Electrode member for ion sensor, ion sensor, and method for analyzing ions in medium

Abstract

Provided is an electrode member for an ion sensor, the electrode member comprising: an electrode layer; and a solid electrolyte layer that is located on the electrode layer and that has a first main surface and a second main surface opposite to the first main surface. The solid electrolyte layer contains a solid electrolyte and a valence fluctuation substance disposed in the solid electrolyte.

Description

Electrode member for ion sensor, ion sensor, and method for analyzing ions in a medium

[0001] The present invention relates to an electrode member for an ion sensor, an ion sensor, and a method for analyzing ions in a medium.

[0002] Conventionally, ion sensors have been used to measure ion concentrations using a reference electrode, which maintains a constant potential even when the composition of the sample solution being measured changes. The reference electrode measures the minute potential changes at the working electrode due to ion concentration as the potential difference with the reference electrode.

[0003] Classically, a reference electrode containing an internal liquid is used, and the internal liquid and the internal electrode are housed in a glass support tube. In the case of an electrode containing an internal liquid, a through-hole is provided at the tip of the support tube, which is filled with an inorganic porous material or a porous organic material, or a glass sleeve is used to form a liquid junction through which the internal liquid flows out, and the sample liquid and the internal liquid come into contact, maintaining an electrical connection.

[0004] Electrodes containing such internal liquids require a container with a certain volume or more to use the liquid, and reducing the amount of liquid causes performance degradation due to evaporation of the solvent. Furthermore, electrodes containing internal liquids have the problem of being costly due to the complicated manufacturing process and the difficulty of automating the manufacturing process.

[0005] In light of these problems, several electrodes that do not contain an internal liquid have been proposed. For example, Patent Document 1 (JP 2019-530879 A) describes an ion sensor having a reference electrode and a working electrode, where the working electrode has a layer structure including a single-phase conductive layer, a solid electrolyte layer, and an ion-sensitive membrane, in that order. Furthermore, Patent Document 2 (CN101852761A) describes a sodium ion sensor having a contact electrode (reference electrode) and a reaction electrode, where the sensor has a layer structure including a solid electrolyte layer on the reaction electrode and a sodium ion-sensitive membrane on the solid electrolyte layer. In Patent Documents 1 and 2, ions are adsorbed and desorbed on the surface of the ion-sensitive membrane opposite the solid electrolyte layer, and the ion concentration can be measured by measuring the voltage at this time.

[0006] Special table 2019-530879 publication CN101852761A

[0007] However, in either case, there is a limit to maintaining the potential of the reference electrode constant when measuring the minute potential difference between the reference electrode and the ion concentration, and the accuracy of measuring the ion concentration from a long-term perspective is not good.

[0008] An object of the present invention is to provide an ion sensor that can be miniaturized and that can measure ion concentrations with high accuracy.

[0009] In order to solve the above-described problems, an electrode member for an ion sensor according to one aspect of the present disclosure includes: an electrode layer; and a solid electrolyte layer located on the electrode layer, the solid electrolyte layer having a first main surface and a second main surface opposite to the first main surface, wherein the solid electrolyte layer includes a solid electrolyte and a valence variable substance disposed within the solid electrolyte.

[0010] In the present disclosure, a solid electrolyte layer is brought into contact with a measurement medium, and ions to be measured (hereinafter also referred to as "measurement ions") contained in the measurement medium are captured in the solid electrolyte layer. These measurement ions can diffuse within the solid electrolyte layer, thereby allowing the measurement ions to be inserted into and removed from the valence variable substance. This causes the valence of the valence variable substance to change. The change in the valence of the valence variable substance causes a change in the value of the current flowing from the electrode layer. An ion sensor using the ion sensor electrode member of the present disclosure can measure this change in current value to determine the ion concentration. Since the present invention can directly measure the change in current value, it is possible to improve measurement accuracy. Furthermore, by selecting an appropriate valence variable substance, the type of measurement ion is not limited, and a wide variety of measurement ions can be measured.

[0011] An ion sensor according to one aspect of the present disclosure includes a first electrode and a second electrode, and at least one of the first electrode and the second electrode is the ion sensor electrode member of the present disclosure.

[0012] With the above configuration, an ion sensor with high measurement accuracy can be obtained.

[0013] A method for analyzing ions in a medium according to one aspect of the present disclosure uses the ion sensor of the present disclosure, in which the first electrode and the second electrode are arranged to face in the same direction relative to the measurement medium.

[0014] With the above configuration, it is possible to measure the ion concentration even with a small amount of measurement medium.

[0015] A method for analyzing ions in a medium according to one aspect of the present disclosure uses the ion sensor of the present disclosure, in which the first electrode and the second electrode are arranged opposite each other with a measurement medium interposed therebetween.

[0016] With the above configuration, there is no need to configure a flow path between the electrodes, and therefore measurement can be performed with a simple structure.

[0017] According to the present disclosure, it is possible to provide an ion sensor that can be miniaturized and that can measure ion concentrations with high accuracy.

[0018] FIG. 1 is a schematic diagram illustrating a method of using the ion sensor of the first embodiment. FIG. 2 is a schematic diagram of an XZ cross section showing a first electrode included in the ion sensor of the first embodiment. FIG. 3 is a schematic diagram of an XZ cross section showing an example of a first electrode of the first embodiment. FIG. 4 is a schematic diagram illustrating a modified example of a method of using the ion sensor of the first embodiment. FIG. 5 is a schematic diagram illustrating a method of using the ion sensor of the second embodiment. FIG. 6 is a schematic diagram illustrating a modified example of a method of using the ion sensor of the second embodiment. FIG. 7 is a schematic diagram of an XZ cross section explaining a first electrode of the prior art.

[0019] Hereinafter, an ion sensor according to one aspect of the present disclosure will be described in detail with reference to the illustrated embodiments. Note that the drawings include some schematic views and may not reflect actual dimensions or proportions.

[0020] <First embodiment> Fig. 1 is a schematic diagram showing a method of using an ion sensor 10 in a first embodiment. Fig. 2 is a schematic cross-sectional view showing a first electrode included in the ion sensor 10. Fig. 3 is a schematic cross-sectional view showing an example of the first electrode.

[0021] As shown in FIG. 1 , an ion sensor 10 is used to measure the content of ions to be measured in a measurement medium 9. As shown in FIGS. 1 and 2 , the ion sensor 10 includes a first electrode 1 and a second electrode 1A, and a power supply and an ammeter electrically connected to the first electrode 1 and the second electrode 1A. The positional relationship between the power supply and the ammeter is not limited to the illustrated embodiment and may be reversed. The positive and negative poles of the power supply may be reversed. The power supply is a source of electrical power, and examples of such power sources include a battery and a generator. While the first electrode 1 and the second electrode 1A are rectangular as shown in FIG. 1 , they may have other shapes, such as a cylindrical shape.

