Secondary battery

Abstract

The secondary battery includes an electrode body formed by stacking a positive electrode and a negative electrode using a separator. The separator includes a first layer and a second layer with a smaller thermal shrinkage rate than the first layer, and the separator has a cylindrical portion formed in a cylindrical shape that constitutes the outermost part of the electrode body. At least one axial end of the cylindrical portion of the separator constituting the outermost part of the electrode body, a strip for pressing the axial end is attached from one side to the other in the stacking direction of the electrode body.

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] In recent years, the demand for rechargeable batteries has been increasing in various applications. Among them, lithium-ion rechargeable batteries using non-aqueous electrolytes offer high energy density and are therefore widely used in automotive applications, energy storage, and various electronic devices. A rechargeable battery comprises an electrode body including a positive electrode, a negative electrode, and a separator. The electrode body has a structure where the separator is sandwiched between the positive and negative electrodes, thereby preventing contact between the positive and negative electrodes. Furthermore, numerous methods have been proposed to reliably prevent internal short circuits caused by contact between the positive and negative electrodes.

[0003] For example, in Patent Document 1, to prevent internal short circuits caused by misalignment of the stacked positions of the positive and negative electrodes, a method is proposed to provide an adhesive layer on the surface of the separator and perform hot pressing on the electrode body, thereby bonding the surface of the separator to the surface of the electrode. In addition, in Patent Document 2, to prevent internal short circuits caused by conductive foreign matter, a secondary battery with a separator is proposed, wherein the separator is formed by forming a porous heat-resistant layer containing inorganic particles on the surface of a substrate.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-56142

[0007] Patent Document 2: Japanese Patent Application Publication No. 2018-49758 Summary of the Invention

[0008] On the outermost surface of an electrode body where there are no opposing electrodes, the electrodes are also covered by separators in a manner that conceals the composite material layer of the electrodes. However, the ends of the separators may curl up, and sometimes a portion of the composite material layer may be exposed. When the outermost electrode composite material layer of the electrode body is exposed, the exposed portion may detach and mix into the electrode body, potentially puncturing the separator and causing a micro-short circuit. This is especially true when using separators containing two or more layers with different thermal shrinkage rates and manufacturing the electrode body through a hot-pressing process, the lifting and curling of the ends of the separators become more pronounced.

[0009] The secondary battery disclosed herein comprises: an electrode body formed by stacking a positive electrode and a negative electrode separated by a separator, the separator comprising a first layer and a second layer having a thermal shrinkage rate smaller than the first layer, and the separator having a cylindrical portion formed in a cylindrical shape and constituting the outermost part of the electrode body, and at least one axial end of the cylindrical portion of the separator having a strip attached from one side to the other side in the stacking direction of the electrode body to press the axial end.

[0010] The secondary battery disclosed herein can more reliably prevent the ends of the separator from warping up, thus exposing the outermost composite material layer of the electrode. This prevents internal short circuits caused by the detachment of the electrode composite material layer. Attached Figure Description

[0011] Figure 1 A perspective view showing the appearance of a secondary battery as an example of an embodiment.

[0012] Figure 2 This is a perspective view of an electrode body as an example of an implementation method.

[0013] Figure 3 This is a perspective view of an electrode body as another example of an implementation. Detailed Implementation

[0014] Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that it is initially contemplated that the various embodiments and modifications illustrated below can be selectively combined.

[0015] Figure 1 A perspective view showing the appearance of a secondary battery 10 as an example of an embodiment. Figure 2 This is a perspective view of the electrode body 11 constituting the secondary battery 10. Hereinafter, a secondary battery 10, a so-called square battery in which the electrode body 11 is housed in a square outer casing 14, is illustrated. However, the outer casing of the battery is not limited to the outer casing 14; for example, it may be an outer casing made of a laminate containing a metal layer and a resin layer. Furthermore, a stacked electrode body 11, consisting of multiple positive electrodes and multiple negative electrodes sandwiched with separators, is illustrated below; however, the electrode body may also be a wound type.

