Secondary battery

Abstract

This secondary battery is characterized in that: the secondary battery comprises an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) therebetween, a negative electrode current collector plate (17) electrically connected to the negative electrode (12), and an electrolyte solution; the negative electrode (12) includes a belt-like negative electrode core body and a negative electrode mixture layer disposed on the negative electrode core body; the electrode body (14) of the negative electrode core body includes, at one end in the winding axis direction thereof, a negative electrode core body exposed part (44) on which the negative electrode mixture layer is not disposed; the negative electrode core body exposed part (44) is joined to the negative electrode current collector plate (17); the positive electrode (11) includes a belt-like positive electrode core body and a positive electrode mixture layer disposed on the positive electrode core body; the positive electrode mixture layer includes a positive electrode active material and carbon nanotubes; and the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

Description

secondary battery

[0001] The present disclosure relates to secondary battery technology.

[0002] The secondary battery includes, for example, a wound electrode body in which a separator is disposed between a positive electrode having a positive electrode mixture layer disposed on a positive electrode core and a negative electrode having a negative electrode mixture layer disposed on a negative electrode core, and the positive electrode and negative electrode are wound together while being insulated by the separator.

[0003] Among secondary batteries equipped with a wound electrode assembly, there is known a battery that employs an end-face current collection structure from the viewpoint of improving battery output. The end-face current collection structure is, for example, a structure in which exposed portions of an electrode core disposed at both ends of the electrode assembly in the direction of the winding axis are joined to current collector plates.

[0004] However, when a secondary battery is fast-charged, for example, a large current flows through the negative electrode, generating heat through resistance. This heat accumulates in the positive electrode, which has a lower thermal conductivity than the negative electrode. In the case of a secondary battery that employs an end-face current collection structure, the electrolyte has a low heat dissipation function through thermal convection. If heat accumulates in the positive electrode, the electrolyte deteriorates due to the heat. This results in a problem of reduced fast-charge characteristics.

[0005] Conventionally, known techniques for improving the heat dissipation performance of batteries that employ an end-face current collection structure include, for example, a technique of providing a notch in the exposed portion of the electrode core that is joined to the current collector plate (e.g., Patent Document 1) and a technique of attaching heat dissipation tape to the uncoated portion on the innermost periphery of the positive electrode (e.g., Patent Document 2). However, both of these techniques are insufficient to improve the heat dissipation performance of the positive electrode, and therefore there is room for improvement in the rapid charging characteristics of the battery.

[0006] JP 2000-77054 A Features 2022-553025 A

[0007] Therefore, an object of the present disclosure is to provide a secondary battery with excellent rapid charging characteristics.

[0008] A secondary battery according to one aspect of the present disclosure includes an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a negative electrode current collector plate electrically connected to the negative electrode, and an electrolyte, wherein the negative electrode has a strip-shaped negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, and one end of the negative electrode core in the winding axis direction of the electrode body is provided with a negative electrode core exposed portion on which the negative electrode mixture layer is not arranged, and the negative electrode core exposed portion is joined to the negative electrode current collector plate, and the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, and the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, and the carbon nanotubes contain at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0009] Moreover, a secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a positive electrode current collector plate electrically connected to the positive electrode, and an electrolyte, wherein the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, and one end of the positive electrode core in the winding axis direction of the electrode body is provided with a positive electrode core exposed portion on which the positive electrode mixture layer is not arranged, and the positive electrode core exposed portion is joined to the positive electrode current collector plate, and the positive electrode mixture layer includes a positive electrode active material and carbon nanotubes, and the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0010] Furthermore, a secondary battery according to an aspect of the present disclosure includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a negative electrode current collector plate electrically connected to the negative electrode, a positive electrode current collector plate electrically connected to the positive electrode, and an electrolyte, wherein the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and a positive electrode core exposed portion on which the positive electrode mixture layer is not disposed is provided at one end of the positive electrode core in the winding axis direction of the electrode assembly, and the positive electrode core exposed portion is joined to the positive electrode current collector plate. The negative electrode has a band-shaped negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, and the other end of the negative electrode core in the winding axis direction of the electrode body is provided with a negative electrode core exposed portion where the negative electrode mixture layer is not arranged, and the negative electrode core exposed portion is joined to the negative electrode current collector plate, and the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, and the carbon nanotubes contain at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0011] According to one aspect of the present disclosure, a secondary battery with excellent rapid charging characteristics can be provided.

