wound around a stainless steel cylinder roller. The distance between the conductive tip and the cylinder roller was 15 cm, and a voltage of 15 kV was applied between the conductive tip and the cylinder roller.

[0098] Next, a polymer solution constituting the solid electrolyte was prepared. The polymer solution was prepared by mixing 1.5 g of polyethylene oxide (PEO) and 0.98 g of LiTSFI in 30 ml of acetonitrile at 25°C and stirring until a uniform solution was obtained. The polymer solution was cast from the microfiber layer side of the two-layer nonwoven fabric substrate using a doctor blade 220 to coat the microfiber layer containing the microfibers 22 of polyethylene terephthalate (PET) to form a film of polyethylene oxide. The film was vacuum dried at 60°C for 24 hours to remove the acetonitrile solvent. Finally, the two-layer nonwoven fabric substrate containing the film was hot pressed at 110°C and 20 MPa for 20 seconds to obtain the nonwoven fabric-reinforced solid electrolyte sheet of Example 1.

[0099] 5-1-2. Example 2 A two-layer nonwoven fabric substrate was produced under the same conditions as in Example 1, except that the amount of nanofibers of polyvinylidene fluoride (PVDF) contained in the nanofiber layer of the two-layer nonwoven fabric substrate and the electrospinning conditions when forming the nanofiber layer were changed as shown in Table 1. Furthermore, a nonwoven fabric-reinforced solid electrolyte sheet of Example 2 was obtained under the same conditions as in Example 1, except that the polymer solution applied to the two-layer nonwoven fabric substrate and the hot pressing conditions were changed as shown in Table 2.

[0100] 5-1-3. Example 3 The amount of microfibers of polyethylene terephthalate (PET) contained in the microfiber layer of the two-layer nonwoven fabric substrate and the conditions of electrospinning when forming the nanofiber layer were changed as shown in Table 1. Otherwise, the two-layer nonwoven fabric substrate was manufactured under the same conditions as in Example 1. Further, the polymer solution applied to the two-layer nonwoven fabric substrate and the conditions of hot pressing were changed as shown in Table 2. Otherwise, the nonwoven fabric-reinforced solid electrolyte sheet of Example 3 was obtained under the same conditions as in Example 1.

[0101]

Table 1

[0102]

Table 2

[0103] 5-2. Evaluation and evaluation results 5-2-1. Thermal stability test Using the nonwoven fabric-reinforced solid electrolyte sheet of Example 1, the thermal stability of the nonwoven fabric-reinforced solid electrolyte sheet was evaluated. The nonwoven fabric-reinforced solid electrolyte sheet of Example 1 was cut into a circle with a diameter of 20 mm and placed in an oven set at a predetermined temperature for 20 minutes. As a reference example, a solid polymer electrolyte composed of polyethylene oxide (PEO)-LiTFSI of the same size was prepared, and the thermal stability was evaluated under the same conditions as the nonwoven fabric-reinforced solid electrolyte sheet of Example 1.

[0104] FIG. 9 is a diagram showing the results of the thermal stability test of the nonwoven fabric-reinforced solid electrolyte sheet 1 of Example 1. FIGS. 9(a1), (a2), (a3), and (a4) are photographs showing the states of the nonwoven fabric-reinforced solid electrolyte sheet of Example 1 after being left in a thermostat at RT (without heat history), 160° C., 180° C., and 200° C. for 20 minutes, respectively. FIGS. 9(b1), (b2), (b3), and (b4) are photographs showing the states of the solid polymer electrolyte of the reference example after being left in a thermostat at RT (without heat history), 160° C., 180° C., and 200° C. for 20 minutes, respectively. As shown in FIG. 9(b2), the solid polymer electrolyte of the reference example shrank at 160° C. and melted at 180° C. and 200° C. as shown in FIGS. 9(b3) and (b4). On the other hand, as shown in FIG. 9(a4), the nonwoven fabric-reinforced solid electrolyte sheet of Example 1 showed no change in shape even at 200° C. That is, it can be seen that the nonwoven fabric-reinforced solid electrolyte sheet according to the embodiment has significantly improved thermal stability compared to the conventional solid polymer electrolyte. According to the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, it can be seen that a solid polymer electrolyte excellent in thermal stability and usable in a wide temperature range, particularly in a high-temperature region, can be provided.