[0016] like Figure 1 and Figure 2 As shown, the secondary battery 10 includes: an electrode body 11 formed by stacking a positive electrode 20 and a negative electrode 30 with a separator 40; a bottomed rectangular outer container 14 for housing the electrode body 11; and a sealing plate 15 that seals the opening of the outer container 14. The outer container 14 is a flat, generally rectangular metal container with an opening at one end along the axis, and the sealing plate 15 has an elongated rectangular shape. The outer container 14 and the sealing plate 15 are, for example, made of a metal material with aluminum as the main component.

[0017] For ease of explanation, the vertical direction of the outer can 14 is referred to as the "vertical direction" of the secondary battery 10 and each structural component, with the sealing plate 15 side as "up" and the bottom side of the outer can 14 as "down". The direction along the length of the sealing plate 15 is referred to as the "horizontal direction" of the secondary battery 10 and each structural component. In addition, in the electrode body 11, the portion of the separator 40 described later, excluding the cylindrical portion 43, is sometimes referred to as the "electrode assembly".

[0018] The secondary battery 10 includes an electrolyte housed together with the electrode body 11 in an outer casing 14. The electrolyte can be an aqueous electrolyte, preferably a non-aqueous electrolyte. The non-aqueous electrolyte may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent may be, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these solvents. The non-aqueous solvent may also contain halogen-substituted products obtained by substituting at least a portion of the hydrogen atoms of these solvents with halogen atoms such as fluorine. The electrolyte salt may be, for example, a lithium salt such as LiPF6.

[0019] The electrode body 11 includes a plurality of positive electrodes 20 and a plurality of negative electrodes 30, and has a structure in which the positive electrodes 20 and negative electrodes 30 are alternately stacked layer by layer with spacers 40 in between. The electrode body 11 typically includes one more negative electrode 30 than the number of positive electrodes 20, and the negative electrodes 30 are arranged on both sides of the electrode assembly stacking direction. Furthermore, the spacers 40 have a cylindrical portion 43 that is formed and constitutes the outermost part of the electrode body 11. That is, the outermost part of the electrode body 11 has a spacer 40 that is wound in a cylindrical shape more than once, and the negative electrodes 30 arranged on both sides of the electrode assembly stacking direction are covered by the spacer 40.

[0020] The electrode body 11 has a stacked structure with a bent separator 40 sandwiched between the positive electrode 20 and the negative electrode 30. Furthermore, this separator 40 forms a cylindrical portion 43. It should be noted that the separator sandwiched between the positive and negative electrodes, and the outermost separator constituting the electrode body, can be independent. The electrode body may also include multiple separators, one for each of the positive and negative electrodes, and a single separator constituting the cylindrical portion.

[0021] The electrode body 11 has a plurality of positive electrode tabs 23 and a plurality of negative electrode tabs 33 extending on the sealing plate 15 side. For example, the positive electrode tabs 23 are formed by protruding a part of the core of the positive electrode 20, and similarly, the negative electrode tabs 33 are formed by protruding a part of the core of the negative electrode 30. The positive electrode 20 and the negative electrode 30 are stacked in a manner with the positive electrode tabs 23 and the negative electrode tabs 33 facing the same direction, the positive electrode tabs 23 located on one lateral end side of the electrode body 11, and the negative electrode tabs 33 located on the other lateral end side of the electrode body 11, respectively, by means of a separator 40.

[0022] A positive terminal 12 and a negative terminal 13 are mounted on the sealing plate 15. For example, the positive electrode tab 23 is electrically connected to the positive terminal 12 via a positive current collector (not shown), and the negative electrode tab 33 is electrically connected to the negative terminal 13 via a negative current collector (not shown). The positive terminal 12 and the negative terminal 13 are external connection terminals for electrical connection with other secondary batteries 10, electronic devices, etc., and are mounted on the sealing plate 15 with the aid of insulating members. In addition, the sealing plate 15 is generally provided with an electrolyte injection section 16 for injecting electrolyte and a gas venting valve 17 for opening and venting gas in the event of a battery malfunction.

