Electrode layer and battery

Abstract

The invention relates to an electrode layer and a battery. The main purpose of the present invention is to provide an electrode layer having little increase in resistance due to charging and discharging. In the present invention, the above-described problem is solved by providing an electrode layer containing an electrode active material containing an Si element and a binder containing an unsaturated bond, the electrode layer being characterized in that after the binder is dyed by Os dyeing, the electrode active material containing the Si element and the binder containing the unsaturated bond are bonded together. When the degree of overlap (D) between the Si element and the Os element is calculated on the basis of an element map image obtained by SEM-EDX measurement, the degree of overlap (D) is greater than 0.047.

Description

Technical Field

[0001] This invention relates to electrode layers and batteries. Background Technology

[0002] In recent years, battery development has been booming. For example, in the automotive industry, batteries for battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs) are under development. Furthermore, silicon (Si) is known as an electrode active material used in batteries. For example, Patent Document 1 discloses an active material containing Si, wherein voids exist within the primary particles.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-167083 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Electrode active materials containing silicon have a high theoretical capacity, which is effective for achieving high energy density in batteries. On the other hand, electrode active materials containing silicon experience significant volume changes due to charge and discharge. If the volume change due to charge and discharge is large, the electrode active material and other materials in contact with it (such as solid electrolytes or conductive materials) are prone to peeling off during repeated charge and discharge cycles. This results in an increase in battery resistance.

[0008] The present invention was made in view of the above-mentioned actual situation, and its main purpose is to provide an electrode layer with less increase in resistance caused by charging and discharging.

[0009] Methods for solving problems [1]

[0011] An electrode layer comprising an electrode active material containing Si and a binder containing unsaturated bonds, wherein, after the binder is stained by Os staining, when the overlap D between the Si and Os elements is calculated based on an elemental mapping image obtained by SEM-EDX measurement, the overlap D is greater than 0.047. [2]

[0013] According to the electrode layer described in [1], wherein the D is 0.07 or higher. [3]

[0015] According to the electrode layer described in [1] or [2], wherein the D is 0.50 or less. [4]

[0017] According to any one of [1] to [3], the electrode layer has an oxygen content of 1.0% by mass or more and 10% by mass or less, and the electrode layer contains a solvent component whose Hansen solubility parameter (HSP) δp is 6.0 MPa. 0.5 the following. [5]

[0019] According to any one of [1] to [4], the electrode layer has an oxygen content of 1.0% by mass or more and 10% by mass or less, and the electrode layer contains a solid electrolyte, wherein the δp of the Hansen solubility parameter (HSP) of the solid electrolyte is 10.0 MPa. 0.5 Above and 15.0 MPa 0.5 the following. [6]

[0021] According to the electrode layer described in [5], the solid electrolyte is a sulfide solid electrolyte. [7]

[0023] The electrode layer according to any one of [1] to [6], wherein the electrode active material is porous. [8]

[0025] The electrode layer according to any one of [1] to [7], wherein the electrode active material has a silicon inclusion complex type crystal phase. [9]

[0027] The electrode layer according to any one of [1] to [8], wherein the electrode active material is a negative electrode active material.

[10]

[0029] A battery having a positive electrode layer, a negative electrode layer and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer or the negative electrode layer is an electrode layer as described in any one of [1] to [9].

[11]

[0031] According to the battery described in

[10] , the electrolyte layer contains a solid electrolyte.

[0032] Invention Effects

[0033] In this invention, the effect of obtaining an electrode layer with minimal increase in resistance due to charging and discharging is achieved. Attached Figure Description

[0034] Figure 1 This is a schematic cross-sectional view illustrating the battery of the present invention.

[0035] Figure 2 It is a mapped image of Si.

[0036] Figure 3 It is a mapping image of Os.

[0037] Figure 4 It is an image formed by superimposing the binarized image of Si and the binarized image of Os.

[0038] Figure 5 This is a graph illustrating the overlap D between Si and Os. Detailed Implementation

[0039] The electrode layer and battery of the present invention will be described in detail below.

[0040] A. Electrode layer

[0041] The electrode layer of the present invention contains an electrode active material comprising Si and a binder having unsaturated bonds. Furthermore, after staining the binder with Os staining, when calculating the overlap D between Si and Os elements based on the elemental mapping image obtained by SEM-EDX measurement, the aforementioned D is within a specified range.

[0042] According to the present invention, the overlap D is within a specified range, thus resulting in an electrode layer with minimal increase in resistance due to charging and discharging. As mentioned above, Si has a large theoretical capacity, which is effective for achieving high energy density in batteries. On the other hand, Si exhibits a large volume change due to charging and discharging. If the volume change due to charging and discharging is large, the electrode active material and other materials in contact with the electrode active material (e.g., solid electrolyte or conductive material) are easily peeled off during repeated charging and discharging. As a result, the battery resistance tends to increase. In contrast, in the present invention, by selectively distributing a large amount of binder around the electrode active material containing Si, the volume change of the electrode active material (Si) due to charging and discharging makes it difficult for the electrode active material and other materials in contact with the electrode active material (e.g., solid electrolyte or conductive material) to peel off. As a result, an electrode layer with minimal increase in resistance due to charging and discharging is achieved.

