Support for secondary battery, solid electrolyte sheet, and secondary battery

Abstract

A support for a secondary battery, which is a support for holding a solid electrolyte of a secondary battery, the support for a secondary battery being substantially free of non-fibrillated fibers and being formed of at least one selected from the group consisting of paper and nonwoven fabric, and having a permeability of 1 to 15% with respect to a thickness direction of perfluoropolyether.

Description

Technical Field

[0001] The present invention relates to a support for a secondary battery that holds a solid electrolyte, a solid electrolyte sheet, and a secondary battery having the support. Background Technology

[0002] Lithium-ion secondary batteries, which utilize a liquid electrolyte (hereinafter referred to as electrolyte), are high-energy-density rechargeable batteries. A lithium-ion secondary battery using an electrolyte has the following configuration: a separator is sandwiched between the positive and negative electrodes, and the electrolyte is held within the separator.

[0003] In lithium-ion secondary batteries, organic electrolytes are primarily used as the electrolyte. However, organic electrolytes can present problems such as leakage and flammability due to their liquid nature. Therefore, to improve the safety of lithium-ion secondary batteries, secondary batteries using solid electrolytes instead of liquid electrolytes (hereinafter referred to as all-solid-state batteries) have been developed. All-solid-state batteries, needless to say, have a solid electrolyte, thus eliminating leakage. Furthermore, compared to liquid electrolytes, they exhibit flame retardancy and higher heat resistance, making them a highly desirable type of secondary battery. Due to their high safety, all-solid-state batteries are being mass-produced for small-scale applications such as wearable devices that come into direct contact with the skin.

[0004] Furthermore, unlike lithium-ion rechargeable batteries that use electrolytes, all-solid-state batteries exhibit less performance degradation at high temperatures, thus eliminating the need for cooling devices. This also makes them advantageous for increasing the energy density per unit volume of the battery pack. Given the advantages of all-solid-state batteries as rechargeable batteries with high volumetric energy density, we anticipate their further scaling up for applications such as electric vehicles.

[0005] Unlike secondary batteries that use an electrolyte between the positive and negative electrodes, all-solid-state batteries do not have a separator to hold the electrolyte; instead, they have a solid electrolyte layer sandwiched between them. For example, in the case of a lithium-ion all-solid-state battery, during charging, lithium ions travel from the positive electrode through the solid electrolyte layer to the negative electrode.

[0006] On the other hand, during discharge, lithium ions travel from the negative electrode to the positive electrode through the solid electrolyte layer. As for the types of ions that conduct between the positive and negative electrodes (hereinafter referred to as charge carrier ions), in the case of all-solid-state batteries, lithium ions are self-evident, but from the perspective of avoiding stable resource supply issues, various ion types such as sodium ions have also been studied. For these charge carrier ions to travel back and forth between the positive and negative electrodes through the solid electrolyte layer, a pass line needs to be formed relative to the thickness direction of the solid electrolyte layer.

[0007] In other words, for the solid electrolyte layer sandwiched between the positive and negative electrodes in an all-solid-state battery, it is required to have the function of ion conduction between the positive and negative electrodes and to prevent short circuits between the positive and negative active materials. On this basis, in order to achieve excellent volumetric energy density and reduce internal resistance, the thickness of the solid electrolyte layer is required to be thin.

[0008] Methods for forming a solid electrolyte layer include mixing a solid electrolyte with a binder and calendering it under heat to form a sheet, and coating a solid electrolyte slurry onto an electrode and drying it.

[0009] However, in the formation of solid electrolyte layers for all-solid-state batteries used in large batteries such as electric vehicles, solid electrolyte layers obtained by methods such as forming sheets through rolling under heat are prone to cracking and breakage during operation. Furthermore, if a method is used to coat the electrode with a slurry containing the solid electrolyte and then dry it, the solid electrolyte layer will experience strain and cracking during drying. Therefore, it is difficult to stably form a thin and uniform solid electrolyte layer. If a thin and uniform solid electrolyte layer cannot be stably formed, ion conductivity will deteriorate, leading to short circuits.

[0010] On the other hand, to prevent short circuits, the thickness of the solid electrolyte layer can be increased. However, with a thicker layer, the volumetric energy density decreases, the inter-electrode distance increases, and the internal resistance increases.

[0011] To address the above issues, a solid electrolyte sheet integrating a thin-film sheet (hereinafter referred to as the support) with a solid electrolyte has been proposed for use in all-solid-state batteries. Furthermore, various configurations related to the support for all-solid-state batteries and the nonwoven fabric substrate for lithium-ion battery separators have been proposed.

[0012] For example, a technique involving a solid electrolyte sheet having multiple through-holes formed by etching a thin film serving as a support has been disclosed (see, for example, Patent Document 1). In this technique, a solid electrolyte is filled into the through-holes formed by the etching process, thereby constructing an all-solid-state battery with excellent energy density and output characteristics.

[0013] Furthermore, a technique involving a solid electrolyte sheet obtained using a support with a porosity of 60% or more and 95% or less, and a thickness of 5 μm or more and less than 20 μm, has been disclosed (see, for example, Patent Document 2). This solid electrolyte sheet is disclosed to be thin yet self-supporting.

[0014] Furthermore, a technology involving a nonwoven fabric substrate for lithium-ion battery separators, comprising unstretched polyester fibers and thermo-adhesive fibers as binder fibers, is disclosed (see, for example, Patent Document 3). This technology discloses that the unstretched polyester fibers are softened or melted through hot pressing processes such as calendering, allowing them to bond firmly with other fibers. The thermo-adhesive fibers, when wet, flow or easily deform, exhibit adhesive properties. By including these binders in the nonwoven fabric substrate, a nonwoven fabric substrate for lithium-ion battery separators with high tensile strength and high productivity is constructed.

[0015] Existing technical documents

[0016] Patent documents

[0017] Patent Document 1: Japanese Patent Application Publication No. 2017-103146

[0018] Patent Document 2: Japanese Patent Application Publication No. 2020-77488

[0019] Patent Document 3: Japanese Patent Application Publication No. 2020-161243 Summary of the Invention

[0020] The problem the invention aims to solve

[0021] However, in the technology described in Patent Document 1, when manufacturing the solid electrolyte sheet, the solid electrolyte is filled into the through-holes, thus only filling the interior of the formed through-holes with solid electrolyte. Therefore, apart from the through-holes, a thin film portion remains as an insulator, creating an interface between the positive and negative electrodes and the thin film portion where charge carrier ions cannot pass through. As a result, the interfacial resistance between the solid electrolyte sheet and the positive and negative electrodes tends to be high, leading to a higher resistance in the all-solid-state battery using this support.