[0012] 1 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment;

[0013] The drawings referred to in the following description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual components.

[0014] Fig. 1 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. The secondary battery 10 shown in Fig. 1 includes a wound electrode assembly 14, an electrolyte (not shown), an outer can 15 that houses the electrode assembly 14, the electrolyte, etc., and a sealing body 16 that closes the opening of the outer can 15. For ease of explanation, the sealing body 16 side will be referred to as "top" and the bottom side of the outer can 15 will be referred to as "bottom."

[0015] The electrolyte solution has, for example, lithium ion conductivity. The electrolyte solution includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt includes, for example, LiPF ６ Lithium salts such as

[0016] Fig. 2 is a perspective view showing an example of the configuration of a wound-type electrode assembly. In Fig. 2, the ends of the members constituting the electrode assembly are shown in a developed state in order to explain the configuration of the wound-type electrode assembly. As shown in Figs. 1 and 2, the electrode assembly 14 is a wound-type electrode assembly having a positive electrode 11, a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12, and the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween.

[0017] As shown in FIG. 2 , the positive electrode 11 has a strip-shaped positive electrode core 30 and positive electrode mixture layers 32 disposed on both sides of the positive electrode core 30. Furthermore, the positive electrode mixture layer 32 is not disposed at the upper end of the positive electrode core 30 in the winding axis direction of the electrode body 14, and a positive electrode core exposed portion 34 where the positive electrode core 30 is exposed is provided. The positive electrode core exposed portion 34 is provided, for example, from one end to the other end in the longitudinal direction of the positive electrode core 30. Furthermore, the negative electrode 12 has a strip-shaped negative electrode core 40 and negative electrode mixture layers 42 disposed on both sides of the negative electrode core 40. Furthermore, the negative electrode core 40 has a lower end of the negative electrode core 40 in the winding axis direction of the electrode body 14 where the negative electrode mixture layer 42 is not disposed, and a negative electrode core exposed portion 44 where the negative electrode core 40 is exposed is provided. The negative electrode substrate exposed portion 44 is provided, for example, from one end to the other end in the longitudinal direction of the negative electrode substrate 40. That is, in the electrode body 14 shown in FIG. 2 , the upper end of the electrode body 14 in the winding axis direction is formed by the positive electrode substrate exposed portion 34, and the lower end of the electrode body 14 in the winding axis direction is formed by the negative electrode substrate exposed portion 44. The width of the positive electrode substrate exposed portion 34 (the length of the electrode body 14 in the winding axis direction) is, for example, 2 mm or more and 20 mm or less. Furthermore, the width of the negative electrode substrate exposed portion 44 (the length of the electrode body 14 in the winding axis direction) is, for example, 2 mm or more and 20 mm or less.

[0018] The positive electrode core 30 constituting the positive electrode 11 may be made of, for example, a metal foil such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 50 μm or less. The positive electrode mixture layer 32 contains a positive electrode active material and carbon nanotubes. The positive electrode mixture layer 32 may contain a conductive agent, a binder, or the like in addition to the carbon nanotubes.

[0019] Examples of the positive electrode active material include lithium-containing metal composite oxides. Examples of metal elements contained in the lithium-containing metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0020] The carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The inclusion of carbon nanotubes with high thermal conductivity in the positive electrode mixture layer 32 can improve the heat dissipation properties of the positive electrode mixture layer 32, and therefore the heat dissipation properties of the positive electrode 11. In terms of improving the heat dissipation properties of the positive electrode mixture layer 32, it is preferable that the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0021] Single-walled carbon nanotubes (SWCNTs) are carbon nanostructures in which a single layer of graphene sheets forms a cylindrical shape, while multi-walled carbon nanotubes (MWCNTs) are carbon nanostructures in which two or more layers of graphene sheets are concentrically stacked to form a cylindrical shape. A graphene sheet refers to a layer in which carbon atoms in sp2 hybrid orbitals that form graphite crystals are located at the vertices of a regular hexagon. The shape of the carbon nanotube is not limited. Examples of such shapes include needles, cylindrical tubes, fishbone shapes (fishbone or cup stacked shapes), playing cards (platelets), and coil shapes.