[0043] In this invention, the cross-section of the electrode layer is stained with Os, and the adhesive in the electrode layer is stained. Specifically, the unsaturated bonds contained in the adhesive are reacted with OsO4 (osmium oxide) to stain the adhesive. Then, the cross-section of the electrode layer is measured by SEM-EDX to obtain an elemental mapping image. Based on the obtained elemental mapping image, the overlap degree D between Si and Os elements is calculated. The overlap degree D is an index based on the so-called correlation coefficient. Details of the calculation method for the overlap degree D are described in the embodiments described later. The overlap degree D is typically greater than 0.047, and can be 0.05 or greater, 0.07 or greater, 0.09 or greater, 0.15 or greater, or 0.20 or greater. If the overlap degree D is too low, it may not be sufficient to reduce the increase in resistance caused by charging and discharging. On the other hand, the overlap degree D is, for example, 0.50 or less, 0.40 or less, or 0.30 or less. It should be noted that in this invention, the adhesive is stained by Os staining, but the same result can be obtained even if the adhesive is stained by, for example, the known Ru staining.

[0044] 1. Electrode active material

[0045] The electrode active material in this invention contains the element Si. Examples of electrode active materials include elemental Si, Si alloys, Si oxides, and Si carbides. Si alloys are alloys with Si as the main component. Examples of metals other than Si in Si alloys include Na, W, Mo, Cr, V, Nb, Fe, Ti, Zr, and Hf. Si alloys may contain only one metal other than Si, or they may contain two or more metals other than Si. Examples of Si oxides include SiO. Examples of Si carbides include SiC.

[0046] The oxygen content of the electrode active material is not particularly limited, but may be, for example, 1.0% by mass or more and 10% by mass or less. The oxygen content of the electrode active material may be 3.0% by mass or more, or 5.0% by mass or more. On the other hand, the oxygen content of the electrode active material may be 9.0% by mass or less, 8.0% by mass or less, or 7.0% by mass or less. The oxygen content of the electrode active material is typically the oxygen content present on the surface of the electrode active material, for example, a value measured using an oxygen-nitrogen-hydrogen (ONH) analyzer. For example, if the electrode active material is washed with an aqueous hydrofluoric acid solution, hydrogen terminals are generated on the surface of the electrode active material, and the oxygen content on the surface of the electrode active material decreases.

[0047] The electrode active material is typically in particle form. It can be primary particles or secondary particles formed by aggregates of primary particles. Preferably, the electrode active material is porous (porous Si). That is, the electrode active material preferably has voids within the primary particles. The proportion of voids in the primary particles (porosity) is, for example, 4% or more, or 10% or more. Alternatively, the porosity is, for example, 40% or less, or 20% or less. The porosity can be determined, for example, by the following steps: First, the electrode layer containing the electrode active material is exposed by ion milling. Then, the cross-section is observed using SEM (scanning electron microscope) to obtain a photograph of the particles. Using image analysis software, the silicon portion and the void portion are strictly distinguished from the obtained photograph, and binarization is performed. The areas of the silicon portion and the void portion are calculated, and the porosity (%) is calculated according to the following formula.

[0048] Porosity (%) = 100 × (Area of ​​voids) / ((Area of ​​silicon) + (Area of ​​voids))

[0049] The electrode active material preferably has a large number of pores with a diameter of 5 nm or less. The porosity P1 of these pores with a diameter of 5 nm or less is, for example, 0.015 cc / g or more, 0.020 cc / g or more, or 0.023 cc / g or more. Alternatively, the porosity P1 may be, for example, 0.05 cc / g or less, 0.04 cc / g or less, or 0.035 cc / g or less. In this invention, the porosity refers to the cumulative pore volume, which can be determined, for example, by BET measurement, gas adsorption method, mercury porosimetry, 3D-SEM, or 3D-TEM.

[0050] The electrode active material preferably has a large number of pores with a diameter of 10 nm or less. The amount of pores with a diameter of 10 nm or less, P2, is, for example, 0.030 cc / g or more, and can be 0.035 cc / g or more, or 0.040 cc / g or more. Alternatively, the amount of pores P2 is, for example, 0.08 cc / g or less, and can be 0.07 cc / g or less, or 0.06 cc / g or less. Furthermore, the ratio of pore amount P1 to pore amount P2 (P1 / P2) is, for example, 50% or more, and can be 55% or more, or 57% or more. Alternatively, P1 / P2 is, for example, 80% or less, and can be 70% or less, or 65% or less.

[0051] The electrode active material preferably has a large number of pores with a diameter of 100 nm or less. The amount of pores with a diameter of 100 nm or less, P3, is, for example, 0.10 cc / g or more, and can be 0.20 cc / g or more, or 0.32 cc / g or more. Alternatively, the amount of pores P3 is, for example, 0.50 cc / g or less, and can be 0.45 cc / g or less, or 0.38 cc / g or less. Furthermore, the ratio of pore amount P1 to pore amount P3 (P1 / P3) is, for example, 6.0% or more, and can be 6.5% or more, or 6.9% or more. Alternatively, P1 / P3 is, for example, 15% or less, and can be 12% or less, or 10% or less.

[0052] As an example of a method for manufacturing porous electrode active materials, the following method can be listed: An alloy of Li and Si (Li-Si alloy) is manufactured, and then Li is removed from the Li-Si alloy. The Li-Si alloy can be obtained, for example, by mixing Li and Si. The Li-to-Si ratio (Li / Si) is, for example, 1.0 or more, 2.0 or more, 3.0 or more, or 4.0 or more. On the other hand, the Li / Si ratio is, for example, 8.0 or less. As a method for removing Li from the Li-Si alloy, a method of reacting the Li-Si alloy with a Li extraction material can be listed, for example. Examples of Li extraction materials include: alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acids such as acetic acid, formic acid, propionic acid, and oxalic acid.

