Cylindrical non-aqueous electrolyte secondary battery

Abstract

The present invention provides a cylindrical non-aqueous electrolyte secondary battery having a high capacity and improved safety. A non-aqueous electrolyte secondary battery according to an aspect of the present disclosure comprises: an exterior can which has a bottomed cylinder shape and which has grooved part at an opening part thereof; an electrode body and a non-aqueous electrolyte which are housed in the exterior can; a sealing body which, at the opening part, is fixed by crimping between the grooved part and an opening end part; and an upper insulating plate which is inserted between the electrode body and the sealing body. The upper insulating plate has a first insulating plate which is in the shape of a disc smaller than the inner diameter of the grooved part, and a second insulating plate which is in the shape of a ring and which is disposed below the first insulating plate. The first insulating plate has higher heat resistance than the second insulating plate.

Description

[Technical Field]

[0001] The present disclosure relates to a cylindrical non-aqueous electrolyte secondary battery. [Background technology]

[0002] Secondary batteries may generate gas due to repeated charging and discharging, and have a mechanism to release the gas when the pressure inside the battery exceeds a predetermined value. Secondary batteries are also required to be durable enough to withstand external impacts. Patent Document 1 discloses a technology for improving the safety of secondary batteries by setting the planar compressive strength of an upper insulating plate placed on an electrode assembly and the aperture ratio of through-holes provided in the upper insulating plate within specific ranges. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-53262 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the applications of secondary batteries have expanded to include power sources for electric vehicles and power storage devices for utilizing natural energy, resulting in an ever-increasing demand for higher capacity. From the perspective of increasing capacity, efforts have been made to expand the space in which the electrode assembly can be housed by making the outer can thinner and the separator thinner, but from the perspective of safety, there are limits to how thin the outer can and the separator can be made. The technology disclosed in Patent Document 1 does not consider increasing the capacity of batteries, and there is still room for further study.

[0005] An object of the present disclosure is to provide a cylindrical non-aqueous electrolyte secondary battery with high capacity and improved safety. [Means for solving the problem]

[0006] A cylindrical nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a cylindrical, bottomed outer can having a grooved opening, an electrode assembly and a nonaqueous electrolyte housed in the outer can, a sealing member that is fixed at the opening by crimping between the grooved opening and the open edge, and an upper insulating plate inserted between the electrode assembly and the sealing member, wherein the upper insulating plate has a disk-shaped first insulating plate that is smaller in diameter than the grooved opening, and a ring-shaped second insulating plate that is disposed below the first insulating plate, and the first insulating plate has higher heat resistance than the second insulating plate. [Effects of the Invention]

[0007] The cylindrical nonaqueous electrolyte secondary battery according to the present disclosure can achieve both high battery capacity and safety. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view illustrating an exploded state of an upper insulating plate in the example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] An example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail below with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the cylindrical secondary battery. Furthermore, when multiple embodiments and variations are included in the following description, it is assumed from the outset that the characteristic features of these embodiments and variations can be appropriately combined and used.

[0010] Fig. 1 is a longitudinal cross-sectional view of a secondary battery 10 according to an embodiment. In the secondary battery 10 shown in Fig. 1, an electrode assembly 14 and a non-aqueous electrolyte (not shown) are housed in an outer can 15. For ease of explanation, the following description will refer to the sealing body 16 side as "top" and the bottom side of the outer can 15 as "bottom."

[0011] The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The positive electrode 11 has a strip-shaped positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector. The positive electrode current collector may be, for example, a foil of a metal such as aluminum, or a film having such a metal disposed on its surface.

[0012] The positive electrode mixture layer is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of a positive electrode current collector, followed by drying and compression. Examples of the positive electrode active material include lithium transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. Examples of the conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins.

[0013] The negative electrode 12 includes a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on both sides of the negative electrode current collector. Examples of the negative electrode current collector include a foil of a metal such as copper, and a film having such a metal disposed on its surface.

[0014] The negative electrode mixture layer is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, water, etc., to both sides of a negative electrode current collector, followed by drying and compression. Examples of the negative electrode active material include carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and oxides containing these. Examples of the binder include styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid or its salts, polyvinyl alcohol, etc.

[0015] A porous sheet having ion permeability and insulating properties is used as the separator 13. Specific examples of the porous sheet include a microporous membrane, a woven fabric, and a nonwoven fabric. The separator is preferably made of an olefin resin such as polyethylene or polypropylene.

