Current collector and battery

Abstract

The present invention provides a current collector containing the element Al and having a reduced battery resistance, and a battery containing this current collector. [Solution] A current collector comprising: a first layer containing the element Al; a second layer disposed on the first layer, having an oxidation-reduction potential of 2.3V or higher relative to Li, and containing a metallic element M excluding amphoteric elements; and a third layer disposed on the second layer and containing resin.

Description

[Technical Field]

[0001] This disclosure relates to current collectors and batteries. [Background technology]

[0002] The electrodes of a secondary battery, such as a lithium-ion secondary battery, generally include a metal-containing component called a current collector and an electrode layer containing an electrode active material placed on top of the current collector. In recent years, attempts have been made to replace copper, which is widely used as a material for the negative electrode current collector, with other metals in order to reduce the manufacturing cost of batteries and to make batteries lighter. For example, Patent Document 1 describes a lithium-ion secondary battery in which aluminum or an aluminum alloy is used as the material for the negative electrode current collector. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-85523 [Overview of the project] [Problems that the invention aims to solve]

[0004] Aluminum is widely used as a current collector in the positive electrode of secondary batteries. On the other hand, using an aluminum-containing current collector as a negative electrode current collector presents problems such as the formation of an alloy due to a reaction between the aluminum (Al) element in the current collector and lithium (Li) ions. In view of the above circumstances, this disclosure aims to provide a current collector containing Al element and having a reduced battery resistance, and a battery containing this current collector. [Means for solving the problem]

[0005] The means to solve the above problems include the following: <1> The first layer contains the element Al, The second layer is placed on top of the first layer, has a redox potential of 2.3V or higher relative to Li, and contains metal elements M excluding amphoteric elements. A current collector comprising a third layer containing resin, positioned on top of the second layer. <2> The aforementioned metal element M includes at least one selected from the group consisting of Ni, Cr, and Fe. <1> The current collector described above. <3> For use as a current collector in solid-state batteries, <1> ~ <3> A current collector as described in any one of the items. <4> The structure includes a first current collector, a first electrode layer, an intermediate layer, a second electrode layer, and a second current collector arranged in this order. The first current collector consists of a first layer containing Al element, The second layer is placed on top of the first layer, has a redox potential of 2.3V or higher relative to Li, and contains metal elements M excluding amphoteric elements. A third layer, which is placed on top of the second layer and contains resin, The third layer is in contact with the first electrode layer; this is a battery. <5> The aforementioned metal element M includes at least one selected from the group consisting of Ni, Cr, and Fe. <4> The battery listed. <6> The intermediate layer contains a solid electrolyte. <4> or <5> The battery listed. <7> The first electrode layer comprises an electrode active material, and the electrode active material comprises at least one element selected from the group consisting of Si and C. <4> ~ <6> A battery as described in any one of the items. [Effects of the Invention]

[0006] This disclosure provides a current collector containing the element Al and having a reduced battery resistance, and a battery containing this current collector. [Brief explanation of the drawing]

[0007] [Figure 1] This is an electron microscope image showing an example of the layer structure of a current collector. [Figure 2] This is a schematic cross-sectional view showing an example of the configuration of an electrode stack structure included in a battery. [Figure 3]It is a cross-sectional view schematically showing an example of the configuration of an electrode laminate structure included in a battery.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the present disclosure.

[0009] In the present disclosure, a numerical range represented using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the term "step" includes not only an independent step but also the step even when it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0010] <Current collector> One embodiment of the present disclosure is a first layer containing an Al element, a second layer disposed on the first layer and having a redox potential based on Li of 2.3 V or more and containing a metal element M excluding amphoteric elements, a third layer disposed on the second layer and containing a resin, and is a current collector including the same.

[0011] As shown in the embodiments described later, a battery using a current collector in which a second layer containing a metal element M is placed on a first layer containing an Al element, and a third layer containing a resin is placed on the second layer, exhibits suppressed reaction between the Al element and Li ions, and a lower battery resistance, compared to a battery using a current collector that does not satisfy the above conditions. The reason for this is presumed to be, for example, as follows. The current collector of this disclosure has a redox potential of 2.3V or higher with respect to Li, and a second layer containing a metallic element M (excluding amphoteric elements) is arranged on top of a first layer containing an Al element. The second layer suppresses the reaction between the Al element contained in the first layer and Li ions. Furthermore, the current collector of this disclosure has a third layer containing resin disposed on top of the second layer. The third layer, together with the second layer, suppresses the reaction between the Al element contained in the first layer and Li ions, and also enhances the adhesion of the current collector to the electrode layer containing the electrode active material. As a result, the increase in battery resistance caused by the peeling of the electrode layer from the current collector is suppressed. Furthermore, since the current collector of this disclosure is less likely to produce compounds (such as copper sulfide) through reaction with sulfur, it is also suitable for use as a current collector in batteries that use sulfides as electrolytes.