[0022] The first electrode 1 is a first ion sensor electrode member. The first ion sensor electrode member includes a first electrode layer 2 having a first main surface 2a and a second main surface 2b facing each other, and a solid electrolyte layer 3 located on the first electrode layer 2 and having a first main surface 3a and a second main surface 3b facing the first main surface 3a. The first electrode layer 2 and the solid electrolyte layer 3 are arranged so that the first main surface 2a and the first main surface 3a face each other and contact each other. As shown in FIG. 3 as an example, the solid electrolyte layer 3 includes a solid electrolyte 5 and a valence variable substance 4 disposed within the solid electrolyte 5. Here, "disposed" means that the valence variable substance 4 is contained within the solid electrolyte 5. For example, the valence variable substance 4 is dispersed within the solid electrolyte 5.

[0023] As shown in FIG. 1 , the second electrode 1A is a second ion sensor electrode member. The second ion sensor electrode member includes a second electrode layer 2A having a first principal surface 2aA and a second principal surface 2bA facing each other, and a solid electrolyte layer 3A located on the second electrode layer 2A and having a first principal surface 3aA and a second principal surface 3bA facing the first principal surface 3aA. The second electrode layer 2A and the solid electrolyte layer 3A are disposed such that the first principal surface 2aA and the first principal surface 3aA face each other and contact each other. The second ion sensor electrode member may have the same configuration as the first ion sensor electrode member, or may have a different configuration. In one aspect, the second ion sensor electrode member has the same configuration as the first ion sensor electrode member. In another aspect, the second ion sensor electrode member has a different configuration from the first ion sensor electrode member. For example, the valence variable substance of the second ion sensor electrode member may be the same as or different from the valence variable substance 4 of the first ion sensor electrode member. The second electrode layer 2A may have the same configuration as the first electrode layer 2 or a different configuration.

[0024] 2 and 3 , for the sake of convenience, the direction from the first electrode layer 2 toward the solid electrolyte layer 3 in the first electrode 1 is referred to as the Z direction. Among the directions orthogonal to the Z direction, a direction parallel to the first main surface 2 a of the first electrode layer 2 is referred to as the X direction, and a direction orthogonal to the Z direction and the X direction, which forms a right-handed system when arranged in the order X, Y, Z, is referred to as the Y direction.

[0025] The first electrode 1 and the second electrode 1A may each have a size in the X direction of 0.25 mm or more and 100 mm or less, a size in the Y direction of 0.05 mm or more and 100 mm or less, and a thickness in the Z direction of 0.05 mm or more and 10 mm or less.

[0026] The first electrode layer 2 has a first main surface 2a and a second main surface 2b that face each other. The first main surface 2a contacts the first main surface 3a of the solid electrolyte layer 3. The second main surface 2b is electrically connected to a power source.

[0027] The first electrode layer 2 preferably contains a metal. The metal may be a conductive material such as gold, silver, nickel, copper, tin, lead, aluminum, or a carbon material, or an alloy thereof, such as copper. The first electrode layer 2 may be a single layer or may have multiple layers.

[0028] The thickness of the first electrode layer 2 is, for example, 1 nm to 1 cm, and preferably 100 nm to 100 μm. The length of one side (e.g., the side in the X direction) of the second main surface 2 b of the first electrode layer 2 is, for example, 0.25 mm to 100 mm, and the length of the other side (e.g., the side in the Y direction) is, for example, 0.05 mm to 100 mm.

[0029] The second electrode layer 2A has a first principal surface 2aA and a second principal surface 2bA that face each other. The first principal surface 2aA is in contact with the first principal surface 3aA of the solid electrolyte layer 3A. The second principal surface 2bA is electrically connected to a power source.

[0030] The second electrode layer 2A preferably contains a metal. The metal may be a conductive material such as gold, silver, nickel, copper, tin, lead, aluminum, or a carbon material, or an alloy thereof, such as copper. In one embodiment, the first electrode layer 2 is gold, and the second electrode layer 2A is copper.

[0031] The second main surface 2bA of the second electrode layer 2A may be the same size as or different from the second main surface 2b of the first electrode layer 2. The thickness of the second electrode layer 2A may be the same as or different from the thickness of the first electrode layer 2. For example, the second electrode layer 2A has the same size and thickness as the first electrode layer 2.

[0032] The solid electrolyte layers 3 and 3A are layers each including a solid electrolyte 5 and a valence variable substance 4 disposed in the solid electrolyte 5.

[0033] The solid electrolyte layer 3 has a first main surface 3 a and a second main surface 3 b facing each other. The first main surface 3 a of the solid electrolyte layer 3 contacts the first main surface 2 a of the first electrode layer 2. That is, the solid electrolyte layer 3 and the first electrode layer 2 are in direct contact with each other.

[0034] The solid electrolyte layer 3A has a first main surface 3aA and a second main surface 3bA that face each other. The first main surface 3aA of the solid electrolyte layer 3 contacts the first main surface 2aA of the first electrode layer 2. That is, the solid electrolyte layer 3A and the second electrode layer 2A are in direct contact with each other. In the following description, the solid electrolyte layer 3A may have the same configuration as the solid electrolyte layer 3, unless otherwise specified.

[0035] The thickness of the solid electrolyte layer 3 (thickness in the Z direction) may be in the range of 10 to 50% of the thickness of the first electrode 1. The thickness of the solid electrolyte layer 3 may be in the range of 10 to 50% of the thickness of the first electrode layer 2.

[0036] The solid electrolyte layer 3 is formed by coating a slurry, drying, pressing, laminating, sintering, or the like. The solid electrolyte layer 3 has a layer thickness of about 1 nm to about 1 cm, particularly about 1 nm to about 1,000 nm. One side of the second main surface 3b of the solid electrolyte layer 3 is, for example, in the range of 0.25 mm to 100 mm, and the other side is, for example, in the range of 0.05 mm to 100 mm.

