Cylindrical secondary battery

Abstract

Provided is a cylindrical secondary battery in which poor bonding and poor elongation are suppressed. This cylindrical secondary battery is provided with: an electrode body in which a first electrode and a second electrode having mutually different polarities are wound with a separator therebetween; a non-aqueous electrolyte; and a bottomed cylindrical outer can that accommodates the electrode body and the non-aqueous electrolyte. The first electrode has a first core body and a first mixture layer formed on the surface of the first core body. A first core body exposed part, at which the first core body is exposed, is disposed at one end of the electrode body in the winding axis direction. The first core body exposed part has a first bent point and is joined to a first current collector plate. When the first core body exposed part is divided into a first region on the first current collector plate side with respect to the first bent point and a second region on the first mixture layer side with respect to the first bent point, the surface hardness H1 of the first region and the surface hardness H2 of the second region satisfy the relationship H1 < H2.

Description

Cylindrical secondary battery

[0001] The present disclosure relates to a cylindrical secondary battery.

[0002] Cylindrical secondary batteries have been known in which an electrode core protrudes from an axial end face of an electrode assembly and the protruding core is laser-welded to a current collector plate. For example, Patent Document 1 discloses a current collector plate having a convex pressing surface on the side facing the core, with the aim of increasing the contact area between the current collector plate and the core and suppressing the electrical resistance of the electrode.

[0003] JP 2010-257851 A

[0004] As a result of intensive research by the inventors, it was found that if the core is too soft, poor bonding between the current collector plate and the core may occur, and if the core is too hard, the electrode may stretch due to plastic deformation caused by repeated charging and discharging, increasing the risk of short circuiting. The technology described in Patent Document 1 does not consider how to suppress both poor bonding and poor elongation, and there is still room for improvement.

[0005] Therefore, an object of the present disclosure is to provide a cylindrical secondary battery in which poor bonding and poor elongation are suppressed.

[0006] A cylindrical secondary battery according to one aspect of the present disclosure comprises an electrode assembly in which a first electrode and a second electrode having opposite polarities are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the first electrode has a first core and a first mixture layer formed on the surface of the first core, and a first core exposed portion at which the first core is exposed is disposed at one end of the electrode assembly in the winding axis direction, the first core exposed portion has a first bending point and is joined to a first current collector plate, and when the first core exposed portion is divided into a first region on the first current collector plate side from the first bending point and a second region on the first mixture layer side from the first bending point, the surface hardness H1 of the first region and the surface hardness H2 of the second region satisfy the relationship H1 < H2.

[0007] According to the cylindrical secondary battery according to the present disclosure, poor bonding and poor elongation can be suppressed.

[0008] Fig. 2 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure. Fig. 3 is a perspective view of a wound electrode body included in the cylindrical secondary battery shown in Fig. 1. Fig. 4 is an enlarged view of the vicinity of the upper end of the electrode body included in the cylindrical secondary battery shown in Fig. 1. Fig. 5 is an enlarged view of the vicinity of the lower end of the electrode body included in the cylindrical secondary battery shown in Fig. 1.

[0009] Conventionally, cylindrical secondary batteries have been known in which a positive electrode core and a negative electrode core protrude from the upper and lower ends of the electrode assembly in the winding axis direction, and these cores are joined to two current collector plates arranged above and below the electrode assembly. As a result of extensive research, the inventors have found that a hard core can cause poor bonding between the current collector plate and the core, while a soft core can cause the electrode to stretch due to plastic deformation during repeated charge and discharge, increasing the risk of short circuiting. If the core is hard, the core may not bend sufficiently, which could result in poor bonding when the core is welded to the current collector plate. On the other hand, if the core is soft, repeated charge and discharge can cause the electrode to stretch and reach the current collector plate opposite the one it is joined to, potentially causing a short circuit.

[0010] After further intensive research, the inventors have found that both poor bonding and poor elongation can be suppressed by adjusting the hardness of the core constituting at least one of the positive and negative electrodes for each predetermined region. Specifically, the above effect can be achieved by making the surface hardness of the region from the bending point to the current collector plate smaller than the surface hardness of the region from the bending point to the mixture layer.

[0011] 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.

[0012] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present disclosure, and Fig. 2 is a perspective view illustrating the structure of an electrode assembly 14. As shown in Fig. 1, the cylindrical secondary battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 15 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, 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 the "top" and the bottom side of the outer can 15 as the "bottom."

