Current collector, electrode for power storage device, and secondary battery

Abstract

To provide a current collector having excellent resistance to non-aqueous electrolytes. [Solution] A current collector comprising a resin layer and a conductive layer, wherein a differential scanning calorimetry curve of the resin layer measured during a temperature rise process in a temperature range of 30°C to 300°C has at least one endothermic peak, and when the temperature range at which the peak intensity of the endothermic peak having the highest absolute value is 80% of the peak intensity among the at least one endothermic peak is T1 and the peak temperature is T2, the ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.9% or less.

Description

[Technical Field]

[0001] The present disclosure relates to a current collector, an electrode for an electricity storage device, and a secondary battery. [Background technology]

[0002] It has been proposed to use a composite material in which a conductive layer is formed on one or both sides of a resin film as a current collector for a secondary battery. Patent Document 1 discloses a current collector for a secondary battery in which such a composite material is used as the current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-102429 Summary of the Invention [Problem to be solved by the invention]

[0004] In an electricity storage device equipped with a non-aqueous electrolyte, such as a lithium ion secondary battery, decomposition products of the non-aqueous electrolyte can cause peeling of the conductive layer of the current collector. When the current collector of the above-described composite material is used in an electricity storage device equipped with a non-aqueous electrolyte, such as a lithium ion secondary battery, the current collector is preferably resistant to the non-aqueous electrolyte.

[0005] The present disclosure provides a current collector that has excellent resistance to non-aqueous electrolyte solutions, and also provides an electrode for a power storage device and a secondary battery that include such a current collector. [Means for solving the problem]

[0006] In order to solve the above problems, the present disclosure provides the following current collector, electrode for an electricity storage device, and secondary battery. [1] a resin layer; a conductive layer; Equipped with a differential scanning calorimetry curve of the resin layer measured during a temperature rise in a temperature range of 30°C to 300°C has at least one endothermic peak; A current collector in which, for the endothermic peak having the highest absolute value of peak intensity among the at least one endothermic peak, when a temperature range where the peak intensity is 80% is defined as T1 and the peak temperature is defined as T2, the ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.9% or less. [2] The current collector according to [1], wherein the ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.5% or less. [3] The current collector according to [1] or [2], wherein T2 is 70°C or higher and 280°C or lower. [4] The current collector according to any one of [1] to [3], wherein the resin layer contains at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, polyamide, polyethylene, polyvinyl chloride, and polystyrene. [5] The current collector according to any one of [1] to [4], wherein the conductive layer contains at least one selected from the group consisting of Al, Ag, Cu, and Ni. [6] A first intermediate layer is further provided between the resin layer and the conductive layer, The current collector according to any one of [1] to [5], wherein the first intermediate layer contains at least one element selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta and W. [7] The current collector according to [6], wherein the first intermediate layer has a thickness of 1 nm or more and 100 nm or less. [8] The current collector according to any one of [1] to [7], wherein the resin layer contains polypropylene. [9] A current collector according to any one of [1] to [8], an active material layer; An electrode for an electricity storage device comprising:

[10] a negative electrode; a positive electrode facing the negative electrode; a separator located between the negative electrode and the positive electrode; and [9] A secondary battery, wherein at least one of the negative electrode and the positive electrode is the electrode according to [9]. [Effects of the Invention]

[0007] The present disclosure provides a current collector that has excellent resistance to non-aqueous electrolyte solutions, and also provides an electrode for a power storage device and a secondary battery that include such a current collector. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a current collector according to the first embodiment. [Figure 2] FIG. 2 shows an example of a differential scanning calorimetry (DSC) curve of the resin layer. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of a current collector according to the second embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a current collector according to the third embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view showing an example of a current collector according to the fourth embodiment. [Figure 6] FIG. 6 is an exploded perspective view of an electrode for an electricity storage device according to one embodiment. [Figure 7] FIG. 7 is a schematic external view showing an example of a lithium ion secondary battery according to an embodiment. [Figure 8] FIG. 8 is an exploded perspective view showing a cell extracted from the lithium ion secondary battery shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the current collector, electrode for an electricity storage device, and secondary battery of the present disclosure will be described with reference to the drawings. The numerical values, shapes, materials, etc. presented in the following description are merely examples, and various modifications are possible as long as no technical contradictions occur. Furthermore, each embodiment described below is merely an example, and various combinations are possible as long as no technical contradictions occur.

[0010] The thickness, size, shape, and the like of components shown in the drawings of the present disclosure may be exaggerated for the convenience of explanation. Furthermore, in the drawings of the present disclosure, some components may be shown isolated or some elements may be omitted to avoid excessive complexity. Therefore, the dimensions of each component and the arrangement of each component shown in the drawings of the present disclosure may not reflect the dimensions of each component and the arrangement of each component in an actual device.

[0011] In this specification, the term "cell" refers to a structure in which at least one pair of positive and negative electrodes are integrally assembled. In this specification, the term "battery" is used to encompass various forms, such as a battery module and a battery pack, which have one or more "cells" electrically connected to each other.