[0012] The current collector of this disclosure may be used as a positive electrode current collector or a negative electrode current collector, but the effect of suppressing the reaction between Al and Li ions is more pronounced when used as a negative electrode current collector. Furthermore, aluminum has a smaller mass per unit volume compared to copper. Therefore, using the current collector of this disclosure as the negative electrode current collector instead of a copper current collector contributes to reducing the weight of the battery. Furthermore, aluminum is less scarce than copper. Therefore, using the current collector of this disclosure as a negative electrode current collector instead of a copper current collector contributes to reducing and stabilizing the manufacturing cost of batteries.

[0013] (1st layer) The material of the first layer is not particularly limited as long as it contains the element Al, and can be selected considering the desired properties of the current collector, such as conductivity and strength. For example, the proportion of Al elements in the first layer may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, relative to the total amount of metallic elements. For example, the proportion of Al elements in the first layer may be 100% by mass, 90% by mass or less, or 80% by mass or less relative to the total amount of metallic elements.

[0014] The first layer may contain only the element Al as a metallic element, or it may contain Al and other metallic elements. In other words, the material of the first layer may be pure aluminum or an aluminum alloy. Other metallic elements besides Al include Mn, Mg, Cr, Si, Fe, Cu, Zn, and Ti.

[0015] The thickness of the first layer is not particularly limited and can be selected considering the type and scale of the battery obtained using the current collector. For example, the thickness of the first layer may be 5 μm or more, 10 μm or more, or 20 μm or more. For example, the thickness of the first layer may be 100 μm or less, 70 μm or less, or 50 μm or less.

[0016] (2nd layer) The material of the second layer is not particularly limited as long as it has a redox potential of 2.3V or higher relative to Li and contains metallic elements M other than amphoteric elements, and can be selected considering the desired properties of the current collector (conductivity, strength, etc.).

[0017] Specific examples of metal elements M included in the second layer include Ni (2.8V), Cr (2.3V), Fe (2.6V), and Co (2.8V). The values ​​in parentheses indicate the oxidation-reduction potential of the corresponding metal element relative to lithium. The metal element M is preferably Ni, Cr, or Fe, with Ni being more preferred. The second layer may contain only one or more metallic elements M.

[0018] The second layer may contain only metal element M as a metal element, or it may contain metal element M and metal elements other than metal element M (i.e., metal elements other than amphoteric elements whose oxidation-reduction potential relative to Li is less than 2.3V, or amphoteric elements). From the viewpoint of suppressing the reaction between the Al element in the first layer and the Li ions, the proportion of the metal element M in the second layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total amount of metal elements.

[0019] The thickness of the second layer is not particularly limited and can be selected considering the type and size of the battery obtained using the current collector. For example, the thickness of the second layer may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more. For example, the thickness of the second layer may be 10 μm or less, 5 μm or less, or 3 μm or less.

[0020] While increasing the thickness of the second layer tends to improve the effect of suppressing the reaction between Al and Li ions, it also increases the manufacturing cost of the battery. The current collector of this disclosure can effectively suppress the reaction between Al and Li ions without increasing the thickness of the second layer by placing a third layer on top of the second layer.

[0021] The method for placing the second layer on top of the first layer is not particularly limited. Methods for forming the second layer on top of the first layer include forming the second layer on top of the first layer by methods such as plating, vapor deposition, or coating, and attaching the metal foil for the second layer to the metal foil for the first layer. From the viewpoint of controlling the thickness of the second layer, ensuring adhesion of the second layer to the first layer, and productivity, the method for forming the second layer is preferably plating or vapor deposition, and more preferably plating.

[0022] If necessary, an uneven surface may be formed on the surface of the second layer. By forming an uneven surface on the surface of the second layer, for example, the adhesion force to the electrode layer of the current collector can be increased.

[0023] The second layer may completely or partially cover the surface of the first layer. From the viewpoint of effectively suppressing the reaction between the Al element contained in the first layer and the Li ions, it is preferable that the coverage rate of the surface of the first layer by the second layer is 50% or more, 70% or more, 80% or more, or 100%. The aforementioned coverage ratio is a percentage of the value obtained by dividing the area of ​​the second layer in the current collector by the area of ​​the first layer.

[0024] (3rd layer) The material of the third layer is not particularly limited as long as it contains resin, and can be selected considering the desired properties of the current collector (conductivity, strength, etc.).