[0105] 5-2-2. Tensile Strength Analysis The tensile strength of the nonwoven fabric-reinforced solid electrolyte sheet of Example 2 was analyzed. For the tensile strength test, a tabletop tensile compression tester Force Tester MCT-2150 manufactured by A&D Company was used.

[0106] Figure 10 is a diagram shown to explain the results of the tensile strength test of the nonwoven fabric reinforced electrolyte sheet of the present invention. In Figure 10, the horizontal axis of the graph indicates strain (unit: %), and the vertical axis indicates stress (unit: MPa). As shown in Figure 10, the nonwoven fabric reinforced solid electrolyte sheet (nPPV-SPE) of Example 2 had a tensile stress of 15.8 MPa at a strain of 47.7%. This is an excellent result compared to the solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI, which was evaluated as a reference example and had a tensile strength of 1.7 MPa at a strain of 20.9%. Also, this value of tensile strength is excellent compared to the values of tensile strength of solid polymer electrolytes (5 - 10 MPa) reported in recent papers (References 1 - 6).

[0107] This is considered to be an effect achieved by appropriately combining the microfiber layer 20 containing the microfibers 22 containing polyethylene terephthalate (PET) and the nanofiber layer 30 having the nanofibers 32 containing polyvinylidene fluoride.

[0108] [Reference 1 (Ref.1)] J. Membrane Sci., 2019,589,117250 [Reference 2 (Ref.2)] ACS Appl. Mater.Interfaces,2022,14,4,5932 - 5939 [Reference 3 (Ref.3)] J. Power Sources, 2021,484,229287 [Reference 4 (Ref.4)] ACS Appl. Mater.Interfaces,2020,12,10,11657 - 11668 [Reference 5 (Ref.5)] J. Membrane Sci.,2021,621,119023 [Reference 6 (Ref.6)] J. Mater. Chem.A, 2021,9,26939 - 26948

[0109] In the solid polymer electrolytes reported in the paper, the maximum tensile strength is about 6 MPa. On the other hand, the tensile strength of the non-woven fabric reinforced solid electrolyte sheet of Example 2 is 15.8 MPa. It can be seen that the tensile strength is excellent compared to the solid polymer electrolytes reported in the paper.

[0110] 5-2-3. Ion Conductivity Evaluation For the non-woven fabric reinforced solid electrolyte sheet of Example 2 and the non-woven fabric reinforced solid electrolyte sheet with the ratio of PEO and LiTFSI changed with respect to the non-woven fabric reinforced solid electrolyte sheet of Example 2, a symmetric stainless steel cell was fabricated and the ion conductivity was evaluated. The molar ratios of the PEO monomer and LiTFSI were set at four levels of 10:1 (nPPV-SEP-10, Example 2), 14:1 (nPPV-SEP-14), 18:1 (nPPV-SEP-18), and 22:1 (nPPV-SEP-22). Note that the ratio of PEO and LiTFSI of the non-woven fabric reinforced solid electrolyte sheet of Example 2 is 10:1 (nPPV-SEP-10).

[0111] The evaluation of the ion conductivity was carried out at each temperature of 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C. The bulk resistance of the non-woven fabric reinforced solid electrolyte sheet was measured using a Metrohm electrochemical workstation, and the ion conductivity σ was calculated by the following formula. Equation 1

[0112] σ = L / RS Here, L represents the thickness of the non-woven fabric reinforced solid electrolyte sheet, R represents the bulk resistance of the non-woven fabric reinforced solid electrolyte sheet, and S represents the area, respectively.