[0012] [Current collector] (First embodiment) The current collector according to the first embodiment will now be described. FIG. 1 is a schematic cross-sectional view showing an example of the current collector according to this embodiment. The current collector according to this embodiment can be used as a current collector for either the positive or negative electrode of an electricity storage device such as a lithium ion secondary battery. The current collector 101 includes a resin layer 10 and a conductive layer 20. Each layer of the current collector 101 will now be described.

[0013] ((Resin layer)) The resin layer 10 functions as a support for the conductive layer 20 in the current collector 101. Furthermore, when an electricity storage device is constructed by having a density smaller than that of the conductive layer 20, the resin layer 10 can contribute to increasing the charge capacity per unit weight.

[0014] The resin layer 10 has electrical insulation properties and contains a resin. The resin layer 10 may have thermoplastic properties. Examples of resins include polyethylene terephthalate (PET), polypropylene (PP), polycarbonate, polyamide (PA), polyimide (PI), polyethylene (PE), polyvinyl chloride, polystyrene (PS), phenolic resin (PF), and epoxy resin (EP). One type of resin may be used alone, or two or more types may be used in combination. The resin layer 10 may be a single layer, or may be configured by laminating two or more layers. In this case, at least one of the multiple layers may contain a different resin.

[0015] The resin layer 10 preferably contains polypropylene, which tends to provide the current collector 101 with even better resistance to non-aqueous electrolytes. Examples of polypropylene include homopolypropylene, random polypropylene, block polypropylene, and acid-modified polypropylene obtained by graft-modifying polypropylene, which tends to provide the current collector 101 with even better resistance to non-aqueous electrolytes.

[0016] The resin content in the resin layer 10 may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, 99% by mass or more, or 100% by mass. The polypropylene content in the resin layer 10 may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, 99% by mass or more, or 100% by mass.

[0017] FIG. 2 shows an example of a differential scanning calorimetry (DSC) curve of the resin layer 10. The horizontal axis of the DSC curve represents the temperature of the resin layer 10 (unit: °C). The vertical axis of the DSC curve represents the heat flow per unit mass of the resin layer 10 (unit: μW / mg). A differential scanning calorimetry curve of the resin layer 10 measured during a temperature rise process in a temperature range from 30°C to 300°C has at least one endothermic peak. The temperature range where the peak intensity of the endothermic peak with the highest absolute value is 80% is defined as T1 (unit: °C). The peak temperature of the endothermic peak with the highest absolute value is defined as T2 (unit: °C). The ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.9% or less. The peak intensity of an endothermic peak is the value (height from the baseline) obtained by subtracting the heat flow value at the baseline from the heat flow value at the peak top of the endothermic peak. The baseline is created by connecting the value of heat flow per unit mass at a temperature obtained by multiplying T2 by 0.8 (T2 × 0.8) with the value of heat flow per unit mass at a temperature obtained by multiplying T2 by 1.2 (T2 × 1.2). The peak temperature of the endothermic peak is the temperature at the peak top. Differential scanning calorimetry may be performed in a nitrogen atmosphere. The heating rate for differential scanning calorimetry may be 1°C / min. If a conductive layer is formed on the surface of the resin layer, the conductive layer may be etched using a metal etchant such as nitric acid or sodium persulfate aqueous solution, leaving only the resin layer, and then differential scanning calorimetry may be performed.

[0018] The ratio of T1 to T2 (T1 / T2) in the resin layer 10 can be adjusted, for example, by heat-treating the resin layer 10. That is, for example, the resin layer 10 is formed by heat-treating a resin film containing the above-mentioned resin. Heat-treating the resin film promotes bonding between the resin molecules contained in the resin film. This reduces low-molecular-weight molecules in the resin contained in the resin film. The reduction in low-molecular-weight molecules reduces the ratio of T1 to T2 (T1 / T2). In other words, the resin layer 10 has a ratio of T1 to T2 (T1 / T2) greater than 0 and not greater than 0.9%, so it contains few low-molecular-weight molecules. When the current collector is used in a lithium-ion secondary battery, hydrofluoric acid is generated in a high-temperature environment. If the resin layer contains a large amount of low-molecular-weight molecules, the low-molecular-weight molecules are etched by hydrofluoric acid, causing peeling between the conductive layer and the resin layer. In the current collector 101, the resin layer 10 containing a small amount of low-molecular-weight molecules is used, thereby preventing the conductive layer 20 from peeling off from the resin layer 10 in a high-temperature environment.

[0019] The heat treatment of the resin film may be carried out before forming the conductive layer on the resin film, or may be carried out after forming other layers on the resin film.

[0020] The ratio of T1 to T2 (T1 / T2) may be 0.01% or more, 0.03% or more, or 0.05% or more. The ratio of T1 to T2 (T1 / T2) is 0.90% or less, preferably 0.70% or less, more preferably 0.50% or less, even more preferably 0.35% or less, still more preferably 0.20% or less, and particularly preferably 0.10% or less. When the ratio of T1 to T2 (T1 / T2) is 0.70% or less, the current collector 101 tends to have even better resistance to non-aqueous electrolyte solutions.