[0037] Preferably, the content of the valence variable substance 4 on the second main surface 3b of the solid electrolyte layer 3 is 10 mass% or less. Here, the content of the valence variable substance 4 on the second main surface 3b of the solid electrolyte layer 3 is a value measured in a portion of the solid electrolyte layer 3 from the upper surface (i.e., the second main surface 3b) to 10% of the thickness of the solid electrolyte layer 3 (i.e., the region between the second main surface 3b and the first position) in a cross section perpendicular to the first main surface 3a and the second main surface 3b of the solid electrolyte layer 3. This configuration can suppress side reactions between the measurement ions and the valence variable substance 4 on the second main surface 3b of the solid electrolyte layer 3. The amount of the valence variable substance 4 contained on the second main surface 3b of the solid electrolyte layer 3 may be zero. In this case, no valence variable substance 4 is contained on the second main surface 3b of the solid electrolyte layer 3. The valence variable substance 4 contained on the second main surface 3b of the solid electrolyte layer 3 can be measured using, for example, SEM-EDX.

[0038] Preferably, in a cross section orthogonal to the first and second main surfaces 3a and 3b of the solid electrolyte layer 3, the content of the valence variable substance 4 in the second region 32, which is a region between the second main surface 3b and the first position 30, is 10% of the thickness from the second main surface 3b toward the first main surface 3a, relative to 100% of the thickness between the first and second main surfaces 3a and 3b. The second region 32 has a smaller content of the valence variable substance 4 than the content of the valence variable substance 4 in the first region 31, which is a region between the first position 30 and the first main surface 3a. When the content of the valence variable substance 4 in the second region 32 is smaller, ions contained in the measurement medium are more likely to be inserted into and removed from the valence variable substance 4 in the first region 31. This increases the current flowing through the first electrode layer 2, further improving the accuracy of ion measurement.

[0039] Preferably, as schematically shown in FIG. 3 , the solid electrolyte layer 3 includes a first solid electrolyte layer 301 and a second solid electrolyte layer 302. The first solid electrolyte layer 301 is located on the first electrode layer 2. The second solid electrolyte layer 302 is located on the first solid electrolyte layer 301. The second solid electrolyte layer 302 does not include a valence variable substance 4. This allows the measured ions to easily enter the first solid electrolyte layer 301, increasing the amount of current flowing through the first electrode layer 2 and further improving the accuracy of ion measurement. Note that while the valence variable substance 4 is shown in FIG. 3 for clarity, the valence variable substance 4 is also present in other drawings. The position of the interface between the first solid electrolyte layer 301 and the second solid electrolyte layer 302 can be obtained by observing an image of a cross section perpendicular to the first main surface 3 a and the second main surface 3 b of the solid electrolyte layer 3 obtained by SEM. Here, "not including the valence variable substance 4" may mean that the valence variable substance 4 is completely absent or may be present in an amount of 10 mass % or less. For example, the second solid electrolyte layer 302 may not contain the valence variable substance 4 at all.

[0040] The first solid electrolyte layer 301 may contain, in addition to the solid electrolyte 5 and the valence variable substance 4, residues of an auxiliary agent (sintering auxiliary agent), alcohol, a binder, and the like used in forming the first solid electrolyte layer 301. Examples of the auxiliary agent include Li ４ B ２ O ５Examples of the alcohol include toluene, acetone, ethanol, and polymers of toluene, acetone, and ethanol. Examples of the binder include butyral resin.

[0041] The first solid electrolyte layer 301 may further include a conductive material and its residue. Examples of the conductive material include Ag particles. For example, the first solid electrolyte layer 301 may have the above-described configuration when it is included in the solid electrolyte layer 3A.

[0042] The second solid electrolyte layer 302 may contain, in addition to the solid electrolyte 5, residues of an auxiliary agent (sintering auxiliary agent), alcohol, binder, and the like used in forming the second solid electrolyte layer 302. The auxiliary agent, alcohol, and binder may be the same as those described above.

[0043] Preferably, in a cross section perpendicular to the first main surface 3a and the second main surface 3b of the solid electrolyte layer 3, the thickness of the second solid electrolyte layer 302 is 50% or more, and preferably 70% or more, of the solid electrolyte layer 3. In the first cross section perpendicular to the first main surface 3a and the second main surface 3b, the lower limit of the thickness of the second solid electrolyte layer 302 is not particularly limited, but is, for example, 50% of the thickness of the solid electrolyte layer 3. The above configuration improves measurement accuracy.

[0044] The porosity of the solid electrolyte layer 3 may be 3% or less. For example, the porosity of the first solid electrolyte layer 301 may be 3% or less, and the porosity of the second solid electrolyte layer 302 may be 3% or less. The lower limit of the porosity is not particularly limited, but is, for example, 0% or more. The porosity value can be obtained by using an SEM to measure a cross section (i.e., an XZ cross section) of the second solid electrolyte layer 302 in a direction perpendicular to a surface that can be connected to the first solid electrolyte layer 301.

[0045] Measurement ions can diffuse within the solid electrolyte 5. The measurement ions diffuse within the solid electrolyte 5 and can be inserted into or desorbed from the valence variable substance 4 contained in the solid electrolyte 5. The solid electrolyte 5 is stable with respect to the measurement medium 9, and even if the solid electrolyte 5 and the measurement medium 9 come into direct contact with each other, the solid electrolyte 5 is not easily decomposed.

[0046] The solid electrolyte 5 preferably contains an oxide. The oxide is a metal oxide. The oxide may be a composite oxide. The metal in the metal oxide preferably contains lithium. The metal may contain lanthanum, zirconium, tantalum, silicon, phosphorus, titanium, aluminum and / or iron in addition to lithium. Specifically, the solid electrolyte 5 contains Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ etc.

[0047] The solid electrolyte 5 may be, for example, a lithium ion conductive solid compound. Examples of the solid compound include oxide solid electrolytes such as garnet, Nasicon, LISICON, perovskite, and β-alumina, and sulfide solid electrolytes such as LGPS, argyrodite, and thioLISICON. The solid compound may also be a polymer electrolyte.

[0048] Examples of lithium ion conductive solid compounds having a garnet structure include those having the composition formula (Li[7-ax-(b-4)y]A ｘ ) La ３ Zr （２－ｙ） B ｙ O １２ (wherein A is at least one element selected from the group consisting of Ga, Al, Mg, Zn and Sc, B is at least one element selected from the group consisting of Nb, Ta, W, Te, Mo and Bi, 0≦x≦0.5, 0≦y≦2.0, a is the average valence of A, and b is the average valence of B). Examples of preferred lithium ion conductive solid compounds having a garnet structure include those represented by the formula (Li ６．４ Ga ０．０５ Al ０．１５ ) La ３ Zr ２ O １２ , (Li ６．４ Al ０．２ ) La ３ Zr ２ O １２ , (Li ６．４ Ga ０．１５ Sc ０．０５) La ３ Zr ２ O １２ , Li ６．７５ La ３ (Zr １．７５ Nb ０．２５ ) O １１ , (Li ６．４５ Al ０．１ ) La ３ (Zr １．７５ Nb ０．２５ ) O １２ , (Li ６．１７５ Al ０．１ ) La ３ (Zr １．４７５ Ta ０．１０５ Bi ０．４２ ) O １２ , Li ６．６ La ３ (Zr １．６ Ta ０．４ ) O １２ etc.