[0023] The following is a detailed description of the positive electrode 20, the negative electrode 30, and the separator 40 constituting the electrode body 11, especially the layer structure and configuration of the separator 40.

[0024] [positive electrode]

[0025] The positive electrode 20 has a positive electrode core and a positive electrode composite material layer formed on the surface of the positive electrode core. The positive electrode core can be a foil of a metal that is stable within the potential range of the positive electrode 20, such as aluminum or aluminum alloy, or a thin film with the metal disposed on its surface. The positive electrode composite material layer preferably includes a positive electrode active material, a conductive material, and a binder material, and is disposed on both sides of the positive electrode core. The positive electrode 20 can be manufactured, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binder material onto the positive electrode core, drying the coating, and then compressing it to form the positive electrode composite material layer on both sides of the positive electrode core.

[0026] Lithium transition metal composite oxides can be used as positive electrode active materials. Examples of metal elements contained in lithium transition 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. Preferably, at least one of Ni, Co, and Mn is included. Examples of ideal composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al.

[0027] Examples of conductive materials included in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binder materials included in the positive electrode composite layer include fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. Additionally, these resins can be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO).

[0028] [negative electrode]

[0029] The negative electrode 30 has a negative electrode core and a negative electrode composite material layer formed on the surface of the negative electrode core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode 30, such as copper, or a thin film with the metal disposed on its surface. The negative electrode composite material layer preferably contains a negative electrode active material and a binder material, and is formed on both sides of the negative electrode core. The negative electrode 30 can be manufactured, for example, by coating the surface of the negative electrode core with a negative electrode composite material slurry containing a negative electrode active material and a binder material, drying the coating, and then compressing it to form the negative electrode composite material layer on both sides of the negative electrode core.

[0030] In the negative electrode composite material layer, the negative electrode active material can include, for example, a carbon-based active material capable of reversibly absorbing, storing, and releasing lithium ions. Ideal carbon-based active materials include natural graphite such as flake graphite, block graphite, and amorphous graphite, as well as artificial graphite such as blocky graphite (MAG) and graphitized mesophase carbon microspheres (MCMB). Alternatively, the negative electrode active material can be a Si-based active material composed of at least one of Si and Si-containing compounds, or a combination of carbon-based and Si-based active materials can be used.

[0031] The binder material included in the negative electrode composite layer is the same as that in the positive electrode 20, and can be fluoropolymers, PAN, polyimide, acrylic resins, polyolefins, etc., but styrene-butadiene rubber (SBR) is preferred. In addition, the negative electrode composite layer preferably also includes CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Among these, the use of SBR and CMC or its salts, and PAA or its salts is ideal.

[0032] [Separator]

[0033] The separator 40 can be a porous sheet with ion permeability and insulation. The separator 40 comprises at least two layers with different thermal shrinkage rates, namely a first layer and a second layer with a thermal shrinkage rate smaller than that of the first layer. For example, it comprises: a resin layer as the first layer, i.e., a porous resin substrate, and a porous heat-resistant layer containing inorganic particles as the second layer. The heat-resistant layer is formed on one side of the resin substrate. By providing the heat-resistant layer, the separator 40 is less likely to break due to conductive foreign matter, and the shrinkage of the separator 40 when the temperature rises can be suppressed. In order to suppress the increase in the thickness of the electrode body 11 and improve the cost-effectiveness, it is ideal to form the heat-resistant layer only on one side of the resin substrate. It should be noted that the thermal shrinkage rate means the degree of shrinkage (change in length) when the separator 40 is heated. Furthermore, the thermal shrinkage rate of the second layer is smaller than that of the first layer at, for example, 110°C (the temperature at which the electrode body is heated while under load, as described later).

[0034] It should be noted that the separator 40 may also have a third layer. In addition, the separator 40 may also contain a resin with a higher melting point or softening point than the resin constituting the resin substrate, such as a resin layer with high heat resistance composed of aramid resin, polyimide, polyamide-imide, etc., or may replace the heat-resistant layer.