[0053] Another example of a method for manufacturing porous electrode active materials is as follows: An alloy of Mg and Si (Mg-Si alloy) is manufactured, and then Mg is removed from the Mg-Si alloy. The Mg-Si alloy can be obtained, for example, by heating a mixture of Mg and Si. The ratio of Mg to Si (Mg / Si) is, for example, 1.0 or more, 1.5 or more, or 2.0 or more. On the other hand, the Mg / Si ratio is, for example, 6.0 or less. As a method for removing Mg from the Mg-Si alloy, for example, the Mg in the Mg-Si alloy is converted to MgO by heating the Mg-Si alloy in an oxygen-containing inert gas atmosphere, and then the MgO is removed using an acid solution. An aqueous solution containing hydrochloric acid (HCl) and hydrogen fluoride (HF) can be cited as an example of an acid solution.

[0054] Electrode active materials can be crystalline or amorphous. When the electrode active material is crystalline, it typically possesses a Si crystalline phase. A diamond-type crystalline phase is an example of a Si crystalline phase. Ordinary Si contains a diamond-type crystalline phase as its main Si crystalline phase. Electrode active materials can also contain a diamond-type crystalline phase as the main phase of their Si crystalline structure.

[0055] Other examples of Si crystalline phases include silicon cladding phases. These can be either type I or type II silicon cladding phases. In these phases, multiple Si elements form a polyhedron (cage) containing pentagons or hexagons. This polyhedron has internal spaces capable of containing metal ions such as Li ions. By inserting metal ions into these spaces, volume changes caused by charging and discharging can be suppressed. Electrode active materials can contain either type I or type II silicon cladding phases as the main Si phase. One method for preparing silicon cladding phases is, for example, reacting Na with Si to form a Na-Si alloy, then sintering the Na-Si alloy to remove Na.

[0056] The average particle size (D) of the electrode active material 50 There are no specific limitations; for example, it can be 0.1 μm or larger and 50 μm or smaller, or it can be 0.5 μm or larger and 30 μm or smaller. Average particle size (D) 50 For example, it can be calculated based on scanning electron microscopy (SEM). Furthermore, the BET specific surface area of ​​the electrode active material is not particularly limited, for example, it can be 30 m². 2 / g or more, can be 40m 2 / g or more, can be 50m 2 / g or above, or 60m 2 / g or more. On the other hand, the BET specific surface area of ​​the electrode active material is, for example, 150m². 2 / g or less.

[0057] The electrode active material may or may not be coated with a coating layer containing a solid electrolyte. The solid electrolyte constituting the coating layer is not particularly limited; examples of solid electrolytes described in "3. Solid Electrolytes" (described later) can be included, with sulfide solid electrolytes being preferred. The coverage ratio of the coating layer relative to the electrode active material is, for example, 50% or more, 70% or more, or 90% or more. The thickness of the coating layer is, for example, 1 nm or more and 100 nm or less, 5 nm or more and 50 nm or less, or 10 nm or more and 30 nm or less.

[0058] The proportion of electrode active material in the electrode layer is, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the proportion of electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of electrode active material in the electrode layer is, for example, 80% by mass or less, 70% by mass or less, or 60% by mass or less. If the proportion of electrode active material is too high, the ionic conductivity and electronic conductivity of the electrode layer may be relatively reduced.

[0059] 2. Adhesive

[0060] The adhesive contains unsaturated bonds. The adhesive is colored by reacting these unsaturated bonds with OsO4 (osmium oxide). The unsaturated bonds are preferably olefinic unsaturated bonds. The adhesive can have unsaturated bonds in the main chain or in the side chains. Examples of adhesives include: styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), and other butadiene rubber-based adhesives (BR-type adhesives); styrene-butadiene-styrene block copolymers such as styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS); and ethylene-propylene-diene copolymers (EPDM).

[0061] The proportion of binder in the electrode layer is, for example, 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more. If the proportion of binder is too low, it may not be sufficient to reduce the increase in resistance caused by charging and discharging. On the other hand, the proportion of binder in the electrode layer is, for example, 5% by mass or less, or 3% by mass or less. If the proportion of binder is too high, the proportion of electrode active material may be relatively low, resulting in a lower energy density.

[0062] 3. Solid electrolytes

[0063] The electrode layer can contain a solid electrolyte. Adding a solid electrolyte improves the ionic conductivity of the electrode layer. The solid electrolyte can be an inorganic solid electrolyte such as a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, or a complex hydride solid electrolyte, or an organic solid electrolyte such as a gel electrolyte. Among these, a sulfide solid electrolyte is preferred because of its high ionic conductivity. Sulfide solid electrolytes are electrolytes whose main component is sulfur (S) as an anionic element.

[0064] Sulfide solid electrolytes typically contain at least Li and S elements. Preferably, sulfide solid electrolytes further contain Me (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). Additionally, sulfide solid electrolytes may contain halogen elements such as F, Cl, Br, and I.