[0022] Furthermore, in the technology described in Patent Document 2, the support is a support with sufficient porosity. However, when the supporting material contains fine fibers, it becomes a support with a dense structure. As a result, it is difficult for the solid electrolyte slurry to penetrate into the interior of the support and difficult for it to permeate in the thickness direction. Therefore, the formation of the pathway for charge carrier ions relative to the thickness direction of the solid electrolyte sheet becomes insufficient, resulting in a solid electrolyte sheet with high internal resistance.

[0023] Furthermore, in the technology described in Patent Document 2, regarding the support body, when the number of fibers constituting the support body is small, the permeability of the solid electrolyte slurry relative to the thickness direction of the support body becomes too high, thus raising concerns about the retention of the solid electrolyte slurry. As a result, the solid electrolyte slurry cannot remain on the support body, the retention effect of the support body on the solid electrolyte cannot be fully obtained, and the resistance becomes high.

[0024] Furthermore, in the technology described in Patent Document 3, the wet-heat adhesive fibers contained in the nonwoven substrate, as described above, undergo flow or deformation when performing their adhesive function, and therefore sometimes fail to maintain their fiber state, thus filling the pores inside the nonwoven substrate. Furthermore, if a large number of adhesive fibers that cannot maintain their shape are included, the density becomes high. As a result, the permeability of the solid electrolyte slurry towards the interior of the nonwoven substrate, and its permeability relative to the thickness direction of the nonwoven substrate, become insufficient. Therefore, the number of pathways for charge carrier ions formed inside the solid electrolyte sheet decreases, and the resistance of the all-solid-state battery increases.

[0025] To address the aforementioned problems, the present invention provides a secondary battery support capable of reducing the internal resistance of a solid electrolyte layer, a solid electrolyte sheet using the support, and a secondary battery using the support.

[0026] Solution for solving the problem

[0027] The secondary battery support of the present invention is a support for holding the solid electrolyte of a secondary battery. The secondary battery support is substantially free of nonfibrillated fibers and is formed from at least one selected from paper and nonwoven fabrics, with a perfluoropolyether transmittance of 1 to 15% relative to the thickness direction.

[0028] Furthermore, in the solid electrolyte sheet of the present invention, a solid electrolyte is held in a thin film-like support, the support being substantially free of nonfibrillated fibers and formed of at least one selected from paper and nonwoven fabric, and the thickness direction of the support having a permeability of 1 to 15% for perfluoropolyether.

[0029] Furthermore, the secondary battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. In this secondary battery, the solid electrolyte layer is formed in the form of a solid electrolyte sheet in which the solid electrolyte is held by a support. The solid electrolyte sheet includes: a support that substantially does not contain non-fibrillated fibers, is formed of at least one selected from paper and nonwoven fabric, and has a permeability of 1 to 15% in the thickness direction to perfluoropolyether; and a solid electrolyte held in the support.

[0030] The effects of the invention

[0031] According to the present invention, a secondary battery support capable of reducing the internal resistance of the solid electrolyte layer, a solid electrolyte sheet using the support, and a secondary battery using the secondary battery support can be provided. Detailed Implementation

[0032] Hereinafter, examples of methods for implementing the present invention will be described, but the present invention is not limited to the following examples.

[0033] It should be noted that the explanations are given in the following order.

[0034] 1. Implementation method of support for secondary batteries (first implementation method)

[0035] 2. Implementation method of secondary battery (second implementation method)

[0036] <1. Embodiment of a Support for a Secondary Battery (First Embodiment)>

[0037] The following describes a specific embodiment of the support for a secondary battery.

[0038] The secondary battery support (hereinafter also referred to as the support) of this method is used to form a solid electrolyte layer sandwiched between the positive and negative electrodes in the secondary battery. The support is used to hold the solid electrolyte of the secondary battery and is formed of at least one selected from paper and nonwoven fabric, with a perfluoropolyether transmittance of 1 to 15% relative to the thickness direction.

[0039] It should be noted that, in this application, the numerical range indicated by "~" includes the values ​​shown as upper and lower limits.

[0040] The solid electrolyte layer sandwiched between the positive and negative electrodes is required to facilitate the conduction of charge carrier ions between them during charging and discharging. Therefore, pathways for charge carrier ions need to be formed between the positive electrode and the solid electrolyte layer, within the solid electrolyte layer, and between the solid electrolyte layer and the negative electrode. In other words, if the interfacial resistance between the positive electrode and the solid electrolyte layer, between the solid electrolyte layer and the negative electrode, and the resistance within the solid electrolyte layer can be reduced, the overall resistance of the all-solid-state battery can be lowered.

[0041] The inventors of this application have discovered that the permeability of the liquid relative to the thickness direction of the support is a major factor hindering further reduction of the internal resistance of the solid electrolyte sheet. Therefore, in the support of this method, unlike the conventional gas-based permeability, by using liquid as in the actual coating process, the diffusion of the solid electrolyte slurry toward the interior of the support and the retention of liquid by the support are evaluated.

[0042] If the permeability of the liquid relative to the thickness of the support is too low, the pathways for charge carrier ions to form inside the solid electrolyte sheet are reduced. On the other hand, if the permeability of the liquid relative to the thickness of the support is too high, the support has poor retention of the solid electrolyte slurry, resulting in less solid electrolyte slurry remaining on the support and fewer pathways for charge carrier ions to form inside the solid electrolyte sheet. As a result, in either of these cases, the resistance of the resulting solid electrolyte sheet is high.

[0043] Therefore, by optimizing the permeability of the liquid relative to the thickness direction of the support, the pathways for charge carrier ions formed inside the solid electrolyte sheet can be increased. As a result, the resistance of the solid electrolyte layer can be reduced.