[0025] From the viewpoint of suppressing an increase in battery resistance, it is preferable that the third layer exhibits conductivity. The material of the conductive third layer is not particularly limited and can be a combination of resin and a conductive substance, or a conductive resin. Examples of resins included in the third layer include polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, polyvinyl alcohol, polyvinylidene fluoride, polyethylene, polypropylene, ethylene vinyl acetate copolymer, polystyrene, polyurethane, polyamide, polyester, polytetrafluoroethylene, ABS resin, AS resin, acrylic resin, and conductive resins. Examples of conductive resins include polyaniline, polypyrrole, polythiophene, polyacetylene, poly(p-phenylene), polyphenylenevinylene, polyacrylonitrile, and polyoxadiazole. From the viewpoint of adhesion to the electrode layer of the current collector, the third layer preferably contains a thermoplastic resin, and more preferably contains a vinyl resin. In this disclosure, vinyl resin means a resin obtained by polymerizing monomers having vinyl groups.

[0026] Examples of conductive materials include carbon materials, metals, conductive oxides, and conductive nitrides. Specific examples of carbon materials include graphite, carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs). From the viewpoint of increasing the adhesion strength to the electrode layer of the current collector, it is preferable that the third layer contains a carbon material.

[0027] The thickness of the third layer is not particularly limited and can be selected considering the type and size of the battery obtained using the current collector. For example, the thickness of the third layer may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more. For example, the thickness of the third layer may be 10 μm or less, 5 μm or less, or 3 μm or less.

[0028] The total thickness of the current collector of this disclosure may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more. The total thickness of the current collector of this disclosure may be, for example, 120 μm or less, 80 μm or less, or 60 μm or less.

[0029] From the viewpoint of increasing the adhesion force of the current collector to the electrode layer, it is preferable that the third layer be deformable to conform to the shape of the electrode active material at the interface with the electrode layer. When the third layer is deformable to conform to the shape of the electrode active material, an anchoring effect is exerted by the electrode active material that has entered the third layer, and the peeling of the electrode layer from the current collector is more effectively suppressed.

[0030] (Layer structure of the current collector) The current collector of this disclosure may be arranged in a state where the second and third layers are arranged only on one side of the first layer (layer configuration: first layer / second layer / third layer), or it may be arranged on both sides of the first layer, respectively (layer configuration: third layer / second layer / first layer / second layer / third layer).

[0031] Figure 1 is an electron microscope image showing an example of the layer configuration of the current collector of this disclosure. As shown in Figure 1, the current collector consists of a laminated structure comprising an aluminum foil 1 as the first layer, a nickel-plated layer 2 as the second layer, and a resin layer 3 as the third layer. The resin layer 3 is adjacent to the negative electrode layer 4, which serves as the electrode layer. The interface between the resin layer 3 and the negative electrode layer 4 is deformed to conform to the shape of the silicon particles, which are the active material contained in the negative electrode layer 4.

[0032] The current collector of this disclosure may have one side functioning as a positive electrode current collector and the other side functioning as a negative electrode current collector. Such a current collector can be used, for example, as a current collector in a battery having a bipolar structure. When one side of the current collector of this disclosure functions as a positive electrode current collector and the other side functions as a negative electrode current collector, it is preferable that the second and third layers are arranged on at least the side that functions as the negative electrode current collector.

[0033] The current collector of this disclosure may have electrode layers on one or both sides. When electrode layers are arranged on both sides of the current collector, the electrodes arranged on both sides of the current collector may be either positive or negative electrodes, or one electrode layer on both sides of the current collector may be positive and the other negative. A configuration in which the electrode layers arranged on both sides of the current collector are either positive or negative electrodes is applied, for example, to a battery having a monopolar structure. A configuration in which one electrode layer on both sides of a current collector is the positive electrode and the other is the negative electrode is applied, for example, to a battery having a bipolar structure.

[0034] The electrode layers arranged on one or both sides of the current collector may be in contact with the surface on which the third layer of the current collector is located. The electrode layer in contact with the surface on which the third layer of the current collector is located may be either a positive electrode layer or a negative electrode layer. From the viewpoint of exhibiting the effect of the current collector of this disclosure, which is to suppress the reaction between the Al element contained in the first layer and Li ions, it is preferable that the electrode layer in contact with the surface on which the third layer of the current collector is located is a negative electrode layer.

[0035] The battery to which the current collector of this disclosure is applied may use a liquid electrolyte (electrolyte solution) as the electrolyte, a solid electrolyte as the electrolyte, or only a solid electrolyte as the electrolyte. In this disclosure, a battery that uses a solid electrolyte as at least part of its electrolyte may be referred to as a "solid-state battery," and a battery that uses only a solid electrolyte as its electrolyte may be referred to as an "all-solid-state battery."

[0036] <Battery> One embodiment of this disclosure is, The structure includes a first current collector, a first electrode layer, an intermediate layer, a second electrode layer, and a second current collector arranged in this order (hereinafter also referred to as an electrode stacked structure), The first current collector consists of a first layer containing Al element, The second layer is placed on top of the first layer, has a redox potential of 2.3V or higher relative to Li, and contains metal elements M excluding amphoteric elements. A third layer, which is placed on top of the second layer and contains resin, The third layer is in contact with the first electrode layer and is a battery.