[0016] The nonaqueous solvent (organic solvent) for the nonaqueous electrolyte contained in the outer can 15 can be, for example, carbonates, lactones, ethers, ketones, or esters, and two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC) can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC) can be used as the chain carbonate. The electrolyte salt for the nonaqueous electrolyte can be, for example, LiPF6, LiBF4, LiCF3SO3, or a mixture thereof. The amount of electrolyte salt dissolved in the nonaqueous solvent can be, for example, 0.5 mol / L to 2.0 mol / L.

[0017] The opening of the outer can 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. An upper insulating plate 17 and a lower insulating plate 18 are inserted above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through a through-hole in the upper insulating plate 17 and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, a cap 27, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through-hole in the lower insulating plate 18 toward the bottom side of the outer can 15 and is welded to the inner bottom surface of the outer can 15. In the secondary battery 10, the outer can 15 serves as the negative electrode terminal.

[0018] The outer can 15 has a cylindrical shape with a bottom and has a grooved portion 21 at the opening. The outer can 15 is made of, for example, metal. As will be described later, the grooved portion 21 supports the sealing body 16 on its upper surface. The electrode assembly 14 and non-aqueous electrolyte are accommodated in the portion of the outer can 15 below the grooved portion 21. The grooved portion 21 is preferably present in an annular shape along the circumferential direction of the outer can 15. The grooved portion 21 can be formed, for example, by pressing the side surface of the outer can 15 from the outside.

[0019] The sealing body 16 is fixed by crimping between the grooved portion 21 and the open edge of the outer can 15 at the opening. The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, a PTC thermistor plate 26, and a cap 27, which are stacked in this order from the electrode body 14 side. Each component of 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, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may break, causing the upper valve body 25 to bulge toward the cap 27 and separate from the lower valve body 23, thereby cutting off the electrical connection between them. If the internal pressure increases further, the upper valve body 25 may break, allowing gas to be released through the opening in the cap 27. Furthermore, when an excessive current flows through the secondary battery 10, the temperature of the PTC thermistor plate 26 rises, causing the resistance value of the PTC thermistor plate 26 to rise sharply, thereby cutting off the current.

[0020] Next, the upper insulating plate 17 will be described with reference to FIGS.

[0021] 1, the upper insulating plate 17 has a disk-shaped first insulating plate 17a that is smaller than the inner diameter of the grooved portion 21, and a ring-shaped second insulating plate 17b that is arranged below the first insulating plate 17a. This allows the first insulating plate 17a to be positioned on the inside of the grooved portion 21 while the second insulating plate 17b is arranged below the grooved portion 21, thereby increasing the size of the accommodation portion for the electrode body 14 and improving the battery capacity of the secondary battery 10.

[0022] The ring width of second insulating plate 17b may be greater than the length of protrusion of grooved portion 21 toward the inside of outer can 15. This allows second insulating plate 17b to support first insulating plate 17a from below while suppressing contact between outer can 15 and the upper part of electrode body 14.

[0023] FIG. 2 is a perspective view showing an exploded state of the upper insulating plate 17 in one example of the embodiment. The diameter of the first insulating plate 17a is larger than the inner diameter of the ring of the second insulating plate 17b and smaller than the outer diameter of the ring of the second insulating plate 17b. As shown in FIG. 2, the first insulating plate 17a may have a first hole 30 and a second hole 32. The first hole 30 and the second hole 32 are holes that penetrate the first insulating plate 17a. The first hole 30 has a function of releasing gas generated by a reaction between the electrode and the non-aqueous electrolyte to the upper part of the secondary battery 10. The shape of the first hole 30 is not particularly limited, but may be, for example, a circle. The number of first holes 30 is also not particularly limited as long as it is one or more. The second hole 32 is a hole for passing the positive electrode lead 19. The second hole 32 is, for example, larger than the first hole 30 and has a substantially semicircular shape.

[0024] First insulating plate 17a has higher heat resistance than second insulating plate 17b. As a result, even if secondary battery 10 generates abnormal heat or catches fire, first insulating plate 17a maintains its shape and ensures an exhaust path for gas generated inside the battery, thereby preventing secondary battery 10 from exploding and preventing gas from being emitted from anywhere other than the opening of cap 27.

[0025] Examples of the material for the first insulating plate 17a include thermosetting resins such as phenolic resin, epoxy resin, and unsaturated polyester resin impregnated with insulating fibers such as glass fiber. Phenolic resin (GP) mixed with glass fiber is preferred as the material for the first insulating plate 17a.

