Electrode for power storage device and lithium-ion secondary battery

Abstract

An electrode for an electricity storage device includes a resin layer (11), a conductive layer (12) containing copper disposed on the resin layer (11), and an active material layer (20) containing graphite disposed on the conductive layer (12), wherein, in a case where measurement is performed by an X-ray diffraction method from a surface of the active material layer (20), a ratio A / B of a peak intensity of an intensity A of an X-ray diffraction peak at a highest order in a range of 48° or more and 53° or less of a diffraction angle to a peak intensity of an intensity B of an X-ray diffraction peak at a highest order in a range of 52° or more and 57° or less of the diffraction angle satisfies the following formula (1), 0.3 ≤ A / B ≤ 1 (1).

Description

Technical Field

[0001] This invention relates to electrodes for energy storage devices and lithium-ion secondary batteries. Background Technology

[0002] As a current collector for a secondary battery, a composite material in which conductive layers are formed on both sides of a resin film has been proposed. Patent Document 1 below discloses an electrode for a secondary battery in which such a composite material is applied as a current collector.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-75191 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] In energy storage devices such as lithium-ion secondary batteries, there is a demand for further improvements in rate performance. One embodiment of the present invention provides an electrode for an energy storage device capable of improving the rate performance of such devices.

[0008] Methods for solving technical problems

[0009] An electrode for a storage device according to one embodiment of the present invention includes a resin layer, a copper-containing conductive layer disposed on the resin layer, and a graphite-containing active material layer disposed on the conductive layer. When measured by X-ray diffraction from the surface of the active material layer, the ratio A / B of the intensity of the highest X-ray diffraction peak in the range of diffraction angle (2θ) of 48° or more and 53° or less and the intensity of the highest X-ray diffraction peak in the range of diffraction angle (2θ) of 52° or more and 57° or less satisfies the following formula (1).

[0010] 0.3≤A / B≤1 (1).

[0011] Invention Effects

[0012] According to an embodiment of the present invention, an electrode for a storage device is provided that can improve the rate capability of the storage device. Attached Figure Description

[0013] Figure 1 This is a schematic exploded perspective view showing an example of an electrode for a storage device according to this embodiment.

[0014] Figure 2 yes Figure 1 A schematic enlarged cross-sectional view of a portion of the electrodes used in the energy storage device shown.

[0015] Figure 3This is a schematic diagram illustrating measurements using X-ray diffraction.

[0016] Figure 4 This is a schematic diagram showing an example of an X-ray diffraction pattern of an electrode for an energy storage device according to this embodiment.

[0017] Figure 5 This is a partially cut-off perspective view showing an example of a lithium-ion secondary battery according to this embodiment.

[0018] Figure 6 yes Figure 5 The diagram shows an exploded three-dimensional view of a lithium-ion secondary battery.

[0019] Figure 7 This is an example illustrating the relationship between the A / B ratio and discharge rate characteristics of samples 1-8 and 11-17 in the experimental examples.

[0020] Figure 8 This is an example illustrating the relationship between C / B and discharge rate characteristics for samples 1-8 and 11-17 in the experimental examples.

[0021] Explanation of reference numerals in the attached figures

[0022] 10 collectors

[0023] 10t, Zone 2

[0024] 11 Resin Layer

[0025] 12 conductive layers

[0026] 20 Active Material Layer

[0027] 20s Part 1

[0028] 20t, 30t Part 2

[0029] 30 collectors

[0030] 40 Active Material Layer

[0031] 100 Electrodes for energy storage devices

[0032] 110 Negative electrode

[0033] 120 Positive Electrode

[0034] 170 diaphragm

[0035] 200 Lithium-ion Secondary Battery

[0036] 201 Single Cell

[0037] 250 lead wire

[0038] 260 lead wire

[0039] 290 Electrolytes

[0040] 300 outer packaging Detailed Implementation

[0041] The conductive layer of the current collector, which includes a resin film and a conductive layer, as proposed in Patent Document 1 differs from the metal foil used as a single current collector in the prior art in terms of thickness or manufacturing method. Furthermore, it is not reported which conductive layer is appropriate for improving the charge and discharge characteristics of the energy storage device. In view of this, considering the crystallinity of the conductive layer of the current collector having a resin film and a conductive layer, an electrode for an energy storage device and a lithium-ion secondary battery that can improve rate performance has been conceived.

[0042] Hereinafter, embodiments of the electrode for the energy storage device and the lithium-ion secondary battery according to this embodiment will be described with reference to the accompanying drawings. The numerical values, shapes, materials, steps, and order of steps mentioned in the following description are merely examples, and various modifications can be made as long as they do not create technical inconsistencies. Furthermore, the embodiments described below are also merely illustrative, and various combinations can be made as long as they do not create technical inconsistencies.