[0037] In this disclosure, the first current collector and the second current collector may be referred to as "current collector" without distinction, and the first electrode layer and the second electrode layer may be referred to as "electrode layer" without distinction.

[0038] In the battery of this disclosure, when the first current collector is a negative electrode current collector, the second current collector is a positive electrode current collector, and when the first current collector is a positive electrode current collector, the second current collector is a negative electrode current collector. In the battery of this disclosure, when the first electrode layer is a negative electrode layer, the second electrode is a positive electrode layer, and when the first electrode layer is a positive electrode layer, the second electrode layer is a negative electrode layer.

[0039] In the battery of this disclosure, the first current collector may be used as either a negative electrode current collector or a positive electrode current collector, but the effect of suppressing the reaction between Al and Li ions is more pronounced when the first current collector is used as a negative electrode current collector.

[0040] In the battery of this disclosure, the first electrode layer may be either a negative electrode layer or a positive electrode layer, but the effect of suppressing the reaction between Al and Li ions is more pronounced when the first electrode layer is a negative electrode layer. In the battery of this disclosure, the type of electrode active material included in the first electrode layer is not particularly limited, but the effect of suppressing the reaction between Al and Li ions is more pronounced when the electrode active material included in the first electrode layer includes at least one selected from the group consisting of Si and C elements.

[0041] In the battery of the present disclosure, the details and preferred embodiments of the first current collector are the same as the details and preferred embodiments of the current collector of the present disclosure described above.

[0042] The number of current collectors that satisfy the conditions for the first current collector included in the battery of this disclosure is not particularly limited. From the viewpoint of effectively exhibiting the effect of suppressing the reaction between the Al element and lithium ions, it is preferable that 25% or more of the current collectors in the battery of this disclosure, based on the number, satisfy the conditions for a first current collector, more preferably 35% or more of the current collectors, based on the number, satisfy the conditions for a first current collector, and even more preferably 40% or more of the current collectors, based on the number, satisfy the conditions for a first current collector.

[0043] When the first current collector is a negative electrode current collector, it is preferable that 50% or more of the negative electrode current collectors included in the battery of this disclosure, based on the number, satisfy the conditions for the first current collector; it is more preferable that 70% or more of the negative electrode current collectors, based on the number, satisfy the conditions for the first current collector; and it is even more preferable that 80% or more of the negative electrode current collectors, based on the number, satisfy the conditions for the first current collector.

[0044] Figure 2 is a schematic cross-sectional view showing an example of the configuration of an electrode stacking structure included in the battery of this disclosure. The electrode stacking structure shown in Figure 2 has a structure in which the first current collector 113, the first electrode layer A, the intermediate layer B, the second electrode layer C, and the second current collector 115 are arranged in this order. The first current collector 115 includes a first layer a containing the element Al, a second layer b disposed on top of the first layer a and containing the element M, and a third layer c disposed on top of the second layer b and containing resin. The third layer c is in contact with the first electrode layer A.

[0045] (Current collector) The type of current collector constituting the electrode stacked structure is not particularly limited as long as at least the first current collector satisfies the above-mentioned conditions, and can be selected and used from known current collectors. Specifically, the material of the current collector may be a metal selected from Ag, Cu, Au, Al, Ni, Fe, and Ti, or an alloy containing these metals. The thickness of the current collector is not particularly limited and can be selected considering the type and size of the battery obtained using the current collector. The total thickness of the current collector may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more. The total thickness of the current collector may be, for example, 120 μm or less, 80 μm or less, or 60 μm or less.

[0046] (electrode layer) The type of electrode layer constituting the electrode stacked structure is not particularly limited and can be selected and used from known electrode layers. The electrode layer contains at least an electrode active material and may optionally contain a binder, conductive material, solid electrolyte, etc. If the intermediate layer contains a solid electrolyte, at least one of the first electrode layer and the second electrode layer, which are positioned on both sides of the intermediate layer, may also contain a solid electrolyte. In this disclosure, the electrode active material contained in the first electrode layer is also referred to as the first electrode active material, and the electrode active material contained in the second electrode layer is also referred to as the second electrode active material. When the first electrode layer is the negative electrode layer, the first electrode active material is the negative electrode active material, and when the first electrode layer is the positive electrode layer, the first electrode active material is the positive electrode active material. When the second electrode layer is the negative electrode layer, the second electrode active material is the negative electrode active material, and when the second electrode layer is the positive electrode layer, the second electrode active material is the positive electrode active material.

[0047] Examples of negative electrode active materials include carbon materials, active materials containing Si elements, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides, and transition metal nitrides. Examples of carbon materials include graphite materials, amorphous carbon materials, carbon black, and activated carbon. Examples of graphite materials include natural graphite and artificial graphite. Examples of amorphous carbon materials include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch carbon fiber (MCF). Graphite materials may be coated with metal or amorphous carbon. Active materials containing the Si element include elemental silicon, silicon alloys (for example, alloys of Si with one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co, and Al), porous silicon, silicon clathrate compounds, silicon oxides, and the like.

