Support for a lithium-ion secondary battery using a solid electrolyte, and a lithium-ion secondary battery using the same

Abstract

To provide a support for a lithium ion secondary battery that allows a sufficient path line of lithium ion to be formed and makes it possible to obtain a solid electrolyte layer with low internal resistance.SOLUTION: A solid electrolyte layer included in a lithium-ion secondary battery includes a support. The thermal dimensional change rates of the support in the longitudinal and transverse directions are -10 to 5%. The air permeability is 1 to 50 L / cm2 / min. The longitudinal and transverse stiffnesses after heat treatment are on a range of 5 to 250 mN. Paper or nonwoven fabric satisfying the above is used for the support.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a support for a lithium-ion secondary battery contained in a solid electrolyte layer interposed between a positive electrode and a negative electrode of a lithium-ion secondary battery, and a lithium-ion secondary battery including the solid electrolyte layer having the support.

Background Art

[0002] As a secondary battery with high energy density, a lithium-ion secondary battery using a liquid electrolyte (hereinafter referred to as an electrolytic solution) is used. A lithium-ion secondary battery using an electrolytic solution has a configuration in which a separator is interposed between a positive electrode and a negative electrode and the electrolytic solution is filled.

[0003] In lithium-ion secondary batteries, organic electrolytic solutions are mainly used as the electrolytic solution. Since the organic electrolytic solution is a liquid, there is a concern about liquid leakage, and since it is flammable, there is a concern about ignition. Therefore, in order to improve the safety of lithium-ion secondary batteries, lithium-ion secondary batteries using solid electrolytes (hereinafter referred to as all-solid-state batteries) have been developed instead of electrolytic solutions. Naturally, since the electrolyte of an all-solid-state battery is solid, there is no liquid leakage, and it has high flame retardancy and heat resistance compared to an electrolytic solution, so it is attracting attention as a lithium-ion secondary battery with excellent safety. Since all-solid-state batteries have high safety, small all-solid-state batteries are being mass-produced for wearable devices that directly touch the body.

[0004] In addition, unlike lithium-ion secondary batteries using an electrolytic solution, all-solid-state batteries have small characteristic degradation at high temperatures, so a cooling device is not required, which is also advantageous for improving the energy density per volume of the battery pack. Since all-solid-state batteries are advantageous as secondary batteries with high volumetric energy density, further enlargement is expected for electric vehicles and the like.

[0005] The solid electrolyte layer interposed between the positive electrode and the negative electrode of an all-solid-state battery is required to have a function of allowing lithium ions to conduct ionically between the positive electrode and the negative electrode and a function of preventing a short circuit between the positive electrode active material and the negative electrode active material. In addition, in order to achieve excellent volumetric energy density and low internal resistance, the thickness of the solid electrolyte layer is required to be thin.

[0006] As a method for forming the solid electrolyte layer, a method of mixing a solid electrolyte and a binder and rolling them under heating to form a sheet, a method of coating a solid electrolyte slurry on an electrode and drying it, etc. are adopted.

[0007] However, when forming a solid electrolyte layer for an all-solid-state battery used in a large-sized battery such as for an electric vehicle, for example, the solid electrolyte layer obtained by the method of rolling under heating to form a sheet may crack or develop cracks during handling. Also, when using the method of coating and drying a slurry containing a solid electrolyte on an electrode, stress is generated in the solid electrolyte layer during drying, resulting in cracks. Therefore, it is difficult to stably form a thin and uniform solid electrolyte layer. If a stable, thin, and uniform solid electrolyte layer cannot be formed, the ion conduction deteriorates, and further, a short circuit may occur.

[0008] On the other hand, in order to prevent a short circuit, the thickness of the solid electrolyte layer can be increased. However, when the thickness is large, the size of the battery increases, resulting in a decrease in volumetric energy density, an increase in the inter-pole distance, and an increase in internal resistance.

[0009] In order to solve the above problems, it is known to use, in an all-solid-state battery, a solid electrolyte layer in which a solid electrolyte is included in a thin film-like sheet (hereinafter, a support) and the solid electrolyte and the support are integrated. And various configurations regarding supports for all-solid-state batteries and substrates for lithium-ion secondary batteries have been proposed.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

[0011] Patent Document 1 discloses a technique related to a solid electrolyte sheet having a plurality of through-holes formed by etching a film serving as a support. It is disclosed that by filling the through-holes formed by the etching process with a solid electrolyte, a all-solid-state battery excellent in energy density and output characteristics can be provided. However, when manufacturing the solid electrolyte sheet of Patent Document 1, since the solid electrolyte is filled into the through-holes, the solid electrolyte is only filled inside the formed through-holes. Therefore, since the film portion, which is an insulator except for the through-holes, remains, an interface that cannot pass lithium ions is generated between the positive electrode or the negative electrode and the film portion. That is, the interface resistance between the solid electrolyte sheet and the positive electrode or the negative electrode tends to be high, and even in the all-solid-state battery using this support, further reduction of the resistance of the all-solid-state battery has been demanded.

[0012] Patent Document 2 discloses a technique related to a solid electrolyte sheet containing a solid electrolyte on the surface and inside of a non-woven fabric, and the non-woven fabric has a weight per square meter of 8 g or less and a thickness of 10 to 25 μm. The solid electrolyte layer formed using the nonwoven fabric described in Patent Document 2 as a support can hold the solid electrolyte necessary for ion conduction between the positive and negative electrodes while having self-supporting properties, and a battery with suppressed increase in impedance can be produced.

[0013] Patent Document 3 discloses a technique related to a solid electrolyte sheet in which a solid electrolyte is filled in a support having a porosity of 60% or more and 95% or less and a thickness of 5 μm or more and less than 20 μm and having heat resistance. This solid electrolyte sheet is disclosed to have self-supporting properties even though it is thin and to be excellent in heat resistance, so that short circuits can be prevented even when pressing at high temperatures is carried out. In addition, since this solid electrolyte sheet can be subjected to high-temperature pressing, it contributes to a decrease in the interfacial resistance between solid electrolytes, and the high output of the battery can be achieved.

[0014] However, when the filling of the solid electrolyte is insufficient, the solid electrolyte layer using the support described in Patent Document 2 or Patent Document 3 becomes a battery with high internal resistance. Furthermore, when the positive electrode, the solid electrolyte layer, and the negative electrode are integrally pressed, the support inside the solid electrolyte layer is deformed, and the lithium ion pass line is cut, resulting in an increase in internal resistance.

[0015] In addition, the support of Patent Document 3 contains heat-resistant fibers such as aramid fibers and Al2O3 with little fiber deformation due to heat. However, in order to increase the strength of the solid electrolyte layer, it contains a large amount of binder fibers with large fiber deformation due to heat. Therefore, the thermal dimensional change of the support becomes large. When the thermal dimensional change of the support is large, when the solid electrolyte slurry is coated on the support and the solvent is dried, the support shrinks, and unevenness occurs on the surface of the obtained solid electrolyte layer. When the solid electrolyte layer with unevenness on the surface is overlaid with the positive electrode or the negative electrode, the adhesion at the interface deteriorates, and the internal resistance of the all-solid-state battery increases. In order to improve the adhesion at the interface between the positive electrode or the negative electrode and the solid electrolyte layer, hot pressing can be performed. However, even when using the support of Patent Document 3 that can be hot pressed, due to the deformation of the support inside the solid electrolyte layer by hot pressing, the formed lithium ion pass line is cut off, resulting in a battery with high internal resistance.

[0016] Patent Document 4 discloses a technique related to a nonwoven fabric base material for a lithium secondary battery separator, which is characterized by containing drawn polyester fibers and, as binder fibers, undrawn polyester fibers and wet heat-adhesive fibers. It is disclosed that by containing drawn polyester fibers, a nonwoven fabric base material excellent in heat resistance can be provided, in which the drawn polyester fibers form a skeleton and the nonwoven fabric base material has excellent thermal dimensional stability. In addition, the undrawn polyester fibers are softened or melted by a heat pressing treatment such as calendering and firmly adhere to other fibers. The wet heat-adhesive fibers are disclosed to exhibit an adhesive function by flowing or easily deforming in a wet state. It is disclosed that by containing these binders in the nonwoven fabric base material, a nonwoven fabric base material for a lithium secondary battery separator with high tensile strength and high productivity can be provided.