[0013] As shown in FIG. 2 , the electrode assembly 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound with two long separators 13 interposed therebetween. The positive electrode 11 protrudes upward relative to the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes downward relative to the positive electrode 11 and the separator 13. The positive electrode 11 has a positive electrode core exposed portion 34 in which the positive electrode core 30 is exposed and no positive electrode mixture layer 32 is provided, at an upper end of the long positive electrode 11 in the direction of the winding axis (hereinafter sometimes referred to as the axial direction) from the winding start end to the winding end end in the longitudinal direction of the long positive electrode 11. The negative electrode 12 has a negative electrode core exposed portion 44 in which the negative electrode core 40 is exposed and no negative electrode mixture layer 42 is provided, at a lower end of the long negative electrode 12 in the axial direction from the winding start end to the winding end end in the longitudinal direction of the long negative electrode 12. For this reason, the upper axial end of the electrode body 14 is constituted by a positive electrode core exposed portion 34, and the lower axial end of the electrode body 14 is constituted by a negative electrode core exposed portion 44. The width of the positive electrode core exposed portion 34 (the length in the width direction of the electrode body 14) is, for example, 2 mm or more and 20 mm or less, and the width of the negative electrode core exposed portion 44 (the length in the axial direction of the electrode body 14) is, for example, 2 mm or more and 20 mm or less. In this embodiment, a case will be described in which the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12; however, the first electrode may be a negative electrode 12 and the second electrode may be a positive electrode 11.

[0014] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0015] The liquid electrolyte (electrolytic solution) contains 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. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0016] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0017] The positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 may be made of 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. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be fabricated, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 on one side of the positive electrode substrate 30 is, for example, 10 μm or more and 150 μm or less.

[0018] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide 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.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0020] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. The negative electrode core 40 may be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side 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 .

[0021] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred 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. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0022] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 42, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. The negative electrode mixture layer 42 may contain, in addition to SBR or the like, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0023] A porous sheet having ion permeability and insulating properties is used for the separator 13. 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.

[0024] 1 , the cylindrical secondary battery 10 has a metallic negative electrode current collector 17 made of nickel, nickel alloy, or the like, on the axially lower side of the electrode body 14. An exposed negative electrode substrate portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector 17, which is joined to the inner surface of the bottom plate of an outer can 15. The outer can 15 to which the exposed negative electrode substrate portion 44 is electrically connected via the negative electrode current collector 17 serves as the negative electrode terminal.

[0025] The cylindrical secondary battery 10 has a metallic positive electrode current collector 18 made of aluminum, aluminum alloy, or the like, on the axially upper side of the electrode body 14. An exposed positive electrode substrate portion 34 protruding from the electrode body 14 is joined to the positive electrode current collector 18. The cylindrical secondary battery 10 has a circular insulating plate 19 on the axially upper side of the positive electrode current collector 18.

[0026] The cylindrical secondary battery 10 further includes a sealing body 16 and a connection lead 20 made of a metal such as aluminum or an aluminum alloy. The lower end of the connection lead 20 is joined to the upper surface of the positive electrode current collector plate 18 by welding or the like. The connection lead 20 passes through a through-hole in the insulating plate 19 and extends toward the sealing body 16, and the upper end of the connection lead 20 is connected to the lower surface of a filter 22 of the sealing body 16 by welding or the like. A cap 26 that forms the top plate of the sealing body 16 is electrically connected to the filter 22, and the cap 26 serves as a positive electrode terminal.

[0027] The cylindrical secondary battery 10 further includes a resin gasket 27 disposed between the exterior can 15 and the sealing body 16. The gasket 27 is sandwiched between the exterior can 15 and the sealing body 16 to insulate the sealing body 16 from the exterior can 15. The gasket 27 serves as a sealant to maintain airtightness inside the battery and as an insulating material to insulate the exterior can 15 from the sealing body 16. The exterior can 15 has an annular groove 21 along part of its axial direction.

[0028] The grooved portion 21 can be formed, for example, by spinning a portion of the side surface radially inward to create a recess radially inward. The exterior can 15 has a bottomed tubular portion including the grooved portion 21 and an annular shoulder portion. The bottomed tubular portion accommodates the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion is bent radially inward from the end of the open side of the bottomed tubular portion and extends inward. The shoulder portion is formed when the upper end of the exterior can 15 is bent inward and crimped onto the peripheral edge of the sealing body 16. The sealing body 16 is crimped and fixed to the exterior can 15 with a gasket 27 interposed between the shoulder portion and the grooved portion 21. In this manner, the internal space of the cylindrical secondary battery 10 is sealed.

[0029] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0030] When the cylindrical secondary battery 10 generates abnormal heat and the internal pressure of the cylindrical secondary battery 10 rises, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, cutting off the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures and gas is discharged from the through-hole 26a of the cap 26. This gas discharge prevents the cylindrical secondary battery 10 from exploding due to an excessive rise in internal pressure, thereby improving the safety of the cylindrical secondary battery 10.

[0031] Next, the joining of the electrode body 14 and the positive electrode current collector plate 18 at the upper part of the cylindrical secondary battery 10, and the joining of the electrode body 14 and the negative electrode current collector plate 17 at the lower part of the cylindrical secondary battery 10 will be described with reference to Figures 3 and 4. Figure 3 is an enlarged view of the vicinity of the upper end of the electrode body 14 provided in the cylindrical secondary battery 10, and Figure 4 is an enlarged view of the vicinity of the lower end of the electrode body 14 provided in the cylindrical secondary battery 10.