[0048] Specifically, examples of positive electrode active materials include composite oxides containing lithium and transition metals (hereinafter also referred to as composite oxides). Examples of composite oxides include composite oxides having a layered crystal structure, composite oxides having a spinel-type crystal structure, and composite oxides having an olivine-type crystal structure. Specific examples of composite oxides having a layered crystal structure include compounds represented as LiMO2 (where M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), and compounds to which heterogeneous elements are added. Representative examples of composite oxides having a layered crystal structure include LCO (lithium cobaltate), NCM (lithium nickel-cobalt-manganate), and NCA (lithium nickelate or lithium nickel-cobalt-aluminate). LiMn2O4 is a specific example of a composite oxide having a spinel-type crystal structure. A specific example of a composite oxide having an olivine-type crystal structure is LiMPO4 (where M is Fe, Co, Ni, or Mn).

[0049] The electrode active material contained in the electrode layer may be a single type or a combination of two or more types. The morphology of the electrode active material may be, for example, fibrous, spherical, or flake-like. The volume-average particle size of the electrode active material may be selected from, for example, a range of 5 μm to 50 μm. The volume-average particle size of the electrode active material is defined as the value (D50) at which the cumulative amount from the smaller diameter side in the volume-based particle size distribution obtained using the laser diffraction-scattering method becomes 50%.

[0050] Examples of binders include polyvinylidene fluoride (PVdF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethylcellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and polytetrafluoroethylene (PTFE).

[0051] Examples of conductive materials include carbon materials, metals, conductive oxides, and conductive nitrides. Specifically, carbon materials include graphite, carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs). TM Examples include: The conductive material may be of one type only, or two or more types may be used in combination.

[0052] Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes. From the viewpoint of battery performance, sulfide solid electrolytes and polymer solid electrolytes are preferred as solid electrolytes, and from the viewpoint of thermal stability, sulfide solid electrolytes are more preferred. Solid electrolytes may be used individually or in combination of two or more types.

[0053] Examples of sulfide solid electrolytes include compounds containing a metal element that acts as a conductive ion and sulfur (S). Examples of metallic elements include Li, Na, K, Mg, and Ca. Among these, Li is preferred as a metallic element. The sulfide solid electrolyte may contain Li and S, and at least one selected from the group consisting of P, Si, Ge, Al, and B. Among these, a sulfide solid electrolyte containing Li, S, and P (hereinafter also referred to as an LPS-type sulfide solid electrolyte) is preferred. From the viewpoint of ionic conductivity, sulfide solid electrolytes may contain halogen elements such as Cl, Br, and I. From the viewpoint of chemical stability, sulfide solid electrolytes may contain oxygen (O).

[0054] Specifically, LPS-type sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiBr-LiI-Li2S-P2S5, and Li2S-P2S5-Z. m S n (In the formulas, m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y Examples include (where x and y are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In)

[0055] In the above, the term "Li2S-P2S5" refers to a sulfide solid electrolyte obtained using Li2S and P2S5 as raw materials, and the same applies to other terms.

[0056] Among LPS-type sulfide solid electrolytes, sulfide solid electrolytes obtained using Li2S and P2S5 are preferred, and sulfide solid electrolytes satisfying the following formula are more preferred. Li 3+x+5y P 1-y S4(0 < x ≤ 0.6, 0 < y ≤ 0.2)

[0057] As the oxide solid electrolyte, compounds having a NASICON (Na3Zr2PSi2O 12 )-type crystal structure can be mentioned. Compounds having a NASICON-type crystal structure have high ionic conductivity and excellent stability in the atmosphere. As compounds having a NASICON-type crystal structure, lithium-containing phosphates can be mentioned. As phosphates, composite lithium phosphate salts with Ti (for example, Li 1+x Al x Ti 2-x (PO4)3), compounds in which all or part of Ti in the composite lithium phosphate salt is replaced with a tetravalent transition metal such as Ge, Sn, Hf, Zr, or a trivalent transition metal such as Al, Ga, In, Y, La, etc. can be mentioned. Specifically, as compounds having a NASICON-type crystal structure, Li-Al-Ge-P-O-based materials (Li 1+x Al x Ge 2-x (PO4)3), Li-Al-Zr-P-O-based materials (Li 1+x Al x Zr 2-x (PO4)3), Li-Al-Ti-P-O-based materials (Li 1+x Al x Ti 2-x (PO4)3), etc. can be mentioned.