[0044] In this embodiment, the permeability of the liquid relative to the thickness direction of the support is measured using the permeability of perfluoropolyether relative to the thickness direction. Perfluoropolyether is a chemically inactive substance with low surface tension and is a liquid at room temperature, thus it is a liquid that can be used to evaluate the permeability relative to the thickness direction based on the internal structure of the support.

[0045] For example, when using water for the same evaluation, if the support has high hydrophilicity, the fibers constituting the support will swell due to the influence of water, altering the internal structure of the support. Conversely, if the support has low hydrophilicity, its wettability is low, thus reducing permeability into the support, making it impossible to accurately determine permeability and transmission based on the support structure. Furthermore, water has high surface tension, hindering water permeation into the support, making it impossible to accurately evaluate the influence of the support's internal structure. Additionally, when using common organic solvents for the same evaluation, the low vapor pressure of the organic solvent causes it to evaporate during the experiment, making it impossible to accurately determine the transmission rate.

[0046] That is, compared with other liquids, the interaction between perfluoropolyether and the support is small. Therefore, the test liquid has a slight effect on the fibers constituting the support. Thus, the original properties of the support can be accurately evaluated for supports with different fiber types. It should be noted that in this application, 1,1,2,3,3-hexafluoro-1-propylene (with a surface tension of 16 mN / m) is used as the perfluoropolyether.

[0047] The permeation amount of perfluoropolyether relative to the thickness direction is the mass of perfluoropolyether that is dropped onto the surface of the support, impregnates the interior of the support, diffuses, and permeates to the back side of the support.

[0048] The transmittance of perfluoropolyether relative to the thickness direction is calculated by dividing the amount of perfluoropolyether that transmits in the thickness direction by the mass of the perfluoropolyether added and then rounding it down to a percentage. In other words, by knowing the transmittance of perfluoropolyether, the transmittance of the solid electrolyte slurry relative to the thickness direction of the support can be determined.

[0049] If the perfluoropolyether has low transmittance relative to the thickness direction, it indicates that the solid electrolyte slurry has low transmittance relative to the thickness direction of the support. On the other hand, if the perfluoropolyether has high transmittance relative to the thickness direction, the solid electrolyte slurry has excessively high transmittance towards the inside of the support, thus the support has poor retention of the solid electrolyte slurry.

[0050] The support structure controls the transmittance of perfluoropolyether relative to the thickness direction to be in the range of 1-15%.

[0051] For a support having a perfluoropolyether transmittance relative to the thickness direction within the aforementioned range, the solid electrolyte slurry exhibits excellent permeability and retention relative to the thickness direction of the support, thus allowing for the uniform impregnation of a necessary amount of solid electrolyte slurry within the support. As a result, pathways for a necessary amount of charge carrier ions can be formed within the resulting solid electrolyte sheet. Through these effects, the internal resistance of the solid electrolyte layer can be reduced. In other words, by using this support, the resistance of the all-solid-state battery can be reduced.

[0052] Furthermore, from the viewpoint of the permeability and retention of the support for the solid electrolyte slurry, the permeability of the perfluoropolyether relative to the thickness direction of the support is more preferably in the range of 3 to 13%.

[0053] If the perfluoropolyether transmittance in the thickness direction relative to the support is less than the above range, the transmittance of the solid electrolyte slurry in the thickness direction relative to the support is insufficient, thus reducing the pathways for charge carrier ions formed in the thickness direction inside the solid electrolyte sheet.

[0054] On the other hand, when the permeability of the perfluoropolyether relative to the thickness direction of the support exceeds the above-mentioned range, the amount of solid electrolyte slurry that the support can hold is small. As a result, the pathways for charge carrier ions formed in the thickness direction inside the solid electrolyte sheet become fewer, and the internal resistance of the solid electrolyte sheet becomes higher.

[0055] For the support, as long as the permeability of the perfluoropolyether is within the above-mentioned range, there are no particular limitations on other components such as thickness, basis weight, density, porosity, and tensile strength. If the permeability of the perfluoropolyether is within the above-mentioned range, the composition of the support is not limited, and it is possible to evaluate the sufficient formation of ion-carrying pathways within the solid electrolyte sheet, thereby reducing the internal resistance of the solid electrolyte sheet and the resistance of the all-solid-state battery. From the viewpoint of the support's permeability, retention, and tensile strength in relation to the solid electrolyte slurry, the basis weight of the support is more preferably 1.0~15.0 g / m³. 2 The range.

[0056] The support is formed from at least one selected from paper and nonwoven fabric. Preferably, the support is formed from at least either paper or nonwoven fabric. The reasons are as follows.

[0057] Paper refers to a substance made by bonding plant fibers or other fibers together. Nonwoven fabric, on the other hand, refers to a sheet-like material made without a loom, by treating various fiber webs such as natural, recycled, and synthetic fibers using mechanical, chemical, thermal, or combinations thereof, and binding the fibers together with adhesives or the fibers' own adhesive force.

[0058] That is, paper and nonwoven fabrics are composed of randomly arranged fibers, thus possessing countless pores and through-holes of various sizes within them. Therefore, the coated solid electrolyte slurry can extend not only in the thickness direction but also in the planar direction. Specifically, the coated solid electrolyte includes solid electrolyte remaining on the surface of the support, solid electrolyte remaining inside the support, and solid electrolyte extending from the surface side through the through-holes to the back side.

[0059] Therefore, for solid electrolyte sheets made using at least one of paper and nonwoven fabric as a support, the solid electrolyte not only fills the surface of the support but also its interior, forming a good pathway for charge carrier ions. As a result, the internal resistance of the solid electrolyte sheet can be reduced, as can the interfacial resistance between the solid electrolyte sheet and the positive or negative electrode. Consequently, a reduction in the resistance of all-solid-state batteries can be achieved.

[0060] There are no particular limitations on the materials that can be used as the support structure, as long as they do not repel the solid electrolyte slurry and do not have adverse physical or chemical effects on the solid electrolyte. Examples include organic fibers such as cellulose fibers, polyamide fibers, polyester fibers, polypropylene fibers, and acrylic fibers; and inorganic fibers such as glass fibers and alumina fibers. Furthermore, more than one type of fiber selected from these can be used. By using these fibers, a support structure with excellent solid electrolyte filling properties can be obtained.