[0043] For ease of explanation, the dimensions and shapes of the components shown in the accompanying drawings of this invention are sometimes exaggerated. Furthermore, to avoid excessive complexity in the accompanying drawings of this invention, sometimes only a portion of the components is shown, or some elements are omitted. Therefore, the dimensions of the components and the arrangement of the components shown in the accompanying drawings of this invention may not reflect the dimensions of the components and the arrangement of the components in the actual device. In this disclosure, "perpendicular" and "orthogonal" are not limited to two lines, edges, surfaces, etc., that are strictly at a 90° angle, but also include cases within a range of ±5° from 90°. Additionally, "parallel" includes cases where two lines, edges, surfaces, etc., are within a range of ±5° from 0°.

[0044] In this specification, the term "single cell" refers to a structure integrally assembled with at least one pair of positive electrodes, a separator containing at least an electrolyte, and a negative electrode. The term "battery" in this specification is used to refer to various forms, including battery modules, battery packs, etc., that include one or more "single cells" electrically connected to each other.

[0045] (First Embodiment)

[0046] Figure 1 This is a schematic exploded view showing an example of an electrode for a storage device according to this embodiment. Figure 2 yes Figure 1 The diagram shows a cross-sectional view of a portion of the electrodes used in the energy storage device. For ease of explanation, the accompanying drawings include arrows indicating three mutually orthogonal directions: the X, Y, and Z directions.

[0047] The electrode 100 for the energy storage device includes a resin layer 11, a conductive layer 12, and an active material layer 20. The resin layer 11 and the conductive layer 12 constitute a current collector 10. The current collector 10 includes a first portion 10s and a second portion 10t, wherein the active material layer 20 is disposed in the first portion 10s. The second portion 10t does not have an active material layer 20 and functions as a tab for external electrical connection. The active material layer 20 contains an active material that is oxidized and reduced during charging (or energy storage) and discharging. The current collector 10 supports the active material layer 20, supplies electrons to the active material layer 20, and accepts electrons from the active material layer 20.

[0048] like Figure 2 As shown, the conductive layer 12 is disposed on the resin layer 11, and the active material layer 20 is disposed on the conductive layer 12.

[0049] The active material layer 20 contains graphite as a negative electrode active material for adsorbing and releasing lithium ions. For example, it may contain natural or artificial graphite, carbon nanotubes, difficult-to-graphitize carbon, easily-graphitize carbon (soft carbon), low-temperature calcined carbon, etc.

[0050] The active material layer 20 may further include adhesives, conductive additives, etc. Examples of substances used as adhesives include fluoropolymers such as styrene-butadiene copolymer (SBR), 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), as well as polyacrylate (PAA), polyamide-imide (PAI), and polyimide (PI). The active material layer 20 may contain one or more of the above-mentioned substances.

[0051] Examples of substances that can be used as conductive additives include carbon materials such as carbon powder and carbon nanotubes, metal powders such as nickel, stainless steel, and iron, and powders of conductive oxides such as ITO. The active material layer 20 may contain one or more of the above-mentioned substances.

[0052] In the current collector 10, the conductive layer 12 supplies electrons to the active material layer 20 and also accepts electrons from the active material layer 20. The resin layer 11 supports the conductive layer 12.

[0053] The conductive layer 12 comprises copper. Specifically, the conductive layer 12 comprises copper or an alloy of copper and a metal other than copper. The thickness of the conductive layer 12 is preferably, for example, 0.2 μm or more and 2.0 μm or less. When the thickness is less than 0.2 μm, the cross-sectional area of ​​the conductive layer 12 becomes too small, thereby increasing the resistance of the conductive layer 12. From the viewpoint of conductivity, the thickness of the conductive layer 12 is not limited. However, if the thickness of the conductive layer 12 is greater than 2.0 μm, the overall thickness of the current collector 10 becomes larger. Therefore, in the case of a stacked lithium-ion secondary battery consisting of multiple electrode pairs, the proportion of the portion that does not contribute to energy storage increases, and the energy density may decrease. The crystallographic properties of the conductive layer 12 are described below.

[0054] The conductive layer 12 may contain only copper or a copper alloy layer. In this case, the conductive layer 12 may contain one or more layers of copper or copper alloy. Alternatively, the conductive layer 12 may contain one or more layers of copper or copper alloy, and layers of metals other than copper or alloys of metals other than copper.

[0055] The resin layer 11 is insulating and contains resin. The resin layer 11 may also be thermoplastic. Specifically, the resin layer 11 may contain at least one of polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polyimide (PI), polyethylene (PE), polystyrene (PS), phenolic resin (PF), and epoxy resin (EP).