[0022] The fiber length of the single-walled carbon nanotubes and the multi-walled carbon nanotubes may be, for example, 500 nm or more and 200 μm or less, or 1 μm or more and 100 μm or less, respectively. The fiber length of the carbon nanotubes can be determined by measuring the lengths of 50 arbitrary carbon nanotubes using a field emission scanning electron microscope (FE-SEM) and taking the arithmetic average.

[0023] The outermost diameter (i.e., fiber diameter) of the single-walled carbon nanotube and the multi-walled carbon nanotube may be, for example, 0.5 nm or more and 20 nm or less, or 1 nm or more and 10 nm or less. The outermost diameter of the carbon nanotube can be determined by measuring the outer diameters of 50 arbitrary carbon nanotubes using a field emission scanning electron microscope (FE-SEM) or a transmission electron microscope (TEM) and taking the arithmetic average.

[0024] The multi-walled carbon nanotubes contained in the positive electrode mixture layer 32 have a BET specific surface area of ​​200 m ２The positive electrode mixture layer 32 preferably contains multi-walled carbon nanotubes having a BET specific surface area of ​​300 m / g or more. ２ / g or more. Carbon nanotubes that satisfy the above surface area have high thermal conductivity, so when carbon nanotubes that satisfy the above surface area are contained in the positive electrode mixture layer 32, the heat dissipation performance of the positive electrode mixture layer 32 can be further improved. The upper limit of the BET specific surface area of ​​the multi-walled carbon nanotubes is, for example, 500 m ２ The upper limit of the BET specific surface area of ​​the single-walled carbon nanotube is, for example, 600 m ２ The specific surface area of ​​the carbon nanotubes can be determined by the BET method, which is a general method for measuring specific surface area, using a specific surface area measuring device based on a gas adsorption method.

[0025] The content of the multi-walled carbon nanotubes contained in the positive electrode mixture layer 32 is, for example, preferably 0.01 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.1 parts by mass or less, relative to 100 parts by mass of the positive electrode active material, in order to further improve the heat dissipation property of the positive electrode mixture layer 32. Furthermore, the content of the single-walled carbon nanotubes contained in the positive electrode mixture layer 32 is, for example, preferably 0.0001 parts by mass or more and 0.02 parts by mass or less, and more preferably 0.001 parts by mass or more and 0.01 parts by mass or less, relative to 100 parts by mass of the positive electrode active material, in order to further improve the heat dissipation property of the positive electrode mixture layer 32.

[0026] It is preferable that single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are substantially free of metal catalysts within the tubes. Carbon nanotubes are generally synthesized using metal catalysts, but if metal catalysts remain within the carbon nanotubes, the metal catalysts may cause deterioration of the positive electrode 11 and reduce the characteristics of the secondary battery. Therefore, it is preferable to remove the metal catalysts from the carbon nanotubes, for example, by washing them with an acidic aqueous solution. Here, "substantially free of metal catalysts" means that the metal catalysts are contained only at the lower limit of detection by ICP-AES.

[0027] In addition to carbon nanotubes, the positive electrode mixture layer 32 may contain a particulate conductive agent. Examples of the particulate conductive agent include carbon black such as acetylene black and ketjen black, and carbon materials such as graphite. The content of the particulate conductive agent may be, for example, in the range of 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of the positive electrode active material.

[0028] Examples of the binder include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyethylene oxide (PEO), etc. The content of the binder may be, for example, in the range of 0.1 mass % to 5 mass % with respect to the total mass of the positive electrode mixture layer 32.