[0061] Furthermore, from the viewpoint of maintaining the shape and tensile strength of the support, it is preferable that the support contains fibers with adhesive properties. Examples of fibers with adhesive properties include fibers with fibrils on the fiber surface (hereinafter referred to as fibrillated fibers) and synthetic resin adhesive fibers.

[0062] For example, the adhesive strength of fibrillated cellulose fibers is based on both physical bonding caused by the interweaving of the cellulose fibers and chemical bonding caused by hydrogen bonds formed by the hydroxyl groups in cellulose. Additionally, the adhesive strength of fibrillated polyamide fibers and fibrillated acrylic fibers is based on physical bonding caused by the interweaving of the fibers. Bonding based on any type of fiber contributes to maintaining the shape and tensile strength of the support, and is therefore preferred.

[0063] It should be noted that the support body preferably does not substantially contain fibers that do not have fibrils on the fiber surface (hereinafter referred to as non-fibrillated fibers). Substantially containing no non-fibrillated fibers means that the content of non-fibrillated fibers in all the fibers constituting the support body is less than 1% by mass.

[0064] Synthetic resin adhesive fibers can be categorized into fibers that maintain their fibrous state when forming a support and fibers that cannot maintain their fibrous state, such as becoming membrane-like. Adhesive fibers that maintain their fibrous state when forming a support are preferred in that they do not easily impede impermeability / permeability and can improve the tensile strength of the support.

[0065] The adhesive fibers, which maintain their fibrous shape while forming a support structure, exhibit adhesive strength through thermal bonding at the fiber interlacing points. Therefore, the adhesive fibers, which maintain their fibrous state as a component of the support structure, can reduce breakage from physical impacts, and since bonding occurs only at the fiber joints, it is less likely to hinder the penetration and permeation of the solid electrolyte slurry into the support structure when forming a solid electrolyte sheet.

[0066] On the other hand, for synthetic resin adhesive fibers that cannot maintain their fibrous state when formed into a support structure, during the support manufacturing process, the fibers change into a film due to heat. Heat is applied near the melting or softening point of the resin constituting the fibers to melt the resin, and fusion occurs at the fiber interlacing points. That is, when using a non-fibrous adhesive in the form of a support structure, the adhesive component forms a thin film layer in the fiber gaps of the support structure, filling the pores, while still performing its adhesive function. As a result, this can sometimes hinder the penetration and permeation of solid electrolytes into the support structure, requiring careful attention to the content ratio during use.

[0067] For materials that can be used as synthetic resin binder fibers that maintain fiber shape and have adhesive properties, there are no particular limitations, as long as the fiber does not repel the solid electrolyte slurry and does not have an adverse physical or chemical effect on the solid electrolyte. Examples include: pulped cellulose fibers, pulped polyamide fibers, pulped acrylic fibers, and other fibrillated fibers; polyamide binder fibers, polyester binder fibers, polyethylene binder fibers, polypropylene-polyethylene core-sheath type binder fibers, etc. In addition, one or more fibers selected from these fibers can be used.

[0068] In the support, a method to achieve a perfluoropolyether transmittance in the thickness direction ranging from 1% to 15% is, for example, controlling the fiber length to 0.1 to 2 mm in the case of fibrillated fibers. To obtain fibrillated fibers with a fiber length of 0.1 to 2 mm, methods such as pulping to a CSF ("Canadian Standard" freeness) value of 0 to 400 ml can be cited. It should be noted that this method is not limited to achieving a perfluoropolyether transmittance in the thickness direction ranging from 1% to 15%.

[0069] Fibrous fibers have branch-like fibrils on their surface, allowing for a large number of fibers to support the solid electrolyte. Therefore, when the solid electrolyte is impregnated into the support, the support can retain the solid electrolyte through the fibrils. That is, the support can support a large amount of solid electrolyte, thus suppressing the formation of internal cracks in the resulting solid electrolyte sheet. Consequently, the electrical resistance of the resulting solid electrolyte sheet can be reduced.

[0070] There are no particular limitations on the manufacturing method of the support body; it can be manufactured using dry or wet methods. Preferably, from the viewpoint of homogeneity of the support body's texture, a papermaking method is preferred, which involves stacking fibers dispersed in water on a paper line, followed by dehydration, drying, and paper forming. Regarding the papermaking form of the support body, there are no particular limitations as long as the transmittance of the perfluoropolyether relative to the thickness direction is satisfied. Long-wire papermaking, short-wire papermaking, and cylinder papermaking can be used. Furthermore, multiple layers formed by these papermaking methods can be combined. Additionally, during papermaking, additives such as dispersants, defoamers, and paper strength enhancers can be added. Post-processing such as paper strength enhancement, hydrophilic processing, calendering, hot calendering, and embossing can also be performed after the paper layers are formed.

[0071] <2. Implementation Method of Secondary Battery (Second Implementation Method)>

[0072] Next, an embodiment of a secondary battery using the aforementioned support will be described. The secondary battery is, for example, an all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer. In this case, the solid electrolyte layer is disposed between the positive and negative electrodes. The solid electrolyte layer is configured as a solid electrolyte sheet in which the solid electrolyte is held by a support. The solid electrolyte sheet has the following configuration: it includes a support for the secondary battery and a solid electrolyte, the solid electrolyte is held by the support, and the solid electrolyte and the support are integrated.

[0073] There are no particular limitations on the types of positive and negative electrodes used in all-solid-state batteries. For example, all-solid-state batteries can be composed of known positive and negative electrodes, but are not limited to these.

[0074] Furthermore, there are no particular limitations on the types of all-solid-state batteries. By selecting the materials that constitute an all-solid-state battery, it is possible to form, for example, lithium-ion secondary batteries, sodium-ion secondary batteries, etc.

[0075] The aforementioned all-solid-state batteries can be used as batteries for mobile communication devices, portable electronic devices, electric bicycles, electric two-wheelers, electric vehicles, and small household power storage devices.

[0076] [Positive electrode, negative electrode]

[0077] In secondary batteries, there are no particular limitations on the positive electrode active material used for the positive electrode layer and the negative electrode active material used for the negative electrode layer, as long as the material functions as the positive and negative electrodes of an all-solid-state battery corresponding to various charge carrier ions.

[0078] The positive electrode is formed by a layer of positive electrode active material and a positive electrode current collector. For example, if the all-solid-state battery is a lithium-ion secondary battery, the positive electrode needs to be made of a material that can absorb, store, and release lithium ions.