[0113] FIG. 11 is a diagram showing the measurement results of the ionic conductivity of the nonwoven fabric-reinforced solid electrolyte sheet 1. As shown in FIG. 11, it can be seen that the ionic conductivity of the nonwoven fabric-reinforced solid electrolyte sheet is affected by both the amount of Li ions contained in the solid electrolyte and the temperature. The ionic conductivity of the nonwoven fabric-reinforced solid electrolyte sheet increases as the amount of Li ions contained in the solid electrolyte increases. However, in nPPV-SEP-22 with the highest Li ion concentration, the ionic conductivity shows a smaller value than the other three nonwoven fabric-reinforced solid electrolyte sheets. This is presumably because the mobility of Li ions decreases due to the presence of excessive Li ions (LiTFSI) in the solid electrolyte.

[0114] Regarding the temperature dependence of the ionic conductivity, in all the nonwoven fabric-reinforced solid electrolyte sheets evaluated, the result was that the higher the measurement temperature, the higher the ionic conductivity. This is presumably because local viscosity decreases by raising the temperature.

[0115] 5-2-4 Measurement of Oxidation Potential For the nonwoven fabric-reinforced solid electrolyte sheet (nPPV-SPE) of Example 2, the oxidation potential was measured. Similarly, a solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI was evaluated as a reference example.

[0116] FIG. 12 is a diagram showing the evaluation results of the oxidation current of the nonwoven fabric-reinforced solid electrolyte sheet 1 according to the embodiment. As shown in FIG. 2, the oxidation current of the nonwoven fabric-reinforced solid electrolyte sheet (nPPV-SPE) of Example 2 is stable up to 5.2 V. Also, the current value up to 5.2 V is close to 0 A. This is superior to the solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI evaluated as a reference example.

[0117] 5-2-5 Stability Evaluation of the Nonwoven Fabric-Reinforced Solid Electrolyte Sheet against Li Dendrite Growth The nonwoven fabric-reinforced solid electrolyte sheet (nPPV-SPE) of Example 2, and as a reference example The stability of a solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI against Li dendrite growth was evaluated. The evaluation was carried out by galvanostatic Li plating / stripping in a Li / Li symmetric cell. The current density was 0.1 mAcm -2 and the evaluation temperature was 70 °C.

[0118] Figure 13 is a diagram shown to explain the results of the stability evaluation of the non-woven fabric reinforced solid electrolyte sheet against Li dendrite growth. Specifically, it is a diagram showing the voltage profiles of the Li / nPPV-SPE / Li and Li / PEO-SPE / Li symmetric cells. Figure 14 is an enlarged diagram of the voltage profile from 290 hours to 302 hours among the voltage profiles shown in Figure 12.

[0119] As shown in Figures 13 and 14, in the PEO-SPE, a sharp decrease in voltage is observed 297 hours after the start of the evaluation. This indicates that the polyethylene oxide (PEO)-LiTFSI solid polymer electrolyte was damaged by Li dendrites and a short circuit occurred. On the other hand, in the non-woven fabric reinforced solid electrolyte sheet (nPPV-SPE) of Example 2, it can be seen that after 2000 hours, no short circuit occurred and a stable voltage profile was shown.

[0120] 5-2-6 Cycle Test The non-woven fabric reinforced solid electrolyte sheet (nPPV-SPE) of Example 2 was applied to an all-solid-state Li metal battery (ASSLMB) system composed of a Li metal anode and an NMC532 cathode to evaluate its practical performance. In this system, instead of the LiFePO 4 based material, an NMC-based material was applied. Also, the evaluation temperature was 70 °C. Further, as a reference example, the same evaluation was also carried out for a solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI.