[0056] The thickness of the resin layer 11 is, for example, 3 μm or more and 12 μm or less, preferably 3 μm or more and 6 μm or less. When the thickness of the resin layer 11 is less than 3 μm, its strength as a support may be insufficient. In addition, when the thickness of the resin layer 11 is greater than 12 μm, the overall thickness of the current collector 10 increases. Therefore, in the case of a stacked lithium-ion secondary battery formed by stacking multiple electrode pairs, the proportion of the portion that does not contribute to energy storage increases, and the energy density may decrease.

[0057] The current collector 10 may also include a base layer located between the resin layer 11 and the conductive layer 12. The base layer may be provided to improve the bonding strength between the resin layer 11 and the conductive layer 12, or to suppress the formation of pinholes in the conductive layer. For example, the base layer may be a layer formed of organic materials such as acrylic resin or polyolefin resin, or a layer containing metal formed by sputtering.

[0058] Next, the structure of the conductive layer 12 will be described based on crystallographic properties. In existing lithium-ion secondary batteries, electrolytic copper foil or rolled copper foil is mainly used as the current collector for the negative electrode. In contrast, in the current collector with a conductive layer formed on a resin film as disclosed in Patent Document 1, the thickness of the conductive layer is usually smaller than the thickness of such copper foil, making it difficult to use electrolytic copper foil or rolled copper foil on the resin film. Therefore, thin film formation technology used in semiconductor manufacturing technology is used to form the conductive layer. However, various thin film formation technologies exist, and it is believed that the characteristics of the conductive layer obtained by the formation method may also be different. In addition, since the conductive layer is thin, it is believed that the characteristics of the conductive layer can vary depending on the formation of the active material layer and the thermal experience that the active material layer may be subjected to during formation. Therefore, the inventors of this application have conducted a detailed study on the relationship between the crystallinity of the conductive layer in the electrode for a storage device in the state of having an active material layer and the rate characteristics of a lithium-ion secondary battery made using the electrode for a storage device.

[0059] The crystallinity of the conductive layer was evaluated using X-ray diffraction (XRD). Figure 3 As shown, X-rays are incident from the surface of the active material layer 20, and the intensity of the scattered X-rays is measured. This measurement method is known as out-of-plane measurement and is a common method used for crystallinity evaluation.

[0060] Figure 4 This is a schematic example of the obtained X-ray diffraction pattern. The main X-ray diffraction peaks observed are shown in Table 1 below. In Table 1, the strongest X-ray diffraction peaks observed within each diffraction angle range in the left column are defined as the crystalline phases shown in the right column. Peak assignments are referenced in the literature, etc.

[0061] The crystallinity of the conductive layer 12 can be evaluated before manufacturing the lithium-ion secondary battery. Alternatively, the lithium-ion secondary battery can be manufactured, and after charging and discharging, the battery can be decomposed to evaluate the crystallinity of the conductive layer 12. When evaluating the crystallinity of the conductive layer 12 after manufacturing and charging / discharging the lithium-ion secondary battery, the various components of the electrodes for the energy storage device may be affected by the charging and discharging process. For example, through charging and discharging, lithium ions are inserted into or released into the active material layer, and the crystal structure of the graphite in the active material layer 20 may change. However, even in such cases, X-ray diffraction peaks for carbon and copper were observed within the range shown in Table 1, confirming that they correspond to the crystal orientation shown on the right or the peaks corresponding to the crystal orientation shown on the right.

[0062] [Table 1]

[0063] Range of peak position (2θ) Peak attribution (Miller index) 25° and above but below 30° C(002) 41° and above and 46° and below Cu(111) 48° and above and 53° and below Cu(200) 52° and above and 57° C(004) 72° and above and 77° Cu(220)

[0064] As shown in Table 1, the carbon peaks originate from the graphite in the active material layer 20, with C(002) and C(004) observed. Additionally, the copper peaks originate from the copper in the conductive layer 12, with Cu(111), Cu(200), and Cu(220) observed. Among the X-ray diffraction peaks attributed to copper, the peak intensity of Cu(111), located in the range of 41° to 46° (measured at 2θ), is greater than that of Cu(200) and Cu(220).

[0065] As described below, after fabricating an electrode 100 for a storage device containing a conductive layer 12 under various conditions, a lithium-ion secondary battery was fabricated, and its discharge rate characteristics were measured. The measured lithium-ion secondary battery was discharged to its discharge voltage and then disassembled to remove the electrode 100 for the storage device. The removed electrode 100 was cleaned with DMC (dimethyl carbonate), dried, and the crystallinity of the conductive layer 12 of the electrode 100 was measured by X-ray diffraction. As a result, as described above, a certain correlation was observed between the discharge rate characteristics and the intensity of the diffraction peaks, indicating that a lithium-ion secondary battery with high discharge rate characteristics can be obtained under the conditions described below.