[0026] Examples of materials for the second insulating plate 17b include polypropylene (PP) and polyethylene (PE). PP is preferred as the material for the second insulating plate 17b. PP is easy to process, so the second insulating plate 17b made of PP is easy to manufacture. PP is also easy to deform, so even if the secondary battery 10 is deformed by an external impact, the second insulating plate 17b will not break, and contact between the outer can 15 and the upper part of the electrode assembly 14 can be suppressed.

[0027] The thickness of the first insulating plate 17a is preferably greater than the thickness of the second insulating plate 17b. This improves the heat resistance of the secondary battery 10. Furthermore, by making the second insulating plate 17b thinner than the first insulating plate 17a, the battery capacity of the secondary battery 10 can be improved. Furthermore, by making the second insulating plate 17b a thin ring-shaped plate, even if the secondary battery 10 is deformed by an external impact, the second insulating plate 17b will not break, and contact between the outer can 15 and the upper part of the electrode assembly 14 can be suppressed. The thickness of the first insulating plate 17a is, for example, 0.2 mm to 0.5 mm. The thickness of the second insulating plate 17b is, for example, 0.1 mm to 0.2 mm. [Example]

[0028] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0029] Example 1 [Preparation of positive electrode] As the positive electrode active material, LiNi 0.8 Co 0.15 Al 0.05A lithium transition metal composite oxide represented by O2 was used. 100 parts by mass of this positive electrode active material was mixed with 2.0 parts by mass of acetylene black (AB) as a conductive agent and 2.0 parts by mass of polyvinylidene fluoride (PVdF) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, dried, cut to the specified electrode size, and rolled using a roller to obtain a strip-shaped positive electrode. A positive electrode exposed portion, where the current collector surface was exposed and no mixture layer was present, was provided in the approximate center of the positive electrode's longitudinal direction, and an aluminum positive electrode lead was welded to the positive electrode exposed portion.

[0030] [Preparation of negative electrode] Graphite was used as the negative electrode active material. 100 parts by mass of this negative electrode active material was mixed with 1.0 parts by mass of styrene-butadiene rubber (SBR) as a binder and 1.0 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, dried, cut to the specified electrode size, and rolled using a roller to obtain a strip-shaped negative electrode. A negative electrode exposed portion where the current collector surface was exposed and free of the mixture layer was provided at the outer end of the negative electrode winding, and a nickel-copper negative electrode lead was welded to the negative electrode exposed portion.

[0031] [Preparation of electrode body] The prepared positive and negative electrodes were spirally wound with a microporous membrane separator made of an olefin resin interposed therebetween, to prepare a wound electrode assembly, with one end of the positive electrode connected to the positive electrode lead positioned at the inner end of the winding and one end of the negative electrode connected to the negative electrode lead positioned at the outer end of the winding.

[0032] [Preparation of non-aqueous electrolyte] A non-aqueous electrolyte solution was prepared by adding LiPF6 to a mixed solvent prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DMC=40:60, to give a concentration of 1 mol / L.

[0033] [Preparation of upper insulating plate] Phenolic resin (GP) mixed with glass fiber was selected as the material for the first insulating plate. Polypropylene (PP) was selected as the material for the second insulating plate. As shown in Figure 2, the first insulating plate was formed in a disk shape with a first hole and a second hole, and the second insulating plate was formed in a ring shape. The outer diameter of the first insulating plate was set to a size that approximately inscribed the inner diameter of the grooved portion of the outer can. The thickness of the first insulating plate was set to 0.3 mm. The outer diameter of the second insulating plate was set to a size that approximately inscribed the inner diameter of the grooved portion of the outer can. The ring width of the second insulating plate was set to a size that could sufficiently cover the protruding length of the grooved portion toward the inside to ensure sufficient insulation between the outer can and the electrode body. The thickness of the second insulating plate was set to 0.1 mm. This thickness is thinner than conventional insulating plates.

[0034] [Secondary battery production] The outer can was a cylindrical metal can with a diameter of 18 mm and a height of 65 mm. A lower insulating plate was placed below the electrode body, and an upper insulating plate was placed above the electrode body, in the order of a first insulating plate and a second insulating plate, in that order. The electrode body was then housed in the outer can. Next, the negative electrode lead was welded to the bottom of the outer can, a sealing plate was welded to the positive electrode lead, a groove was formed in the opening of the outer can by pressing, and a nonaqueous electrolyte was poured into the interior of the outer can. The opening of the outer can was then sealed by crimping the sealing plate via gasket 28, producing a cylindrical nonaqueous electrolyte secondary battery. The rated capacity of the produced secondary battery was 5 Ah.