[0121] FIG. 15 is a diagram showing the test results of the life characteristics of a solid-state battery using the nonwoven fabric-reinforced solid electrolyte sheet 1 according to the embodiment. Specifically, it is a diagram showing the evaluation results of the cycle performance of Li / nPPV-SPE / NMC532 and Li / PEO-SPE / NMC532 at a 0.1C-rate. FIG. 16 is a diagram showing the test results of the life characteristics of a solid-state battery using the nonwoven fabric-reinforced solid electrolyte sheet 1 according to the embodiment. Specifically, it is a diagram showing the evaluation results of the rate performance of Li / nPPV-SPE / NMC532 and Li / PEO-SPE / NMC532.

[0122] As shown in FIGS. 15 and 16, it can be seen that the cycle performance of Li / nPPV-SPE / NMC532 using the nonwoven fabric-reinforced solid electrolyte sheet (nPPV-SPE) of Example 2 is greatly improved compared to Li / PEO-SPE / NMC532 using a solid polymer electrolyte (PEO-SPE) composed of polyethylene oxide (PEO)-LiTFSI of the reference example.

[0123] 5. Effects According to the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, the nonwoven fabric-reinforced solid electrolyte sheet includes a two-layer nonwoven fabric substrate, a solid polymer, and a lithium salt dispersed in the solid polymer. Thereby, it becomes possible to make the solid electrolyte sheet thinner. Thereby, when used as the solid electrolyte sheet of a solid-state battery, it is possible to achieve a high density of volumetric energy.

[0124] Furthermore, the nonwoven fabric-reinforced solid electrolyte sheet of the present invention includes a microfiber layer having microfibers containing polyethylene terephthalate, and a nanofiber layer formed on one surface of the microfiber layer and having nanofibers containing polyvinylidene fluoride. Since the microfiber layer and the nanofiber layer are firmly joined, even when the nonwoven fabric-reinforced solid electrolyte sheet is made into a thin film, it has high tensile strength (mechanical stability) and thermal stability. The nonwoven fabric-reinforced solid electrolyte sheet having high tensile strength facilitates the manufacture of a highly reliable all-solid-state battery and can prevent structural failures or losses. Also, from a chemical perspective, increasing the tensile strength of the nonwoven fabric-reinforced solid electrolyte sheet can also enhance its resistance to redox environments. The tensile strength of the nonwoven fabric-reinforced solid electrolyte sheet is also effective in suppressing the formation of dendrites.

[0125] That is, according to one aspect of the nonwoven fabric-reinforced solid electrolyte sheet of the present invention, it is possible to provide a nonwoven fabric-reinforced solid electrolyte sheet that can be made into a thin film, has high tensile strength even when made into a thin film, and further has high thermal stability, to provide an all-solid-state dry battery using such a nonwoven fabric-reinforced solid electrolyte sheet, and to provide a method for manufacturing such a nonwoven fabric-reinforced solid electrolyte sheet.

Explanation of Reference Numerals

[0126] 10... Two-layer nonwoven fabric substrate, 20... Microfiber layer, 22... Microfibers, 30... Nanofiber layer, 32... Nanofibers, 40... Solid polymer, 50... Lithium salt, 82... Anode electrode, 84... Cathode electrode, 86... Solid electrolyte, 90... Li dendrite, 100... Electrospinning device, 110... Syringe, 112... Capillary tip, 120... Collector, 130... Power supply device, 200... Casting device, 210... Glass substrate, 220... Doctor blade

Claims

1. A nonwoven solid electrolyte sheet comprising a two-layer nonwoven substrate, a solid polymer, and a lithium salt dispersed in the solid polymer, wherein the two-layer nonwoven substrate includes a microfiber layer having microfibers containing polyethylene terephthalate and a nanofiber layer formed on one surface of the microfiber layer and having nanofibers containing polyvinylidene fluoride, and the solid polymer is accommodated in voids formed in the two-layer nonwoven substrate. A nonwoven reinforced solid electrolyte sheet characterized by this.