[0066] Specifically, the ratio A / B of the highest X-ray diffraction peak, Cu(200), in the range of diffraction angle (2θ) of 48° or more and 53° or less, to the highest X-ray diffraction peak, C(004), in the range of diffraction angle (2θ) of 52° or more and 57° or less, satisfies the following equation (1).

[0067] 0.3≤A / B≤1 (1)

[0068] The ratio of peak intensity A / B is more preferably satisfied by the following equation (3).

[0069] 0.4≤A / B≤1 (3)

[0070] In addition, the ratio C / B of the highest X-ray diffraction peak intensity in the range of diffraction angle (2θ) of 72° and above to 77°, i.e., the peak intensity C of Cu (220), to the highest X-ray diffraction peak intensity B in the range of diffraction angle (2θ) of 52° and above to 57°, i.e., the peak intensity B of C (004), satisfies the following equation (2).

[0071] 0<C / B≤0.5 (2)

[0072] The ratio of peak intensity C / B is more preferably satisfied by the following equation (4).

[0073] 0.03≤C / B≤0.32 (4)

[0074] According to the non-patented journal *Journal of the Japan Society for Metals*, Vol. 67, No. 7 (2003), 342-347, "Thermal Stability and Internal Stress of Highly Oriented Cu Films" (hereinafter referred to as Document 1), it is explained that if a non-oriented Cu film is heat-treated, the peaks of Cu(111), Cu(200), and Cu(220) become stronger depending on the heat treatment temperature, and the resistivity of the Cu film decreases. Furthermore, in a highly oriented Cu(111) film, the peaks of Cu(200) and Cu(220) are not observed using conventional measurement methods, demonstrating that even after heat treatment, the peak intensity of Cu(111) does not change, and a certain low resistivity value is exhibited regardless of heat treatment.

[0075] In addition, according to the Journal of Materials Science, Vol. 56, No. 10 (2007) 907-912, “Microstructure Dependence of Mechanical Properties of Copper Thin Films” (hereinafter referred to as Document 2), which is a non-patent document, it is recorded that during the growth of copper film, the (111) crystal plane, which is the densest plane of copper crystals, tends to grow preferentially, but even if the plating conditions are the same, the crystal orientation is not always the same.

[0076] According to the inventors' detailed research, the peak of Cu(111) is strong, but the peak intensity is too large, making it difficult to obtain the correlation between the change in peak intensity and the discharge rate characteristics. In addition, as described in Reference 2 above, the peak intensity of Cu(111) is prone to deviation. On the other hand, it is known that the peak deviation of Cu(200) and Cu(220) is small, and a certain correlation with the discharge rate characteristics has been observed.

[0077] To suppress the deviation of peak intensity caused by measurement conditions, the intensity of C(004), which is a peak other than copper and has the same intensity as the peak intensity of Cu(200) and Cu(220), is divided by the peak intensity of Cu(200) and Cu(220). Thus, as an indicator that is difficult to depend on measurement conditions, the peak intensity of Cu(200) and Cu(220) can be used as an indicator of crystallinity, and the correlation with discharge rate characteristics can be found.

[0078] Regarding the peak of Cu(200), when A / B is less than 0.3, the low crystallinity of the conductive layer 12 leads to an increase in the resistance of the conductive layer 12, which in turn increases the internal resistance of the electrode 100 for the energy storage device, thereby reducing the discharge rate characteristic.

[0079] On the other hand, when A / B is greater than 1, the discharge rate characteristic also decreases. The reason for this is unclear at present. According to the aforementioned reference 1, as the peak intensity of Cu(200) increases, the resistance of the non-oriented copper film decreases and remains at a certain value. Therefore, if the peak intensity of Cu(200) increases, it is difficult to conclude that the resistance of the conductive layer 12, which has decreased at one point, has increased. The decrease in discharge rate characteristic is considered to be caused by factors other than the resistance of the conductive layer 12.

[0080] Regarding Cu(220), as long as a peak can be observed, i.e., if C / B is above 0, the discharge rate characteristic is relatively high. On the other hand, when C / B exceeds 0.5, the discharge rate characteristic sometimes decreases. The reason is the same as for the peak of Cu(200), which is unclear at the current moment.

[0081] As will be described later, regardless of the manufacturing method of the conductive layer 12, as long as the relationship of equations (1) to (4) is satisfied, the electrode 100 for the energy storage device of this embodiment can exhibit excellent discharge rate characteristics.

[0082] The electrode 100 for the energy storage device can be manufactured, for example, by the following method.

[0083] First, prepare a resin layer 11 of the above materials, and form a conductive layer 12 on the resin layer 11.

[0084] There are no particular limitations on the method for forming the conductive layer 12; it can be formed using various methods employed in semiconductor thin film technology. Specifically, it can be formed using vapor deposition methods such as vacuum evaporation and sputtering, or it can be formed using plating methods such as electrolytic plating and electroless plating. Furthermore, if the conductive layer 12 comprises two or more metal films, the two or more metal films can be formed using the same method, or they can be formed using different methods.