[0035] The resin substrate can function as a separator even on its own. The resin substrate can be a porous film with ion permeability and insulation properties. The thickness of the resin substrate is, for example, 1 μm to 20 μm, preferably 5 μm to 15 μm. Examples of materials that can be used as the resin substrate include olefin resins such as polyethylene, polypropylene, ethylene-propylene copolymers, ethylene, propylene, and copolymers with other α-olefins. The melting point of the resin substrate is typically below 200°C.

[0036] The heat-resistant layer is primarily composed of inorganic particles. Preferably, the heat-resistant layer consists of insulating inorganic particles and an adhesive material that bonds the particles together and to the resin substrate. Like the resin substrate, the heat-resistant layer exhibits ion permeability and insulation. The thickness of the heat-resistant layer is, for example, 1 μm to 10 μm, preferably 1 μm to 6 μm.

[0037] As inorganic particles, at least one selected from alumina, boehmite, silica, titanium dioxide, and zirconium oxide can be used. Alumina or boehmite is preferred. The content of inorganic particles is preferably 85% to 99.9% by mass, more preferably 90% to 99.5% by mass, relative to the mass of the heat-resistant layer.

[0038] The binder material constituting the heat-resistant layer can be, for example, a fluorinated resin such as PVdF, or an SBR, the same resin used in the positive electrode composite layer and the negative electrode composite layer. The content of the binder material is preferably 0.1% to 15% by mass, more preferably 0.5% to 10% by mass, relative to the mass of the heat-resistant layer. The heat-resistant layer can be formed, for example, by coating a slurry containing inorganic particles and the binder material onto one side of a resin substrate and allowing the coating to dry.

[0039] An adhesive layer is formed on at least one surface of the separator 40, for example, to adhere to the surfaces of the positive electrode 20 or the negative electrode 30. The adhesive layer may also be formed on both sides of the separator 40, in which case the composition of the adhesive layer on one side and the other side may be different. An example of the thickness of the adhesive layer is 0.1 μm to 1 μm, or 0.2 μm to 0.9 μm. The adhesive layer can be formed, for example, by applying an emulsion adhesive, consisting of adhesive components dispersed in water, to the surface of the separator 40 and allowing the coating to dry. The adhesive layer may also be formed in a dotted pattern, for example.

[0040] The adhesive layer preferably has no adhesiveness at room temperature (25°C) but exhibits adhesiveness upon heating. An example of an adhesive constituting the adhesive layer is an adhesive with acrylic resin as its main component. The electrode body 11 is manufactured, for example, by laminating the negative electrode 30 / separator 40 with adhesive layer / positive electrode 20 / separator 40 with adhesive layer in the order of hot pressing (hot pressing process). It should be noted that in this hot pressing process, the resin substrate is heated, which may sometimes cause thermal shrinkage.

[0041] The separator 40 is preferably arranged with the heat-resistant layer facing the positive electrode 20. That is, the separator 40 is arranged between the positive electrode 20 and the negative electrode 30 with the resin substrate in contact with the negative electrode 30 and the heat-resistant layer in contact with the positive electrode 20. In this case, compared with the configuration where the resin substrate faces the positive electrode 20, the oxidative degradation of the resin substrate of the separator 40 caused by the positive electrode potential is suppressed. In this embodiment, heat-resistant layers are provided on both sides of all positive electrodes 20.

[0042] The separator 40 is bent and sandwiched between the positive electrode 20 and the negative electrode 30, and is formed in a cylindrical shape, constituting the outermost part of the electrode body 11. The cylindrical portion 43 of the separator 40, which constitutes the outermost part of the electrode body 11, is formed by winding the separator 40 in a cylindrical shape more than once along the side of the electrode assembly, and covers the entire side of the electrode assembly in such a way that the side of the electrode assembly is not exposed. Here, the side of the electrode assembly refers to the surface along the vertical direction of the electrode body 11, which means the two end surfaces of the electrode assembly in the stacking direction (in this embodiment, the surfaces of the negative electrodes 30 arranged at the two end surfaces of the electrode assembly in the stacking direction where there are no opposing positive electrodes 20) and the surface along the stacking direction of the electrode assembly.