[0021] The heat treatment temperature for the resin film can be appropriately set depending on the type of resin contained in the resin film. When the melting point (°C) of the resin film is M1, the heat treatment temperature for the resin film is preferably equal to or greater than M1 minus 40°C (M1-40), more preferably equal to or greater than M1 minus 15°C (M1-15), and even more preferably equal to or greater than M1 minus 5°C (M1-5). When the heat treatment temperature for the resin film is equal to or greater than the above-mentioned lower limit, the current collector 101 tends to have even better resistance to non-aqueous electrolyte solutions. The heat treatment temperature for the resin film is preferably equal to or less than M1 plus 100°C (M1+100). When the heat treatment temperature for the resin film is equal to or less than the above-mentioned upper limit, thermal decomposition of the resin film can be suppressed. The melting point (°C) of the resin film may be measured using a differential scanning calorimeter.

[0022] The thickness of the resin layer 10 is, for example, 0.1 μm or more and 12 μm or less. The thickness of the resin layer 10 may be 3 μm or more and 6 μm or less. When the thickness of the resin layer 10 is 0.1 μm or more, sufficient strength as a support is obtained. Furthermore, when the thickness of the resin layer 10 is 12 μm or less, the overall thickness of the current collector 101 can be reduced. Therefore, when a stacked lithium ion secondary battery is constructed by stacking multiple electrode pairs, the proportion of parts that do not contribute to energy storage can be reduced, and the energy density can be increased. When the thickness of the resin layer 10 is 6 μm or less, the overall thickness of the current collector 101 can be further reduced, and the energy density of the stacked lithium ion secondary battery can be increased.

[0023] T1 may be 0.01° C. or more, 0.02° C. or more, 0.05° C. or more, or 0.08° C. or more. T1 may be 2.50° C. or less, 2.00° C. or less, 1.50° C. or less, 1.00° C. or less, 0.75° C. or less, 0.50° C. or less, or 0.25° C. or less.

[0024] From the viewpoint of being higher than the upper limit of the recommended use temperature of a lithium ion battery, T2 is preferably 70° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher. T2 is preferably 280° C. or lower, since this tends to maintain a good temperature distribution during heat treatment of the resin film.

[0025] ((Conductive layer)) The conductive layer 20 is a main current path in the current collector 101, and transfers electrons between the positive electrode active material or negative electrode active material and a terminal or the like connected to the current collector.

[0026] The thickness of the conductive layer 20 is, for example, 0.3 μm or more and 2 μm or less. When the thickness of the conductive layer 20 is 0.3 μm or more, the resistance of the conductive layer 20 tends to be reduced. For example, when an electricity storage device is produced, energy loss due to resistance in the current collector can be reduced. Furthermore, when the thickness of the conductive layer 20 is 2 μm or less, the ratio of the conductive layer 20 to the resin layer 10 becomes relatively small, and the weight of the current collector tends to be reduced by using the resin layer 10. The thickness of the conductive layer 20 may be 0.5 μm or more and 1.2 μm or less.

[0027] Examples of the main component of the conductive layer 20 include metals and metal oxides. The conductive layer 20 may contain, for example, one metal selected from the group consisting of Al, Ag, Cu, Ni, and Ni-Cu alloys. The conductive layer 20 may also contain, for example, a metal oxide of at least one element selected from the group consisting of Ni, Cr, Nb, Mo, Ta, and W. When the current collector 101 is used as a positive electrode, the conductive layer 20 may contain Al. When the current collector 101 is used as a negative electrode, the conductive layer 20 may contain one metal selected from the group consisting of Ag, Cu, Ni, and Ni-Cu alloys. The term "main component" refers to the component that is contained in the largest proportion, expressed in mole percent, when a member contains one or more components.

[0028] The conductive layer 20 may or may not include a seed layer. When the conductive layer 20 has a seed layer, the conductive layer 20 includes the seed layer and a main layer. The seed layer and the main layer each contain metal as a main component and may be made of the same metal. The seed layer is formed by, for example, a sputtering method or a vacuum deposition method, and the main layer is formed by a plating method. This is because, if the conductive layer 20 is relatively thick and the entire conductive layer 20 is formed by a sputtering method or a vacuum deposition method, the formation time becomes long, reducing productivity and preventing significant damage to the resin layer 10 during the formation of the conductive layer 20.

[0029] Second Embodiment The current collector according to the second embodiment will be described below. Points not described below are the same as those of the current collector according to the first embodiment unless inconsistencies arise. FIG. 3 is a schematic cross-sectional view showing an example of a current collector according to this embodiment. The current collector 102 includes a resin layer 10, a conductive layer 20, and a first intermediate layer 31 located between the resin layer 10 and the conductive layer 20. The current collector 102 differs from the current collector according to the first embodiment in that it includes the first intermediate layer 31.

[0030] ((First middle layer)) The first intermediate layer 31 may contain, for example, at least one element selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta, and W. The content of these elements may be 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol% based on the total amount of elements contained in the first intermediate layer 31.