[0085] For example, the conductive layer 12 can be formed by electrolytically plating a copper film onto the seed layer after a nickel-chromium (NiCr) seed layer is formed on the surface of the resin layer 11 by sputtering. After the conductive layer 12 is formed, it can be heat-treated at a temperature of about 50°C to 250°C.

[0086] Then, an active material layer 20 is formed on the conductive layer 12. The above-mentioned graphite, conductive additive, and binder are prepared, and a solvent is added to prepare a slurry. Various solvents suitable for negative electrode mixtures in energy storage devices can be used as the solvent. The formed slurry is applied to the conductive layer 12 using a doctor blade, screen printing, or similar method.

[0087] The slurry is dried, pressure is applied to the resulting active material layer 20, and the density of the active material layer 20 is adjusted. This yields an electrode 100 for an energy storage device.

[0088] The electrode for the energy storage device of this embodiment contains graphite as an active material. Considering that graphite is a material suitable for the adsorption and release of lithium ions, the electrode for the energy storage device of this embodiment is suitable for use as the negative electrode of a lithium-ion secondary battery. That is, the electrode for the energy storage device of this embodiment can be combined with a positive electrode containing various positive electrode active materials to enable the lithium-ion secondary battery to actually store electricity. Furthermore, not limited to lithium-ion secondary batteries, the electrode for the energy storage device of this embodiment can also be used as the negative electrode of a sodium-ion secondary battery. Additionally, if an active material with an appropriate redox potential is selected, the electrode for the energy storage device of this embodiment can also be used as a positive electrode.

[0089] In this embodiment, the electrode for the energy storage device satisfies any of the relationships in equations (1) to (4). However, this does not mean that the electrode for the energy storage device that satisfies any of the relationships in equations (1) to (4) is the one of this embodiment, only confirmed by X-ray diffraction. For example, by manufacturing the electrode for the energy storage device of this embodiment multiple times under the same conditions, it is confirmed that any of the relationships in equations (1) to (4) are satisfied. If it is reasonably determined that any of the relationships in equations (1) to (4) are satisfied by manufacturing under the same conditions, the electrode for the energy storage device manufactured under the same conditions and not measured by X-ray diffraction is also the electrode for the energy storage device of this embodiment.

[0090] Furthermore, in the electrode for the energy storage device of this embodiment, the current collector 10 has a conductive layer 12 on only one side of the resin layer 11. However, the current collector 10 may also have conductive layers on two opposite sides of the resin layer 11. Additionally, in the electrode for the energy storage device of this embodiment, active material layers may be disposed on each of the two conductive layers.

[0091] (Second Implementation)

[0092] The implementation method of the lithium-ion secondary battery of this embodiment will be described.

[0093] Figure 5 This is a schematic appearance diagram showing an example of a lithium-ion secondary battery 200. Figure 6 Is it to remove Figure 5 The diagram shows an exploded perspective view of a single cell in a lithium-ion secondary battery. Here, a lithium-ion secondary battery, exemplified as either a pouch cell or a laminated cell, is shown. The illustrated lithium-ion secondary battery is a single-layer type, but it could also be a stacked type. In the illustrated example, the positive electrode, separator, and negative electrode constituting the single cell are stacked along the Z-direction of the diagram.

[0094] The lithium-ion secondary battery 200 includes: a single cell 201; a pair of leads 250 and 260 connected to the single cell 201; an outer package 300 covering the single cell 201; and an electrolyte 290.

[0095] The single cell 201 includes a negative electrode 110, a positive electrode 120, and a separator 170 disposed between the negative electrode 110 and the positive electrode 120. In the illustrated example, the single cell 201 is a monolayer single cell containing a pair of electrodes.

[0096] The negative electrode 110 can use the electrode 100 for the energy storage device described in the above embodiment. The negative electrode 110 is as shown in reference... Figure 1 and Figure 2 As explained, it includes a current collector 10 and an active material layer 20. That is, the negative electrode 110 satisfies the relationships of the above equations (1) to (4).

[0097] The positive electrode 120 includes a current collector 30 and an active material layer 40. The current collector 30, like the current collector 10 of the negative electrode, includes a resin layer and a conductive layer. The resin layer is, for example, made of the same material as resin layer 11. The conductive layer is, for example, an aluminum film containing aluminum or an alloy film containing aluminum.

[0098] The active material layer 40 contains an active material. Specifically, the active material layer 40 contains a lithium-containing composite metal oxide. Examples include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium manganese spinel (LiMn2O4), lithium vanadium compounds (LiV2O5), olivine-type LiMPO4 (where M is one or more elements or vanadium oxides selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), and lithium titanate (Li4Ti5O4). 12 General formula: LiNi x Co y Mn z MaO2 (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) represents a composite metal oxide, and the general formula: LiNi x Co y Al z O2 (0.9 < x + y + z < 1.1) represents composite metal oxides, etc.