[0079] As a positive current collector, aluminum can be used, for example.

[0080] Examples of positive electrode active materials include, for example, titanium sulfide (TiS2), molybdenum sulfide (MoS2), iron sulfide (FeS, FeS2), copper sulfide (CuS), and nickel sulfide (Ni3S2) in the sulfide system. Additionally, examples of oxide materials include bismuth oxide (Bi2O3), bismuth lead oxide (Bi2Pb2O5), copper oxide (CuO), and vanadium oxide (V6O). 13 Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), Li(NiCoMn)O2, Li(NiCoAl)O2, Li(NiCo)O2, etc. Alternatively, they can be used in combination.

[0081] In addition, the negative electrode is formed by containing a negative current collector and a negative active material. For example, if the all-solid-state battery is a lithium-ion secondary battery, then metallic lithium, metallic indium, or a material capable of absorbing and releasing lithium ions can be used as the negative active material.

[0082] As a negative current collector, copper can be used, for example.

[0083] Examples of anode active materials include carbon materials, specifically artificial graphite, graphite carbon fibers, resin-sintered carbon, thermally decomposed vapor-grown carbon, coke, mesophase carbon microspheres (MCMB), furfuryl alcohol resin-sintered carbon, polyacene, pitch-based carbon fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. Alternatively, mixtures of these materials may also be used. Additionally, examples include metals such as lithium, indium, aluminum, or silicon, or alloys of these metals combined with other elements or compounds.

[0084] The positive and negative electrodes of an all-solid-state battery are made from two materials that can form electrodes. By comparing the charge and discharge potentials of the two compounds, the compound with the higher potential is used as the positive electrode and the compound with the lower potential is used as the negative electrode, thus forming any battery.

[0085] [Solid electrolyte layer]

[0086] In all-solid-state batteries, the solid electrolyte layer is formed in the form of a solid electrolyte sheet in which the solid electrolyte is held by a support. There is no particular limitation on the type of solid electrolyte constituting the solid electrolyte sheet; for example, known materials that can be used as solid electrolytes in all-solid-state batteries can be used.

[0087] Furthermore, there are no particular limitations on solid electrolytes, as long as they can facilitate the conduction of charge carrier ions between the positive and negative electrodes. Examples include oxide-based solid electrolytes and sulfide-based solid electrolytes. Additionally, other components such as binders can be added as needed.

[0088] For example, sulfide-based solid electrolytes capable of conducting lithium ions include sulfide-based amorphous solid electrolytes and sulfide-based crystalline solid electrolytes. Specific examples of sulfide-based amorphous solid electrolytes include Li₂S-SiS₂, Li₂S-GeS₂, Li₂, S-P₂S₅, Li₂S-B₂S₃, Li₂S-SiS₂-Li₃PO₄, Li₂S-S, iS₂-Li₂SO₄, Li₂S-P₂S₅-LiI, Li₂S-P₂S₅-P₂O₅-, LiI, Li₂S-B₂S₃-LiI, Li₂S-P₂S₅-Li₂O-LiI, Li₂, and S-SiS₂-B₂S₃-LiI.

[0089] It should be noted that sulfide-based amorphous solid electrolytes may also contain other elements.

[0090] Furthermore, as a specific example of a sulfide-based crystalline solid electrolyte, Li can be cited. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S12 Li6PS5Cl, etc., but sulfide-based crystalline solid electrolytes are not limited to these elements.

[0091] Solid electrolytes can be any electrolyte other than sulfide-based and oxide-based solid electrolytes. Other examples include semi-solid polymer electrolytes containing charge carrier ions, such as those made of ethylene oxide, polypropylene oxide, polyvinylidene fluoride, or polyacrylonitrile. Solid electrolytes can also be so-called gel-type electrolytes, such as those made of polyethylene oxide-based polymers or polymers containing at least one selected from polyorganosiloxane chains and polyoxyalkylene chains, which maintain the electrolyte in a specific state.

[0092] [Manufacturing method of solid electrolyte sheets]

[0093] There are no particular limitations on the manufacturing method of solid electrolyte sheets; common methods in this technical field can be applied.

[0094] For example, methods can be listed for preparing a slurry by dispersing a solid electrolyte in a solvent, coating the prepared slurry onto a support, and drying it. There are no particular limitations on the solvent used in the preparation of the solid electrolyte slurry, as long as it does not adversely affect the performance of the solid electrolyte. For example, non-aqueous solvents can be listed.

[0095] There are no particular limitations on the coating method of applying a slurry containing a solid electrolyte to both sides or one side of a support. Examples include sliding die coating, comma die coating, comma reverse coating, gravure coating, and gravure reverse coating.

[0096] Drying after coating a slurry containing a solid electrolyte can be performed, for example, by using a drying device that employs hot air, a heater, a high frequency, etc.

[0097] It should be noted that the solid electrolyte sheet can be the dried sheet itself, or it can be further pressurized to increase its mechanical strength and density. Examples of pressurization methods include sheet pressing and roller pressing.

[0098] [Manufacturing methods for all-solid-state batteries]

[0099] All-solid-state batteries can be manufactured by placing a solid electrolyte layer containing solid electrolyte sheets between the positive and negative electrode layers, and then bonding them together. There are no particular limitations on the bonding method; examples include stacking the sheets and applying pressure / pressing, or applying pressure by passing them between two rollers (roller-to-roll).

[0100] It should be noted that, in order to improve the adhesion between the solid electrolyte layer and the positive or negative electrode layer, an active material with ion conductivity and an adhesive material that does not hinder ion conductivity can be configured at the bonding interface.

[0101] Example

[0102] Hereinafter, specific embodiments of the support body according to the present invention will be described.

[0103] First, the supports for Examples 1-5 and Comparative Examples 1-6 were manufactured using the methods described below. It should be noted that, except for Comparative Example 3, the supports were made of paper or wet nonwoven fabric formed using a papermaking process.

[0104] [Example 1]

[0105] Cellulose fibers with a CSF value of 10 ml and an average fiber length of 1.0 mm were used for long-wire papermaking.

[0106] The resulting paper was calendered to obtain a thickness of 5 μm and a basis weight of 4.0 g / m². 2 Density is 0.80 g / cm³ 3 The support structure.