[0029] The positive electrode 11 can be fabricated by applying a positive electrode mixture slurry containing a positive electrode active material, carbon nanotubes, and the like to a positive electrode core 30, drying the coating, and then rolling the coating to form a positive electrode mixture layer 32 on the positive electrode core 30. To improve the dispersibility of the carbon nanotubes, it is preferable to add at least one of a hydrogenated nitrile butadiene copolymer (HNBR) and a cellulose derivative to the positive electrode mixture slurry. In other words, by including a hydrogenated nitrile butadiene copolymer and a cellulose derivative in the positive electrode mixture layer 32, the carbon nanotubes in the positive electrode mixture layer 32 remain highly dispersed, thereby further improving the heat dissipation properties of the positive electrode mixture layer 32. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30 or on both sides. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core 30.

[0030] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. Examples of the negative electrode core 40 include a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, and a film with such a metal disposed on the surface layer. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 50 μm or less. The negative electrode mixture layer 42 includes, for example, a negative electrode active material, a binder, and the like. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the like onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side or both sides of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0031] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Examples of carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. In addition to carbon materials, examples of negative electrode active materials include metals that alloy with lithium, such as Si and Sn, alloys containing such metals, and compounds containing such metals. Examples of binders include the same materials as those used in the positive electrode 11. The negative electrode mixture layer 42 may also contain a conductive agent.

[0032] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0033] The secondary battery 10 shown in FIG. 1 has a negative electrode current collector 17 arranged below the electrode body 14. The negative electrode current collector 17 is a metal plate made of, for example, nickel or a nickel alloy. A negative electrode core exposed portion 44 at the lower end of the electrode body 14 is joined to the negative electrode current collector 17 by welding or the like. The negative electrode current collector 17 is also joined to the inner surface of the bottom plate of the outer can 15 by welding or the like. In other words, the negative electrode core exposed portion 44 is electrically connected to the outer can 15 via the negative electrode current collector 17, and the outer can 15 serves as the negative electrode terminal.

[0034] The outer can 15 is, for example, a cylindrical metal container with a bottom. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure airtightness inside the battery. The outer can 15 has, for example, a grooved portion 21 that protrudes inward from a portion of its side surface and supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its upper surface.

[0035] The sealing body 16 shown in FIG. 1 has a structure in which, in order from the electrode body 14 side, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each component constituting the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. If the internal pressure of the secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 23 may deform and rupture, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure further increases, the upper valve body 25 may rupture, and gas may be discharged through the through-hole 26a of the cap 26.

[0036] The secondary battery 10 shown in FIG. 1 also includes a positive electrode current collector 18 disposed above the electrode assembly 14, a circular insulating plate 19 disposed on the positive electrode current collector 18, and a connection lead 20. The positive electrode current collector 18 is a metal plate made of, for example, aluminum or an aluminum alloy. The connection lead 20 is a metal member made of, for example, aluminum or an aluminum alloy. A positive electrode core exposed portion 34 at the upper end of the electrode assembly 14 is joined to the positive electrode current collector 18 by welding or the like. The lower end of the connection lead 20 is joined to the upper surface of the positive electrode current collector 18 by welding or the like. The connection lead 20 extends toward the sealing body 16 through a through-hole in the insulating plate 19, and the upper end of the connection lead 20 is joined to the lower surface of the filter 22 of the sealing body 16 by welding or the like. The positive electrode core exposed portion 34 is electrically connected to the filter 22 via the positive electrode current collector 18 and the connection lead 20. In other words, the cap 26 electrically connected to the filter 22 serves as the positive electrode terminal.

[0037] 1 employs an end surface current collecting structure in which exposed portions of the cores located at the ends of the electrode body 14 in the winding axis direction are joined to current collecting plates in both the positive electrode 11 and the negative electrode 12, and current is collected directly from the cores. However, in the secondary battery of this embodiment, one of the positive electrode and the negative electrode may have an end surface current collecting structure, and the other electrode may have a structure in which, instead of the end surface current collecting structure, an electrode lead is connected to the other electrode and current is collected via the electrode lead, for example.