[0031] When the conductive layer 20 is made of Cu, the first intermediate layer 31 can be made of, for example, Ni, Cr, a Ni-Cr alloy, Co, Mo, or W. When the conductive layer 20 is made of Al, the first intermediate layer 31 can be made of, for example, Ni or Cr. The first intermediate layer 31 can be formed using a known thin film formation technique used in the manufacture of semiconductor devices, such as a vacuum deposition method or a sputtering method.

[0032] The thickness D1 of the first intermediate layer 31 is, for example, 1 nm or more and 120 nm or less. If the thickness D1 of the first intermediate layer 31 is 1 nm or more, a continuous film can be formed, making it easier to control the orientation of the entire conductive layer 20 to be formed. If the thickness D1 of the first intermediate layer 31 is 120 nm or less, the time required to form the first intermediate layer 31 is not too long, and the influence of damage caused by the conditions during the formation of the first intermediate layer 31, such as heat or plasma, on the resin layer 10 is reduced, thereby suppressing deterioration of the resin layer 10. The thickness of the first intermediate layer 31 may be 1 nm or more and 100 nm or less, or 2 nm or more and 100 nm or less.

[0033] The current collector 102 may further include an undercoat layer located between the resin layer 10 and the first intermediate layer 31. The undercoat layer may be provided to increase the bonding strength between the resin layer 10 and the first intermediate layer 31, or to prevent pinholes from being formed in the first intermediate layer 31. For example, the undercoat layer may be a layer formed from an organic material such as an acrylic resin or a polyolefin resin, or a layer containing a metal formed by sputtering.

[0034] (Third embodiment) The current collector according to the third embodiment will be described below. Points not described below are the same as those for the current collector according to the second embodiment unless inconsistencies arise. FIG. 4 is a schematic cross-sectional view showing an example of a current collector according to this embodiment. A current collector 103 according to this embodiment includes a resin layer 10, a conductive layer 20, a first intermediate layer 31, and a second intermediate layer 32. The first intermediate layer 31 is located between the resin layer 10 and the conductive layer 20. The second intermediate layer 32 is located between the first intermediate layer 31 and the resin layer 10. The current collector 102 differs from the current collector 102 according to the second embodiment in that it further includes the second intermediate layer 32.

[0035] ((Second Middle Class)) The second intermediate layer 32 improves adhesion between the resin layer 10 and a layer formed on the resin layer 10. To this end, the second intermediate layer 32 contains a metal oxide. The content of the metal oxide may be 50 mol % or more, 60 mol % or more, 70 mol % or more, 80 mol % or more, 90 mol % or more, 95 mol % or more, 99 mol % or more, or 100 mol % based on the total amount of elements contained in the second intermediate layer 32.

[0036] The second intermediate layer 32 may be in contact with the resin layer 10. When the second intermediate layer 32 contains a metal oxide, the adhesion to the resin layer 10 is improved compared to when the conductive layer 20 or the first intermediate layer 31 is in contact with the resin layer 10.

[0037] The thickness D2 of the second intermediate layer 32 is, for example, 0.5 nm or more and 20 nm or less. When the thickness D2 of the second intermediate layer 32 is 0.5 nm or more, a continuous second intermediate layer 32 is formed, which makes it easier to achieve improved adhesion. When the thickness of the second intermediate layer 32 is 20 nm or less, the time required to form the second intermediate layer 32 can be shortened, and the influence of damage caused by the conditions during the formation of the second intermediate layer 32, such as heat or plasma, on the resin layer 10 can be reduced, thereby suppressing deterioration of the resin layer 10. The thickness of the second intermediate layer 32 may be 1 nm or more, or may be 2 nm or more. Alternatively, the thickness of the second intermediate layer 32 may be 10 nm or less.

[0038] The thickness D1 of the first intermediate layer 31 and the thickness D2 of the second intermediate layer 32 may satisfy the relationship D1 / D2≦10. By satisfying D1 / D2≦10, it is believed that a decrease in adhesion between the second intermediate layer 32 and the resin layer 10 due to a large stress being applied to the second intermediate layer 32 caused by the first intermediate layer 31 becoming too thick is suppressed. D1 / D2 may satisfy the relationship 2≦D1 / D2≦10.

[0039] The second intermediate layer 32 may contain an oxide of at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta, and W. These metal oxides are passive and do not easily oxidize. In other words, the second intermediate layer 32 itself is poorly soluble in the decomposition products of the electrolyte in the nonaqueous electrolyte. This prevents dissolution of the second intermediate layer 32 at the interface with the resin layer 10, thereby maintaining high adhesion for a long period of time. The second intermediate layer 32 can be formed, for example, by sputtering using a metal oxide as a target or by sputtering using a metal as a target in an oxygen-containing atmosphere.

[0040] The ratio of oxygen in the metal oxide contained in the second intermediate layer 32 may be 0.3 or more in molar ratio to the metal element 1. That is, the metal oxide may be represented by the following composition formula. MO x (x≧0.3) Here, M is at least one selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta and W.