[0107] [Example 2]

[0108] Using polyamide fibers with a CSF value of 0 ml and an average fiber length of 0.2 mm, long-wire papermaking was performed to obtain a paper with a thickness of 22 μm and a basis weight of 15.0 g / m². 2 The density is 0.69 g / cm³ 3 The support structure.

[0109] [Example 3]

[0110] Using a raw material consisting of 50% by mass of cellulose fibers with a CSF value of 390 ml and an average fiber length of 2 mm, and 50% by mass of polyamide fibers with a CSF value of 5 ml and an average fiber length of 0.5 mm, cylinder papermaking was performed to obtain a paper with a thickness of 8 μm and a basis weight of 1.4 g / m². 2 The density is 0.18 g / cm³ 3 The support structure.

[0111] [Example 4]

[0112] Using cellulose fibers with a CSF value of 100 ml and an average fiber length of 1.1 mm, short-wire papermaking was performed to obtain a paper with a thickness of 15 μm and a basis weight of 3.0 g / m². 2 Density is 0.20 g / cm³ 3 The support structure.

[0113] [Example 5]

[0114] Using a raw material consisting of 70% by mass of cellulose fibers with a CSF value of 3 ml and an average fiber length of 0.5 mm, and 30% by mass of polyamide fibers with a CSF value of 120 ml and an average fiber length of 1.5 mm, short-wire papermaking was performed to obtain a paper with a thickness of 40 μm and a basis weight of 10.0 g / m². 2 Density is 0.25 g / cm³ 3 The support structure.

[0115] [Comparative Example 1]

[0116] Using a raw material comprising 15% by mass of polyester fibers with an average fiber diameter of 16 μm and an average fiber length of 5 mm, and 85% by mass of polyester binder fibers with an average fiber diameter of 4 μm and an average fiber length of 3 mm, and referring to the support manufacturing method described in Example 1 of Patent Document 2, cylinder papermaking was performed to obtain a thickness of 19 μm and a basis weight of 3.8 g / m². 2 Density is 0.20 g / cm³ 3 The support structure.

[0117] [Comparative Example 2]

[0118] Using a raw material comprising 40% by mass of polyester fibers with an average fiber diameter of 2.3 μm and an average fiber length of 3 mm, 50% by mass of polyester binder fibers with an average fiber diameter of 4.2 μm and an average fiber length of 3 mm, and 10% by mass of ethylene-vinyl alcohol fibers with an average fiber diameter of 7.2 μm and an average fiber length of 5 mm, and referring to the support manufacturing method described in Example 1 of Patent Document 3, short-wire papermaking and hot-press calendering were performed to obtain a thickness of 12 μm and a basis weight of 7.0 g / m². 2 The density is 0.58 g / cm³ 3 The support structure.

[0119] [Comparative Example 3]

[0120] A support body was manufactured using the same method as described in Example 2 of Patent Document 1, resulting in the support body of Comparative Example 3. In Comparative Example 3, a polyimide film was etched to form 200 μm square holes, resulting in a thickness of 30 μm and a basis weight of 8.8 g / m². 2 Its density is 0.29 g / cm³. 3 The support structure.

[0121] [Comparative Example 4]

[0122] Using polyamide fibers with a CSF value of 0 ml and an average fiber length of 0.1 mm, long-wire papermaking was performed to obtain a paper thickness of 18 μm and a basis weight of 16.0 g / m². 2The density is 0.89 g / cm³ 3 The support structure.

[0123] [Comparative Example 5]

[0124] Using a raw material composed of 70% by mass of cellulose fibers with a CSF value of 410 ml and an average fiber length of 2.5 mm and 30% by mass of polyamide fibers with a CSF value of 100 ml and an average fiber length of 0.7 mm, short-wire papermaking was performed to obtain a paper with a thickness of 15 μm and a basis weight of 2.3 g / m². 2 The density is 0.15 g / cm³ 3 The support structure.

[0125] [Comparative Example 6]

[0126] Using cellulose fibers with a CSF value of 0 ml and an average fiber length of 0.04 mm, short-wire papermaking was performed, but a paper layer could not be formed and a support could not be obtained.

[0127] [Fabrication of all-solid-state batteries]

[0128] Next, an all-solid-state battery was fabricated using the support structures from the above embodiments and comparative examples. The specific fabrication method is described below.

[0129] (Positive electrode structure)

[0130] LiNiCoAlO2 ternary powder was used as the positive electrode active material, Li2S-P2S5 amorphous powder was used as the sulfide-based solid electrolyte, and carbon fiber was used as a conductive additive, and these were mixed together. A dehydrated xylene solution containing SBR (styrene-butadiene rubber) as a binder was mixed into this mixed powder to prepare the positive electrode coating solution. The positive electrode coating solution was coated onto an aluminum foil current collector, which served as the positive electrode current collector, and then dried and further calendered to obtain the positive electrode structure.

[0131] (Negative electrode structure)

[0132] Graphite was used as the negative electrode active material, Li2S-P2S5 amorphous powder as the sulfide-based solid electrolyte, PVdF (polyvinylidene fluoride) as the binder, and NMP (N-methyl-2-pyrrolidone) as the solvent, and these were mixed to prepare the negative electrode coating solution. The negative electrode coating solution was then coated onto a copper foil current collector, which served as the negative electrode current collector, and dried. Further rolling was then performed to obtain the negative electrode structure.

[0133] (Solid electrolyte tablets)

[0134] Li2S-P2S5 amorphous powder was used as the sulfide-based solid electrolyte, SBR was used as the binder, and xylene was used as the solvent. The mixture was then used to prepare a solid electrolyte slurry.

[0135] Solid electrolyte slurry was coated onto the support of each of the above embodiments and comparative examples, and then dried to obtain solid electrolyte sheets.

[0136] [Manufacturing of all-solid-state batteries]

[0137] A negative electrode structure with dimensions of 88mm×58mm, a solid electrolyte sheet with dimensions of 92mm×62mm, and a positive electrode structure with dimensions of 87mm×57mm are stacked, dry-laminated, and bonded together to obtain a single cell of an all-solid-state battery.

[0138] The obtained single cells are placed in an aluminum laminate film with terminals installed, degassed, heat-sealed, and packaged.