[0017] However, even for the nonwoven fabric substrate with excellent thermal dimensional stability in Patent Document 4, in order to obtain a nonwoven fabric substrate for a lithium-ion secondary battery separator with high productivity, it is necessary to include a large amount of binder fibers in the constituent fibers. Similar to the support in Patent Document 3, the thermal dimensional change becomes large, resulting in a battery with high internal resistance. In addition, as described above, the wet heat adhesive fibers contained in the nonwoven fabric substrate undergo flow or deformation when the adhesive function is exhibited. Therefore, the wet heat adhesive fibers in this nonwoven fabric substrate cannot maintain their fibrous state and may block the fiber gaps. Furthermore, when a large amount of binder fibers that cannot maintain their fiber shape are included, the density becomes high. As a result, the penetration of the solid electrolyte into the nonwoven fabric substrate is insufficient, and it is difficult to uniformly fill the solid electrolyte inside the nonwoven fabric substrate, resulting in a battery with high internal resistance.

[0018] As other related technologies, technologies related to separators for electrochemical elements with excellent heat resistance are disclosed.

[0019] Patent Document 5 discloses a technology related to a separator for an electrochemical element, which is a wet nonwoven fabric containing fibrillated heat-resistant fibers with a softening point, melting point, and thermal decomposition temperature all of 250°C or higher and 700°C or lower, and having a dimensional change rate of -3 to +1% when heat-treated at 250°C for 50 hours. It is disclosed that by using the separator for an electrochemical element described in Patent Document 5, an element obtained by winding can have excellent reliability even when heat-treated at a high temperature, that is, a highly heat-resistant and low-resistance electrochemical element can be obtained.

[0020] Patent Document 6 discloses a technology related to a substrate for a separator for a lithium-ion secondary battery, which is characterized by having a thermal shrinkage rate of 2.0% or less at 150°C. The substrate for a separator described in Patent Document 6 is used as a separator for a lithium-ion battery by providing a coating layer containing inorganic particles on the substrate for a separator. The separator base material described in Patent Document 6 is disclosed to be less likely to develop unevenness on the separator even when the separator is heated and dried during battery assembly because its thermal shrinkage rate is 2.0% or less. Further, in the case of a separator having coating layers on both sides of the separator base material, it is disclosed that in addition to the problem of unevenness occurring on the separator during heating and drying at the time of battery assembly, the problem of curling toward the side with the thinner coating layer can also be solved.

[0021] The present invention has been made in view of the above problems, and aims to contribute to reducing the interfacial resistance between the positive electrode or negative electrode and the solid electrolyte layer by reducing the unevenness on the surface of the solid electrolyte layer and improving the interfacial adhesion between the positive electrode or negative electrode and the solid electrolyte layer. Further, it aims to obtain a solid electrolyte layer with a low internal resistance by sufficiently forming lithium ion path lines inside the solid electrolyte layer. In addition, when integrating the positive electrode, solid electrolyte layer, and negative electrode under pressure, it aims to contribute to reducing the resistance of the solid electrolyte layer by suppressing the deformation of the support inside the solid electrolyte layer and maintaining the lithium ion path lines. Also, it aims to provide a lithium ion secondary battery with a low internal resistance by using this support.

Means for Solving the Problems

[0022] The support according to the present invention is made for the purpose of solving the above problems, and for example, has the following configuration. That is, it is a support included in the solid electrolyte layer of a lithium ion secondary battery, and the Before and after heating at 200°C for 1 hour thermal dimensional change rates in the longitudinal and transverse directions of the support are -10 to 5% respectively, the air permeability is 1 to 50 L / cm 2 / min., After heating at 200°C for 1 hour and the longitudinal and transverse stiffness-flexibility in the range of 5 to 250 mN respectively, and is paper or non-woven fabric. Further, the lithium ion secondary battery of the present invention is characterized by including a solid electrolyte layer having the support of the above invention.

Effects of the Invention

[0023] According to the present invention, by improving the thermal dimensional stability of the support, the interfacial resistance between the positive electrode or the negative electrode and the solid electrolyte layer can be reduced. Further, by improving the permeability of the solid electrolyte into the support, a support capable of reducing the internal resistance of the solid electrolyte layer can be obtained. Furthermore, by optimizing the stiffness and flexibility of the support after heat treatment, deformation of the support inside the solid electrolyte layer can be suppressed, and by maintaining the lithium ion pass line formed inside the solid electrolyte layer, a support capable of contributing to the reduction of the internal resistance of the solid electrolyte layer can be obtained. Also, by using the support of the present invention in a lithium ion secondary battery, it is possible to contribute to the reduction of the internal resistance of the battery.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments for carrying out the present invention will be described in detail.

[0025] In the present invention, a support used for forming a solid electrolyte layer existing between a positive electrode and a negative electrode in a lithium ion secondary battery configured as an all-solid-state battery is configured. The support of the present invention is a support included in the solid electrolyte layer of a lithium ion secondary battery, and the thermal dimensional change rates in the longitudinal and transverse directions of the support are -10 to 5% respectively, the air permeability is 1 to 50 L / cm 2 / min., and the stiffness and flexibility in the longitudinal and transverse directions after heat treatment are in the range of 5 to 250 mN, which is paper or non-woven fabric.

[0026] It is required that lithium ions conduct between the positive electrode and the negative electrode during charge and discharge in the solid electrolyte layer existing between the positive electrode and the negative electrode. For this purpose, it is necessary to form a pass line for lithium ions between the positive electrode and the solid electrolyte layer, inside the solid electrolyte layer, and between the solid electrolyte layer and the negative electrode. That is, if the interfacial resistance between the positive electrode and the solid electrolyte layer and between the solid electrolyte layer and the negative electrode can be reduced, and the resistance inside the solid electrolyte layer can be reduced, the internal resistance of the all-solid-state battery can be lowered.

[0027] In a conventional support, as a factor that inhibits further reduction of the interfacial resistance between the solid electrolyte layer and the positive electrode or the negative electrode, it has been found that the interfacial adhesion between the solid electrolyte layer and the positive electrode or the negative electrode deteriorates due to the unevenness generated on the surface of the solid electrolyte layer. The unevenness on the surface of this solid electrolyte layer occurred when the solid electrolyte slurry was coated on the support and dried, and the support changed in dimensions due to the heat during drying. In order to improve the interfacial adhesion, it is possible to increase the pressure when laminating, pressurizing, and integrating the positive electrode, the solid electrolyte layer, and the negative electrode. However, if the pressure is increased, the support inside the solid electrolyte layer is deformed, and the lithium ion pass line formed inside the solid electrolyte layer is cut off, and the internal resistance of the solid electrolyte layer may increase. On the other hand, in order to enhance the thermal dimensional stability of the support, heat-resistant fibers can be used. However, in order to form a sheet with excellent handleability, it is necessary to contain a large amount of binder fibers with a large thermal dimensional change. As a result, the permeability of the solid electrolyte deteriorates.

[0028] Conventionally, when the solid electrolyte slurry was coated on the support and then dried, the dimensions in the longitudinal and transverse directions of the support might change respectively. This thermal dimensional change is a phenomenon that occurs even when only the support is dried. The fibers constituting the support are deformed by heating that exceeds the melting point or softening point. When the fibers constituting the support are deformed, thick and thin portions of the support are generated, and unevenness may occur on the surface of the support. The support coated with the solid electrolyte slurry changes in dimensions due to heating before the solvent contained in the solid electrolyte slurry is completely dried, resulting in the generation of unevenness and a decrease in strength on the surface of the obtained solid electrolyte layer.

[0029] When a solid electrolyte layer with unevenness on its surface, a positive electrode, and a negative electrode are overlapped, pressed, and integrated, the adhesion at the interface between the positive electrode or the negative electrode and the solid electrolyte layer has deteriorated. That is, it has been found that by reducing the thermal dimensional change of the support and suppressing deformation, the interfacial resistance between the solid electrolyte layer and the positive electrode or the negative electrode can be further reduced. If the interfacial resistance between the solid electrolyte layer and the positive electrode or the negative electrode can be reduced, the internal resistance of the all-solid-state battery can be further reduced.