[0065] Sulfide solid electrolytes can be glass-based (amorphous), glass-ceramic, or crystalline. They can also possess crystalline phases. Examples of such crystalline phases include the Thio-LiSiCon type, the sulfide-germanium sulfide type, and the LGPS type.

[0066] The composition of sulfide solid electrolytes is not particularly limited; examples include xLi₂S·(1-x)P₂S₅ (0.5 ≤ x < 1) and yLiI·zLiBr·(100-yz)(xLi₂S·(1-x)P₂S₅) (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). In these compositions, x preferably satisfies 0.7 ≤ x ≤ 0.8. Another example of a sulfide solid electrolyte composition is Li₂S·(1-x)P₂S₅ (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). 7-x PS 6-x X x X is at least one of F, Cl, Br, and I, and x satisfies 0 ≤ x < 2. Another example of a sulfide solid electrolyte composition is Li. 4-x Me 1-x P x S4 (0 < x < 1). Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0067] The δp (polarity term) in the Hansen solubility parameter (HSP) of solid electrolytes is, for example, 10.0 MPa. 0.5 The above can be 12.0 MPa 0.5 The above can also be 12.5 MPa. 0.5 That's all. Additionally, the δp of solid electrolytes is, for example, 15.0 MPa. 0.5 The following is an example of how the Hansen solubility parameter δp (polarity term) can be derived from Hansen Solubility Parameters: A user's handbook, Second Edition. Boca Raton, Fla: CRC Press. (Hansen, Charles (2007)).

[0068] The proportion of solid electrolyte in the electrode layer can be, for example, 10% by mass or more, 20% by mass or more, or 30% by mass or more. If the proportion of solid electrolyte is too low, the ion conduction pathways in the electrode layer may be insufficient. On the other hand, the proportion of solid electrolyte in the electrode layer can be, for example, 60% by mass or less, or 50% by mass or less. If the proportion of solid electrolyte is too high, the proportion of electrode active material may be relatively low, resulting in a lower energy density.

[0069] 4. Conductive materials

[0070] The electrode layer may contain conductive materials. Adding conductive materials improves the electronic conductivity of the electrode layer. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), as well as fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0071] The proportion of conductive material in the electrode layer can be, for example, 0.1% by mass or more, 0.5% by mass or more, or 1.0% by mass or more. If the proportion of conductive material is too low, there may be insufficient electron conduction pathways in the electrode layer. On the other hand, the proportion of conductive material in the electrode layer can be, for example, 5% by mass or less, or 3% by mass or less. If the proportion of conductive material is too high, the proportion of electrode active material may be relatively low, resulting in a lower energy density.

[0072] 5. Electrode layer

[0073] The electrode layer may contain solvent components. These solvent components may be, for example, residual components of the solvent (dispersion medium) used during the fabrication of the electrode layer. Preferably, the solvent component has low polarity. If the solvent component has high polarity, for example, the dispersibility of the solid electrolyte is improved; however, if solvent components remain in the electrode layer, the solid electrolyte may deteriorate due to these residual components. On the other hand, if the solvent component has low polarity, it is possible to suppress the deterioration of the solid electrolyte due to residual solvent components.

[0074] The δp in the Hansen solubility parameter (HSP) of the solvent component is, for example, 6.0 MPa. 0.5 The following can be 5.5 MPa 0.5 The following can be 4.0 MPa 0.5 The following can be 3.5 MPa 0.5 The following can be 2.0 MPa 0.5 The following can be 1.5 MPa 0.5 The following can also be 1.0 MPa. 0.5 Below. On the other hand, the δp of the solvent component can be 0 MPa. 0.5It can also be greater than 0 MPa 0.5 Examples of solvent components include tetrahydronaphthalene, diisobutyl ketone, dodecane, isodecane, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, and toluene.

[0075] The proportion of solvent in the electrode layer can be, for example, 10 ppm or more, 50 ppm or more, or 100 ppm or more. If the proportion of solvent is too low, the load on the electrode layer drying process may increase. On the other hand, the proportion of solvent in the electrode layer can be, for example, 15,000 ppm or less, 5,000 ppm or less, or 500 ppm or less. If the proportion of solvent is too high, the formability of the electrode layer may decrease. The proportion of solvent in the electrode layer can be determined, for example, using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS).

[0076] As described above, the electrode layer contains at least an electrode active material and a binder comprising unsaturated bonds, and may further contain a solid electrolyte. In this invention, an organic compound having two or more benzene rings may be present between the electrode active material and the solid electrolyte. The aforementioned organic compound exhibits high chemical stability, thus suppressing the degradation of the solid electrolyte associated with charging and discharging (e.g., reductive decomposition, oxidative decomposition). Therefore, the increase in resistance caused by charging and discharging can be further suppressed. Particularly preferred is the conjugated extension of the interior of one benzene ring to the exterior of that benzene ring (e.g., another benzene ring). Furthermore, the aforementioned organic compound may be dispersed in the binder present between the electrode active material and the solid electrolyte.

[0077] Organic compounds having two or more benzene rings include, for example, compounds represented by the following general formula (1) or general formula (2).

[0078]

[0079] (where R is in the formula) 1 and R 2 Each is an independent organic group, R 3 ~R 10 Each is independently a hydrogen atom or a substituent, n 1 (Integers between 0 and 4.)

[0080] As a compound represented by general formula (1), for example, 9,9-bis(4-glycidoxyphenyl)fluorene, represented by the following chemical formula (1), can be listed.