[0043] The separator 40 is installed in such a way that it completely covers the composite material layer of the negative electrode 30 disposed on the outermost side in the stacking direction. That is, the separator 40 is wound into a cylindrical shape on the side of the electrode assembly to form a cylindrical portion 43, such that the composite material layer of the negative electrode 30 is not exposed on the outermost side of the electrode body 11. In this embodiment, the separator 40 is wound twice on a portion of the side of the electrode assembly, and the separator 40 is in a state of two overlapping sheets. That is, a portion of the cylindrical portion 43 is composed of two layers of separator 40, and the remaining portion is composed of one layer of separator 40.

[0044] At the outermost end of the separator 40 located on the electrode body 11, a strip 45 is attached to maintain the shape of the cylindrical portion 43. The strip 45 is attached, for example, from the winding stop end of the second layer of separator 40 located on the outside of the cylindrical portion 43, across the first layer of separator 40 on the inside. The cylindrical portion 43 may also be formed by winding the separator 40 three or more times on the side of the electrode assembly, consisting of three or more layers of separator 40, but preferably consisting of one or two layers of separator 40. When the number of layers of separator 40 constituting the cylindrical portion 43 increases, it is easier to suppress the lifting or warping of the ends of the separator 40, but for example, excess separator 40 may absorb electrolyte, and the charge-discharge cycle characteristics will decrease.

[0045] At least one axial end (in this embodiment, one end of the separator 40 in the width direction) of the cylindrical portion 43 of the separator 40, a strip 46 is attached to press the axial end from one side to the other in the stacking direction of the electrode body 11. By pressing the axial end of the cylindrical portion 43 with the strip 46, the lifting of the end of the separator 40, which would expose the outermost layer of the negative electrode 30 of the electrode body 11, can be prevented. Thus, internal short circuits caused by the peeling off of the composite material layer can be prevented.

[0046] Figure 2 In the example shown, the attachment 46 is affixed to the upper end of the cylindrical portion 43, which is one axial end, but not to the lower end, which is the other axial end. Typically, the width of the separator 40 is wider than the width of the negative electrode 30 (the width of the portion where the negative electrode tab 33 is not formed), and the separator 40 is in a state where the upper end of the cylindrical portion 43 is larger than the lower end. In this case, the separator 40 is prone to lifting or warping at the upper end of the cylindrical portion 43; therefore, it is preferable to affix the attachment 46 at least to the upper end.

[0047] At the upper end of the cylindrical portion 43, the strip 46 is attached to the outermost side of the electrode body 11 in the stacking direction (hereinafter referred to as the "front surface of the electrode body 11"), extends along the stacking direction above the electrode body 11, and is attached to the outermost side of the electrode body 11 in the stacking direction (hereinafter referred to as the "rear surface of the electrode body 11"). Figure 2 In the example shown, similar to strip 45, strip 46 is attached across the separator 40 of the first and second layers on the front surface of electrode body 11. It should be noted that strip 46 can also extend along the winding stop end of separator 40 to the lower part of electrode body 11, thus serving as strip 45.

[0048] The strip 46 is attached taut and without bending from the upper end of the front surface to the upper end of the rear surface of the electrode body 11. At this time, the upper end of the cylindrical portion 43 is pulled inward, thus preventing it from lifting or curling. The strip 46 covers a portion of the upper surface of the electrode body 11 and extends along the stacking direction of the electrode body 11. Furthermore, the strip 46, for example, passes between the positive electrode tab 23 and the negative electrode tab 33, and is positioned at a distance equidistant from both tabs. It should be noted that the strip 46 preferably avoids the position directly below the liquid injection portion 16, and is attached in a manner that does not overlap with the liquid injection portion 16 in the vertical direction.