[0099] The current collector 10 includes a second portion 10t without an active material layer 20 that functions as a tab, and a lead 250 is provided in the second portion 10t. Similarly, the current collector 30 includes a second portion 30t without an active material layer 40 that functions as a tab, and a lead 260 is provided in the second portion 30t. A portion of the lead 250 and a portion of the lead 260 are located outside the outer packaging 300.

[0100] An electrolyte 290 is also disposed in the space inside the outer packaging 300. The electrolyte 290 is, for example, a non-aqueous electrolyte. When a non-aqueous electrolyte is used for the electrolyte 290, typically, a sealing material (e.g., a resin film such as polypropylene) can be disposed between the outer packaging 300 and the lead 250, and between the outer packaging 300 and the lead 260, to prevent leakage of the electrolyte. Figure 5 (Not shown in the image).

[0101] The lithium-ion secondary battery 200 can be manufactured, for example, by the following method. First, the negative electrode 110 is manufactured as described in the above embodiment. The positive electrode 120 is also manufactured by the same method.

[0102] Then, the negative electrode 110 and the positive electrode 120 are held opposite each other with the active material layers separated by the separator 170, and inserted into the space of the outer packaging 300. By placing the electrolyte 290 in the space of the outer packaging 300 and sealing the outer packaging 300, the lithium-ion secondary battery 200 is completed.

[0103] According to the lithium-ion secondary battery 200, as described in the first embodiment, a high discharge rate characteristic can be achieved by satisfying any one of the relationships in equations (1) to (4) above through the negative electrode 110.

[0104] (Experimental Example)

[0105] 1. Sample preparation

[0106] The results of fabricating electrodes for energy storage devices and lithium-ion secondary batteries under various conditions, and measuring crystallinity and discharge rate characteristics, are explained.

[0107] [Fabrication of electrodes for energy storage devices of samples 1-8 and 11-17]

[0108] Samples 1-8 and 11-17 were fabricated as electrodes for the energy storage device described in the first embodiment. The thicknesses of the active material layer, the conductive layer, and the resin layer are shown in Tables 2 and 3. The method for manufacturing the conductive layer 12 of the electrodes for the energy storage device of samples 1-8 and 11-17 is described below.

[0109] [Manufacturing method of conductive layer 12]

[0110] A 0.05 μm Cu seed layer was formed in an argon atmosphere using a sputtering method on a resin layer of the thicknesses shown in Tables 2 and 3. Then, electroplating was performed under the following conditions to form a Cu plating layer. The Cu seed layer was integrated with the Cu plating layer through the Cu plating layer formation process, becoming a Cu conductive layer.

[0111] Sample 1: Plating current density: 1.5 A / dm 2 Plating time: 60 seconds.

[0112] Sample 2: Plating current density: 2.0 A / dm 2 Plating time: 45 seconds.

[0113] Sample 3: Plating current density: 2.5 A / dm 2 Plating time: 35 seconds.

[0114] Sample 4: Plating current density: 3.0 A / dm 2 Plating time: 30 seconds.

[0115] Sample 5: Plating current density: 3.5 A / dm 2 Plating time: 50 seconds.

[0116] Sample 6: Plating current density: 4.0 A / dm 2 Plating time: 35 seconds.

[0117] Sample 7: Plating current density: 4.5 A / dm 2 Plating time: 45 seconds.

[0118] Sample 8: Plating current density: 5.0 A / dm 2 Plating time: 40 seconds.

[0119] Sample 11: Plating current density: 2.0 A / dm 2 Plating time: 45 seconds.

[0120] Sample 12: Plating current density: 2.5 A / dm 2 Plating time: 35 seconds.

[0121] Sample 13: Plating current density: 3.0 A / dm 2 Plating time: 30 seconds.

[0122] Sample 14: Plating current density: 3.5 A / dm 2 Plating time: 50 seconds.

[0123] Sample 15: Plating current density: 4.0 A / dm 2 Plating time: 35 seconds.

[0124] Sample 16: Plating current density: 4.5 A / dm 2 Plating time: 20 seconds.

[0125] Sample 17: Plating current density: 5.0 A / dm 2 Plating time: 40 seconds.

[0126] [Table 2]

[0127]

[0128] [Table 3]

[0129]

[0130] [Fabrication of lithium-ion batteries for samples 1-8 and 11-17]

[0131] Lithium-ion secondary batteries were fabricated using the electrodes for energy storage devices from samples 1-8 and 11-17, as described in the second embodiment. Lithium cobalt oxide (LiCoO2) was used as the positive electrode active material.