[0041] When x is 0.3 or more, polarity is generated in the second intermediate layer 32, and intermolecular forces act more easily between the second intermediate layer 32 and the resin layer 10, thereby improving adhesion. x is not limited to an integer. The upper limit of x depends on the largest valence of the stable oxidation states that the metal can assume.

[0042] The second intermediate layer 32 may further contain a metal carbide. By containing a carbide of at least one metal selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta, and W, the adhesion to the resin layer 10 can be further improved.

[0043] Furthermore, the element constituting the metal oxide contained in the second intermediate layer 32 may be the same element as the metal contained in the first intermediate layer 31. In this case, for example, the second intermediate layer 32 and the first intermediate layer 31 can be formed successively by a sputtering method using targets of the same metal, and the adhesion between the second intermediate layer 32 and the first intermediate layer 31 can also be improved.

[0044] According to the current collector 103 of this embodiment, by providing the second intermediate layer 32 containing a metal oxide, the adhesion between the conductive layer and the resin layer can be improved compared to when the conductive layer and the resin layer are in direct contact. Furthermore, by including the first intermediate layer 31 containing a metal, the conductive layer 20 comes into contact with the first intermediate layer 31, which is mainly composed of a metal rather than a metal oxide, unlike when only the second intermediate layer 32 is provided. Therefore, the crystallinity of the conductive layer 20 can be improved when the conductive layer 20 is formed, and the corrosion resistance of the conductive layer 20 to electrolyte decomposition products in the non-aqueous electrolyte can be improved.

[0045] (Fourth embodiment) The current collector according to the fourth embodiment will be described below. Points not described below are the same as those for the current collector according to the third embodiment unless inconsistencies arise. FIG. 5 is a schematic cross-sectional view showing an example of a current collector according to this embodiment. The current collector 104 includes a resin layer 10 having a first surface 10a and a second surface 10b located on the opposite side of the first surface 10a. The first surface 10a of the resin layer 10 has a structure similar to that of the current collector 103 described above.

[0046] A structure similar to that of the current collector 103 is also formed on the second surface 10b of the resin layer 10. Specifically, the current collector 104 further includes a conductive layer 20', a first intermediate layer 31', and a second intermediate layer 32'. The first intermediate layer 31' is located between the resin layer 10 and the conductive layer 20'. The second intermediate layer 32' is located between the first intermediate layer 31' and the resin layer 10. The materials and thicknesses constituting the conductive layer 20', the first intermediate layer 31', and the second intermediate layer 32', as well as the functions of these layers, may be similar to those of the corresponding conductive layer 20, the first intermediate layer 31, and the second intermediate layer 32.

[0047] [Electrodes for energy storage devices] An electrode for an electricity storage device according to one embodiment will now be described. The electrode for an electricity storage device according to this embodiment can be used as either a positive electrode or a negative electrode of an electricity storage device. FIG. 6 is an exploded perspective view of the electrode for an electricity storage device according to this embodiment. As shown in FIG. 6, the electrode for an electricity storage device 201 includes a current collector 210 and an active material layer 220. The current collector 210 includes a first portion 210s and a second portion 210t, and the active material layer 220 is disposed in the first portion 210s. The second portion 210t is not provided with the active material layer 220 and functions as a tab for electrical connection to the outside. The active material layer 220 contains an active material that is oxidized and reduced in association with charging (or electricity storage) and discharging. The current collector 210 supports the active material layer 220, supplies electrons to the active material layer 220, and receives electrons from the active material layer 220.

[0048] Current collector 210 is current collectors 101, 102, 103, and 104. When current collector 104 is used, another active material layer not shown in FIG. 6 is disposed on first portion 210s on the back surface side of current collector 210 (the side on which active material layer 220 is not disposed).

[0049] The active material layer 220 includes a positive electrode active material or a negative electrode active material that absorbs and releases lithium ions. The positive electrode active material includes, for example, a composite metal oxide containing lithium. Examples of composite metal oxides containing lithium include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium manganese spinel (LiMn2O4), lithium vanadium compound (LiVO5), olivine-type LiMPO4 (where M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr, or vanadium oxide), lithium titanate (Li4Ti5O 12 ), general formula: LiNi x Co y Mn z M aComposite metal oxides represented by O2(x + y + z + a = 1, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 ≤ a < 1, where M in the above general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, and Cr), and the general formula: LiNi x Co y Al z O2(0.9 < x + y + z < 1.1), etc. can be mentioned. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc. as a material capable of occluding and releasing lithium ions.

[0050] The active material layer 220 may further contain at least one of a binder and a conductive aid. Various known materials can be used for the binder. As the binder in the active material layer 220 used for the positive electrode, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF) can be used.

[0051] As the binder, a vinylidene fluoride-based fluororubber may be used. For example, vinylidene fluoride - hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride - pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride - pentafluoropropylene - tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride - chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), etc. may be applied to the binder of the active material layer 220 used for the positive electrode.

[0052] Examples of the conductive aid are carbon materials such as carbon powder and carbon nanotubes. Carbon black etc. can be applied to the carbon powder. Other examples of the conductive aid of the active material layer 220 used for the positive electrode are metal powders such as nickel, stainless steel, and iron, and powders of conductive oxides such as ITO. Two or more of the above-described materials may be mixed and contained in the active material layer 220.