[0049] The lithium ion conducting solid compound having a Nasicon structure is, for example, represented by the formula Li ｘ M ｙ (P.O. ４ ) ３ (wherein x is a number within the range of 1≦x≦2, y is a number within the range of 1≦y≦2, and M contains one or more elements selected from the group consisting of Ti, Ge, Al, Ga, and Zr), and specifically, Li １．５ Al ０．５ Ti １．５ (P.O. ４ ) ３ In this case, part of P in the above formula may be substituted with B, Si, etc. １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ and Li １．２ Al ０．２ Ti １．８ (P.O. ４ ) ３It is also possible to use a mixture of two or more compounds having different compositions of the lithium ion conductive solid compound having a Nasicon structure, such as: In addition, as the lithium ion conductive solid compound having a Nasicon structure used in the solid electrolyte 5, it is also possible to use a material containing a crystalline phase of the lithium ion conductive solid compound having a Nasicon structure, or a glass that precipitates a crystalline phase of the lithium ion conductive solid compound having a Nasicon structure by heat treatment.

[0050] Examples of lithium ion conductive compounds having a LISICON structure include those having the composition formula (Li[3-ax+(5-b)]A ｘ ) MO ４ (wherein A is at least one element selected from the group consisting of Mg, Al, Ga, and Zn, M is at least one element selected from the group consisting of Zn, Al, Ga, Si, Ge, Ti, P, and V, 0≦x≦1.0, a is the average valence of A, and b is the average valence of M). Examples of the LISICON-type lithium ion conductive compound that can be preferably used include those represented by the formula: ３．２ (V ０．８ Si ０．２ ) O ４ , Li ３．４ (V ０．６ Si ０．４ ) O ４ , Li ３．４ (V ０．８ Ge ０．４ ) O ４ , Li ３．５ (Ge ０．５ P ０．５ ) O ４ , Li ３．５ (P ０．５ Si ０．５ ) O ４ , (Li ３．３ Al ０．０３ ) (V ０．６ Si ０．４ ) O ４ etc.

[0051] Examples of sulfide solid electrolytes include LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P２ O ５ 、 LiI - Li ３ PO ４ -P ２ S ５ 、 Li ２ S - P ２ S ５ 、 LiI - Li ３ PS ４ 、 LiI - LiBr - Li ３ PS ４ 、 Li ３ PS ４ 、 Li ２ S - P ２ S ５ 、 Li ２ S - P ２ S ５ -LiI、 Li ２ S - P ２ S ５ -Li ２ O、 Li ２ S - P ２ S ５ -Li ２ O - LiI、 Li ２ S - SiS ２ 、 Li ２ S - SiS ２ -LiI、 Li ２ S - SiS ２ -LiBr、 Li ２ S - SiS ２ -LiCl、 Li ２ S - SiS ２ -B ２ S ３ -LiI、 Li ２ S - SiS ２ -P ２ S ５ -LiI、 Li ２ S - B ２ S ３ 、 Li ２ S - P ２ S ５ -Z ｍ S ｎ (However, m and n are positive numbers, and Z is any one of Ge, Zn, and Ga)、 Li ２ S - GeS ２ 、 Li ２ S - SiS ２ -Li ３ PO４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In), Li ７ P ３ S １１ , Li ２ P ２ S ６ , Li ４ , P ２ S ６ , Li ７ P ３ S １１ , α-Li ３ P.S. ４ , β-Li ３ P.S. ４ , γ-Li ３ P.S. ４ , LT-Li ７ P.S. ６ , HT-Li ７ P.S. ６ The sulfide solid electrolyte may be, for example, Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a skeleton include LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ Li ４ P ２ S ７ Examples of the sulfide solid electrolyte having a skeleton include a Li-P-S solid electrolyte called LPS (for example, Li ７ P ３ S １１ Examples of sulfide solid electrolytes include Li （４－ｘ） Ge （１－ｘ） Pｘ S ４ (wherein x satisfies 0<x<1), or the like may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing Li ２ S-P ２ S ５ As the halogen-containing sulfide solid electrolyte, an argyrodite-type solid electrolyte (Li ６ P.S. ５ X (wherein X is Cl, Br, or I).

[0052] The valence of the valence variable substance 4 varies due to the insertion and desorption of the measurement ion inserted into the valence variable substance 4 contained in the solid electrolyte layer 3. The change in the valence of the valence variable substance 4 causes a current to flow, and the ion concentration can be measured based on the current value.

[0053] The valence variable substance 4 preferably contains an oxide. The oxide is a metal oxide. With the above configuration, the insertion and desorption of the measurement ion into and from the valence variable substance 4 becomes easy.

[0054] Examples of the oxide in the valence variable substance 4 include lithium-containing phosphate compound particles having a Nasicon structure, lithium-containing phosphate compound particles having an olivine structure, lithium-containing layered oxide particles, lithium-containing oxide particles having a spinel structure, etc. Specific examples of lithium-containing phosphate compounds having a Nasicon structure that are preferably used include Li ３ V ２ (P.O. ４ ) ３ Specific examples of lithium-containing phosphate compounds having an olivine structure that are preferably used include Li ３ Fe ２ (P.O. ４ ) ３ , LiMnPO ４ Specific examples of the lithium-containing layered oxide particles that are preferably used include LiCoO ２ , LiCo １／３ Ni １／３ Mn １／３ O２ Specific examples of lithium-containing oxides having a spinel structure that are preferably used include LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ , Li ４ Ti ５ O １２ Among them, LiCoO ２ , LiCo １／３ Ni １／３ Mn １／３ O ２ It is more preferable to use lithium-containing layered oxides such as: These oxides may be used alone or in combination of two or more kinds.

[0055] Furthermore, an oxide having a LISICON-type crystal structure may be used as the oxide in the valence variable substance 4, and may be represented by the chemical formula (Li[3-ax+(5-b)y]A ｘ ) (V （１－ｙ） B ｙ ) O ４ (wherein A is at least one element selected from the group consisting of Na, K, Mg, Ca, Al, Ga, Zn, Fe, Cr, and Co; B is at least one element selected from the group consisting of Zn, Al, Ga, Si, Ge, Sn, P, As, Ti, Mo, W, Fe, Cr, and Co; 0≦x≦1.0, 0≦y≦0.6, a is the valence of A, and b is the valence of B). In the above chemical formula, it is more preferable that 0≦x≦0.2 and 0.1≦y≦0.4. By making 0.1≦y, the utilization rate of the oxide having a LISICON-type crystal structure can be increased. Furthermore, by making y≦0.4, the initial reversible capacity can be increased.