[0030] It is preferable that the thermal dimensional change rates in the longitudinal and transverse directions of the support of the present invention are each in the range of -10 to 5%. Further, from the viewpoint of suppressing the unevenness on the surface of the solid electrolyte layer, it is more preferable that the thermal dimensional change rates in the longitudinal and transverse directions of the support are each in the range of -8 to 3%. The thermal dimensional change rate in the present invention refers to the thermal dimensional change rate before and after heating at 200°C for 1 hour. Heating at 200°C for 1 hour is a thermal condition that can sufficiently dry the solvent used in the solid electrolyte slurry. That is, if the thermal dimensional change rates in the longitudinal and transverse directions of the support before and after heating at 200°C for 1 hour are each in the range of -10 to 5%, the generation of unevenness on the surface of the obtained solid electrolyte layer can be suppressed. And the adhesion at the interface when integrating the positive electrode or the negative electrode and the solid electrolyte layer can be improved, and the interfacial resistance between the positive electrode or the negative electrode and the solid electrolyte layer can be lowered. In addition, when there is a -(minus) sign in the thermal dimensional change rate, it indicates shrinkage, and when there is no sign, it indicates expansion.

[0031] When either the thermal dimensional change rate in the longitudinal or transverse direction of the support is less than -10% (more than 10% shrinkage), the thermal shrinkage of the support is large during the drying of the solid electrolyte slurry, and large unevenness occurs on the surface of the obtained solid electrolyte layer. That is, the interfacial adhesion between the positive electrode or the negative electrode and the solid electrolyte layer is poor, and the interfacial resistance becomes high. In order to improve the interfacial adhesion, the pressure when integrating the positive electrode, the solid electrolyte layer, and the negative electrode can be increased, but the support inside the solid electrolyte layer may be deformed and the lithium ion path line may be cut, which may lead to an increase in the internal resistance of the all-solid-state battery. In addition, when either the longitudinal or transverse thermal dimensional change rate of the support exceeds 5% (expansion exceeding 5%), it indicates that the support has melted due to heat and cannot maintain its shape. Also, the adhesiveness at the contact points between the fibers constituting the support may decrease, leading to a decrease in the strength of the support. That is, in reality, it is preferable that the longitudinal and transverse thermal dimensional change rates of the support are each 5% or less.

[0032] Furthermore, the following reasons can be considered as one of the factors that inhibited further reduction of the internal resistance when using a conventional support. Although there are voids inside the conventional support, there are cases where the openings on the surface of the support are small, etc., and it is considered that the solid electrolyte could not sufficiently penetrate from the surface of the support into the inside. As a result, a lithium ion path line by the solid electrolyte could not be formed inside the support, and the internal resistance of the solid electrolyte layer became high.

[0033] The inventors of the present invention have found that in order to form a lithium ion path line between the positive electrode and the negative electrode, it is important to form a solid electrolyte layer having a continuous connection from the surface to the inside of the support by the solid electrolyte. That is, it is important not only to uniformly form the solid electrolyte on the surface of the support, but also to sufficiently fill the inside of the support. By increasing the permeability of the solid electrolyte to the support, a lithium ion path line can be formed inside the solid electrolyte layer, and a solid electrolyte layer with a low internal resistance can be formed.

[0034] In the embodiment of the present invention, the air permeability is adopted as an index for measuring the permeability of the solid electrolyte into the support. The air permeability indicates the amount of air flowing per unit area and per unit time under a certain differential pressure. The higher the air permeability, the more air is flowing. That is, the higher the air permeability of the support, the higher the gas permeability of the support. If the air permeability of the support is high, it is considered that the permeability of the solid electrolyte into the support is also high. That is, a support with a high air permeability can be filled with a sufficient amount of solid electrolyte inside the support.

[0035] The support of the present invention has an air permeability in the range of 1 to 50 L / cm 2 / min. Further, from the viewpoints of the permeability of the solid electrolyte and the formation of a uniform solid electrolyte layer, the air permeability is more preferably in the range of 2 to 40 L / cm 2 / min. The support having an air permeability within the above range is excellent in the permeability of the solid electrolyte, has an appropriate overlap of fibers in the thickness direction, and when the solid electrolyte penetrates the support, the internal penetration is not hindered. Therefore, not only can the solid electrolyte be formed on the surface of the support, but also the solid electrolyte can penetrate into the support. As a result, the all-solid-state battery using this support can reduce the internal resistance.

[0036] When the air permeability is less than 1 L / cm 2 / min., the solid electrolyte may not be uniformly penetrated into the support. This is considered to be due to the following reasons. When the solid electrolyte penetrates the support, an air permeability of less than 1 L / cm 2 / min. means that the number of fibers constituting the support is large and dense, which becomes a resistance when the solid electrolyte penetrates into the support. As a result, the solid electrolyte stays on the surface of the support, making it difficult for the solid electrolyte to uniformly penetrate into the support.

[0037] On the other hand, when the air permeability exceeds 50 L / cm 2 / min., the effect of using the support cannot be obtained. A support with an air permeability exceeding 50 L / cm 2 / min. is too coarse to hold and reinforce the solid electrolyte, and even if the solid electrolyte penetrates, the solid electrolyte cannot stay on the support. Therefore, the formation of the solid electrolyte layer may not be possible, or the strain of the solid electrolyte layer generated during drying may not be suppressed, leading to the occurrence of cracks. That is, the support cannot hold and reinforce the solid electrolyte, and a thin and uniform solid electrolyte layer cannot be obtained, which is not preferable.

[0038] In addition, it has been found that the stiffness and flexibility of the support after heating affect the increase in the internal resistance of the solid electrolyte layer using a conventional support. When integrating the positive electrode, the solid electrolyte layer, and the negative electrode under pressure using a conventional support, the support deforms, resulting in the cutting of the lithium ion path line inside the pre-formed solid electrolyte layer, leading to a high internal resistance. The solid electrolyte layer formed by infiltrating a solid electrolyte slurry into the support and drying it is pressurized to integrate with the positive electrode and the negative electrode. That is, stress is applied in the plane direction of the solid electrolyte layer. Since the solid electrolyte layer, the positive electrode, and the negative electrode are not completely flat, this stress is not completely uniform with respect to the surface of the solid electrolyte layer. That is, when integrating under pressure, strong and weak areas of force will occur on the surface of the solid electrolyte layer. As a result, it has been found that the support inside the solid electrolyte layer deforms in response to the force, cracks occur in the solid electrolyte layer, and the lithium ion path line formed inside the solid electrolyte layer is cut.

[0039] In the embodiment of the present invention, the stiffness and flexibility of the support after heat treatment are adopted as an index of resistance to non-uniform force in the plane direction after the formation of the solid electrolyte layer. Here, the heat treatment refers to the state after heating at 200 °C for 1 hour, which is a heat condition that can sufficiently dry the solvent used in the solid electrolyte slurry. The stiffness and flexibility in the present invention are obtained from the maximum pressing force when placing a test piece on a sample stage with a gap of 6.5 mm in slit width and lowering the blade 8 mm from the surface of the sample stage. That is, the higher the maximum pressing force, the more difficult it is for the support to deform.

[0040] The support of the present invention controls the stiffness and flexibility in the longitudinal and transverse directions after heat treatment within the range of 5 to 250 mN respectively. Furthermore, from the viewpoint of suppressing the increase in internal resistance due to the integration of the positive electrode, the solid electrolyte layer, and the negative electrode under pressure, it is more preferable that the stiffness and flexibility in the longitudinal and transverse directions after heat treatment are within the range of 10 to 230 mN respectively.

[0041] A support having the stiffness and flexibility after heat treatment within the above range can withstand the non-uniform stress applied to the solid electrolyte layer and suppress the deformation of the support. Then, while maintaining the lithium ion path line inside the pre-formed solid electrolyte layer, the positive electrode, solid electrolyte layer, and negative electrode can be integrally pressed, and an increase in internal resistance can be suppressed. As a result, by using this support, the internal resistance of the all-solid-state battery can be lowered.