[0132] 2. Measurement

[0133] [Measurement of rate capability]

[0134] For the lithium-ion secondary batteries of samples 1-8 and 11-17, a secondary battery charge-discharge test apparatus (manufactured by Hokuto Electric Co., Ltd.) was used. First, the batteries were charged at a constant current rate of 0.2C (the current value at which charging ends within 5 hours when constant current charging is performed at 25°C) until the battery voltage reached 4.2V. Then, the batteries were discharged at a constant current rate of 0.2C until the battery voltage reached 2.8V, and the initial discharge capacity C1 was determined.

[0135] Next, the battery was charged at a constant current rate of 0.2C (the current value at which charging ends within 5 hours when constant current charging is performed at 25°C) until the battery voltage reached 4.2V. Then, it was discharged at a constant current rate of 5C (the current value at which charging ends within 0.2 hours when constant current charging is performed at 25°C) until the battery voltage reached 2.8V. The 5C discharge capacity C5 was then calculated.

[0136] The 5C rate characteristic can be obtained from the initial discharge capacity C1 and the 5C discharge capacity C5 according to the following formula.

[0137] 5C rate characteristic [%) = C5 / C1 × 100

[0138] For samples 1–7, the 5C rate characteristic when the 5C rate characteristic of sample 8 is set to 100 is used as the capacity retention rate. For samples 11–16, the 5C rate characteristic when the 5C rate characteristic of sample 17 is set to 100 is used as the capacity retention rate. The results are shown in Tables 2 and 3.

[0139] [Measurement by X-ray diffraction]

[0140] The lithium-ion secondary batteries of samples 1-8 and 11-17, whose rate performance was measured, were discharged to their discharge voltage and then decomposed. The electrodes of samples 1-8 and 11-17, which served as negative electrodes, were then removed. After cleaning and drying the removed electrodes with DMC (dimethyl carbonate), the crystallinity of the conductive layer of the electrodes of samples 1-8 and 11-17 was measured by X-ray diffraction.

[0141] The apparatus and measurement conditions used in the measurement are described below.

[0142] Device Name: Rigaku UltimaIV

[0143] Accelerating voltage: 40kV

[0144] Current: 40mA

[0145] Scanning speed: 4 deg / min.

[0146] Sampling width: 0.02deg.

[0147] Based on the obtained X-ray diffraction patterns, for each sample, the peaks of C(004), Cu(200), and Cu(220) were determined, and the peak intensities A of Cu(200), B of C(004), and C of Cu(220) were calculated. The values ​​of A / B and C / B were then calculated. Tables 2 and 3 show the values ​​of peak intensities A, B, C, A / B, and C / B.

[0148] 3. Results and Investigation

[0149] For samples 1-8 and 11-17, the relationship between A / B and the capacity retention rate of the discharge rate characteristic is shown in the figure. Figure 7 Similarly, for samples 1–8 and 11–17, the relationship between C / B and the capacity retention rate of the discharge rate characteristics is shown in the figure. Figure 7 .exist Figure 7 and Figure 8 In the diagram, circles represent data for samples 1 to 8, and triangles represent data for samples 11 to 17.

[0150] The results from samples 1-8 and 11-17 show that when a conductive layer is formed by plating, the crystallinity of the conductive layer changes by varying the current density.

[0151] according to Figure 7 It can be seen that as the value of A / B increases from 0, the discharge rate characteristic improves; if A / B is around 1 or higher, the discharge rate characteristic decreases. Reference 1 et al. teach that as the peak intensity of Cu(200) increases, the resistance of the copper film decreases. Figure 7The results suggest that during the period when A / B is around 1, the crystallinity of the conductive layer increases, the resistance of the conductive layer decreases, thereby reducing the internal resistance of the lithium-ion secondary battery and improving the discharge rate characteristics.

[0152] On the other hand, if the value of A / B is greater than approximately 1, the discharge rate characteristic decreases. As explained in the implementation, the reason for this is not clear at the present moment.

[0153] Furthermore, the discharge rate characteristics of samples 1–7 were generally greater than those of samples 11–16. However, the tendency for variation in discharge rate characteristics relative to A / B was roughly the same. According to Figure 7 It is believed that if the A / B ratio is above 0.3 and below 1.0, a generally good discharge rate characteristic can be expected, and if the A / B ratio is above 0.4 and below 1.0, a better discharge rate characteristic can be expected.

[0154] In this experimental example, by using 2.0 A / dm 2 Above 4.5A / dm 2 The following current densities are achieved by plating to form a conductive layer, resulting in an A / B ratio of 0.3 or higher and 1.0 or lower, at a current density of 2.5 A / dm². 2 Above 4.0A / dm 2 The following current densities are achieved by plating to form a conductive layer, resulting in an A / B ratio of 0.4 or higher and 1.0 or lower.