[0038] As mentioned above, heat generated in an electrode during rapid charging and discharging is likely to accumulate in the positive electrode, which has lower thermal conductivity than the negative electrode. One reason for this is thought to be the use of oxides with low thermal conductivity as the positive electrode active material contained in the positive electrode mixture layer. Furthermore, in secondary batteries employing an end-face current collection structure in at least one of the positive and negative electrodes, the heat dissipation function through thermal convection in the electrolyte is poor, so if heat accumulates in the positive electrode, the electrolyte deteriorates due to the heat. However, in this embodiment, carbon nanotubes are added to the positive electrode mixture layer to enhance the heat dissipation ability of the positive electrode mixture layer, making it less likely for heat to accumulate in the positive electrode. Therefore, in this embodiment, in a secondary battery employing an end-face current collection structure, electrolyte deterioration is suppressed even during rapid charging, resulting in a battery with excellent rapid charging characteristics.

[0039] In particular, in the case of a secondary battery in which the plate lengths (lengths of the electrodes in the longitudinal direction) of the positive and negative electrodes are each 3000 mm or more, heat is likely to be trapped in the positive electrode during rapid charging, resulting in a significant deterioration in rapid charging characteristics. However, by adding carbon nanotubes to the positive electrode mixture layer as in this embodiment, the rapid charging characteristics are improved even in the case of a secondary battery in which the plate lengths of the positive and negative electrodes are each 3000 mm or more.

[0040] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0041] Example 1 [Preparation of Positive Electrode] 100 parts by mass of a positive electrode active material and 0.4 parts by mass of multi-walled carbon nanotubes (MWCNT, BET specific surface area 400 m ２ 1 / g) and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. ０．８８ Co ０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (1) was used. Next, the positive electrode mixture slurry was applied to both sides of the aluminum foil so as to form the above-mentioned exposed portion of the positive electrode core. This coating was dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. The electrode plate length (longitudinal length) of the positive electrode was 3000 mm.

[0042] [Preparation of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of silicon oxide (SiO), 1 part by mass of sodium carboxymethyl cellulose (CMC-Na), and 1 part by mass of styrene butadiene rubber (SBR) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the copper foil so as to form the aforementioned negative electrode core exposed portion. This coating was dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. The electrode plate length (longitudinal length) of the negative electrode was 3,300 mm.

[0043] [Preparation of Electrolyte Solution] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ An electrolyte solution was prepared by dissolving 1.5 mol / liter of ammonium hydroxide in water.

[0044] [Test Cell Preparation] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. A positive electrode current collector and a negative electrode current collector were placed on the top and bottom of the electrode assembly, respectively. The exposed positive electrode substrate at the top end and the exposed negative electrode substrate at the bottom end of the electrode assembly were bent inward and then welded to the positive electrode current collector and the negative electrode current collector. The electrode assembly was then placed in a bottomed cylindrical outer can, and the negative electrode current collector was welded to the bottom of the bottomed cylindrical outer can. The positive electrode current collector and the seal were connected with a connecting tab. After pouring a nonaqueous electrolyte into the outer can, the opening of the outer can was sealed with a seal via a gasket to prepare a cylindrical test cell.

[0045] Example 2 A test cell was produced in the same manner as in Example 1, except that in the production of the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.2 parts by mass of single-walled carbon nanotubes (SWCNT).

[0046] Example 3 A test cell was prepared in the same manner as in Example 1, except that in preparing the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.2 parts by mass of multi-walled carbon nanotubes and 0.01 parts by mass of single-walled carbon nanotubes.

[0047] Example 4 A test cell was prepared in the same manner as in Example 1, except that in preparing the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.01 parts by mass of multi-walled carbon nanotubes and 0.001 parts by mass of single-walled carbon nanotubes.

[0048] Example 5 A test cell was prepared in the same manner as in Example 1, except that in preparing the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.5 parts by mass of multi-walled carbon nanotubes and 0.02 parts by mass of single-walled carbon nanotubes.