[0042] If either the longitudinal or transverse stiffness and flexibility of the support after heat treatment is less than 5 mN, the support is likely to deform. Therefore, the supported part to which a strong force is applied follows the force and deforms, and the solid electrolyte layer also deforms and unevenness occurs. As a result, a gap is formed at the interface between the positive electrode or negative electrode and the solid electrolyte layer, and the lithium ion path line is cut off.

[0043] On the other hand, when the longitudinal and transverse stiffness and flexibility of the support after heat treatment exceed 250 mN, the support contained in the solid electrolyte layer is difficult to deform, that is, it is too hard. Therefore, when the positive electrode, solid electrolyte layer, and negative electrode are integrally pressed, a change in the support structure such as the support breaking may occur. If the structure of the support changes, the solid electrolyte layer also deforms, resulting in cracks, leading to the cutting of the lithium ion path line and an increase in internal resistance.

[0044] The support of the present invention is made of paper or non-woven fabric. This is for the following reasons. Paper refers to a material manufactured by adhering plant fibers and other fibers. Non-woven fabric refers to a sheet-like material made by processing various fiber webs such as natural, recycled, and synthetic fibers mechanically, chemically, thermally, or a combination thereof without using a loom, and joining the constituent fibers to each other by an adhesive or the fusing force of the fibers themselves. That is, since the paper or non-woven fabric has a structure in which the fibers are randomly arranged, the support made of paper or non-woven fabric has innumerable voids and through-holes of various sizes inside. Therefore, there are solid electrolytes that remain on the surface of the support, those that penetrate and remain inside the support, and those that penetrate through the through-holes from the permeating surface side to the back surface side, and each is continuous. That is, a support made of paper or non-woven fabric can form a solid electrolyte layer on the surface of the support and can be filled with a solid electrolyte inside the support. Therefore, the solid electrolyte layer produced using paper or non-woven fabric as a support is filled not only on the surface of the support but also inside the support with a solid electrolyte, and can form a good lithium ion pass line. As a result, while reducing the internal resistance of the solid electrolyte layer, the interfacial resistance between the solid electrolyte layer and the positive electrode or negative electrode can be lowered. As a result, it can lead to a reduction in the internal resistance of the all-solid-state battery.

[0045] In addition, the thickness of the support of the present invention is preferably in the range of 5 to 40 μm. More preferably, it is in the range of 8 to 30 μm. When the thickness is less than 5 μm, the solid electrolyte layer will have a thin thickness, making it difficult to prevent a short circuit between the positive and negative electrodes. Also, in order to prevent a short circuit by widening the distance between the electrodes, a thick solid electrolyte layer can be formed on the surface of the support, but a layer consisting only of the solid electrolyte will be formed. That is, in the portion without the support, it may not be possible to suppress the strain of the solid electrolyte layer generated during drying, leading to the occurrence of cracks. On the other hand, when the thickness exceeds 40 μm, the thickness of the solid electrolyte layer becomes thick, which does not contribute to the miniaturization of the all-solid-state battery.

[0046] The density of the support is preferably in the range of 0.15 to 0.50 g / cm 3 More preferably, it is in the range of 0.17 to 0.48 g / cm 3 of the range. When the density is 0.15 g / cm 3If it is less than this value, the number of fibers constituting the support decreases, and the voids in the support increase. Therefore, the solid electrolyte does not stay in the support, and it becomes difficult to uniformly hold and reinforce the solid electrolyte. On the other hand, when the density is more than 0.50 g / cm 3 When it exceeds this value, the permeability of the solid electrolyte into the support deteriorates, and there are cases where the solid electrolyte cannot be sufficiently filled inside the support. As a result, the internal resistance of the all-solid-state battery increases.

[0047] From the viewpoint of forming a uniform solid electrolyte layer, the maximum through-hole area of the support according to the present invention is preferably in the range of 0.001 to 0.3 mm 2 in area. Since the support according to the present invention is composed of paper or a non-woven fabric, the support has a structure in which fibers are laminated. As a result, in the thickness direction of the support, there are portions where no fibers exist, that is, through-holes. When the solid electrolyte penetrates from the front surface to the back surface of the support, it passes through the through-holes of the support. The maximum through-hole area in the present invention indicates the area of the largest through-hole that the support has. That is, the areas of the countless through-holes that the support has are less than or equal to the maximum through-hole area. A support with a maximum through-hole area in the range of 0.001 to 0.3 mm 2 has excellent permeability of the solid electrolyte in the thickness direction of the support and can hold and reinforce the solid electrolyte, so that a uniform solid electrolyte layer can be formed. When the maximum through-hole area is less than 0.001 mm 2 the permeability of the solid electrolyte in the thickness direction into the support deteriorates, and a uniform solid electrolyte layer cannot be formed. Also, when the maximum through-hole area exceeds 0.3 mm 2 since the through-hole is large, there will be portions on the support where the solid electrolyte cannot be held. As a result, cracks occur and a uniform solid electrolyte layer cannot be formed, resulting in a solid electrolyte layer with a high internal resistance.

[0048] In the support according to the present invention, the tensile strength of the support is preferably 1.0 N / 15 mm or more. When the tensile strength is less than 1.0 N / 15 mm, breakage is likely to occur during the filling of the solid electrolyte.

[0049] From the viewpoint of maintaining the shape of the support and increasing tensile strength, it is desirable for the support to contain adhesive fibers, such as beaten cellulose fibers, beaten polyamide fibers, and synthetic resin binders. The adhesive strength of beaten cellulose fibers is due to physical bonds between entangled cellulose fibers and chemical bonds between hydrogen bonds of hydroxyl groups in cellulose. The adhesive strength of beaten polyamide fibers is due to physical bonds between entangled polyamide fibers. Both types of fiber bonding are preferred because they contribute to maintaining the shape of the support and developing tensile strength.

[0050] The synthetic resin binder fibers may be classified into those that maintain a fibrous state while forming a support, and those that cannot maintain a fibrous state and have become, for example, in a film form. The synthetic resin binder fibers that maintain their fibrous form while forming the support exhibit adhesive strength by thermally bonding the fiber intertwining points. Therefore, the synthetic resin binder fibers that maintain their fibrous form as a constituent material of the support can reduce breakage during the formation of the solid electrolyte layer, and because only the fiber contact points are bonded, they are less likely to inhibit the penetration of the solid electrolyte into the support. On the other hand, synthetic resin binder fibers that cannot maintain a fibrous state when used to form a support are transformed into a film-like state by heat during the support manufacturing process. When heat is applied near the melting point or softening point of the resin that forms the fibers, the resin melts and fuses at the intertwining points of the fibers. In other words, when a binder that is not in a fibrous state is used to form a support, the binder component forms multiple film layers between the fibers of the support to exhibit its binder function, thereby blocking voids. This can undesirably inhibit the penetration of the solid electrolyte into the support.

[0051] The materials that can be used as the fibers having adhesion are those that do not repel the solid electrolyte slurry, and there is no particular limitation as long as they are fibers that do not physically or chemically affect the solid electrolyte and have insulation properties. For example, beaten cellulose fibers, beaten polyamide fibers, polyamide binder fibers, polyester binder fibers, etc. can be mentioned. Also, one or more fibers selected from these fibers can be used.

[0052] The materials that can be used as other constituent materials are fibers that can maintain a fibrous state even after heating at 200°C for 1 hour, do not repel the solid electrolyte slurry, do not physically or chemically affect the solid electrolyte, and have insulation properties. There is no particular limitation as long as they are such fibers. For example, organic fibers such as cellulose fibers, polyamide fibers, and polyester fibers, and inorganic fibers such as glass fibers and alumina fibers can be mentioned. Also, one or more fibers selected from these fibers can be used. By using these fibers, it is possible to obtain a support that suppresses the thermal dimensional change of the support, has excellent filling properties and heat resistance of the solid electrolyte, and is suitable for the hardness and softness after heat treatment.

[0053] As means for making the thermal dimensional change rates in the longitudinal and transverse directions of the support be in the range of -10 to 5% respectively, for example, methods such as containing 20 to 100% by mass of fibers with a thermal fiber length change rate of -8 to 1% and heat-treating the sheet at over 200°C can be mentioned, but it is not limited to this.