[0139] [Methods for determining the characteristics of support structures and all-solid-state batteries]

[0140] The properties of the fabricated support and the all-solid-state battery were determined under the following conditions and methods.

[0141] [CSF value]

[0142] The CSF value was determined according to "JIS P8121-2 Pulp - Determination of drainability - Part 2: Canadian Standard freeness method" (ISO 5267-2 Pulps - Determination of drainability - Part 2: "Canadian Standard" freeness method).

[0143] Average fiber length

[0144] [Fiber length]

[0145] The apparatus described in "JIS P 8226-2 Pulps - Determination of Fibre 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) was used here, with the FiberTester PLUS (manufactured by Lorentzen & Wettre) used for the determination, and the average fiber length under length load was taken as the fiber length.

[0146] [Fiber length of polyester fiber and polyester binder fiber]

[0147] Polyester fibers and polyester binder fibers are optically transparent, making it impossible to accurately identify them through images, and therefore impossible to accurately determine fiber length using the aforementioned automated optical analysis method. Therefore, for polyester fibers and polyester binder fibers, the fiber length is determined using the following method.

[0148] Prepare microscope specimens with randomly dispersed fibers. Measure the fiber length of the fibers on the microscope specimens directly using a scale.

[0149] [thickness]

[0150] The thickness of the support was measured by changing the measuring force of the micrometer described in "5.1.1 Measuring instrument and measuring method a. When using an external micrometer" of "JIS C 2300-2 Electrical Cellulose Paper - Part 2: Test Methods" to 1.5 N and changing the diameter of the pressure surface to 14.3 mmφ, and by folding the paper into 10 sheets as described in "5.1.3 When measuring the thickness by folding the paper".

[0151] [Basis Weight]

[0152] The basis weight of the support in an absolutely dry state was determined by the method specified in "JIS C 2300-2 Electrical Cellulose Paper - Part 2: Test Methods 6 Basis Weight".

[0153] [density]

[0154] The density of the support is calculated using the following formula.

[0155] Density (g / cm³) 3 =W / T

[0156] W: Basis weight (g / m³) 2 T: Thickness (μm)

[0157] Porosity

[0158] The porosity of the support is calculated using the following formula. It should be noted that when multiple materials constituting the support are mixed, a calculation proportional to the mixing ratio is performed to determine the average specific gravity of the constituent fibers, and then the porosity is calculated.

[0159] Porosity (%) = (1 - (D / S)) × 100

[0160] D: Support density (g / cm³) 3 S: Specific gravity of the fiber (g / cm³) 3 )

[0161] [Transmittance of perfluoropolyether relative to the thickness direction]

[0162] A 50mm x 50mm test piece was fixed to the bottom of a cylinder with an inner diameter of 12mm and an outer diameter of 15mm. The cylinder with the test piece was placed in contact with the glass plate. 0.1ml of perfluoropolyether was added dropwise to the inside of the cylinder, and the mass of the added perfluoropolyether was measured. After adding the perfluoropolyether, the cylinder was left for 1 minute, and then the cylinder with the test piece was removed. The mass of perfluoropolyether that permeated from the inside of the cylinder, passed through the support, and adhered to the glass plate was measured. The transmittance of the perfluoropolyether relative to the thickness of the support was calculated using the following formula.

[0163] Transmittance (%) = w2 / w1 × 100

[0164] w1: Mass of perfluoropolyether added (g)

[0165] w2: Mass of perfluoropolyether permeated (g)

[0166] Tensile strength

[0167] The maximum tensile load in the longitudinal direction (manufacturing direction) of the support is determined using the method specified in "JIS P 8113 Paper and board - Determination of 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), with a test width of 15 mm, and is taken as the tensile strength of the support.

[0168] [Evaluation of independence]

[0169] The self-sufficiency of each solid electrolyte sheet produced was evaluated.

[0170] When the solid electrolyte sheet with dimensions of 92mm × 62mm is lifted while holding the short side end, cases where no cracks or breaks are observed visually are recorded as 0, and cases where cracks or breaks are observed visually during lifting are recorded as ×.

[0171] [Internal resistance of solid electrolyte sheet]

[0172] For all-solid-state batteries, the impedance was measured in the range of 0.1Hz to 1MHz using an LCR meter after charging to 4.0V at 25℃ with a current density of 0.1C. The resulting Coulomb-Coulomb plot was fitted to a semicircle with the x-axis as its base, and the value of the portion where the right end of the semicircle intersects the x-axis was taken as the resistance value.

[0173] [Discharge capacity of solid electrolyte sheet]

[0174] For all-solid-state batteries, they are charged to 4.0V at a current density of 0.1C at 25℃, and then discharged to 2.5V at a current density of 0.1C. The discharge capacity at this point is then measured.

[0175] The names and blending ratios of the fibers used in each support of Examples 1 to 5 and Comparative Examples 1 to 6 described above are shown in Table 1.

[0176] [Table 1]

[0177]

[0178] Table 2 shows the evaluation results of the characteristics of each support, the self-support of the solid electrolyte sheet, and the battery characteristics of each embodiment and comparative example described above.

[0179] [Table 2]

[0180]

[0181] The following details the evaluation results of all-solid-state batteries using the supports of each embodiment and comparative example.

[0182] Solid electrolyte sheets using the supports of the various embodiments can form self-supporting solid electrolyte sheets.

[0183] Furthermore, the all-solid-state batteries using the supports of each embodiment have lower resistance and higher discharge capacity compared to the all-solid-state batteries using the supports of Comparative Examples 1 to 5.

[0184] Comparative Example 6 could not produce a support. It is believed that because the fiber length of the fiber used in the support of Comparative Example 6 was as short as 0.04 mm, it did not have the strength to withstand the manufacturing process.

[0185] That is, based on the comparison between each embodiment and Comparative Example 6, the fiber length of the fiber used in the support is preferably 0.1 mm or more.

[0186] The all-solid-state batteries using the supports of Comparative Examples 1 and 5 have higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of the embodiments. Furthermore, the supports of Comparative Examples 1 and 5 have higher perfluoropolyether transmittance in the thickness direction compared to the supports of the embodiments.