[0049] Example 6 A test cell was produced in the same manner as in Example 1, except that in the production of the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.2 parts by mass of multi-walled carbon nanotubes and 0.01 parts by mass of single-walled carbon nanotubes, and 1% of hydrogenated nitrile butadiene copolymer (HNBR) was added to the positive electrode mixture slurry.

[0050] Example 7 A test cell was prepared in the same manner as in Example 1, except that in the preparation of the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 0.2 parts by mass of multi-walled carbon nanotubes and 0.01 parts by mass of single-walled carbon nanotubes, the electrode plate length of the positive electrode was set to 800 mm, and the electrode plate length of the negative electrode was set to 880 mm.

[0051] Comparative Example 1 A test cell was prepared in the same manner as in Example 1, except that in preparing the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 1 part by mass of carbon black (CB).

[0052] Comparative Example 2 A test cell was fabricated in the same manner as in Example 1, except that 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 1 part by mass of carbon black in the fabrication of the positive electrode, and the positive and negative electrodes were changed from an end-face current collection structure to a tab structure. The tab structure was as follows: A positive electrode substrate exposed portion was formed in the longitudinal center of the positive electrode, and a positive electrode tab was joined to the positive electrode substrate exposed portion. Furthermore, a negative electrode substrate exposed portion was formed at one longitudinal end of the negative electrode, and a negative electrode tab was joined to the negative electrode substrate exposed portion. The wound electrode including these positive and negative electrodes was housed in a bottomed cylindrical outer can, the negative electrode tab was welded to the bottom of the bottomed cylindrical outer can, and the positive electrode tab was joined to a seal. After a nonaqueous electrolyte was poured into the outer can, the opening of the outer can was sealed with a seal via a gasket, to fabricate a cylindrical test cell.

[0053] Comparative Example 3 A test cell was prepared in the same manner as in Comparative Example 2, except that in preparing the positive electrode, 1 part by mass of carbon black was replaced with 0.4 parts by mass of multi-walled carbon nanotubes.

[0054] Comparative Example 4 A test cell was prepared in the same manner as in Comparative Example 2, except that in preparing the positive electrode, 1 part by mass of carbon black was replaced with 0.02 parts by mass of single-walled carbon nanotubes.

[0055] Comparative Example 5 A test cell was prepared in the same manner as in Comparative Example 2, except that in preparing the positive electrode, 1 part by mass of carbon black was replaced with 0.2 parts by mass of multi-walled carbon nanotubes and 0.01 parts by mass of single-walled carbon nanotubes.

[0056] Comparative Example 6 A test cell was prepared in the same manner as in Example 1, except that in the preparation of the positive electrode, 0.4 parts by mass of multi-walled carbon nanotubes was replaced with 1 part by mass of carbon black, the electrode plate length of the positive electrode was set to 800 mm, and the electrode plate length of the negative electrode was set to 880 mm.

[0057] [Measurement of Initial Resistance] In an environment of 25°C, the test cells of each Example and Comparative Example were charged at a constant current of 0.1 C until the battery voltage reached 4.2 V, and then at a constant voltage of 0.05 mA at 4.2 V. After a 10-minute rest, the cells were discharged at 0.1 C until the current reached 2.5 V. Furthermore, after charging the test cells under the above charging conditions, AC impedance measurements were performed in the range of 10 mHz to 100 kHz, and a Cole-Cole plot was created. The resistance was calculated from the size of the approximate semicircle appearing in the obtained Cole-Cole plot, and this was taken as the initial resistance. The results are shown in Table 1. However, the initial resistances shown in Table 1 are shown relative to the initial resistance of Comparative Example 2 (100).

[0058] [Resistance Measurement After Rapid Charge Test] In a 25°C environment, the test cells of each Example and Comparative Example were charged at a constant current of 2 C to a battery voltage of 4.2 V, and then discharged at a constant current of 0.5 C to 2.5 V. This charge / discharge cycle was repeated 800 times. Furthermore, the test cells were charged at a constant current of 0.1 C to a battery voltage of 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.05 mA. The impedance measurement described above was performed on the test cells in this charged state, and the resistance was calculated from the size of the approximate semicircle appearing in the resulting Cole-Cole plot. This was used as the resistance after the rapid charge test. The results are shown in Table 1. Note that the resistance after the rapid charge test shown in Table 1 is relative to the initial resistance of Comparative Example 2 (100), and the resistance after the rapid charge test of each Example and Comparative Example is shown.