[0053] The negative electrode active material contains a carbon material. Examples of the carbon material include, for example, natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, graphitizable carbon (soft carbon), low-temperature fired carbon, etc. The negative electrode active material may contain materials other than the carbon material. The negative electrode active material may contain, for example, alkali metals and alkaline earth metals such as metallic lithium, metals such as tin or silicon, silicon-carbon composites, amorphous compounds mainly composed of oxides (SiO x (0 < x < 2), tin dioxide, etc.), and may contain particles such as lithium titanate (Li4Ti5O 12 ).

[0054] The binder and conductive additive for the negative electrode active material layer 220 may be the same as those described above. Alternatively, cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide, polyamide-imide, acrylic resin, etc. may be used as the binder for the negative electrode.

[0055] The positive and negative electrodes for an electricity storage device can be produced by a known production method.

[0056] The electrode for an electricity storage device of this embodiment includes a current collector that has excellent resistance to a non-aqueous electrolyte solution. Therefore, even when a lithium ion secondary battery including the electrode for an electricity storage device of this embodiment is used under conditions where the electrolyte is likely to decompose, such as at high temperatures, deterioration of the battery characteristics due to deterioration of the current collector is suppressed.

[0057] [Secondary battery] A lithium-ion secondary battery will be described below as an example of a secondary battery according to an embodiment. FIG. 7 is a schematic external view showing an example of a lithium-ion secondary battery according to this embodiment, and FIG. 8 is an exploded perspective view showing a cell removed from the lithium-ion secondary battery shown in FIG. 7. Here, a pouch-type or laminate-type lithium-ion secondary battery is exemplified as the lithium-ion secondary battery. The lithium-ion secondary battery shown in the figure is a single-layer type, but may also be a laminate type. In the example shown in the figure, the positive electrode, separator, and negative electrode constituting the cell are stacked along the Z direction in the figure.

[0058] The lithium ion secondary battery 301 includes a cell 310, a pair of leads 311 connected to the cell 310, an exterior body 313 that covers the cell 310, and an electrolyte 314. The cell 310 includes an electricity storage device electrode 201, an electricity storage device electrode 201', and a separator 320 disposed therebetween. In the example shown, the cell 310 is a single-layer cell that includes a pair of electrodes.

[0059] The electrode 201 for the electricity storage device and the electrode 201' for the electricity storage device are the electrodes 201 for the electricity storage device according to the above embodiment, one being configured as a positive electrode containing a positive electrode active material and the other being a negative electrode containing a negative electrode active material.

[0060] Separator 320 is an insulating porous material. Examples of separator 320 that can be used include a single-layer film or laminated film of polyolefin such as polyethylene or polypropylene, or a nonwoven fabric or porous film made of at least one type of fiber selected from the group consisting of cellulose, polyester, polyacrylonitrile, polyimide, polyamide (e.g., aromatic polyamide), polyethylene, and polypropylene.

[0061] An electrolyte 314 is further disposed in the space inside the exterior body 313. The electrolyte 314 is a non-aqueous electrolyte containing lithium ions, for example, a non-aqueous electrolyte solution containing lithium ions. When a non-aqueous electrolyte solution is used as the electrolyte 314, a sealant (for example, a resin film such as polypropylene, not shown in FIG. 7) is typically disposed between the exterior body 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte solution.

[0062] For example, a non-aqueous electrolyte solution containing a metal salt such as a lithium salt and an organic solvent can be used as the electrolyte 314. Examples of the lithium salt that can be used include LiPF6, LiClO4, LiBF4, LiCF3SO3, LiCF3CF2SO3, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(CF3CF2CO)2, and LiBOB. One of these lithium salts may be used alone, or two or more may be mixed.

[0063] For example, cyclic carbonates and chain carbonates can be used as the solvent for the electrolyte 314. Specifically, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, etc. can be used.

[0064] The lithium ion secondary battery 301 can be manufactured, for example, by the following method. First, the electrodes 201 and 201' are fabricated as described in the above embodiment. Then, the electrode 201 and the electrode 201' are held with the separator 320 interposed between them so that the active material layers face each other, and are inserted into the space in the exterior body 313. The electrolyte 314 is placed in the space in the exterior body 313, and the exterior body 313 is sealed, thereby completing the lithium ion secondary battery 301.

[0065] The secondary battery of this embodiment includes a current collector that has excellent resistance to non-aqueous electrolyte solutions, and therefore, even when the lithium ion secondary battery is used at high temperatures, deterioration of the battery characteristics due to deterioration of the current collector is suppressed. [Example]

[0066] The present disclosure will be described below based on examples, but the present disclosure is not limited to the following examples.

[0067] [Preparation of current collector] Example 1 A current collector including a resin layer and a conductive layer was fabricated. A polyethylene terephthalate resin film (thickness: 6 μm, melting point: 245°C, referred to as "PET" in Table 1) was prepared as the material for the resin layer. A Cu conductive layer (thickness: 1 μm) was formed by electrolytic plating. The resin film was subjected to a heat treatment under the conditions shown in Table 1. A current collector was fabricated in this manner.