[0081]

[0082] As another example of an organic compound having two or more benzene rings, compounds represented by the following general formula (3) can be listed.

[0083]

[0084] (In the formula, S is a single bond or an organic group, R) 11 ~R 20 Each can be an independent hydrogen atom or a substituent.

[0085] As a compound represented by general formula (3), for example, 1,3-diphenyl-2,3-epoxy-1-propanone represented by the following chemical formula (2) can be listed.

[0086]

[0087] The electrode layer in this invention is typically used in batteries. The electrode layer can be a negative electrode layer or a positive electrode layer, but the former is preferred. The thickness of the electrode layer is, for example, 0.1 μm or more and 1000 μm or less, 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0088] The method for manufacturing the electrode layer is not particularly limited. For example, a manufacturing method comprising the following steps can be listed: a preparation step of preparing the aforementioned electrode active material; a mixing step of mixing the aforementioned electrode active material, the aforementioned binder, and a solvent to obtain an electrode slurry; and an electrode layer forming step of forming an electrode layer using the aforementioned electrode slurry. In this invention, such a method for manufacturing an electrode layer can also be provided.

[0089] The above-described preparation step is the process of preparing the aforementioned electrode active material. Regarding the aforementioned electrode active material, the content is the same as described in "1. Electrode Active Material" above. Furthermore, the mixing step is the process of mixing the aforementioned electrode active material, the aforementioned binder, and the solvent to obtain an electrode slurry. Regarding the aforementioned solvent (dispersion medium), the content is the same as described above. In this invention, it is also possible to provide an electrode slurry containing the aforementioned electrode active material, the aforementioned binder, and the aforementioned solvent.

[0090] The above-described electrode layer forming process involves forming an electrode layer using the aforementioned electrode paste. The method for forming the electrode layer is not particularly limited, and known methods can be employed. Examples of methods for forming the electrode layer include coating the electrode paste onto an electrode current collector and then drying it. During electrode layer formation, a pressing process can be performed to press the electrode layer in the thickness direction. Examples of pressing processes include rolling and flatbed pressing.

[0091] B. Battery

[0092] Figure 1 This is a schematic cross-sectional view illustrating the battery of the present invention. Figure 1 The battery 10 shown has a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. In this invention, the positive electrode layer 1 or the negative electrode layer 2 is the electrode layer described in "A. Electrode Layer" above.

[0093] According to the present invention, by using the above-described electrode layer, a battery with minimal increase in resistance due to charging and discharging is achieved. As described above, the electrode layer can be either a negative electrode layer or a positive electrode layer, but the former is preferred. Hereinafter, the battery will be described in detail with regard to the case where the electrode layer is a negative electrode layer.

[0094] 1. Negative electrode layer

[0095] The negative electrode layer is a layer containing at least a negative electrode active material. Regarding the negative electrode layer, the content is the same as described in "A. Electrode Layer" above, therefore, the description here is omitted.

[0096] 2. Positive electrode layer

[0097] The positive electrode layer is a layer containing at least a positive electrode active material. In addition, the positive electrode layer may, as needed, contain at least one of an electrolyte, a conductive material, and a binder.

[0098] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include: LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt; LiMn2O4, Li4Ti5O 12 Li(Ni) 0.5 Mn 1.5 Spinel-type active substances such as O4; olivine-type active substances such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0099] A coating containing a Li-ion-conducting oxide can also be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte (especially a sulfide solid electrolyte). Examples of Li-ion-conducting oxides include LiNbO3. The coating thickness is, for example, 1 nm or more and 30 nm or less. Additionally, Li₂S can be used as a positive electrode active material, for example.

[0100] The shape of a positive electrode active material can be, for example, particulate. The average particle size (D) of the positive electrode active material... 50There is no particular limitation; for example, it can be 10 nm or larger, or even 100 nm or larger. On the other hand, the average particle size (D) of the positive electrode active material... 50 For example, it can be below 50μm, or it can be below 20μm.

[0101] Regarding the electrolyte used in the positive electrode layer, the same information is described in "3. Electrolyte Layer". Furthermore, regarding the conductive materials and binders used in the positive electrode layer, the same information is described in "A. Electrode Layer" above, and therefore, descriptions are omitted here. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, or it can be 0.1 μm or more and 500 μm or less, or it can be 0.1 μm or more and 100 μm or less.

[0102] 3. Electrolyte layer

[0103] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least one electrolyte. The electrolyte can be a solid electrolyte or a liquid electrolyte (electrolyte).

[0104] Regarding solid electrolytes, the content described in "A. Electrode Layer" above is the same, so it is omitted here. On the other hand, the electrolyte preferably contains a supporting salt and a solvent. Examples of supporting salts (lithium salts) for electrolytes with lithium-ion conductivity include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. Examples of solvents used in the electrolyte include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC); and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). The electrolyte preferably contains two or more solvents.

[0105] The thickness of the electrolyte layer can be, for example, 0.1 μm or more and 1000 μm or less, or 0.1 μm or more and 500 μm or less.

[0106] 4. Other components

[0107] The battery of the present invention preferably has a positive current collector for collecting current in the positive electrode layer and a negative current collector for collecting current in the negative electrode layer. Examples of materials for the positive current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative current collector include SUS, copper, nickel, and carbon.