[0187] The supports in Comparative Examples 1 and 5 have high perfluoropolyether transmittance of 46.0% and 15.6% respectively in the thickness direction, resulting in a smaller amount of solid electrolyte slurry that can be held by the supports. Consequently, it is believed that there are fewer pathways for charge carrier ions to form in the thickness direction within the solid electrolyte sheet.

[0188] In the support of Comparative Example 5, compared with the embodiments, fibers with a CSF value as high as 410 ml and a fiber length of up to 2.5 mm were used. As a result, it was believed that the internal space of the obtained support was large, the perfluoropolyether transmittance in the thickness direction was higher, and the amount of perfluoropolyether that the support could retain was less.

[0189] That is, as can be seen from the comparison of each embodiment with Comparative Example 1 and Comparative Example 5, the transmittance of the perfluoropolyether in the thickness direction of the support is preferably 15% or less. In addition, as can be seen from the comparison of each embodiment with Comparative Example 5, the CSF value of the fibers used in the support is preferably 400 ml or less, and the fiber length is preferably 2 mm or less.

[0190] The all-solid-state batteries using the supports of Comparative Examples 2 and 4 exhibited higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of each embodiment. The support of Comparative Example 2 contained 10% by mass of ethylene-vinyl alcohol fibers that underwent shape changes due to moisture and heat. Therefore, in the state where the support was formed, a thin film layer was formed inside the support instead of a fiber state, filling the fiber gaps. This is considered to hinder the penetration of the solid electrolyte slurry into the support. Furthermore, the basis weight of the support of Comparative Example 4 was as high as 16.0 g / m³. 2 Therefore, it is believed that the large number of fibers inside the support body hinders the permeation and penetration of the perfluoropolyether in the thickness direction of the support body when a specified amount of perfluoropolyether is added.

[0191] Compared to the supports of the embodiments, the perfluoropolyether in Comparative Examples 2 and 4 had a transmittance of only 0.4% in the thickness direction, resulting in insufficient transmission of the solid electrolyte slurry in the thickness direction of the support. Consequently, it was believed that there were fewer pathways for charge carrier ions to form within the solid electrolyte sheet in the thickness direction.

[0192] That is, as can be seen from the comparison between the various embodiments and Comparative Example 2, the amount of synthetic resin adhesive fibers that cannot maintain their fibrous state is preferably less than 10% by mass. Furthermore, as can be seen from the comparison between the various embodiments and Comparative Example 4, the basis weight is more preferably 15.0 g / m³. 2 Furthermore, as can be seen from the comparison between the various embodiments and Comparative Examples 2 and 4, the transmittance of the perfluoropolyether in the thickness direction relative to the support is preferably 1% or more.

[0193] The all-solid-state battery using the support of Example 3 has higher resistance and lower discharge capacity compared to the all-solid-state battery using the support of Example 4. Furthermore, the support of Example 3 has higher perfluoropolyether transmittance in the thickness direction compared to the support of Example 4. Regarding the perfluoropolyether transmittance in the thickness direction, the support of Example 3 has 14.8%, which is higher than the 12.6% of the support of Example 4.

[0194] Furthermore, the all-solid-state battery using the support of Example 2 has higher resistance and lower discharge capacity compared to the all-solid-state battery using the support of Example 5. Additionally, the perfluoropolyether in Example 2 has lower transmittance in the thickness direction compared to the support of Example 5. Regarding the transmittance of perfluoropolyether in the thickness direction, the support of Example 2 has 1.2%, which is lower than the 2.3% of the support of Example 5.

[0195] That is, as can be seen from the comparison of Examples 2 and 3 with Examples 4 and 5, the transmittance of perfluoropolyether relative to the thickness direction of the support is more preferably 2 to 13%.

[0196] The support in Comparative Example 3 differs from the supports of the other embodiments, which are made of paper or nonwoven fabric. It is a support formed by creating through-holes in a thin film. Solid electrolyte can be filled into the through-holes of the support in Comparative Example 3, but only within the formed through-holes. Furthermore, it is believed that the solid electrolyte sheet containing the support of Comparative Example 3 has an interface between the solid electrolyte sheet and the positive or negative electrode, which is an insulating material. As a result, it is believed that the all-solid-state battery using the support of Comparative Example 3 has higher resistance and lower discharge capacity compared to the all-solid-state batteries using the supports of the other embodiments.

[0197] As can be seen from the comparison between the various embodiments and Comparative Example 3, paper and nonwoven fabric are suitable as supports in order to reduce the resistance of all-solid-state batteries.

[0198] The above-described embodiments are merely examples. For instance, those skilled in the art can appropriately modify the composition of charge carrier ions, solid electrolyte, positive electrode, and negative electrode.

[0199] As explained above, by fabricating paper and nonwoven fabrics with a permeability of 1-15% in the thickness direction using perfluoropolyether, a support with excellent permeability to the solid electrolyte slurry can be obtained. As a result, a necessary amount of carrier ion pathways relative to the thickness direction of the support can be formed. Using this support, an all-solid-state battery with low resistance can be obtained.

[0200] It should be noted that the present invention is not limited to the configuration described in the above embodiments. In addition, various modifications and alterations can be made without departing from the scope of the present invention.

Claims

1. A support for a secondary battery, which is used to hold the solid electrolyte of the secondary battery. The secondary battery support is substantially free of non-fibrillated fibers and is formed of at least one material selected from paper and nonwoven fabrics. The transmittance of perfluoropolyether relative to the thickness direction is 1~15%.

2. The support for a secondary battery according to claim 1, wherein, The paper and the nonwoven fabric comprise fibrillated fibers.

3. The support for a secondary battery according to claim 2, wherein, The CSF value of the fibrillated fiber is 0~400ml.

4. The support for a secondary battery according to claim 2, wherein, The fibrillated fiber has a fiber length of 0.1~2mm.

5. A solid electrolyte sheet, wherein, A solid electrolyte is retained in a thin-film support, which is substantially free of nonfibrillated fibers and is formed of at least one material selected from paper and nonwoven fabrics. The transmittance of the support in the thickness direction for perfluoropolyether is 1 to 15%.

6. A secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte sheet disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte sheet comprises: The support, substantially free of nonfibrillated fibers, is formed of at least one selected from paper and nonwoven fabrics, and has a thickness-direction permeability to perfluoropolyether of 1-15%; and A solid electrolyte, which is held in the support.

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