[0058] Examples of polymeric solid electrolytes include mixtures (complexes) of polymer compounds and electrolyte salts. Specific examples of polymer compounds include polyether-based polymer compounds such as polyethylene oxide (PEO) and polypropylene oxide (PPO), polyamine-based polymer compounds such as polyethyleneimine (PEI), and polysulfide-based polymer compounds such as polyalkylene sulfide (PAS). Among these, polyether-based polymer compounds are preferred.

[0059] (Middle class) Examples of intermediate layers used in batteries according to this disclosure include separators used in batteries that use an electrolyte, and electrolyte layers used in all-solid-state batteries. In this disclosure, "electrolyte layer" means a layer containing a solid electrolyte. The thickness of the intermediate layer is not particularly limited and can be selected from a range of, for example, 1 μm to 30 μm.

[0060] If the intermediate layer is a separator, the type of separator is not particularly limited and can be selected and used from known separators. Specifically, examples of separators include porous sheets made from resins such as polyethylene, polypropylene, polymethylpentene, polyester, cellulose, and polyamide.

[0061] When the intermediate layer is an electrolyte layer, the type of solid electrolyte contained in the electrolyte layer is not particularly limited. For example, it may be selected and used from the solid electrolytes that may be contained in the electrode layer as described above. If the intermediate layer is an electrolyte layer, the first electrode layer and the second electrode layer may each contain a solid electrolyte. In this case, the types of solid electrolytes contained in each layer may be the same or different.

[0062] Figure 3 is a schematic cross-sectional view showing an example of an electrode stacking structure where the intermediate layer is an electrolyte layer. The electrode stacked structure shown in Figure 3 comprises a first current collector 113, a first electrode layer A, an electrolyte layer B, a second electrode layer C, and a second current collector 115. The first electrode layer A contains a first electrode active material 101, a conductive material 105, a binder 109, and a solid electrolyte 102. The second electrode layer C contains a second electrode active material 103, a conductive material 107, a binder 111, and a solid electrolyte 102. Electrolyte layer B contains a solid electrolyte. Electrolyte layer B may be a single layer or a multilayer structure of two or more layers.

[0063] If the battery of this disclosure includes a solid electrolyte, it may also include an electrolyte solution in an amount of less than 10% by mass relative to the total amount of electrolyte. If the battery of this disclosure includes a solid electrolyte, the solid electrolyte may be a composite solid electrolyte comprising an inorganic solid electrolyte and a polymer electrolyte.

[0064] If the battery of this disclosure includes an electrolyte solution as the electrolyte, the type of electrolyte solution is not particularly limited, and known electrolyte solutions can be used. Specific examples of electrolytes include liquids obtained by dissolving lithium salts such as LiPF6 and LiFSi in an organic solvent. Specific examples of organic solvents include cyclic or linear carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The solvent may be a mixture of two or more solvents, or a mixture containing both cyclic and linear carbonates. The solvent may contain additives such as vinylene carbonate (VC).

[0065] (Exterior) The battery of this disclosure may further include an outer casing. The outer casing at least houses the electrode laminate described above. Examples of outer casings include laminate-type outer casings and case-type outer casings. A laminate-type outer casing may be formed from a laminate (laminate film) having a metal layer containing a metal such as aluminum and a heat-seal layer containing a resin that melts upon heating.

[0066] (Restraining member) The battery of this disclosure may further include a restraining member. The restraining member applies restraining pressure in the thickness direction to the electrode stack described above. The restraining pressure applied in the thickness direction of the electrode stack may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. The restraining pressure applied in the thickness direction of the electrode stack may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0067] <Battery Uses> The applications of the battery disclosed herein are not particularly limited. Typical applications include power sources for vehicles, electronic equipment, and electric storage systems. Of these, the battery disclosed herein is preferably used as a power source for vehicles, and more preferably as a power source for hybrid vehicles, plug-in hybrid vehicles, or electric vehicles. Examples of vehicles include electric four-wheeled vehicles, electric two-wheeled vehicles, gasoline-powered vehicles, and diesel-powered vehicles. Examples of electric four-wheeled vehicles include battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs). Examples of electric two-wheeled vehicles include electric motorcycles and electric-assist bicycles. [Examples]

[0068] Embodiments of this disclosure will be described below with reference to examples. However, this disclosure is not limited to these examples. Details of the materials indicated by abbreviations are as follows. Sulfide solid electrolyte represented by the chemical formula SE:Li2S-P2S5 NCA:LiNi 0.8 Co 0.15 Al 0.05 Positive electrode active material represented by the composition formula of O2 NBR: Acrylonitrile Butadiene Rubber PVdF: Polyvinylidene fluoride VGCF: Vapor-phase grown carbon fiber SUS: Stainless steel

[0069] <Example 1> (Fabrication of the negative electrode current collector) As the material for the negative electrode current collector, aluminum foil with a nickel-plated layer formed on one side was prepared. A resin layer slurry was prepared by mixing vinyl resin (80 parts by mass) and carbon black (20 parts by mass) with a solvent (2-ethylhexanol). This resin layer slurry was coated onto the nickel-plated layer of the aluminum foil by the blade method and dried to form a resin layer on the nickel-plated layer, thereby obtaining the negative electrode current collector. The thicknesses of the aluminum foil, nickel plating layer, and resin layer observed in the cross-section of the negative electrode current collector were measured using a scanning electron microscope (SEM) and were found to be 15 μm, 0.7 μm, and 2 μm, respectively. The resistance of a sample formed using only the resin layer slurry was measured using the four-terminal resistance method. The result was 10 Ω·cm, confirming that the sample exhibited conductivity.