[0155] Depend on Figure 8 It can be seen that for samples 1 to 8, as the C / B value increases from 0, the discharge rate characteristic improves; if the C / B is above approximately 0.5, the discharge rate characteristic decreases. It is believed that, similar to A / C, when C / B ranges from 0 to approximately 0.5, the crystallinity of the conductive layer increases, and the resistance of the conductive layer decreases, thereby reducing the internal resistance of the lithium-ion secondary battery and improving the discharge rate characteristic. Furthermore, if the C / B value is greater than approximately 0.5, the reason for the decrease in discharge rate characteristic is unclear at this time.

[0156] On the other hand, regarding samples 11-17, it can be seen that as the C / B value increases from 0, the discharge rate characteristic improves; if C / B becomes approximately 0.3 or higher, the discharge rate characteristic decreases. Regarding samples 11-17, if C / B becomes approximately 0.3 or higher, the discharge rate characteristic decreases, but the reason is not yet clear at this time.

[0157] according to Figure 8 It is believed that if the C / B ratio is above 0.0 and below 0.5, a generally good discharge rate characteristic can be expected, and if the C / B ratio is above 0.03 and below 0.32, a better discharge rate characteristic can be expected.

[0158] In this experimental example, by using 4.5 A / dm 2 The following current densities are used to form a conductive layer through plating, where the C / B ratio is 0.0 or higher and 0.5 or lower, at a current density of 2.5 A / dm². 2 Above 4.0A / dm 2 The following current densities are used to form a conductive layer through plating, with a C / B ratio of 0.03 or higher and 0.32 or lower.

[0159] In this embodiment, the crystallinity of the conductive layer is changed by varying the current density. However, as shown in Reference 1 above, it is believed that the crystallinity and resistance of the conductive layer can also be changed by heat treatment. That is, it is believed that the relationship between the values ​​of A / B and C / B and the discharge rate characteristics is not limited to the specific manufacturing method of the conductive layer.

[0160] Industrial availability

[0161] The electrodes for the energy storage device according to embodiments of the present invention are useful for power supplies of various electronic devices, electric motors, etc. The energy storage device according to embodiments of the present invention can be applied, for example, to power supplies for vehicles such as bicycles and passenger cars, power supplies for communication devices such as smartphones, power supplies for various sensors, and power supplies for unmanned aerial vehicles (UAVs).

Claims

1. An electrode for a storage device, characterized in that: include: Resin layer; A copper-containing conductive layer disposed on the resin layer; and An active material layer containing graphite disposed on the conductive layer. When measured by X-ray diffraction from the surface of the active material layer, let A be the intensity of the highest X-ray diffraction peak, Cu(200), in the range of diffraction angle 2θ being 48° or higher and 53° or lower, and let B be the intensity of the highest X-ray diffraction peak, C(004), in the range of diffraction angle 2θ being 52° or higher and 57° or lower. Then the ratio of the peak intensities of A to B, A / B, satisfies the following equation (1). 0.3≤A / B≤1 (1).

2. The electrode for a storage device as described in claim 1, characterized in that: When measured by X-ray diffraction from the surface of the active material layer, let the intensity of the highest X-ray diffraction peak, Cu(220), in the range of diffraction angle 2θ being 72° or higher and 77° or lower be C, and let the intensity of the highest X-ray diffraction peak, C(004), in the range of diffraction angle 2θ being 52° or higher and 57° or lower be B. Then the ratio of the peak intensities of C and B, C / B, satisfies the following equation (2). 0<C / B≤0.5 (2)。 3. The electrode for a storage device as described in claim 1 or 2, characterized in that: The conductive layer has a thickness of 0.2 μm or more and 2.0 μm or less.

4. The electrode for a storage device as described in claim 1, characterized in that: The ratio of peak intensity A / B satisfies the following equation (3): 0.4≤A / B≤1 (3).

5. The electrode for a storage device as described in claim 2, characterized in that: The ratio of peak intensity C / B satisfies the following equation (4): 0.03≤C / B≤0.32 (4)。 6. The electrode for a storage device as described in any one of claims 1 to 5, characterized in that: When measured by X-ray diffraction from the surface of the active material layer, it exhibits X-ray diffraction peaks with greater intensity than intensities A and C in the range of diffraction angles above 41° and below 46°.

7. The electrode for a storage device as described in any one of claims 1 to 6, characterized in that: The resin layer comprises at least one of polyethylene terephthalate, polypropylene, polyamide, polyimide, polyethylene, polystyrene, phenolic resin, and epoxy resin.

8. A lithium-ion secondary battery, characterized in that: include: The negative electrode comprises the electrode for an energy storage device as described in any one of claims 1 to 7; The positive electrode comprises a positive electrode active material layer and a positive electrode current collector; A diaphragm disposed between the negative electrode and the positive electrode; and Non-aqueous electrolyte, which contains lithium ions.

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