[0049] The 46 can also be formed over a wide area without interfering with the positive electrode tab 23 and the negative electrode tab 33, and without overlapping with the liquid injection section 16 in the vertical direction. Figure 2 In the example shown, the width of strip 46 is narrower than the width of strip 45, and strip 46 is wider than strip 45. An example of the width of one strip 46 is 10mm to 20mm, and is 5% to 30% of the lateral length of electrode body 11. The vertical length of strip 46 attached along the front and rear surfaces of electrode body 11 is, for example, 5mm to 15mm, and is more than 5% of the vertical length of electrode body 11.

[0050] In this embodiment, the positive electrode 20 and the negative electrode 30 each have a generally rectangular shape when viewed from the front. Furthermore, the strip 46 is attached to a position coinciding with the center of the long side of the positive electrode 20 and the negative electrode 30. The separator 40 is most prone to lifting or curling at the center of the long side of the front and rear surfaces of the electrode body 11; therefore, this method of attaching the strip 46 is effective in preventing the separator 40 from lifting or curling.

[0051] like Figure 3 As shown, the strip 46 can also be attached one by one at at least one axial end of the cylindrical portion 43, on both lateral sides of the electrode body 11. Figure 3 In the example shown, a strip 46 is attached near one of the transverse ends of the electrode body 11, between the positive electrode tab 23 and the transverse end. Similarly, a strip 46 is attached near the other transverse end of the electrode body 11, between the negative electrode tab 33 and the transverse end.

[0052] It should be noted that, Figure 3 In the example shown, no strip 46 is attached between the positive electrode tab 23 and the negative electrode tab 33. In the cylindrical portion 43, in addition to the two strips 46 on both sides of the electrode body 11, a strip 46 can also be attached to the central portion. The number of strips 46 is not particularly limited, and more than four strips can be attached, but from a productivity point of view, three or fewer strips are preferred. In addition, the strips 46 can be attached to the upper and lower ends of the cylindrical portion 43, and the attachment methods of the strips 46 at the upper and lower ends of the cylindrical portion 43 can also be different.

[0053] Tapes 45 and 46 are, for example, adhesive tapes comprising an insulating resin substrate and an adhesive layer. Tapes 45 and 46 can be made of the same tape. The thickness of tapes 45 and 46 is, for example, 10 μm to 60 μm, preferably 15 μm to 40 μm. The resin substrate need only have durability relative to the electrolyte, and can be, for example, composed of polyesters such as polyethylene terephthalate, polypropylene, polyimide, polyphenylene sulfide, polyetherimide, polyamide, etc.

[0054] Like conventional separators, separator 40 is expected to shrink during the aforementioned hot-pressing process. In conventional separators, the axial end of the cylindrical portion is prone to lifting and warping due to heat shrinkage. However, separator 40 and belt 46 can suppress this lifting and warping, effectively preventing the outermost layer of the electrode body 11 from exposing the composite material layer of the negative electrode 30. It should be noted that separator 40 may also shrink due to heat generated during the use of the secondary battery 10, not only during the aforementioned hot-pressing process.

[0055] In the cylindrical portion 43, the separator 40 is preferably arranged such that the first layer with a large heat shrinkage rate faces the inner side of the electrode body 11, and the second layer with a smaller heat shrinkage rate faces the outer side of the electrode body 11. In this embodiment, the separator 40 is arranged such that the resin substrate faces the inner side and the heat-resistant layer faces the outer side. At this time, the heat-resistant layer functions as a rigid body layer that maintains the shape of the separator 40, suppressing the axial end of the cylindrical portion 43 from bending and warping outward. By adopting such a configuration, the lifting and warping of the axial end of the cylindrical portion 43 is further suppressed.

[0056] <Example>

[0057] The present disclosure will be further described in detail below with reference to the embodiments, but the present disclosure is not limited to these embodiments.

[0058] <Example 1>

[0059] [The production of the positive electrode]

[0060] Lithium-nickel-cobalt-manganese composite oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed at a solid component mass ratio of 97:2:1, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare the positive electrode composite slurry. Then, the positive electrode composite slurry was coated on both sides of the positive electrode core, which was formed from a 13 μm thick aluminum foil, leaving portions for positive electrode tabs. After drying and compressing the coating, it was cut to the specified electrode size, resulting in a positive electrode (76 mm × 139 mm) with a positive electrode composite layer (thickness: 62 μm on one side) formed on both sides of the positive electrode core. It should be noted that a 20 mm wide positive electrode tab is formed on the positive electrode, protruding from a portion of the core.