[0056] Alternatively, Li metal may be used as the valence variable substance 4 .

[0057] The valence variable substance 4 may be contained in an amount of 10 mass % or more relative to the solid electrolyte layer 3. The valence variable substance 4 may be contained in an amount of 40 mass % or less relative to the solid electrolyte layer 3. The valence variable substance 4 may be contained in an amount of 10 mass % or more and 40 mass % or less relative to the solid electrolyte layer 3. The concentration of the valence variable substance 4 can be measured by SEM-EDX (energy dispersive X-ray spectroscopy) using a scanning electron microscope (SEM).

[0058] The valence variable substance 4 may be contained in an amount of 10 mass % or more relative to the first solid electrolyte layer 301. The valence variable substance 4 may be contained in an amount of 40 mass % or less relative to the first solid electrolyte layer 301. The valence variable substance 4 may be contained in an amount of 10 mass % or more and 40 mass % or less relative to the first solid electrolyte layer 301.

[0059] The valence variable substance 4 may be present in greater amounts on the first main surface 3a side than on the second main surface 3b side of the solid electrolyte layer 3. Here, the second main surface 3b side refers to a portion extending from the second main surface 3b to 10% of the thickness of the solid electrolyte layer 3 in a cross section perpendicular to the first main surface 3a and the second main surface 3b of the solid electrolyte layer 3. The first main surface 3a side refers to a portion extending from the first main surface 3a to 10% of the thickness of the solid electrolyte layer 3 in a cross section perpendicular to the first main surface 3a and the second main surface 3b of the solid electrolyte layer 3.

[0060] Preferably, the valence variable substance 4 is a substance containing atoms whose valence changes due to insertion / desorption of the ion to be measured. With the above configuration, a current flows, and the concentration of the ion can be measured.

[0061] The ion sensor 10 is used by arranging the first electrode 1 and the second electrode 1A so that they come into contact with the measurement medium 9.

[0062] 1 , the first electrode 1 and the second electrode 1A are arranged so as to face the same direction with respect to the measurement medium 9. That is, the second main surface 3b of the solid electrolyte layer 3 and the second main surface 3bA of the solid electrolyte layer 3A of the first electrode 1 and the second electrode 1A face the same direction. The contact surface between the first electrode 1 and the measurement medium 9 is on the same plane as the contact surface between the second electrode 1A and the measurement medium 9. Note that the contact surface between the first electrode 1 and the measurement medium 9 and the contact surface between the second electrode 1A and the measurement medium 9 do not have to be completely on the same plane, and there may be some deviation.

[0063] In another embodiment, as shown in Fig. 4, the first electrode 1 and the second electrode 1A may be disposed opposite each other with the measurement medium 9 interposed therebetween. That is, in the ion sensor 10A, the second main surface 3b of the first electrode 1 and the second main surface 3bA of the second electrode 1A may not be on the same plane but may face each other with the measurement medium 9 interposed therebetween. By adopting the above embodiment, it is possible to measure measurement media 9 that exist in a variety of shapes. The first electrode 1 and the second electrode 1A do not have to face each other completely, and there may be some misalignment therebetween.

[0064] The measurement medium 9 is a solution containing a compound containing a measurement ion and a solvent. The measurement ion is not particularly limited, but for example, Li ＋ , Na ＋ , K. ＋ , F ＋ , H ＋ , H － , Cu ＋ , Ag ＋ , O ２－ , Mg ２＋ The ion concentration to be measured is not particularly limited as long as it is within a range that can be measured by the ion sensor 10, but is, for example, in the range of 1 μM to 100 M. If the ion concentration becomes too high and cannot be measured by the ion sensor 10, the measurement medium 9 may be diluted before measurement. The compound containing the ion to be measured may be dissolved in a solvent, but is not particularly limited, for example, LiPF ６, LiFSI, LiTFSI, etc. The solvent is not particularly limited as long as it can dissolve a compound containing the ion to be measured, and examples thereof include water, an organic solvent, etc. In FIG. 1 , the measurement medium 9 has a rectangular shape along the ion sensor 10, but the shape of the measurement medium 9 is not particularly limited as long as it is in contact with the first electrode 1 and the second electrode 1A.

[0065] As shown in FIG. 7 , a conventional ion sensor 10P uses an electrode member 1P having an electrode layer 2, a solid electrolyte layer 3P, and an ion-sensitive membrane 7, in this order. In this electrode member 1P, the ions to be measured are repeatedly adsorbed and desorbed (adsorption / desorption) on the surface of the ion-sensitive membrane 7 that contacts the measurement medium, and the potential difference between the potential generated by this adsorption / desorption and the potential of the reference electrode is measured. Because the potential difference is measured, the measurement accuracy of the ion sensor 10P is low. Furthermore, because measurement is performed using the ion-sensitive membrane 7, the types of ions that can be measured are limited due to compatibility between the ion-sensitive membrane 7 and the ions to be measured.

[0066] In contrast, as described above, the ion sensor 10 of the present invention does not have a reference electrode. Furthermore, the ion sensor 10 of the present invention does not have an ion-sensitive membrane 7. In the present invention, the solid electrolyte layers 3 and 3A are brought into contact with the measurement medium 9, and measurement ions contained in the measurement medium 9 are captured by the solid electrolyte layer 3. These measurement ions can be inserted into and removed from the solid electrolyte layer 3, thereby allowing them to access the valence variable substance 4. This causes the valence of the valence variable substance 4 to change. The change in the valence of the valence variable substance 4 causes a change in the current flowing through the electrode layer 2. The ion sensor 10 using the ion sensor electrode member of the present disclosure can measure this change in current value to determine the ion concentration. Since the present invention can directly measure the change in current value, measurement accuracy can be improved. Furthermore, since measurement ions are inserted and removed, the type of measurement ion is not limited, and a wide variety of measurement ions can be measured.

[0067] Second Embodiment Fig. 5 is a schematic diagram showing a method of using the ion sensor 10B in a second embodiment. The second embodiment differs from the first embodiment in that the second electrode 1A of the first embodiment is replaced with a third electrode 1B including a metal layer. This difference will be described below. The other configurations are the same as those of the first embodiment, and the same reference numerals as those of the first embodiment are used, and description thereof will be omitted. Note that the "third electrode 1B" corresponds to the "second electrode" described in the claims.