[0108] The battery of the present invention may further include a constraint clamp that applies constraint pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer along the thickness direction. Particularly when the electrolyte layer is a solid electrolyte layer, it is preferable to apply constraint pressure in order to form good ion conduction paths and electron conduction paths. The constraint pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the constraint pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0109] 5. Battery

[0110] The type of battery used in this invention is not particularly limited, but is typically a lithium-ion battery. Furthermore, the battery of this invention can be a liquid battery with an electrolyte layer containing an electrolyte solution, or a solid-state battery with an electrolyte layer containing a solid electrolyte. The solid-state battery can be a semi-solid-state battery or a fully solid-state battery. In this invention, a semi-solid-state battery is a battery whose electrolyte layer contains both an inorganic solid electrolyte and a liquid component (e.g., an ionic liquid). In this invention, a fully solid-state battery is a battery whose electrolyte layer contains only an inorganic solid electrolyte as the electrolyte. Additionally, the battery of this invention can be a primary battery or a secondary battery, with a secondary battery being preferred. This is because it can be repeatedly charged and discharged, making it useful, for example, as a vehicle battery.

[0111] Batteries are used in various applications, including as power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can also be used as power sources for mobile bodies other than vehicles (such as trains, ships, and airplanes), and as power sources for electrical products such as information processing devices.

[0112] It should be noted that this invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any technical solution that has substantially the same structure and performs the same effect as the technical concept described in the claims of this invention is included within the technical scope of this invention.

[0113] Example

[0114] [Example 1]

[0115] (Preparation of electrode active materials)

[0116] Metallic Li and Si powders were weighed in a molar ratio of 4:1 and mixed in a mortar under an Ar atmosphere at room temperature for 0.5 hours to allow them to react. This yielded Li₄Si. The obtained Li₄Si was then reacted with ethanol under an Ar atmosphere. The resulting reaction product was assumed to contain Si and CH₃CH₂OLi. The reaction product was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain porous Si powder.

[0117] Using the obtained porous Si, and with NaH as the Na source, a Na-Si alloy was prepared. It should be noted that the NaH used was pre-washed with hexane. NaH and porous Si were weighed at a molar ratio of 1.05:1 and mixed using a shredder. The mixture of NaH and porous Si was heated in a furnace under an Ar atmosphere at 475°C for 40 hours to obtain a powdered Na-Si alloy.

[0118] Using the obtained Na-Si alloy, AlF3 was further used as a Na scavenger to generate silicon inclusion compounds via a solid-state method. The Na-Si alloy and AlF3 were weighed at a molar ratio of 1:0.35 and mixed using a shredder to obtain the reaction raw materials. The resulting powdered reaction raw materials were placed in a stainless steel reaction vessel and heated in a furnace under an Ar atmosphere at 310°C for 60 hours to induce a reaction, yielding the precursor active material.

[0119] It was assumed that the obtained precursor active material contained NaF and Al as byproducts. Therefore, the precursor active material was washed with a mixed solvent consisting of HNO3 and H2O in a volume ratio of 10:90. This removed the byproducts from the reaction product. After washing, the mixture was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain the electrode active material.

[0120] (Making the negative electrode)

[0121] The obtained electrode active material, sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), conductive material (VGCF), tetrahydronaphthalene solution containing binder (BR-type binder) at a ratio of 5% by mass, and tetrahydronaphthalene were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device (UH-50 manufactured by SMT). Next, the container was vibrated for 30 minutes using an oscillator (TTM-1 manufactured by Shibata Scientific Co., Ltd.) to obtain a negative electrode slurry. The mass ratio of electrode active material, sulfide solid electrolyte, conductive material, and binder was electrode active material: sulfide solid electrolyte: conductive material: binder = 51.27: 42.7: 0.77: 2.89. Furthermore, the solid content concentration of the slurry was 31% by mass. The obtained negative electrode slurry was coated onto a negative electrode current collector (Cu foil, manufactured by UACJ) using a scraper and dried on a hot plate at 100°C for 30 minutes. Thus, a negative electrode with a negative electrode current collector and a negative electrode layer was obtained.

[0122] (The production of the positive electrode)

[0123] Add positive electrode active material (LiNi) to the polypropylene container 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (average particle size 6 μm), sulfide solid electrolyte (Li2S-P2S5 glass-ceramic), conductive material (VGCF), butyl butyrate solution containing PVDF binder at a ratio of 5% by mass, and butyl butyrate were stirred for 30 seconds using an ultrasonic dispersion device (UH-50 manufactured by SMT). Next, the container was vibrated for 3 minutes using an oscillator (TTM-1 manufactured by Shibata Scientific Co., Ltd.), then stirred for 30 seconds using the ultrasonic dispersion device, and vibrated for 3 minutes using the oscillator to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a positive current collector (Al foil, manufactured by Showa Denko) using a scraper method with a coater, and dried on a hot plate at 100°C for 30 minutes. This yielded a positive electrode having a positive current collector and a positive electrode layer. It should be noted that the area of ​​the positive electrode is smaller than that of the negative electrode.

[0124] (Fabrication of the solid electrolyte layer)

[0125] A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a heptane solution containing BR-type binder at a ratio of 5% by mass, and heptane were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device (UH-50 manufactured by SMT). Next, the container was vibrated for 30 minutes using an oscillator (TTM-1 manufactured by Shibata Scientific Co., Ltd.) to obtain a slurry. The obtained slurry was applied to a release sheet (Al foil) using a doctor blade method with a spreader and dried on a hot plate at 100°C for 30 minutes. This yielded a transfer component having a release sheet and a solid electrolyte layer.