[0068] The details of the heat treatment conditions shown in Table 1 are as follows, where M1 is the melting point (° C.) of the resin film: The melting point of the resin film is measured by a differential scanning calorimeter. High temperature condition: The heating temperature (℃) is equal to or greater than M1 minus 15 (℃) (M1-15) and less than M1 plus 100 (M1+100). Medium temperature conditions: The heating temperature (℃) is equal to or greater than M1 minus 40 (℃) (M1-40) and less than M1 minus 15 (℃) (M1-15). Low temperature conditions: Heating temperature (℃) is less than M1 minus 40 (℃) (M1-40)

[0069] Example 2 A current collector was produced in the same manner as in Example 1, except that the heat treatment conditions were changed as shown in Table 1.

[0070] Example 3 A current collector was produced in the same manner as in Example 1, except that a polypropylene resin film (thickness: 4.5 μm, melting point: 167° C., referred to as “PP” in Table 1) was used instead of the polyethylene terephthalate resin film.

[0071] Example 4 A current collector was produced in the same manner as in Example 3, except that the heat treatment conditions were changed as shown in Table 1.

[0072] Example 5 A current collector was fabricated having a resin layer, a first intermediate layer, and a conductive layer in this order. The same polypropylene resin film as in Example 3 was prepared as the material for the resin layer. The first intermediate layer was formed by sputtering using a CuNi target. The thickness of the first intermediate layer was 5 nm, and the thickness was adjusted by the deposition time and output. The resin film was subjected to a heat treatment. The heat treatment conditions were as shown in Table 1. This resulted in the fabrication of a current collector.

[0073] Example 6 A current collector was produced in the same manner as in Example 5, except that the heating temperature in the heat treatment was set to a temperature 10° C. higher than that in Example 5 under high temperature conditions.

[0074] Example 7 A current collector was produced in the same manner as in Example 5, except that the heating temperature in the heat treatment was set to a temperature 10° C. higher than that in Example 6 under high temperature conditions.

[0075] Example 8 A current collector was produced in the same manner as in Example 5, except that the heat treatment conditions were changed as shown in Table 1.

[0076] (Comparative Example 1) A current collector was produced in the same manner as in Example 1, except that the heat treatment was not carried out.

[0077] (Comparative Example 2) A current collector was produced in the same manner as in Example 3, except that the heat treatment was not carried out.

[0078] (Comparative Example 3) A current collector was produced in the same manner as in Example 3, except that the heat treatment conditions were changed as shown in Table 1.

[0079] Comparative Example 4 A current collector was produced in the same manner as in Comparative Example 3, except that the heating temperature in the heat treatment was set to a temperature 20° C. higher than that in Comparative Example 3 under low temperature conditions.

[0080] (Comparative Example 5) A current collector was produced in the same manner as in Comparative Example 4, except that the heating temperature in the heat treatment was set to a temperature 20° C. higher than that in Comparative Example 4 under low temperature conditions.

[0081] [Differential scanning calorimetry of resin layer] Differential scanning calorimetry (DSC) was performed on the resin layer of each current collector in each example and comparative example. Specifically, other layers were peeled off from the resin layer of the current collector to obtain a resin layer test piece. Differential scanning calorimetry (DSC) was performed in a nitrogen atmosphere from 30°C to 300°C at a heating rate of 1°C / min using a thermal analysis measuring device (Hitachi High-Tech Science Corporation, product name: DSC7000X). The obtained DSC curve was checked for the presence or absence of endothermic peaks during the heating process from 30°C to 300°C. The endothermic peak with the highest absolute value of peak intensity was determined as T2. The baseline was created by connecting the heat flow per unit mass at a temperature obtained by multiplying T2 by 0.8 (T2 × 0.8) with the heat flow per unit mass at a temperature obtained by multiplying T2 by 1.2 (T2 × 1.2). The peak intensity of the endothermic peak was calculated by subtracting the heat flow value at the baseline from the heat flow value at the peak top of the endothermic peak (height from the baseline). The temperature range (T1) and peak temperature (T2) at which the peak intensity was 80% were determined, and the ratio of T1 to T2 (T1 / T2) was calculated. The results are shown in Table 1.

[0082] [evaluation] (High temperature storage of current collectors) The current collectors of each example and comparative example were stored in an environment similar to that of a lithium-ion secondary battery, and their electrolyte resistance was evaluated. Specifically, an electrolyte solution of dimethyl carbonate containing LiPF6 at a concentration of 1 mol% was prepared. Furthermore, water was added to the electrolyte solution at a rate of 1000 mass ppm to prepare an electrolyte solution. The electrolyte solution was placed in a container, and the prepared current collector was immersed in the electrolyte solution in the container. The entire assembly was sealed with a laminate film and stored in a thermostatic chamber at 85°C for 72 hours. The current collector was then removed from the laminate film and washed with an organic solvent.