[0070] (Formation of the negative electrode layer) A negative electrode slurry was prepared by mixing silicon (49 parts by mass), SE (41.2 parts by mass), VGCF (7.5 parts by mass), and PVdF (6.6 parts by mass) as negative electrode active materials with a solvent (butyl butyrate). This negative electrode slurry was coated onto the resin layer of the negative electrode current collector and dried to form the negative electrode layer.

[0071] (Fabrication of negative electrode laminates) SE slurry was prepared by mixing SE (99.4 parts by mass) and NBR (0.6 parts by mass) with solvents (heptane and butyl butyrate). This SE slurry was coated onto SUS foil and dried to form an electrolyte layer (SE layer). A SUS foil with an SE layer formed on it was placed on a negative electrode layer formed on a negative electrode current collector, and a press treatment was performed under conditions of 50 kN / cm and 160°C. After that, the SUS foil was peeled off from the SE layer and the SE layer 1 was transferred to the negative electrode layer. Furthermore, a SUS foil with a separately fabricated SE layer formed on top of SE layer 1 was placed on top of SE layer 1, and a preliminary pressing treatment was performed under conditions of 100 MPa and 25°C. After that, the SUS foil was peeled off from the SE layer, and an additional SE layer 2 was transferred onto SE layer 1 to obtain a negative electrode laminate (layer structure: negative electrode current collector / negative electrode layer / SE layer 1 / SE layer 2).

[0072] (Fabrication of positive electrode stacks) A positive electrode slurry was prepared by mixing NCA (78.3 parts by mass), SE (18.8 parts by mass), VGCF (2.9 parts by mass), and PVdF (2.8 parts by mass) as positive electrode active materials with a solvent (butyl butyrate). This positive electrode slurry was coated onto aluminum foil and dried to form a positive electrode layer. A SUS foil with an SE layer formed on it, prepared in the same manner as that used for the negative electrode laminate, was placed on top of a positive electrode layer formed on an aluminum foil, and pressed under conditions of 50 kN / cm and 160°C. Subsequently, the SUS foil was peeled off the SE layer and the SE layer 3 was transferred onto the positive electrode layer.

[0073] (Fabrication of a battery stack for battery resistance measurement) 1.08cm 2 SE layer 2 with a negative electrode laminate molded to be circular, and 1.00 cm 2 A positive electrode laminate was placed on top of a negative electrode laminate so that it faced the SE layer 3 of the positive electrode laminate, which was molded to be circular. Next, a press treatment was carried out under conditions of 50 kN / cm and 160°C to obtain a battery laminate (layer configuration: negative electrode current collector / negative electrode layer / SE layer 1 / SE layer 2 / SE layer 3 / positive electrode layer / positive electrode current collector).

[0074] (Preparation of a half-cell for measuring current values) The battery stack and lithium foil used as the positive electrode current collector, prepared using the method described above, were molded into circular shapes with a diameter of 11.28 mm. SE (100 mg) was pressed at 100 MPa using a jig with a 10 mm diameter hole to produce SE pellets with a diameter of 10 mm. A half-cell was fabricated by arranging a negative electrode current collector, SE pellets, and a positive electrode current collector in that order in a cylindrical container with a diameter of 11.28 mm, and then restraining them with a restraining jig so that a pressure of 2 MPa was applied to them.

[0075] <Example 2> A negative electrode current collector was fabricated in the same manner as in Example 1, except that the thickness of the nickel plating layer formed on one side of the aluminum foil was changed from 0.7 μm to 1.6 μm. A battery stack was fabricated in the same manner as in Example 1, except that this negative electrode current collector was used.

[0076] <Comparative Example 1> A negative electrode current collector was fabricated in the same manner as in Example 1, except that aluminum foil without a nickel plating layer was used instead of aluminum foil with a nickel plating layer formed on one side. A battery stack was fabricated in the same manner as in Example 1, except that this negative electrode current collector was used.

[0077] <Comparative Example 2> A negative electrode current collector was fabricated in the same manner as in Example 1, except that a resin layer was not formed on the nickel plating layer formed on one side of the aluminum foil. A battery stack was fabricated in the same manner as in Example 1, except that this negative electrode current collector was used.