[0054] Also, as means for making the hardness and softness after heat treatment in the longitudinal and transverse directions of the support be in the range of from 5 to 250 mN respectively, methods such as using fibers with a fiber length of 0.5 to 5 mm, making the basis weight be in the range of 1 to 12 g / m 2 and heat-treating the sheet at over 200°C can be mentioned, but it is not limited to this.

[0055] It is preferable to use fibers constituting the support of the present invention having an average fiber diameter of 1 to 20 μm. By using fibers having an average fiber diameter of 1 to 20 μm, holes of various sizes can be uniformly distributed throughout the resulting paper or nonwoven fabric. As a result, a support excellent in the permeability of the solid electrolyte, the stiffness and softness after heat treatment, and having a uniform thickness can be formed.

[0056] The manufacturing method of the support is not particularly limited, and it can be manufactured by a dry method or a wet method. Preferably, a wet method in which fibers dispersed in water are deposited on a wire, dehydrated, dried, and then lifted up is preferable from the viewpoint of the uniformity such as the texture of the support. In the embodiments for carrying out the present invention, as the manufacturing method of the support, paper or a wet nonwoven fabric formed by using a papermaking method was adopted. The papermaking form of the support is not particularly limited as long as it can satisfy the thermal dimensional change rate, air permeability, stiffness and softness after heat treatment, thickness, and density. Papermaking forms such as long wire papermaking, short wire papermaking, and cylinder papermaking can be adopted, and a plurality of layers formed by these papermaking methods may be combined. Further, when papermaking, additives such as a dispersant, an antifoaming agent, and a paper strength enhancer may be added, and post-processing such as paper strength enhancement processing, liquid affinity processing, calendering processing, thermal calendering processing, and embossing processing may be performed after the paper layer is formed.

[0057] (Method for manufacturing support and all-solid-state battery and method for measuring characteristics) The method for manufacturing the support and all-solid-state battery and the method for measuring the characteristics in this embodiment were carried out under the following conditions and methods.

[0058] 〔CSF value〕 The CSF value was measured according to "JIS P8121-2 'Pulp - Drainability test method - Part 2: Canadian Standard drainability method' (ISO5267-2 'Pulps - Determination of drainability - Part 2: "Canadian Standard" freeness method')".

[0059] 〔Average fiber length〕 〔Fiber length of fiber〕 The apparatus described in "JIS P 8226-2 'Pulp - Method for measuring fiber length by automated optical analysis - Part 2: Unpolarized light method'" (ISO 16065-2 'Pulps - Determination of Fibre length by automated optical analysis - Part 2: Unpolarized light method'), where measurement was carried out using Fiber Tester PLUS (manufactured by Lorentzen & Wettre), and the length - weighted average fiber length was taken as the fiber length of the fibers.

[0060] 〔Fiber length of polyester fiber and polyester binder fiber〕 Since polyester fibers and polyester binder fibers are optically transparent and the fibers cannot be accurately recognized as images, the fiber length measurement by the above - mentioned automated optical analysis method could not be accurately performed. Therefore, for polyester fibers and polyester binder fibers, the fiber length was measured by the following method. A prepared sample with randomly dispersed fibers was made. The fiber length of the fibers on the prepared sample was measured directly using a scale.

[0061] 〔Rate of change of hot fiber length〕 The average fiber length before and after heating at 200 °C for 1 hour was measured. Then, the rate of change of hot fiber length was calculated by the following formula. Rate of change of hot fiber length (%) = [(L2 - L1) / L1]×100 L1: Average fiber length before heating at 200 °C for 1 hour L2: Average fiber length after heating at 200 °C for 1 hour

[0062] 〔Thickness〕 The thickness of one sheet of the support was measured at equal intervals using a dial thickness gauge of G type (measurement reaction force 2 N, measuring head: φ10 mm), and the average value of the measurement points was taken as the thickness (μm) of the support.

[0063] 〔Grammage〕 The grammage of the support in the absolutely dry state was measured by the method specified in "JIS C 2300-2 'Cellulose paper for electrical use - Part 2: Test methods' 6 Grammage".

[0064] 〔Density〕 The density of the support was calculated using the following formula. Density (g / cm 3 ) = W / T W: Grammage (g / m 2 ), T: Thickness (μm)

[0065] 〔Porosity〕 The porosity of the support was calculated using the following formula. When a plurality of materials constituting the support are mixed, the calculation is performed in proportion to the mixing ratio to obtain the average specific gravity of the constituent fibers, and then the calculation is performed. Porosity (%) = (1 - (D / S)) × 100 D: Support density (g / cm 3 ), S: Specific gravity of constituent fibers (g / cm 3 )

[0066] 〔Air permeability〕 The air permeability of the support was measured by the method specified in "JIS L 1096 'Test Methods for Fabrics and Knitted Fabrics' Air Permeability Method A (Frazer Type)".

[0067] 〔Maximum penetration area〕 100 arbitrary penetration parts were extracted from the range of 5 mm × 5 mm. The area of the extracted penetration parts was approximated as a polygon, and the area was calculated. The largest area among the 100 measured penetration areas was taken as the maximum penetration area.

[0068] 〔Thermal dimensional change rate〕 The lengths in the longitudinal and transverse directions of a test piece cut out from the support to 100 mm × 100 mm were measured. Next, the test piece of the support was heated at 200 °C for 1 hour, and the lengths of each test piece after heating were measured. The thermal dimensional change rates in the longitudinal and transverse directions were calculated by the following formula. Thermal dimensional change rate (%) = [(L2 - L1) / L1] × 100 L1: Length before heating at 200 °C for 1 hour, L2: Length after heating at 200 °C for 1 hour

[0069] 〔Rigidity and flexibility after heat treatment〕 The sample heated at 200 °C for 1 hour was cut out into a size of 200×200 mm. The obtained test pieces were used to measure the stiffness in the longitudinal and transverse directions after heat treatment by the method specified in "JIS L 1096 'Textile and Knitted Fabric Test Methods' 8.21.5 Stiffness E Method (Handle-Ometer Method)".

[0070] 〔Tensile Strength〕 The maximum tensile load in the longitudinal direction (manufacturing direction) of the support was measured with a test width of 15 mm by the method specified in "JIS P 8113 'Paper and Paperboard - Test Methods for Tensile Properties - Part 2: Constant Rate of Elongation Method'" (ISO 1924-2 'Paper and board - Determination of tensile properties - Part 2: Constant rate of elongation method'), and the tensile strength of the support was obtained.

[0071] 〔Fabrication Process of All-Solid-State Battery〕 All-solid-state batteries were fabricated using the supports of the following Examples, Comparative Examples, Conventional Examples, and Reference Examples. The specific fabrication method is as follows.

[0072] (Positive Electrode Structure) A ternary system powder of LiNiCoAlO2 was used as the positive electrode active material, an amorphous powder of Li2S-P2S5 was used as the sulfide-based solid electrolyte, and carbon fiber was used as the conductive assistant, and they were mixed respectively. To this mixed powder, a dehydrated xylene solution in which SBR (styrene-butadiene rubber) was dissolved as a binder was mixed to prepare a positive electrode coating liquid. The positive electrode coating liquid was coated on an aluminum foil current collector as the positive electrode current collector, dried, and further rolled to obtain a positive electrode structure.

[0073] (Negative Electrode Structure) Graphite was used as the negative electrode active material, an amorphous powder of Li2S-P2S5 was used as the sulfide-based solid electrolyte, PVdF (polyvinylidene fluoride) was used as the binder, and NMP (N-methyl-2-pyrrolidone) was used as the solvent, and they were mixed respectively to prepare a negative electrode coating liquid. The negative electrode coating liquid was coated on a copper foil current collector as the negative electrode current collector, dried, and further rolled to obtain a negative electrode structure.

[0074] (Solid electrolyte layer) As a sulfide-based solid electrolyte, Li2S-P2S5 amorphous powder was used, SBR was used as a binder, and xylene was used as a solvent, and they were mixed to prepare a solid electrolyte coating solution. The solid electrolyte coating solution was applied to the supports of the following examples, comparative examples, each conventional example, and reference example, and dried to obtain a solid electrolyte layer.