[0126] (Fabrication of all-solid-state batteries)

[0127] A bonding solid electrolyte layer is deposited on the positive electrode layer of the positive electrode, and the stack is pressed on a roller press at 100 kN / cm and 165°C. This yields the first laminate. Next, the negative electrode is placed on a roller press and pressed at 60 kN / cm and 25°C. This yields the pressed negative electrode. Then, a bonding solid electrolyte layer and a transfer member are sequentially deposited from the negative electrode layer side. The bonding solid electrolyte layer and the solid electrolyte layer of the transfer member are positioned opposite each other. The resulting laminate is placed on a planar uniaxial press and pre-pressed for 10 seconds at 100 MPa and 25°C. Then, a release sheet is peeled off from the solid electrolyte layer. This yields the second laminate. Next, the bonding solid electrolyte layer of the first laminate and the solid electrolyte layer of the second laminate are positioned opposite each other and pressed on a planar uniaxial press at 200 MPa and 120°C for 1 minute. This yields an all-solid-state battery.

[0128] [Example 2]

[0129] When preparing the negative electrode slurry, diisobutyl ketone was used instead of tetrahydronaphthalene, and the operation was otherwise the same as in Example 1 to obtain an all-solid-state battery.

[0130] [Example 3]

[0131] After drying at 120°C for at least 3 hours, the material was treated with an HF aqueous solution for 1 hour, filtered, and the filtered solid components were dried at 120°C for at least 3 hours. Otherwise, the process was the same as in Example 1 to obtain the electrode active material (negative electrode active material). Additionally, the sulfide solid electrolyte (Li2S-P2S5 glass-ceramic) was immersed in a tetrahydronaphthalene solution containing a binder (BR-type binder) at a 5% by mass ratio for 1 hour and then dried to obtain a sulfide solid electrolyte with a surface coating. When preparing the negative electrode slurry, the obtained electrode active material (negative electrode active material) and the obtained sulfide solid electrolyte were used, otherwise the process was the same as in Example 1 to obtain an all-solid-state battery.

[0132] [Comparative Example 1]

[0133] After drying at 120°C for more than 3 hours, the solid components were treated with an HF aqueous solution for 1 hour, filtered, and then dried at 120°C for more than 3 hours. Otherwise, the process was the same as in Example 1 to obtain the electrode active material (negative electrode active material). When preparing the negative electrode slurry, the obtained electrode active material (negative electrode active material) was used, and the amount of binder was changed to 1.14 times. Otherwise, the process was the same as in Example 1 to obtain an all-solid-state battery.

[0134] [evaluate]

[0135] (SEM observation)

[0136] The electrode active materials obtained in Examples 1 and 3 were observed using a scanning electron microscope (SEM). The results confirmed that the electrode active materials are porous, with voids within the primary particles.

[0137] (XRD measurement)

[0138] The electrode active materials obtained in Examples 1 and 3 were subjected to X-ray diffraction (XRD) measurements using CuKα rays. The results confirmed that the electrode active materials have a silicon inclusion compound type II crystal phase as the main phase.

[0139] (Overlap between Si and Os elements)

[0140] The negative electrode layers in the all-solid-state batteries obtained in Examples 1-3 and Comparative Example 1 were cross-sectionally processed using a vacuum electronic staining apparatus (VSC4TWDH). Specifically, staining was performed using 5 volume % OsO4 / naphthalene for 5 hours. After staining, SEM-EDX measurements were performed on the cross-section of the negative electrode layer to obtain mapping images of Si and Os, respectively. The measurement conditions were: EDX magnification set to 1000x, accelerating voltage set to 5kV, and measurement time set to 60 seconds. The mapping images focused on areas larger than 50μm × 50μm.

[0141] The obtained mapped image is digitized using OpenCV, and noise is removed using a Gaussian filter. Figure 2 This is a mapped image of Si. Noise is removed from this mapped image, and then a binarized image is obtained. Additionally, Figure 3 (a) is the mapped image of Os. After removing noise from this mapped image, a binarized image is obtained. It should be noted that... Figure 3 (b) is the binarized image of Os. Next, as... Figure 4 As shown, the binarized images of Si and Os are superimposed to obtain a composite image used to evaluate the overlap between Si and Os. It should be noted that... Figure 4 In the diagram, the areas where Si and Os overlap and are abundantly aggregated are shown in bright light.

[0142] Then, using the resulting composite image, the overlap D is calculated. Specifically, the correlation coefficient between Si and Os is calculated for each pixel (1280×960), and the overall correlation coefficient (overlap D) of the image is obtained. The correlation coefficient is calculated using well-known image processing software. For reference, such as Figure 5As shown in (a) to (c), Si is represented by a mesh pattern, and Os is represented by a dot pattern. Figure 5 As shown in (a), when Si and Os are completely identical, the correlation coefficient is 1. It should be noted that, as... Figure 5 As shown on the right side of (a), regions where neither Si nor Os exist are not counted. On the other hand, as... Figure 5 As shown in (b), when Si and Os are completely inconsistent, the correlation coefficient is -1. Additionally, as... Figure 5 As shown in (c), the correlation coefficient is 0 when Si and Os are consistent in half of the entire region and only Si or only Os are present in the remaining half.