[0035] <Comparative Example 1> A battery was fabricated in the same manner as in Example 1, except that in fabricating the upper insulating plate, PP was selected as the material for the first insulating plate.

[0036] <Comparative Example 2> A battery was fabricated in the same manner as in Example 1, except that in fabricating the upper insulating plate, GP was selected as the material for the second insulating plate.

[0037] <Comparative Example 3> A battery was fabricated in the same manner as in Example 1, except that in fabricating the upper insulating plates, PP was selected as the material for the first insulating plate and GP was selected as the material for the second insulating plate.

[0038] <Comparative Example 4> A battery was fabricated in the same manner as in Example 1, except that in fabricating the upper insulating plate, GP was selected as the material, and a third insulating plate was fabricated so that its shape in plan view was similar to that of the first insulating plate and its outer diameter was the same as that of the second insulating plate, and this was used as the upper insulating plate. The thickness of the third insulating plate was the same as that of the first insulating plate.

[0039] <Comparative Example 5> A battery was fabricated in the same manner as in Example 1, except that in fabricating the upper insulating plate, PP was selected as the material, and a fourth insulating plate was fabricated so that its shape in plan view was similar to that of the first insulating plate and its outer diameter was the same as that of the second insulating plate, and this was used as the upper insulating plate. The thickness of the fourth insulating plate was the same as that of the first insulating plate.

[0040] [Evaluation by flat plate crushing test] A flat plate crush test was conducted on 10 batteries from each of the examples and comparative examples. First, in an environment of 25°C, the batteries were charged at a constant current of 0.3 It until the battery voltage reached 4.2 V, and then constant voltage charging was performed until the current value at 4.2 V reached 1 / 50 It. Subsequently, the batteries were discharged at a constant current of 0.2 It until the battery voltage reached 2.5 V. Next, in an environment of 25°C, the discharged secondary batteries were pressed from the side with a 20 cm × 20 cm square stainless steel plate under conditions of a load of 20 kN and a speed of 15 mm / sec. Five batteries were crushed until they were deformed 10% relative to the diameter of the outer can, and five batteries were crushed until they were deformed 25% relative to the diameter of the outer can. After the test, the batteries were disassembled to check whether a short circuit had occurred at the top of the electrode assembly due to the destruction of the upper insulating plate.

[0041] [Evaluation by combustion test] A combustion test was conducted on five batteries from each of the examples and comparative examples. First, in an environment of 25°C, the batteries were charged at a constant current of 0.3 It until the battery voltage reached 4.2 V, and then constant voltage charging was continued until the current value at 4.2 V reached 1 / 50 It. After charging, the batteries were placed flat on a metal net, which was then covered with an aluminum mesh basket. The sides of the secondary batteries were heated with a burner flame 38 mm directly below the net. After the test, the batteries were inspected for rupture and pinholes.

[0042] The evaluation results of the examples and comparative examples are shown in Table 1. Table 1 shows the number of batteries in which traces of short circuiting were confirmed in the flat plate crush test, and the number of batteries in which rupture or pinholes were confirmed in the combustion test. In the combustion test, if damage was confirmed in any of the five batteries, the presence or absence of pinholes in these batteries was not checked. Table 1 also shows the materials and shapes of the first insulating plate and the second insulating plate.

[0043] [Table 1]

[0044] Within the scope of the claims, it was possible to prevent short circuits caused by cracks in the insulating plate during flat plate crushing tests. In addition, it was possible to prevent combustion gas emissions from sources other than the gas exhaust valve during combustion tests, thereby reducing the risk of unsafe conditions. [Explanation of symbols]

[0045] 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 upper insulating plate, 17a first insulating plate, 17b second insulating plate, 18 lower insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 PTC thermistor plate, 27 cap, 28 gasket, 30 first hole, 32 second hole

Claims

1. an outer can having a cylindrical shape with a bottom and a grooved opening; an electrode assembly and a nonaqueous electrolyte housed in the outer can; a sealing body that is fixed by crimping between the grooved portion and the opening edge in the opening; an upper insulating plate inserted between the electrode body and the sealing body; the upper insulating plate includes a disk-shaped first insulating plate having a diameter smaller than the inner diameter of the grooved portion, and a ring-shaped second insulating plate disposed below the first insulating plate, The cylindrical nonaqueous electrolyte secondary battery, wherein the first insulating plate has higher heat resistance than the second insulating plate.

2. 2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the ring width of the second insulating plate is greater than the length of the grooved portion that protrudes inward from the exterior can.

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