2. The nonwoven reinforced solid electrolyte sheet according to Claim 1, wherein the microfibers include two types of polyesters having different melting points, and at least one of the two types of polyesters is the polyethylene terephthalate. A nonwoven reinforced solid electrolyte sheet characterized by this.

3. The nonwoven reinforced solid electrolyte sheet according to Claim 1, wherein the microfibers include microfibers containing drawn polyethylene terephthalate and undrawn polyethylene terephthalate, and / or microfibers having a core-sheath structure, wherein the core portion contains the polyethylene terephthalate and the sheath portion contains an ester having a melting point lower than that of the polyethylene terephthalate. A nonwoven reinforced solid electrolyte sheet characterized by this.

4. The nonwoven reinforced solid electrolyte sheet according to Claim 1, wherein the microfibers have an average diameter of 1 μm to 20 μm, and the nanofibers have an average diameter of 50 nm to 300 nm. A nonwoven reinforced solid electrolyte sheet characterized by this.

5. The nonwoven reinforced solid electrolyte sheet according to Claim 1, wherein the average pore diameter of the pores when the voids are regarded as pores is 0.1 μm or more and less than 3 μm. A nonwoven reinforced solid electrolyte sheet characterized by this.

6. The nonwoven reinforced solid electrolyte sheet according to Claim 1, wherein the solid polymer includes at least one selected from the group consisting of polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polycarbonate, polysiloxane, starch, sugar, fiber, polyvinyl alcohol, polyphosphazene, and polystyrene. A nonwoven reinforced solid electrolyte sheet characterized by this.

7. The nonwoven reinforced solid electrolyte sheet according to Claim 1, The solid polymer contains polyethylene oxide, and is a non-woven fabric reinforced solid electrolyte sheet characterized by this.

8. The non-woven fabric reinforced solid electrolyte sheet according to claim 1, The lithium salt is at least one selected from the group consisting of LiTFSI, LiPF ６ , LiN(CF ３ SO ２ ), ２ , Li(CF ３ SO ２ ), ３ C, LiN(SOCFCF), and LiB(CO), and is characterized by including at least one selected from the group consisting thereof. A nonwoven fabric-reinforced solid electrolyte sheet

9. The non-woven fabric reinforced solid electrolyte sheet according to claim 1, The non-woven fabric reinforced solid electrolyte sheet is characterized in that the mass ratio of the solid polymer to the lithium salt is 4:1 to 26:

1.

10. The non-woven fabric reinforced solid electrolyte sheet according to any one of claims 1 to 8, The two-layer non-woven fabric substrate has a tensile strength that suppresses the growth of lithium dendrites, and is a non-woven fabric reinforced solid electrolyte sheet characterized by this.

11. The non-woven fabric reinforced solid electrolyte sheet according to claim 10, A cathode electrode, An anode electrode, and an all-solid-state battery characterized by including these.

12. A step of forming a microfiber layer having microfibers containing polyethylene terephthalate, A step of applying a solution containing polyvinylidene fluoride to one surface of the microfiber layer by an electrospinning method to form a nanofiber layer having nanofibers containing polyvinylidene fluoride to obtain a two-layer non-woven fabric substrate, and a casting step of casting a solid electrolyte in which a lithium salt is dispersed from the microfiber layer side of the two-layer non-woven fabric substrate, A hot press step of hot pressing the two-layer non-woven fabric substrate in which the solid electrolyte is cast to accommodate the solid electrolyte in voids formed in the microfiber layer, A method for manufacturing a non-woven fabric reinforced solid electrolyte sheet, characterized by including these.

13. The method for manufacturing a non-woven fabric reinforced solid electrolyte sheet according to claim 12, The hot press step is a step of pressurizing the two-layer non-woven fabric substrate in a temperature range of 80°C to 120°C and a pressure range of 20 MPa to 30 MPa for 10 seconds to 120 seconds, and is a method for manufacturing a non-woven fabric reinforced solid electrolyte sheet characterized by this.

Images