[0061] [Making the negative electrode]

[0062] Graphite was used as the negative electrode active material. A negative electrode composite slurry was prepared by mixing the negative electrode active material, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a solid component mass ratio of 98:1:1, using water as the dispersion medium. Then, the negative electrode composite slurry was coated onto both sides of a negative electrode core formed from an 8 μm thick copper foil, leaving portions for negative electrode tabs. After drying and compressing the coating, it was cut to the specified electrode size, resulting in a negative electrode (78 mm × 143 mm) with a negative electrode composite layer (thickness: 76 μm on one side) formed on both sides of the negative electrode core. It should be noted that a negative electrode tab with a width of 18 mm protrudes from a portion of the core.

[0063] [Making the separator]

[0064] As the resin substrate, a porous polyethylene substrate with a thickness of 12 μm is used. A slurry containing alumina particles and PVdF is coated on one side of the substrate to form a heat-resistant layer with a thickness of 4 μm, resulting in a two-layer structure of a separator (width: 81 mm) consisting of a porous resin substrate and a porous heat-resistant layer. In addition, an adhesive with acrylic resin as the main component is applied in dots on both sides of the separator to form an adhesive layer.

[0065] [Preparation of non-aqueous electrolytes]

[0066] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4 (25°C, 1 atm). LiPF6 was dissolved in this mixed solvent to a concentration of 1 mol / L to prepare a non-aqueous electrolyte.

[0067] [Electrode fabrication]

[0068] After fabricating an electrode assembly by alternately stacking 35 positive electrodes and 36 negative electrodes with the aforementioned bent separators, the separators are wound around the sides of the electrode assembly, and the winding stop end is fixed with adhesive tape, resulting in a laminated body (electrode body before heat pressing) where the entire side of the electrode assembly is covered by the separators. It should be noted that the separators are positioned with the heat-resistant layer facing the positive electrode side between the positive and negative electrodes. Furthermore, on the cylindrical portion of the separators covering the sides of the electrode assembly, a 15mm wide adhesive tape is attached from the front surface to the rear surface of the laminated body in a straight line, pressing down on the upper end of the cylindrical portion. Figure 2 As shown, the tape is attached in such a way that it coincides with the center of the long side of the positive and negative electrodes (the transverse center of the laminate). The length of the portion of the tape attached to the front and rear surfaces of the laminate along the vertical direction is set to 10 mm.

[0069] While applying a 20kN load to the above-mentioned laminate, heat the laminate with a hot plate at 110°C for 43 seconds to obtain the electrode body.

[0070] [Making a Secondary Battery]

[0071] Multiple positive electrode tabs extending from the electrode body are connected to the positive terminal using a current collector, and similarly, multiple negative electrode tabs are connected to the negative terminal using a current collector. The positive and negative terminals are respectively fixed to the sealing plate using insulating components. After the electrode body is housed in a bottomed rectangular outer can, the sealing plate is laser-welded to the periphery of the opening of the outer can. The aforementioned non-aqueous electrolyte is injected through the injection port of the sealing plate, and the injection port is sealed with blind-hole rivets, thereby obtaining a non-aqueous electrolyte secondary battery with external dimensions of 148 mm width × 91 mm height × 26.5 mm thickness.

[0072] <Example 2>

[0073] like Figure 3 As shown, on both sides of the electrode body, the strips at the upper end of the pressing separator are attached one by one from the front surface to the rear surface. Otherwise, the electrode body and the secondary battery are obtained in the same way as in Example 1.

[0074] <Comparative Example 1>

[0075] The electrode body and secondary battery were obtained in the same manner as in Example 1, except that the tape attached from the front surface to the rear surface of the electrode body was not used.