[0068] The third electrode 1B includes a first principal surface 3c and a second principal surface 3d that face each other. The second principal surface 3d is in contact with the measurement medium 9.

[0069] The third electrode 1B is a metal electrode. Examples of metals include Li, Na, and K. Only one type of metal may be used, or multiple types may be used. The third electrode 1B may also include multiple metal layers. Use of the third electrode 1B increases the number of ion types that can be measured.

[0070] The third electrode 1B and the first electrode 1 are arranged to face in the same direction. That is, the second main surface 3b of the solid electrolyte layer 3 and the second main surface 3d of the solid electrolyte layer 3B of the first electrode 1 and the third electrode 1B face in the same direction. The contact surface between the first electrode 1 and the measurement medium 9 is on the same plane as the contact surface between the third electrode 1B and the measurement medium 9. Note that the contact surface between the first electrode 1 and the measurement medium 9 and the contact surface between the third electrode 1B and the measurement medium 9 do not have to be completely on the same plane, and there may be some deviation.

[0071] 6 , the first electrode 1 and the third electrode 1B may be disposed opposite each other with the measurement medium 9 interposed therebetween. That is, in the ion sensor 10C, the second main surface 3b of the first electrode 1 and the second main surface 3d of the third electrode 1B may not be on the same plane, but may face each other with the measurement medium 9 interposed therebetween. The above-described embodiment broadens the range of uses for the ion sensor.

[0072] The present disclosure is not limited to the above-described embodiments, and design modifications are possible within the scope of the present disclosure. For example, the respective features of the first and second embodiments may be combined in various ways.

[0073] The present disclosure includes the following aspects. <1> An electrode member for an ion sensor, comprising: an electrode layer; and a solid electrolyte layer located on the electrode layer, the solid electrolyte layer having a first main surface and a second main surface opposite the first main surface, wherein the solid electrolyte layer has a solid electrolyte and a valence variable substance disposed within the solid electrolyte. <2> The electrode member for an ion sensor according to <1>, wherein the valence variable substance is present in a greater amount on the first main surface side of the solid electrolyte layer than on the second main surface side. <3> The electrode member for an ion sensor according to <1> or <2>, wherein the content of the valence variable substance in the second main surface of the solid electrolyte layer is 10 mass % or less. <4> The electrode member for an ion sensor according to any one of <1> to <3>, wherein, in a cross section of the solid electrolyte layer perpendicular to the first main surface and the second main surface, a content of the valence variable substance in a second region that is a region between the second main surface and a first position that is located at 10% of a thickness from the second main surface toward the first main surface with respect to 100% of a thickness between the first main surface and the second main surface is less than a content of the valence variable substance in the first region that is a region between the first position and the first main surface. <5> The electrode member for an ion sensor according to any one of <1> to <4>, wherein the solid electrolyte layer has a first solid electrolyte layer and a second solid electrolyte layer, the first solid electrolyte layer is located on the electrode layer, the second solid electrolyte layer is located on the first solid electrolyte layer, and the second solid electrolyte layer does not contain the valence variable substance. <6> The electrode member for an ion sensor according to any one of <1> to <5>, wherein the valence variable substance is a substance containing an atom whose valence changes due to insertion and desorption of an ion. <7> The electrode member for an ion sensor according to any one of <1> to <6>, wherein the valence variable substance includes an oxide. <8> The electrode member for an ion sensor according to any one of <1> to <7>, wherein the solid electrolyte includes an oxide. <9> The electrode member for an ion sensor according to any one of <1> to <8>, wherein the electrode member does not have an ion-sensitive film. <10> An ion sensor including a first electrode and a second electrode, wherein at least one of the first electrode and the second electrode is the electrode member for an ion sensor according to any one of <1> to <9>.<11> The ion sensor according to <10>, wherein the first electrode and the second electrode are the electrode member for an ion sensor according to any one of <1> to <9>. <12> The ion sensor according to <10> or <11>, wherein the valence variable substance in the first electrode and the valence variable substance in the second electrode are different valence variable substances. <13> The ion sensor according to <10> or <11>, wherein the valence variable substance in the first electrode and the valence variable substance in the second electrode are the same valence variable substance. <14> The ion sensor according to any one of <10> to <13>, wherein the first electrode is the electrode member for an ion sensor according to any one of <1> to <9>, and the second electrode is a metal electrode. <15> A method for analyzing ions in a medium using the ion sensor according to any one of <10> to <14>, wherein the first electrode and the second electrode are arranged to face the same direction with respect to a measurement medium. <16> The method for analyzing ions in a medium using the ion sensor according to any one of <10> to <14>, wherein the first electrode and the second electrode are arranged opposite each other with the measurement medium interposed therebetween.

[0074] The present disclosure will be explained in more detail through the following examples, but is not limited to these examples.

[0075] Example A first electrode 1 and a second electrode 1A were manufactured as follows.

[0076] <First electrode 1> [Production of solid electrolyte 5] Lithium hydroxide monohydrate (LiOH.H) was used as a raw material. ２ O, lanthanum hydroxide La(OH) ３ , zirconium oxide ZrO ２ , and tantalum oxide Ta ２ O ５ Each raw material was used, with the chemical composition being Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ The mixture was weighed out so that the weight of the raw material was 100 ml, and water was added. The mixture was sealed in a 100 ml polyethylene pot and rotated on a pot rack at 150 rpm for 16 hours to mix the raw materials.２ Considering the Li deficiency during firing, O was charged in an amount 10 wt% in excess of the target composition. The obtained slurry was evaporated and dried, and then calcined at 900°C for 5 hours to obtain the target phase. A mixed solvent of toluene and acetone was added to the obtained calcined powder, and the mixture was pulverized in a planetary ball mill for 6 hours to obtain a pulverized powder. This pulverized powder was dried to obtain powder of solid electrolyte 5. Measurement by inductively coupled plasma atomic emission spectroscopy (ICP) revealed that the composition of the powder was Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ It was confirmed that no deviation occurred.

[0077] [Production of Valence Variable Material 4 for First Electrode 1 (Working Electrode)] ２ is cobalt oxide Co ３ O ４ and lithium carbonate Li ２ CO ３ Specifically, cobalt oxide and lithium carbonate were weighed in a stoichiometric composition and sealed in a polyethylene (PE) bottle together with 1 mm zirconia beads and pure water. This was mixed by rotating it in a pot mill at 200 rpm for 16 hours. The beads were then removed from the mixture, which was then dried and crushed in a mortar. The crushed material was placed in a crucible and fired in a firing furnace at 800°C in an air atmosphere for 20 hours. The fired material thus obtained was crushed in a mortar to obtain LiCoO ２ obtained.