[0083] (Peeling after immersion) The obtained current collectors after high-temperature storage were visually inspected for peeling of the conductive layer from the resin layer and evaluated according to the following criteria. The results are shown in Table 2. ((standard)) A: The conductive layer is not peeled off. B: The edge of the conductive layer is peeled off C: The entire conductive layer is peeled off.

[0084] (Cotton swab wipe) The surface of the conductive layer of the obtained current collector after high-temperature storage was rubbed with a cotton swab. After rubbing, the cotton swab was checked for the presence or absence of the conductive layer, and evaluated according to the following criteria. The results are shown in Table 2. ((standard)) A: No conductive layer is attached to the cotton swab after rubbing. B: A conductive layer remains on the cotton swab after rubbing.

[0085] (peel test) ((Medium adhesive tape)) For the current collector obtained after high-temperature storage, adhesive tape with an adhesive strength of 4 N / 15 mm was applied to the surface of the conductive layer of the current collector and then peeled off. The proportion of the area of ​​the conductive layer adhered to the adhesive tape was determined based on the area of ​​the main surface of the conductive layer, and the evaluation was based on the following criteria. The results are shown in Table 2. The values ​​in parentheses in Table 2 are the proportion of the area of ​​the conductive layer adhered to the adhesive tape based on the area of ​​the main surface of the conductive layer. (((standard))) A: The area ratio of the conductive layer attached to the adhesive tape is 35% or less. B: The area ratio of the conductive layer attached to the adhesive tape is more than 35% and less than 80% C: The area ratio of the conductive layer attached to the adhesive tape is more than 80%

[0086] (peel test) ((High adhesion tape)) For the current collector obtained after high-temperature storage, adhesive tape with an adhesive strength of 6 N / 15 mm was applied to the surface of the conductive layer of the current collector and then peeled off. The proportion of the area of ​​the conductive layer adhered to the adhesive tape was determined based on the area of ​​the main surface of the conductive layer, and the evaluation was based on the following criteria. The results are shown in Table 2. The values ​​in parentheses in Table 2 are the proportion of the area of ​​the conductive layer adhered to the adhesive tape based on the area of ​​the main surface of the conductive layer. (((standard))) A: The area ratio of the conductive layer attached to the adhesive tape is 35% or less. B: The area ratio of the conductive layer attached to the adhesive tape is more than 35% and less than 80% C: The area ratio of the conductive layer attached to the adhesive tape is more than 80%

[0087] (comprehensive evaluation) The evaluation results of the peeling test, wiping with a cotton swab, and peeling after immersion were evaluated according to the following criteria, and the electrolyte resistance was evaluated comprehensively. The results are shown in Table 2. A: The peel test result for high adhesion tape is A. B: The peel test result for medium adhesion tape is A, but the peel test result for high adhesion tape is B or C. C: The evaluation result after wiping with a cotton swab is A, but the peel test result with medium adhesion tape is B or C, and the peel test result with high adhesion tape is C. D: The evaluation result of peeling after immersion is A, but the evaluation result after wiping with a cotton swab is B E: Evaluation result of peeling after immersion is B F: Evaluation result of peeling after immersion is C

[0088] [Table 1]

[0089] [Table 2] [Explanation of symbols]

[0090] 10...resin layer, 20, 20'...conductive layer, 31, 31'...first intermediate layer, 101, 102, 103, 104...current collector, 201, 201'...electrode for electricity storage device, 220...active material layer, 320...separator.

Claims

1. A resin layer; a conductive layer; Equipped with a differential scanning calorimetry curve of the resin layer measured during a temperature rise in a temperature range of 30°C to 300°C has at least one endothermic peak; a current collector in which, for an endothermic peak having the highest absolute value of peak intensity among the at least one endothermic peak, a temperature range where the peak intensity is 80% is defined as T1 and a peak temperature is defined as T2, and a ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.9% or less.

2. The current collector according to claim 1 , wherein the ratio of T1 to T2 (T1 / T2) is greater than 0 and 0.5% or less.

3. 2. The current collector according to claim 1, wherein T2 is 70°C or higher and 280°C or lower.

4. 2. The current collector according to claim 1, wherein the resin layer comprises at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polycarbonate, polyamide, polyethylene, polyvinyl chloride, and polystyrene.

5. The current collector according to claim 1 , wherein the conductive layer contains at least one selected from the group consisting of Al, Ag, Cu, and Ni.

6. a first intermediate layer is further provided between the resin layer and the conductive layer; 2. The current collector according to claim 1, wherein the first intermediate layer contains at least one element selected from the group consisting of Ni, Cr, Co, Ti, Zr, Nb, Mo, Hf, Ta, and W.

7. The current collector according to claim 6 , wherein the first intermediate layer has a thickness of 1 nm or more and 100 nm or less.

8. The current collector of claim 1 , wherein the resin layer comprises polypropylene.

9. The current collector according to any one of claims 1 to 8; an active material layer; An electrode for an electricity storage device comprising:

10. a negative electrode; a positive electrode facing the negative electrode; a separator located between the negative electrode and the positive electrode; and A secondary battery, wherein at least one of the negative electrode and the positive electrode is the electrode according to claim 9.

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