[0076] For each electrode body in the examples and comparative examples, the floating of the outermost separator, warping of more than 90°, and exposure of the negative electrode composite material layer were evaluated according to the following method. The evaluation results are shown in Table 1.

[0077] [Evaluation of separator lifting, warping above 90°, and exposure of the negative electrode composite layer]

[0078] Place the separator of each electrode body in the embodiment and comparative example with the plane of the longitudinal direction of one end facing down on the table, observe the axial end of the cylindrical part of the separator that constitutes the outermost part of the electrode body, and confirm whether the separator is floating, curling up at more than 90° (rolling outward), and whether the negative electrode plate composite material layer is exposed on the outermost part of the electrode body.

[0079] [Table 1]

[0080] float Curving at an angle of 90° or higher Exposure of the negative electrode composite layer Example 1 none none none Example 2 have have none Comparative Example 1 have have have

[0081] As shown in Table 1, in the electrode body of Example 1, it was confirmed that there was almost no floating at the upper end of the separator, and no warping occurred. The outermost layer of the negative electrode composite material was not exposed. In the electrode body of Example 2, floating and curling occurred in the transverse central part of the principle strip, but the degree was small, so the negative electrode composite material layer was not exposed. Similar to the case of Example 1, the effect of suppressing the exposure of the negative electrode composite material layer was confirmed. On the other hand, in the electrode body of Comparative Example 1, the upper end of the separator floated up, warped by more than 90°, and the outermost layer of the electrode body exposed the negative electrode composite material layer.

[0082] Explanation of reference numerals in the attached figures

[0083] 10 Secondary batteries

[0084] 11 Electrode Body

[0085] 12 Positive Extremes

[0086] 13 Negative extremes

[0087] 14 Outer packaging tanks

[0088] 15 Sealing board

[0089] 16 Liquid injection part

[0090] 17 Gas discharge valve

[0091] 20 Positive Electrode

[0092] 23 Positive electrode tab

[0093] 30 Negative electrode

[0094] 33 Negative electrode tab

[0095] 40 Separators

[0096] 43 cylindrical part

[0097] 45, 46

Claims

1. A secondary battery comprising: an electrode body consisting of a positive electrode and a negative electrode stacked together with a separator between them. The separator comprises a first layer and a second layer with a smaller thermal shrinkage rate than the first layer, and the separator has a cylindrical portion formed in a cylindrical shape that constitutes the outermost part of the electrode body. At least one axial end of the cylindrical portion of the separator, a strip for pressing the axial end is attached from one side to the other in the stacking direction of the electrode body. The strip is attached to the lateral sides and / or the lateral center of the electrode body. in, The first layer is a resin layer. The second layer is a heat-resistant layer containing inorganic particles. In the cylindrical portion, the separator is arranged such that the resin layer faces inward and the heat-resistant layer faces outward.

2. The secondary battery according to claim 1, wherein, The electrode body includes a plurality of positive electrodes that are rectangular in shape when viewed from the front and a plurality of negative electrodes that are rectangular in shape when viewed from the front. The tape is attached at a position that coincides with the center of the long side of both the positive and negative electrodes.

3. The secondary battery according to claim 1 or 2, wherein, The electrode body includes a plurality of positive electrodes and a plurality of negative electrodes, and the electrode body has a layered structure in which a bent separator is sandwiched between the positive electrodes and the negative electrodes, and the cylindrical portion is formed by using this separator.

4. The secondary battery according to claim 1 or 2, wherein, The separator is configured such that the heat-resistant layer faces the positive electrode side.

5. The secondary battery according to claim 3, wherein, The separator is configured such that the heat-resistant layer faces the positive electrode side.

6. The secondary battery according to claim 1, 2, or 5, wherein, An adhesive layer is formed on at least one surface of the separator to adhere to the positive electrode or the negative electrode.

7. The secondary battery according to claim 3, wherein, An adhesive layer is formed on at least one surface of the separator to adhere to the positive electrode or the negative electrode.

8. The secondary battery according to claim 4, wherein, An adhesive layer is formed on at least one surface of the separator to adhere to the positive electrode or the negative electrode.

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