[0078] [Production of sintering aid for first electrode 1 (working electrode)] Lithium hydroxide monohydrate (LiOH.H) was used as a raw material. ２ O, and boron oxide B ２ O ３ Each raw material was used. The chemical composition of the sintering aid was Li ４ B ２ O ５ The mixture was thoroughly mixed in a mortar and then calcined at 650° C. for 5 hours.

[0079] [Manufacture of First Electrode 1 (Working Electrode: First Ion Sensor Electrode Member)] (Manufacture of Second Solid Electrolyte Layer 302) Solid electrolyte 5 powder, butyral resin, and alcohol were mixed in a mass ratio of 200:15:140, and then the alcohol was removed on a hot plate at 80°C to obtain solid electrolyte 5 powder coated with butyral resin as a binder. Next, the butyral resin-coated solid electrolyte 5 powder was pressed at 90 MPa using a tablet press to form tablets. The obtained solid electrolyte 5 tablets were thoroughly covered with mother powder and fired at 500°C in an oxygen atmosphere to remove the butyral resin. Subsequently, the mixture was fired at approximately 1200°C for 3 hours in an oxygen atmosphere. The temperature was then lowered to obtain a sintered body of solid electrolyte 5. The surface of the obtained sintered body was polished to obtain the second solid electrolyte layer 302. Cross-sectional observation (XZ cross section, i.e., cross section in a direction perpendicular to the surface of second solid electrolyte layer 302 that can be connected to first solid electrolyte layer 301) using a scanning electron microscope (SEM) confirmed that the porosity of second solid electrolyte layer 302 was 3% or less.

[0080] (Production of First Solid Electrolyte Layer 301) The powder of solid electrolyte 5 (LLZ), the powder of valence variable substance 4 for the working electrode, and the sintering aid powder were weighed out in a volume ratio of 50:40:10 and kneaded with alcohol and a binder to prepare a paste. Next, the paste was applied to the second solid electrolyte layer 302 (i.e., the solid electrolyte substrate) and dried. The binder was then removed by heating to 400°C. Further, a heat treatment (firing) was performed in the air at 800°C for 2 hours to obtain a laminate in which the first solid electrolyte layer 301 was laminated on the second solid electrolyte layer 302.

[0081] (Manufacture of Electrode Layer) Thereafter, a sputtering process was carried out on the surface of the first solid electrolyte layer 301 opposite to the second solid electrolyte layer 302, to form a first electrode layer 2 of Au.

[0082] <Second Electrode 1A> [Production of Valence Variable Substance 4A for Second Electrode 1A (Counter Electrode)] Lithium hydroxide monohydrate (LiOH.H ２ O), vanadium pentoxide (V ２ O ５ ) with the chemical composition Li３ VO ４ The materials were weighed out and mixed thoroughly in a mortar. Next, ethanol was added, the mixture was placed in a 100 ml polyethylene pot, and the pot was rotated at 150 rpm on a pot rack for 16 hours to mix the raw materials. The resulting slurry was dried and then fired in air at 900°C for 5 hours. A toluene-acetone mixed solvent was then added to the fired material, which was then pulverized in a planetary ball mill for 6 hours and then dried to obtain a valence variable material 4A for the counter electrode.

[0083] [Production of sintering aid for second electrode 1A (counter electrode)] Lithium hydroxide monohydrate (LiOH.H) was used as a raw material. ２ O, and boron oxide B ２ O ３ Each raw material was used. The chemical composition of the sintering aid was ３ BO ３ The mixture was weighed appropriately so that the weight ratio was 1:1, mixed thoroughly in a mortar, and then calcined at 650°C for 5 hours to obtain a calcined powder. The calcined powder was then thoroughly crushed and mixed again in a mortar, and then calcined at 680°C for 40 hours. A toluene-acetone mixed solvent was added to the obtained calcined powder, which was then crushed in a planetary ball mill for 6 hours and dried to obtain a sintering aid powder for the counter electrode. ICP measurement confirmed that the above powder had no compositional deviation.

[0084] [Manufacture of Second Electrode 1A (Counter Electrode: Second Ion Sensor Electrode Member)] (Manufacture of Second Solid Electrolyte Layer 302) Solid electrolyte 5 powder, butyral resin, and alcohol were mixed in a mass ratio of 200:15:140, and then the alcohol was removed on a hot plate at 80°C to obtain solid electrolyte 5 powder coated with butyral resin as a binder. Next, the butyral resin-coated solid electrolyte 5 powder was pressed into tablets at 90 MPa using a tablet press. The obtained solid electrolyte 5 tablets were thoroughly covered with mother powder and fired at 500°C in an oxygen atmosphere to remove the butyral resin. Subsequently, the solid electrolyte 5 tablets were fired at approximately 1200°C for 3 hours in an oxygen atmosphere. The temperature was then lowered to obtain a sintered body of solid electrolyte 5. The surface of the obtained sintered body was polished to obtain a second solid electrolyte layer 302 (solid electrolyte layer). Furthermore, cross-sectional observation using an SEM confirmed that the porosity was 3% or less.

[0085] (Manufacture of First Solid Electrolyte Layer 301) Solid electrolyte 5 powder (LLZ), counter electrode valence variable substance 4 powder, sintering aid powder, and conductive material powder (Ag particles) were weighed out in a volume ratio of 35:30:5:30 and kneaded with alcohol and a binder to prepare a paste. Next, the paste was applied to the second solid electrolyte layer 302 (i.e., the solid electrolyte substrate) and dried. The binder was then removed by heating to 400°C. Further, a heat treatment (firing) was performed in the air at 800°C for 2 hours to prepare a laminate in which the first solid electrolyte layer 301 was stacked on the second solid electrolyte layer 302.

[0086] (Manufacture of Electrode Layer) Thereafter, a sputtering process was performed on the surface of first solid electrolyte layer 301 opposite to second solid electrolyte layer 302, to form second electrode layer 2A of Cu.

[0087] Comparative Example A first electrode and a second electrode were manufactured as follows.