[0059] A thermocouple was attached to the side surface of the outer can of the test cell to measure the temperature of the test cell during the rapid charge test. The maximum temperatures of the test cell during the rapid charge test are summarized in Table 1.

[0060]

[0061] As can be seen from Table 1, the resistance after the rapid charge test in Examples 1 to 7 was suppressed to a value significantly lower than the resistance after the rapid charge test in Comparative Examples 1 to 6. Furthermore, the battery temperature during the rapid charge test was also lower in Examples 1 to 7 than in Comparative Examples 1 to 6. From these results, it can be said that in a secondary battery employing an end face current collection structure in which the exposed portion of the substrate is joined to the current collector plate, excellent rapid charge characteristics can be obtained by including carbon nanotubes in the positive electrode mixture layer that constitutes the positive electrode.

[0062] Among the Examples, Examples 3 to 6, in which both single-walled carbon nanotubes and multi-walled carbon nanotubes were contained in the positive electrode mixture layer, were able to reduce the resistance after the rapid charge test compared to Examples 1 and 2, in which either single-walled carbon nanotubes or multi-walled carbon nanotubes were contained. Furthermore, among Examples 3 to 6, Example 6, in which the positive electrode mixture layer contained HNBR as a dispersant, was able to reduce the resistance after the rapid charge test compared to the other Examples.

[0063] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a negative electrode current collector plate electrically connected to the negative electrode, and an electrolyte, wherein the negative electrode has a strip-shaped negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, one end of the negative electrode core in the winding axis direction of the electrode assembly is provided with a negative electrode core exposed portion on which the negative electrode mixture layer is not arranged, and the negative electrode core exposed portion is joined to the negative electrode current collector plate, the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, the positive electrode mixture layer includes a positive electrode active material and carbon nanotubes, and the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. Configuration 2: A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a positive electrode current collector plate electrically connected to the positive electrode, and an electrolyte, wherein the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, one end of the positive electrode core in the winding axis direction of the electrode body is provided with a positive electrode core exposed portion on which the positive electrode mixture layer is not disposed, and the positive electrode core exposed portion is joined to the positive electrode current collector plate, and the positive electrode mixture layer includes a positive electrode active material and carbon nanotubes, and the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.Configuration 3: A secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a negative electrode current collector plate electrically connected to the negative electrode, a positive electrode current collector plate electrically connected to the positive electrode, and an electrolyte, wherein the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, one end of the positive electrode core in the direction of the winding axis of the electrode assembly is provided with a positive electrode core exposed portion on which the positive electrode mixture layer is not arranged, and the positive electrode core exposed portion is joined to the positive electrode current collector, the negative electrode has a strip-shaped negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, the other end of the negative electrode core in the direction of the winding axis of the electrode assembly is provided with a negative electrode core exposed portion on which the negative electrode mixture layer is not arranged, and the negative electrode core exposed portion is joined to the negative electrode current collector, A secondary battery, wherein the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, the carbon nanotubes including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes. Configuration 5: The secondary battery according to any one of Configurations 1 to 4, wherein the content of the single-walled carbon nanotubes is in the range of 0.0001 parts by mass or more and 0.02 parts by mass or less per 100 parts by mass of the positive electrode active material. Configuration 6: The secondary battery according to any one of Configurations 1 to 5, wherein the content of the multi-walled carbon nanotubes is in the range of 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the positive electrode active material. Configuration 7: The secondary battery according to any one of Configurations 1 to 6, wherein the positive electrode mixture layer contains at least one of hydrogenated nitrile butadiene copolymer (HNBR) and a cellulose derivative. Configuration 8: The single-walled carbon nanotubes have a BET specific surface area of ​​300 m. ２ 10. The secondary battery according to any one of claims 1 to 9, further comprising single-walled carbon nanotubes having a BET specific surface area of ​​200 m / g or more. ２ / g or more of multi-walled carbon nanotubes. Configuration 10: The secondary battery of any one of configurations 1 to 9, wherein the multi-walled carbon nanotubes do not contain a metal catalyst. Configuration 11: The secondary battery of any one of configurations 1 to 10, wherein the electrode plate lengths of the positive electrode and the negative electrode are each 3000 mm or more.