[0075] 〔Evaluation of self-supporting property of solid electrolyte layer〕 Each of the prepared solid electrolyte layers was evaluated for self-supporting property. The prepared solid electrolyte layer with a size of 92 mm × 62 mm was evaluated to see if it could be lifted horizontally. When the solid electrolyte layer could be lifted horizontally while maintaining its shape, it was marked as 〇, and when the state was not maintained when lifted horizontally, it was marked as ×.

[0076] 〔Manufacture of all-solid-state battery〕 A negative electrode structure with a size of 88 mm × 58 mm, a solid electrolyte layer with a size of 92 mm × 62 mm, and a positive electrode structure with a size of 87 mm × 57 mm were laminated, and dry lamination processing was performed and bonded together to obtain a single cell of an all-solid-state battery. The obtained single cell was placed in an aluminum laminate film with terminals attached, degassed, heat-sealed, and packed.

[0077] 〔Evaluation method of all-solid-state battery〕 Specific performance evaluation of the manufactured all-solid-state battery was carried out under the following conditions and methods.

[0078] 〔Resistance〕 The all-solid-state battery was charged up to 4.0 V at a current density of 0.1 C in an environment of 25°C, and the impedance in the range of 0.1 Hz to 1 MHz was measured using an LCZ meter. The arc part of the obtained Cole-Cole plot was fitted to a semi-circular shape with the x-axis as the base, and the numerical value at the intersection of the right end of the semi-circle and the x-axis was taken as the resistance value.

[0079] 〔Discharge Capacity〕 For the all-solid-state battery, charging was performed up to 4.0 V at a current density of 0.1 C under an environment of 25°C, and then discharging was performed up to 2.5 V at a current density of 0.1 C, and the discharge capacity at that time was measured.

Example

[0080] Hereinafter, specific examples of the support according to the embodiment of the present invention will be described.

[0081] 〔Example 1〕 Using cellulose fibers with a drainage degree of 650 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.5 mm, a cylinder mold papermaking was carried out to obtain a support with a thickness of 15 μm, a basis weight of 2.4 g / m 2 , and a density of 0.16 g / cm 3 . The characteristics of the support of Example 1 are summarized in Table 2.

[0082] 〔Example 2〕 Using polyamide fibers with a drainage degree of 200 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.2 mm, a fourdrinier papermaking was carried out to obtain a support with a thickness of 15 μm, a basis weight of 2.9 g / m 2 , and a density of 0.19 g / cm 3 . The characteristics of the support of Example 2 are summarized in Table 2.

[0083] 〔Example 3〕 Using a raw material in which 50% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm were mixed, a fourdrinier papermaking was carried out to obtain a support with a thickness of 20 μm, a basis weight of 9.8 g / m 2 , and a density of 0.49 g / cm 3 . The characteristics of the support of Example 3 are summarized in Table 2.

[0084] 〔Example 4〕 Using a raw material in which 50% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm were mixed, a cylinder mold papermaking was carried out. The obtained non-woven fabric was heat-treated to obtain a support with a thickness of 20 μm, a basis weight of 9.4 g / m 2 , and a density of 0.47 g / cm3 A support was obtained. The characteristics of the support of Example 4 are summarized in Table 2.

[0085] [Example 5] Using a raw material obtained by mixing 20% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 80% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm, a wet-laid nonwoven fabric was produced with a thickness of 15 μm and a basis weight of 5.0 g / m 2 and a density of 0.33 g / cm 3 A support was obtained. The characteristics of the support of Example 5 are summarized in Table 2.

[0086] [Example 6] Using a raw material obtained by mixing 20% by mass of polyamide fibers with a thermal fiber length change rate of -5% and a fiber length of 3 mm and 80% by mass of polyamide binder fibers with a thermal fiber length change rate of -11% and a fiber length of 3 mm, a wet-laid nonwoven fabric was produced with a thickness of 38 μm and a basis weight of 9.1 g / m 2 and a density of 0.24 g / cm 3 A support was obtained. The characteristics of the support of Example 6 are summarized in Table 2.

[0087] [Example 7] Using a raw material obtained by mixing 50% by mass of cellulose fibers with a drainage rate of 400 ml, a thermal fiber length change rate of 0% and a fiber length of 1.1 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm, a cylinder-moulded nonwoven fabric was produced. The obtained nonwoven fabric was heat-treated to obtain a support with a thickness of 20 μm and a basis weight of 7.0 g / m 2 and a density of 0.35 g / cm 3 A support was obtained. The characteristics of the support of Example 7 are summarized in Table 2.

[0088] [Example 8] Using a raw material obtained by mixing 50% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm, a cylinder-moulded nonwoven fabric was produced. The obtained nonwoven fabric was heat-treated to obtain a support with a thickness of 9 μm and a basis weight of 2.7 g / m 2 and a density of 0.30 g / cm 3 A support was obtained. The characteristics of the support of Example 8 are summarized in Table 2.

[0089] 〔Example 9〕 Using cellulose fibers with a drainage degree of 200 ml, a thermal fiber length change rate of 0%, and a fiber length of 0.6 mm, a short-form papermaking was carried out to obtain a support with a thickness of 9 μm, a basis weight of 1.7 g / m 2 , and a density of 0.19 g / cm 3 . The characteristics of the support of Example 9 are summarized in Table 2.

[0090] 〔Example 10〕 Using polyamide fibers with a drainage degree of 0 ml, a thermal fiber length change rate of 0%, and a fiber length of 0.8 mm, a long-form papermaking was carried out to obtain a support with a thickness of 6 μm, a basis weight of 2.5 g / m 2 , and a density of 0.42 g / cm 3 . The characteristics of the support of Example 10 are summarized in Table 2.

[0091] 〔Example 11〕 Using a raw material obtained by mixing 50% by mass of polyester fibers with a thermal fiber length change rate of −1% and a fiber length of 5 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of −18% and a fiber length of 5 mm, a short-form papermaking was carried out to obtain a support with a thickness of 28 μm, a basis weight of 11.9 g / m 2 , and a density of 0.43 g / cm 3 . The characteristics of the support of Example 11 are summarized in Table 2.

[0092] 〔Example 12〕 Using a raw material obtained by mixing 50% by mass of cellulose fibers with a drainage degree of 100 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.1 mm and 50% by mass of polyester binder fibers with a thermal fiber length change rate of −18% and a fiber length of 3 mm, a short-form papermaking was carried out to obtain a support with a thickness of 25 μm, a basis weight of 11.0 g / m 2 , and a density of 0.44 g / cm 3 . The characteristics of the support of Example 12 are summarized in Table 2.

[0093] 〔Comparative Example 1〕 Using cellulose fibers with a drainage degree of 750 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.5 mm, a cylinder-form papermaking was carried out to obtain a support with a thickness of 23 μm, a basis weight of 3.0 g / m 2 , and a density of 0.13 g / cm 3A support was obtained. The characteristics of the support of Comparative Example 1 are summarized in Table 2.

[0094] [Comparative Example 2] Using polyamide fibers with a drainage rate of 0 ml, a change rate of hot fiber length of 0%, and a fiber length of 0.8 mm, a wet-laid sheet was made to obtain a support with a thickness of 4 μm, a basis weight of 1.8 g / m 2 , and a density of 0.46 g / cm 3 The characteristics of the support of Comparative Example 2 are summarized in Table 2.

[0095] [Comparative Example 3] Using a raw material obtained by mixing 80% by mass of polyester fibers with a change rate of hot fiber length of -1% and a fiber length of 3 mm and 20% by mass of polyethylene binder fibers with an unmeasurable change rate of hot fiber length and a fiber length of 3 mm, a wet-laid sheet was made to obtain a support with a thickness of 15 μm, a basis weight of 5.0 g / m 2 , and a density of 0.33 g / cm 3 The characteristics of the support of Comparative Example 3 are summarized in Table 2.

[0096] [Comparative Example 4] Using cellulose fibers with a drainage rate of 100 ml, a change rate of hot fiber length of 0%, and a fiber length of 0.4 mm, a wet-laid sheet was made to obtain a support with a thickness of 5 μm, a basis weight of 0.9 g / m 2 , and a density of 0.18 g / cm 3 The characteristics of the support of Comparative Example 4 are summarized in Table 2.