[0088] <First electrode> [Production of solid electrolyte] Lithium hydroxide monohydrate (LiOH.H) was used as a raw material. ２ O, lanthanum hydroxide La(OH) ３ , zirconium oxide ZrO ２, and tantalum oxide Ta ２ O ５ Each raw material was used, with the chemical composition being Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ The mixture was weighed out so that the weight of the raw material was 100 ml, and water was added. The mixture was sealed in a 100 ml polyethylene pot and rotated on a pot rack at 150 rpm for 16 hours to mix the raw materials. ２ Considering the loss of Li during firing, O was charged in an amount 10 wt% in excess of the target composition. The obtained slurry was evaporated and dried, and then calcined at 900°C for 5 hours to obtain the target phase. A mixed solvent of toluene and acetone was added to the obtained calcined powder, which was then pulverized in a planetary ball mill for 6 hours to obtain a pulverized powder. This pulverized powder was dried to obtain a solid electrolyte powder. ICP measurement revealed that the composition of the powder was Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ It was confirmed that no deviation occurred.

[0089] [Manufacture of First Electrode (Working Electrode)] (Manufacture of Solid Electrolyte Layer) Solid electrolyte powder, butyral resin, and alcohol were mixed in a mass ratio of 200:15:140, and then the alcohol was removed on a hot plate at 80°C to obtain a solid electrolyte powder coated with butyral resin as a binder. The butyral resin-coated solid electrolyte powder was then pressed into tablets at 90 MPa using a tablet press. The resulting solid electrolyte tablets were thoroughly covered with mother powder and fired at 500°C in an oxygen atmosphere to remove the butyral resin. The resulting tablets were then fired at approximately 1200°C for 3 hours in an oxygen atmosphere. The temperature was then lowered to obtain a sintered solid electrolyte body. The surface of the resulting sintered body was polished to obtain a solid electrolyte substrate (solid electrolyte layer). Furthermore, cross-sectional observation using an SEM confirmed that the porosity of the solid electrolyte layer was 3% or less.

[0090] (Production of Electrode Layer) An Al electrode layer was formed by performing a sputtering process on the solid electrolyte layer.

[0091] <Second Electrode> [Manufacture of Second Electrode (Counter Electrode)] A solid electrolyte layer was formed in the same manner as in the manufacturing method of the working electrode. A Cu electrode layer was formed on the solid electrolyte layer by sputtering, thereby manufacturing a counter electrode.

[0092] (Measurement of Ion Concentration) The first electrode (working electrode), resin separator, SUS, resin separator, and second electrode (counter electrode) were stacked in this order and placed in a 2032-type coin cell, and a solution prepared to a specified Li ion concentration was dropped into the cell, followed by sealing. In this solution, dimethyl carbonate was used as the solvent and lithium bis(trifluoromethanesulfonyl)imide was used as the Li salt. The cell was then connected to an electrochemical measurement device, and a current was passed through it until the potential between the working electrode and the counter electrode reached 3.1 V. The current value was measured when a voltage of 0.1 V was applied, and the current value was measured 4 seconds after the voltage was applied.

[0093] The measurement results are shown in Table 1.

[0094]

[0095] As shown in Table 1 above, it was found that in Examples 1 to 3, which contain a valence variable substance in the solid electrolyte layer, the current value increases as the Li ion concentration increases. In contrast, in Comparative Examples 1 to 3, measurable current values ​​cannot be obtained. As described above, when the ion sensor of the present invention is used, Li ions can be measured with high measurement accuracy.

[0096] 1, 1A, 1B Electrode 10, 10A, 10B, 10C Ion sensor 2, 2A Electrode layer 3, 3A, 301, 302 Solid electrolyte layer 2a, 2b, 2aA, 2bA, 3a, 3b, 3aA, 3bA, 3c, 3d Main surface 31 First region 32 Second region 301 First solid electrolyte layer 302 Second solid electrolyte layer 4 Valence variable substance 5 Solid electrolyte 9 Measurement medium

Claims

1. An electrode member for an ion sensor, comprising: an electrode layer; and a solid electrolyte layer located on the electrode layer, the solid electrolyte layer having a first main surface and a second main surface opposite the first main surface, wherein the solid electrolyte layer has a solid electrolyte and a valence variable substance disposed within the solid electrolyte.

2. The electrode member for an ion sensor according to claim 1, wherein the valence variable substance is present in a larger amount on the first main surface side than on the second main surface side in the solid electrolyte layer.

3. The electrode member for an ion sensor according to claim 1 or 2, wherein the content of the valence variable substance in the second main surface of the solid electrolyte layer is 10 mass % or less.

4. An electrode member for an ion sensor according to any one of claims 1 to 3, wherein in a cross section of the solid electrolyte layer perpendicular to the first main surface and the second main surface, the content of the valence variable substance in a second region, which is a region between the second main surface and a first position that is 10% of the thickness from the second main surface toward the first main surface with respect to 100% of the thickness between the first main surface and the second main surface, is less than the content of the valence variable substance in the first region, which is a region between the first position and the first main surface.

5. The electrode member for an ion sensor according to any one of claims 1 to 4, wherein the solid electrolyte layer has a first solid electrolyte layer and a second solid electrolyte layer, the first solid electrolyte layer is located on the electrode layer, the second solid electrolyte layer is located on the first solid electrolyte layer, and the second solid electrolyte layer does not contain the valence variable substance.

6. The electrode member for an ion sensor according to any one of claims 1 to 5, wherein the valence variable substance is a substance containing an atom whose valence changes due to insertion and desorption of an ion.

7. The electrode member for an ion sensor according to any one of claims 1 to 6, wherein the valence variable substance includes an oxide.

8. The electrode member for an ion sensor according to any one of claims 1 to 7, wherein the solid electrolyte contains an oxide.

9. An electrode member for an ion sensor according to any one of claims 1 to 8, which does not have an ion-sensitive membrane.

10. An ion sensor comprising a first electrode and a second electrode, wherein at least one of the first electrode and the second electrode is an electrode member for an ion sensor according to any one of claims 1 to 9.

11. The ion sensor according to claim 10, wherein the first electrode and the second electrode are the electrode members for an ion sensor according to any one of claims 1 to 9.

12. The ion sensor according to claim 10 or 11, wherein the valence variable substance at the first electrode and the valence variable substance at the second electrode are different valence variable substances.

13. The ion sensor according to claim 10 or 11, wherein the valence variable substance at the first electrode and the valence variable substance at the second electrode are the same valence variable substance.

14. The ion sensor according to any one of claims 10 to 13, wherein the first electrode is an electrode member for an ion sensor according to any one of claims 1 to 9, and the second electrode is a metal electrode.

15. A method for analyzing ions in a medium using the ion sensor according to any one of claims 10 to 14, wherein the first electrode and the second electrode are arranged to face in the same direction relative to the measurement medium.

16. A method for analyzing ions in a medium using the ion sensor according to any one of claims 10 to 14, wherein the first electrode and the second electrode are arranged opposite each other with the measurement medium interposed therebetween.

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