[0064] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 negative electrode current collector plate, 18 positive electrode current collector plate, 19 insulating plate, 20 connection lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a through hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 34 positive electrode core exposed portion, 40 negative electrode core, 42 negative electrode mixture layer, 44 negative electrode core exposed portion.

Claims

1. A secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a negative electrode current collector electrically connected to the negative electrode; and an electrolytic solution, wherein the negative electrode has a strip-shaped negative electrode core body and a negative electrode mixture layer disposed on the negative electrode core body, and a negative electrode core body exposed portion where the negative electrode mixture layer is not disposed is provided at one end of the negative electrode core body in the winding axis direction of the electrode body, and the negative electrode core body exposed portion is joined to the negative electrode current collector, the positive electrode has a strip-shaped positive electrode core body and a positive electrode mixture layer disposed on the positive electrode core body, the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, and the carbon nanotubes contain at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

2. A secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a positive electrode current collector electrically connected to the positive electrode; and an electrolytic solution, wherein the positive electrode has a strip-shaped positive electrode core body and a positive electrode mixture layer disposed on the positive electrode core body, and a positive electrode core body exposed portion where the positive electrode mixture layer is not disposed is provided at one end of the positive electrode core body in the winding axis direction of the electrode body, and the positive electrode core body exposed portion is joined to the positive electrode current collector, the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, and the carbon nanotubes contain at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

3. A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a negative electrode current collector electrically connected to the negative electrode, a positive electrode current collector electrically connected to the positive electrode, and an electrolytic solution, wherein the positive electrode has a strip-shaped positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and a positive electrode core exposed portion where the positive electrode mixture layer is not disposed is provided at one end of the positive electrode core in the winding axis direction of the electrode body, and the positive electrode core exposed portion is joined to the positive electrode current collector, the negative electrode has a strip-shaped negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and a negative electrode core exposed portion where the negative electrode mixture layer is not disposed is provided at the other end of the negative electrode core in the winding axis direction of the electrode body, and the negative electrode core exposed portion is joined to the negative electrode current collector, the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, and the carbon nanotubes contain at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

4. The secondary battery according to any one of claims 1 to 3, wherein the carbon nanotubes contain single-walled carbon nanotubes and multi-walled carbon nanotubes.

5. The secondary battery according to any one of claims 1 to 3, wherein the content of the single-walled carbon nanotubes is in the range of 0.0001 part by mass or more and 0.02 part by mass or less with respect to 100 parts by mass of the positive electrode active material.

6. The secondary battery according to any one of claims 1 to 3, wherein the content of the multi-walled carbon nanotubes is in the range of 0.01 part by mass or more and 0.5 part by mass or less with respect to 100 parts by mass of the positive electrode active material.

7. The secondary battery according to any one of claims 1 to 3, wherein the positive electrode mixture layer contains at least one of hydrogenated nitrile butadiene copolymer (HNBR) and cellulose derivative.

8. The single-walled carbon nanotube is a single-walled carbon nanotube having a BET specific surface area of 300 m ２ / g or more, and the secondary battery according to any one of claims 1 to 3.

9. The multi-walled carbon nanotube has a BET specific surface area of 200 m ２ / g or more, and the secondary battery according to any one of claims 1 to 3 includes the multi-walled carbon nanotube.

10. The secondary battery according to any one of claims 1 to 3, wherein the multi-walled carbon nanotubes are substantially free of a metal catalyst.

11. The secondary battery according to any one of claims 1 to 3, wherein the plate lengths of the positive electrode and the negative electrode are each 3000 mm or more.

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