[0143] (Oxygen content measurement)

[0144] For the electrode active materials prepared in Examples 1 and 3, the oxygen content was determined using an oxygen, nitrogen, and hydrogen (ONH) analyzer (EMGA-930, manufactured by Horiba Manufacturing Co., Ltd.). The results are shown in Table 1.

[0145] (Determination of the rate of increase in resistance)

[0146] Charge-discharge tests were conducted on the all-solid-state batteries obtained in Examples 1-3 and Comparative Example 1. Specifically, firstly, the batteries were charged at 0.1C to 4.55V using a CCCV method and then discharged at 1C to 3.0V. Next, after charging to 3.9V, they were charged at 0.1C to 3.7V and then discharged at 14.7mA for 5 seconds. The initial resistance was determined based on the voltage drop. Then, the charge-discharge cycle of charging at 1 / 3C to 4.35V and discharging at 1 / 3C to 3.0V was repeated 100 times. The resistance after charge-discharge was then determined in the same manner as above. The difference between the resistance after charge-discharge and the initial resistance was calculated as the resistance increase. The results are shown in Table 1. It should be noted that the resistance increase in Table 1 is a relative value with the result of Comparative Example 1 set to 100.

[0147]

[0148] As shown in Table 1, it was confirmed that compared with Comparative Example 1, Examples 1-3 had a larger overlap (D) between Si and Os elements, resulting in a smaller increase in resistance. In particular, Example 3 showed that the increase in resistance was approximately half that of Comparative Example 1. This is presumably because the abundant binder surrounding the electrode active material (Si) suppressed the path disruption associated with the volume change of the electrode active material caused by charging and discharging. Furthermore, it was suggested that the overlap (D) could be controlled by the surface polarity (oxygen content) of the electrode active material (Si), the polarity of the solvent (dispersion medium) used in the slurry, the polarity of the solid electrolyte, and the amount of binder.

[0149] In this invention, the oxygen content of the electrode active material can be around 9% by mass (7% to 11% by mass), and the δp of the solvent component can be 0.2 MPa, as in Example 1. 0.5 Nearby (0MPa) 0.5 ~1.0MPa 0.5 Especially 0MPa 0.5 ~0.5MPa 0.5 Furthermore, the δp of the solid electrolyte is 13.5 MPa. 0.5 Nearby (12.5MPa) 0.5 ~15.0MPa 0.5 () combination.

[0150] Furthermore, in this invention, the oxygen content of the electrode active material can be around 9% by mass (7% to 11% by mass), and the δp of the solvent component can be 5.4 MPa, as in Example 2. 0.5 Nearby (4.4MPa) 0.5 ~6.4MPa 0.5 Especially 4.9MPa 0.5 ~5.9MPa 0.5 Furthermore, the δp of the solid electrolyte is 13.5 MPa. 0.5 Nearby (12.5MPa) 0.5 ~15.0MPa 0.5 () combination.

[0151] Furthermore, in this invention, the oxygen content of the electrode active material can be around 5% by mass (3% to 7% by mass), and the δp of the solvent component can be 0.2 MPa, as in Example 3. 0.5 Nearby (0MPa) 0.5 ~1.0MPa 0.5 Especially 0MPa 0.5 ~0.5MPa 0.5 Furthermore, the δp of the solid electrolyte is 12.0 MPa. 0.5 Nearby (10.0 MPa) 0.5 ~14.0MPa 0.5 () combination.

[0152] Symbol Explanation

[0153] 1 … Positive electrode layer

[0154] 2 …negative electrode layer

[0155] 3 …electrolyte layer

[0156] 4 …Positive current collector

[0157] 5 … Negative current collector

[0158] 10 … batteries

Claims

1. An electrode layer, which is an electrode layer containing an electrode active material containing a Si element and a binder containing an unsaturated bond, wherein, when the binder is dyed by Os staining and the degree of overlapping of the Si element with the Os element, D, is calculated based on an elemental mapping image obtained by SEM-EDX measurement, the D is greater than 0.

047.

2. The electrode layer of claim 1, wherein, the D is 0.07 or greater.

3. The electrode layer of claim 1, wherein, the D is 0.50 or less.

4. The electrode layer according to claim 1, wherein, the oxygen content of the electrode active material is 1.0 mass% or greater and 10 mass% or less, the electrode layer contains a solvent component, The δp in the Hansen Solubility Parameters HSP of the solvent component is 6.0 MPa 0.5 The following.

5. The electrode layer according to claim 1, wherein, the oxygen content of the electrode active material is 1.0 mass% or greater and 10 mass% or less, the electrode layer contains a solid electrolyte, The δp in the Hansen solubility parameter HSP of the solid electrolyte is 10.0 MPa 0.5 Above and 15.0 MPa 0.5 Below.

6. The electrode layer of claim 5, wherein, the solid electrolyte is a sulfide solid electrolyte.

7. The electrode layer of claim 1, wherein, the electrode active material is porous.

8. The electrode layer of claim 1, wherein, the electrode active material has a crystal phase of a silicon clathrate type.

9. The electrode layer of claim 1, wherein, the electrode active material is a negative electrode active material.

10. A battery, which is a battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein, the positive electrode layer or the negative electrode layer is the electrode layer according to any one of claims 1 to 9.

11. The battery of claim 10, wherein, the electrolyte layer contains a solid electrolyte.

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