[0078] <Measuring battery resistance> The battery resistance was measured using the battery stacks prepared in the examples and comparative examples by the following method. The battery stack was sandwiched between two restraining plates, and the distance between the plates was fixed so that a pressure of 1 MPa was applied to the battery stack. The initial charge and discharge cycle was performed on the battery stack restrained by the restraining plates using the following procedure. (1) Perform constant current charging at 1 / 10C up to 4.05V. (2) Perform constant voltage charging at 4.05V with a cutoff current of 1 / 100C. (3) Perform constant current discharge up to 2.5V at 1 / 10C. (4) Perform constant voltage discharge at 2.5V until the termination current is 1 / 100C.

[0079] After the initial charge and discharge, the battery stack was subjected to constant current charging at 1 / 3C down to 4.05V, followed by constant voltage charging down to a cutoff current of 1 / 100C at 4.05V. Subsequently, constant current discharging was performed at 1 / 3C down to 3.29V, followed by constant voltage discharging down to a cutoff current of 1 / 100C at 3.29V to adjust the state of charge (SOC) of the battery stack. Constant current discharge was performed on a battery stack with adjusted State of Charge (SOC) under conditions of 6C and 5s, and the battery resistance was calculated from the voltage drop. Table 1 shows the battery resistance values ​​of Examples 1 and 2 and Comparative Example 2, with the battery resistance of Comparative Example 1 set to 100%.

[0080] <Measurement of current value> The current values ​​were measured using the half-cells prepared in the examples and comparative examples by the following method. A smaller measured current value indicates that the reaction between Al and Li ions is more suppressed. An electrochemical measuring device (VMP-300, Toyo Technica Co., Ltd.) was used to place a half-cell under a constant voltage condition of 0.15V, and the current flowing after 100 hours was measured. Table 1 shows the current values ​​of Examples 1 and 2 and Comparative Example 2, with the current value of Comparative Example 1 set to 100%.

[0081] [Table 1]

[0082] As shown in Table 1, the battery stacks of Examples 1 and 2, which used a negative electrode current collector with a nickel plating layer and a resin layer formed on aluminum foil, had lower battery resistance values ​​compared to the battery stack of Comparative Example 1, which used a negative electrode current collector with only a resin layer formed on aluminum foil. This result indicates that the formation of a nickel plating layer on aluminum foil suppresses the reaction between the Al element in the aluminum foil and Li ions. In Comparative Example 2, the battery laminate, which used a nickel-plated layer formed only on aluminum foil as the negative electrode current collector, exhibited delamination between the negative electrode layer and the nickel-plated layer, making it impossible to measure the battery resistance. This result indicates that forming a resin layer on top of the nickel-plated layer improves adhesion to the negative electrode layer. As shown in Table 1, the half-cells prepared in Examples 1 and 2 had lower current values ​​compared to the half-cells prepared in Comparative Examples 1 and 2. This result indicates that the reaction between the Al element in the aluminum foil and the Li ions was more suppressed in the half-cells prepared in Examples 1 and 2 compared to the half-cells prepared in Comparative Examples 1 and 2. [Explanation of Symbols]

[0083] 1. Aluminum foil 2 Nickel plating layer 3. Resin layer 4. Negative electrode layer A 1st electrode layer B. Intermediate layer or electrolyte layer C 2nd electrode layer a 1st layer b Second layer c 3rd layer 101 First electrode active material 102 Solid electrolyte 103 Second electrode active material 105, 107 Conductive materials 109, 111 Binders 113 First electrode current collector 115 Second electrode current collector

Claims

1. The first layer contains Al element, The second layer is placed on top of the first layer, has a redox potential of 2.3V or higher relative to Li, and contains metal elements M excluding amphoteric elements. A current collector comprising a third layer containing resin, positioned on top of the second layer.

2. The current collector according to claim 1, wherein the metal element M includes at least one selected from the group consisting of Ni, Cr, and Fe.

3. A current collector according to claim 1 or claim 2, for use as a current collector for a solid-state battery.

4. The structure includes a first current collector, a first electrode layer, an intermediate layer, a second electrode layer, and a second current collector arranged in this order. The first current collector consists of a first layer containing Al element, The second layer is placed on top of the first layer, has a redox potential of 2.3V or higher relative to Li, and contains metal elements M excluding amphoteric elements. A third layer, which is placed on top of the second layer and contains resin, The third layer is in contact with the first electrode layer; this is a battery.

5. The battery according to claim 4, wherein the metal element M includes at least one selected from the group consisting of Ni, Cr, and Fe.

6. The battery according to claim 4 or claim 5, wherein the intermediate layer includes a solid electrolyte.

7. The battery according to claim 4 or claim 5, wherein the first electrode layer comprises an electrode active material, and the electrode active material comprises at least one selected from the group consisting of Si and C elements.

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