[0097] [Conventional Example 1] Using a raw material obtained by mixing 15% by mass of polyester fibers with a change rate of hot fiber length of -1% and a fiber length of 3 mm and 85% by mass of polyester binder fibers with a change rate of hot fiber length of -18% and a fiber length of 3 mm, referring to the support described in Example 1 of Patent Document 3, a cylinder-form wet-laid sheet was made to obtain a support with a thickness of 19 μm, a basis weight of 3.7 g / m 2 , and a density of 0.19 g / cm 3 The characteristics of the support of Conventional Example 1 are summarized in Table 2.

[0098] [Conventional Example 2] A support was produced in the same manner as the method described in Example 2 of Patent Document 1, and the support of Comparative Example 2 was obtained. In Comparative Example 2, a polyimide film was subjected to an etching treatment to form holes with a size of 200 μm square, and a support with a thickness of 30 μm and a basis weight of 8.8 g / m 2 and a density of 0.29 g / cm 3 was obtained. The characteristics of the support of Comparative Example 2 are summarized in Table 2.

[0099] [Comparative Example 3] Using a raw material obtained by mixing 85% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 15% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm, referring to the method for producing a support described in Example 1 of Patent Document 2, a cylinder mold papermaking was performed to obtain a support with a thickness of 10 μm, a basis weight of 3.0 g / m 2 and a density of 0.30 g / cm 3 The characteristics of the support of Comparative Example 3 are summarized in Table 2.

[0100] [Reference Example 1] Using a raw material obtained by mixing 70% by mass of polyester fibers with a thermal fiber length change rate of -1% and a fiber length of 3 mm and 30% by mass of polyester binder fibers with a thermal fiber length change rate of -18% and a fiber length of 3 mm, referring to the method for producing a nonwoven fabric base material 1 of Patent Document 6, a cylinder mold papermaking was performed, and a heat calendering treatment and a heat treatment were carried out to obtain a nonwoven fabric base material with a thickness of 13 μm, a basis weight of 8.2 g / m 2 and a density of 0.63 g / cm 3 The characteristics of the nonwoven fabric base material of Reference Example 1 are summarized in Table 2.

[0101] [Reference Example 2] Using a raw material obtained by mixing 20% by mass of polyamide fibers with a filtration rate of 0 ml, a thermal fiber length change rate of 0%, and a fiber length of 0.7 mm, 20% by mass of acrylic fibers with a thermal fiber length change rate of -10% and a fiber length of 3 mm, 50% by mass of polyamide fibers with a thermal fiber length change rate of 0% and a fiber length of 5 mm, and 10% by mass of cellulose fibers with a filtration rate of 0 ml, a thermal fiber length change rate of 0%, and a fiber length of 0.2 mm, referring to the method for producing a separator 1 for an electrochemical element of Patent Document 5, a cylinder mold papermaking was performed to obtain a thickness of 25 μm and a basis weight of 12.2 g / m 2 and a density of 0.48 g / cm 3A separator for an electrochemical element was obtained. The characteristics of the separator for an electrochemical element of Reference Example 2 are summarized in Table 2.

[0102] [Reference Example 3] Using a raw material obtained by mixing 40% by mass of polyester fibers with a thermal fiber length change rate of -1%, a fiber length of 3 mm, 40% by mass of polyester binder fibers with a thermal fiber length change rate of -18%, a fiber length of 3 mm, and 20% by mass of polyvinyl alcohol fibers with an unmeasurable thermal fiber length change rate and a fiber length of 3 mm, a wet-laid sheet was made, with a thickness of 15 μm and a basis weight of 5.0 g / m 2 , and a density of 0.33 g / cm 3 a support was obtained. The characteristics of the support of Reference Example 3 are summarized in Table 2.

[0103] Table 1 shows the fiber names and blending ratios of the supports, nonwoven fabric substrates, and composite fibers of the separators for electrochemical elements in Examples 1 to 12, Comparative Examples 1 to 4, Conventional Examples 1 to 3, and Reference Examples 1 to 3 described above.

[0104] [Table 1]

[0105] Table 2 shows the evaluation results of the characteristics of the supports, nonwoven fabric substrates, separators for electrochemical elements, self-supportability of the solid electrolyte layer, and battery characteristics in each of the above-described examples, comparative examples, conventional examples, and reference examples.

[0106] [Table 2]

[0107] Hereinafter, the evaluation results of all-solid-state batteries using the supports, nonwoven fabric substrates, and separators for electrochemical elements in each of the examples, comparative examples, conventional examples, and reference examples will be described in detail.

[0108] Unlike the solid electrolyte layers using the supports of each of the examples, the solid electrolyte layers using the supports of Comparative Example 1, Comparative Example 3, and Conventional Example 3, the solid electrolyte layer using the separator base material of Reference Example 1, and in addition, the solid electrolyte layer using the separator for an electrochemical element of Reference Example 2, a self-supporting solid electrolyte layer could be formed.

[0109] Compared with all-solid-state batteries using the supports of Comparative Example 2, Comparative Example 4, Conventional Example 1, Conventional Example 2, and Reference Example 3, all-solid-state batteries using the separator base material of Reference Example 1, and in addition, all-solid-state batteries using the separator for an electrochemical element of Reference Example 2 as a support, the all-solid-state batteries using the supports of each of the examples had a lower resistance and a higher discharge capacity.

[0110] The support of each of the examples had a lower air permeability, a higher density, and a smaller maximum through-hole area compared with the support of Comparative Example 1. The air permeability of the support of Comparative Example 1 was as high as 51.0 L / cm 2 / min, the density was as low as 0.13 g / cm 3 and the maximum through-hole area was as large as 0.316 mm 2 Therefore, when the solid electrolyte coating liquid was coated and dried on the support of Comparative Example 1, it is considered that the support of Comparative Example 1 could not hold and reinforce the solid electrolyte, and the solid electrolyte could not remain uniformly on the support. Therefore, a uniform solid electrolyte layer could not be formed. As a result, an all-solid-state battery could not be manufactured using the support of Comparative Example 1. From the comparison between each of the examples and Comparative Example 1, it can be seen that it is not preferable that the air permeability exceeds 50 L / cm 2 / min, the density is less than 0.15 g / cm 3 and the maximum through-hole area exceeds 0.3 mm 2

[0111] The support of Comparative Example 2 is thinner than the supports of the respective Examples. Therefore, a short circuit occurred in the all-solid-state battery using the support of Comparative Example 2. It is considered that this is because the support of Comparative Example 2 was as thin as 4 μm and could not prevent a short circuit between the positive electrode and the negative electrode. In addition, since a short circuit occurred, various battery evaluations of the all-solid-state battery using the support of Comparative Example 2 could not be performed. From the comparison between each Example and Comparative Example 2, it can be seen that a thickness of less than 5 μm for the support is not preferable.

[0112] The support of Comparative Example 3 expanded such that the thermal dimensional change rate in the longitudinal direction was 5.6% and the thermal dimensional change rate in the lateral direction was 5.1% as compared with the supports of the respective Examples. It is considered that in the support of Comparative Example 3, when the solid electrolyte coating liquid was applied to the support and dried, the polyethylene binder contained in the support thermally changed, and thus the shape of the support could not be maintained and it expanded. Therefore, a uniform solid electrolyte layer could not be obtained. That is, from the comparison between each Example and Comparative Example 3, it can be seen that a thermal dimensional change rate of more than 5% in each of the longitudinal and lateral directions of the support is not preferable.

[0113] The all-solid-state battery using the support of Comparative Example 4 has a higher resistance and a lower discharge capacity as compared with the all-solid-state batteries using the supports of the respective Examples. In addition, the support of Comparative Example 4 has a weak lateral stiffness of 4 mN as compared with the supports of the respective Examples. Since the support of Comparative Example 4 has a weak lateral stiffness, it is considered that when the positive electrode, the solid electrolyte layer, and the negative electrode were integrally pressed after forming the solid electrolyte layer, the formed lithium ion path line was cut. Since the solid electrolyte layer, the positive electrode, and the negative electrode are not completely flat, when these are overlapped and pressed, stress with different strengths is applied to each of them. As a result, when strong stress is locally applied to the support, a part of the support is deformed, and it is considered that the formed lithium ion path line is cut accordingly. That is, from the comparison between each Example and Comparative Example 4, it can be seen that a stiffness of less than 5 mN in each of the longitudinal and lateral directions is not preferable.

[0114] The all-solid-state battery using the support of Comparative Example 1 has a higher resistance and a lower discharge capacity compared to the all-solid-state batteries using the supports of the respective Examples. Compared with the supports of the respective Examples, the support of Comparative Example 1 shrank with a longitudinal thermal dimensional change rate of -11.0% and a lateral thermal dimensional change rate of -10.7%. Therefore, it is considered that when the solid electrolyte coating liquid was applied to the support of Comparative Example 1 and dried, the support shrank significantly. As a result, large irregularities occurred on the surface of the obtained solid electrolyte layer, and when the positive electrode, the solid electrolyte layer, and the negative electrode were integrally pressed, the adhesion at the interface between the positive electrode or the negative electrode and the solid electrolyte layer deteriorated, and it is considered that this is due to the increase in the interface resistance. That is, from the comparison between each Example and Comparative Example 1, it can be seen that a thermal dimensional change rate of less than -10.0% in both the longitudinal and lateral directions is not preferable.

[0115] Unlike the supports of the respective Examples which are paper or non-woven fabric, the support of Comparative Example 2 is a support in which through-holes are formed in a film. Although the through-holes of the support of Comparative Example 2 can be filled with a solid electrolyte, the solid electrolyte can only be filled inside the formed through-holes. In addition, it is considered that an interface between the film which is an insulator and the positive electrode or the negative electrode exists at the interface between the positive electrode or the negative electrode and the solid electrolyte layer formed of the support of Comparative Example 2. Due to this influence, it is considered that the resistance of the all-solid-state battery using the support of Comparative Example 2 is higher than that of the supports of the respective Examples. From the comparison between each Example and Comparative Example 2, it can be seen that paper or non-woven fabric is suitable as the support in order to reduce the resistance of the all-solid-state battery.

[0116] The supports of the respective Examples have a higher tensile strength compared to the support of Comparative Example 3. When the solid electrolyte coating liquid was applied to the support of Comparative Example 3 and the excess coating liquid was removed, tearing occurred. This is presumably because the tensile strength of the support of Comparative Example 3 was as weak as 0.7 N / 15 mm. Since the solid electrolyte layer could not be formed on the support of Comparative Example 3, the fabrication and evaluation of the all-solid-state battery were not carried out. From the comparison between each example and Comparative Example 3, it can be seen that in order to suppress the breakage of the support during the production of the solid electrolyte layer, it is not preferable that the tensile strength is less than 1.0 N / 15 mm.

[0117] Reference Example 1 showed the case where the base material for a separator for a lithium-ion secondary battery with a low thermal shrinkage rate described in Patent Document 6 was used as the support for an all-solid-state battery. The base material for the separator of Reference Example 1 had a lower air permeability of 0.7 L / cm 2 / min, a higher density of 0.63 g / cm 3 and a smaller maximum penetration area of 0.0008 mm 2 compared with each example. Therefore, when the solid electrolyte coating liquid was applied to the base material for the separator of Reference Example 1, the solid electrolyte coating liquid did not penetrate into the support and remained on the surface of the support. Therefore, the solid electrolyte coating liquid was dried in a state of remaining on the surface of the support, and the solid electrolyte layer was formed on the surface of the support. And since the solid electrolyte layer formed on the surface of the support was dried without the support, the solid electrolyte was not reinforced, so cracks occurred, and when the solid electrolyte layer was lifted, cracks occurred and it had no self-supporting property. Although cracks occurred in the solid electrolyte layer using the base material for the separator of Reference Example 1, an all-solid-state battery could be fabricated by laminating it with a positive electrode and a negative electrode. The all-solid-state battery using the base material for the separator of Reference Example 1 had a very high resistance and could not discharge the battery compared with the all-solid-state batteries using the supports of each example. This is considered to be due to the fact that the density was as high as 0.63 g / cm 3 and the maximum penetration area was as small as 0.0008 mm 2 and the air permeability was as low as 0.7 L / cm 2 / min. From the comparison between each example and Reference Example 1, it can be seen that it is not preferable that the air permeability of the support is less than 1 L / cm 2 / min, the density is more than 0.50 g / cm 3 and the maximum penetration area is less than 0.001 mm 2 .

[0118] Reference Example 2 showed the case where a separator for a highly heat-resistant electrochemical element described in Patent Document 5 was used as a support for an all-solid-state battery. The separator for the electrochemical element in Reference Example 2 had a lower air permeability of 0.6 L / cm 2 / min. and a smaller maximum penetration area of 0.0003 mm 2 than those of each Example. As a result, for the same reason as in Reference Example 1, cracks occurred, and a uniform solid electrolyte layer could not be formed, and a self-supporting solid electrolyte layer could not be formed. Although cracks occurred in the solid electrolyte layer using the separator for the electrochemical element in Reference Example 2 as in Reference Example 1, an all-solid-state battery could be fabricated by laminating it with a positive electrode and a negative electrode. The all-solid-state battery using the separator base material of Reference Example 2 had a higher resistance and could not discharge compared with the all-solid-state batteries using the supports of each Example and the all-solid-state battery using the separator base material of Reference Example 1. This is presumably because the longitudinal stiffness-flexibility after heat treatment was as high as 252 mN, that is, it was too hard, and thus the support broke and cracks occurred inside the solid electrolyte layer when the positive electrode, the solid electrolyte layer, and the negative electrode were integrally pressed. It is considered that the lithium ion pass line was cut due to crack generation, resulting in an increase in resistance. That is, from the comparison between each Example and Reference Examples 1 and 2, it can be seen that it is not preferable that the longitudinal and lateral stiffness-flexibilities exceed 250 mN, respectively.

[0119] The support of Reference Example 3 had a lower air permeability compared with Example 5. As a result, the all-solid-state battery using the support of the reference example had a higher resistance and a lower discharge capacity compared with the all-solid-state batteries using the supports of each Example. The support of Reference Example 3 is a support containing 20% by mass of polyvinyl alcohol fibers in addition to polyester fibers and polyester binder fibers. Polyvinyl alcohol fibers are effective fibers for improving tensile strength. Polyvinyl alcohol fibers can reinforce fiber joints due to shape changes caused by wet heat and improve the tensile strength of the support. However, it is considered that in the state of constituting the support, polyvinyl alcohol fibers do not form a fibrous state but form a large number of film layers inside the support, blocking the fiber gaps. As a result, it is considered that the air permeability becomes low, inhibiting the penetration of the solid electrolyte coating liquid into the support. That is, from the comparison between Example 5 and Reference Example 3, it can be seen that the blending of a binder that cannot maintain a fibrous state is not preferable.

[0120] The above-described embodiments are merely examples, and for example, the composition of the solid electrolyte, the positive electrode, the negative electrode, etc. can be appropriately changed by those skilled in the art.

[0121] As described above, by using paper or non-woven fabric with the thermal dimensional change rates in the longitudinal and transverse directions of the support being -10 to 5% respectively, the air permeability being 1 to 50 L / cm 2 / min., and the longitudinal and transverse stiffnesses after heat treatment being 5 to 250 mN respectively, it is possible to obtain a support that can reduce the interfacial resistance between the positive electrode or the negative electrode and the solid electrolyte layer, improve the permeability of the solid electrolyte into the support, and suppress the cutting of the lithium ion path lines formed inside the solid electrolyte layer. By using this support, a all-solid-state battery with low resistance can be obtained.

Claims

1. A support contained in a solid electrolyte layer of a lithium-ion secondary battery, The thermal dimensional change rates in the longitudinal and transverse directions of the substrate before and after heating at 200°C for 1 hour are -10 to 5% respectively, and the air permeability is 1 to 50 L / cm ２ / min. The substrate is paper or non-woven fabric with longitudinal and transverse stiffnesses in the range of 5 to 250 mN after heating at 200°C for 1 hour The support for a lithium-ion secondary battery characterized by the above.

2. The support has a thickness of 5 to 40 μm and a density in the range of 0.15 to 0.50 g / cm ３ The support for a lithium-ion secondary battery according to claim 1, characterized in that it is within the above range.

3. A lithium-ion secondary battery comprising a solid electrolyte layer having the support for a lithium-ion secondary battery according to Claim 1 or Claim 2.

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