[0032] As shown in Fig. 3, the positive electrode substrate exposed portion 34 extends from the upper end surface of the electrode assembly 14 in a direction substantially parallel to the axial direction of the electrode assembly 14. The positive electrode substrate exposed portion 34 is joined to the positive electrode current collector plate 18, which has a bending point 36. The bending point 36 is a point at which the positive electrode substrate exposed portion 34 is inclined inward by 30° or more with respect to the axial direction of the electrode assembly 14 when viewed from the electrode assembly 14 side. Near the bending point 36, the angle of the positive electrode substrate exposed portion 34 changes by approximately 90° from being substantially parallel to the axial direction of the electrode assembly 14 to being substantially parallel to the surface of the positive electrode current collector plate 18.

[0033] When the positive electrode substrate exposed portion 34 is divided into a first region 38 on the positive electrode current collector plate side from the bending point 36 and a second region 39 on the positive electrode mixture layer 32 side from the bending point 36, the surface hardness H1 of the first region 38 and the surface hardness H2 of the second region 39 satisfy the relationship H1<H2. This makes it possible to suppress both poor bonding and poor elongation.

[0034] When the first region 38 is divided in half in the width direction of the electrode body 14, with the side of the bending point 36 being the 1-1 region 38a and the side of the positive electrode current collector plate 18 being the 1-2 region 38b, it is preferable that the surface hardness H1-1 of the 1-1 region 38a and the surface hardness H1-2 of the 1-2 region 38b satisfy the relationship H1-1

[0035] The surface hardness in this specification is a value measured using a dynamic ultra-microhardness tester DUH-211S manufactured by Shimadzu Corporation. A load-unloading test (MODE 2) is performed using this testing machine. More specifically, after a triangular pyramidal indenter (inter-edge angle: 115°C) comes into contact with the sample, a load is applied at a constant loading rate, and after the load reaches 20 mN, the load is maintained for 10 seconds, and then the load is unloaded at a constant rate.

[0036] The surface hardness H1-1 is calculated by averaging the measurement results at five points in the first-1 region 38a. The surface hardness H1-2 is calculated by averaging the measurement results at five points in the first-2 region 38b. The surface hardness H1 is calculated by averaging the measurement results at five points in the first-1 region 38a and the measurement results at five points in the first-2 region 38b. The surface hardness H2 is calculated by averaging the measurement results at ten points in the second region 39.

[0037] The surface hardness H1 and the surface hardness H2 preferably satisfy the relationship H1 / H2<0.6. The surface hardness H1 satisfies, for example, 20 GPa

[0038] ​​As shown in Fig. 4, the negative electrode substrate exposed portion 44 extends from the lower end surface of the electrode body 14 in a direction substantially parallel to the axial direction of the electrode body 14. The negative electrode substrate exposed portion 44 has a bending point 46 and is joined to the negative electrode current collector plate 17. The bending point 46 is a point at which the negative electrode substrate exposed portion 44 is inclined inward by 30° or more with respect to the axial direction of the electrode body 14 when viewed from the electrode body 14 side. Near the bending point 46, the angle of the negative electrode substrate exposed portion 44 changes by approximately 90° from being substantially parallel to the axial direction of the electrode body 14 to being substantially parallel to the surface of the positive electrode current collector plate 18.

[0039] When the negative electrode substrate exposed portion 44 is divided into a third region 48 on the negative electrode current collector plate side from the bending point 46 and a fourth region 49 on the negative electrode mixture layer 42 side from the bending point 46, the surface hardness H3 of the third region 48 and the surface hardness H4 of the fourth region 49 satisfy the relationship H3<H4. By satisfying H1<H2 and H3<H4, the effect of suppressing poor bonding and poor elongation becomes more pronounced.

[0040] The surface hardness H3 and the surface hardness H4 preferably satisfy the relationship H3 / H4<0.6. The surface hardness H3 preferably satisfies, for example, 100 GPa<H3<300 GPa. The surface hardness H4 preferably satisfies, for example, 250 GPa<H4<500 GPa.

[0041] The surface hardness H1 and the surface hardness H3 preferably satisfy the relationship 0.25≦H1 / H3≦1.1, which improves the balance between the hardness of the positive electrode and the negative electrode, and more significantly suppresses poor bonding and poor elongation.

[0042] The surface hardness of the positive electrode substrate exposed portion 34 can be adjusted, for example, by subjecting the positive electrode substrate exposed portion 34 to heat treatment. More specifically, by subjecting only the first region 38 to heat treatment and not subjecting the second region 39 to heat treatment, the relationship H1 < H2 can be satisfied. By increasing the heat treatment temperature, the positive electrode substrate exposed portion 34 becomes softer and the surface hardness value decreases. Furthermore, the surface hardness value of the positive electrode substrate exposed portion 34 can also be decreased by increasing the heat treatment time. The heat treatment temperature can be, for example, 100°C or higher and 250°C or lower. The heat treatment time can be, for example, 3 seconds or higher and 60 seconds or lower.

[0043] The heat treatment of the positive electrode substrate exposed portion 34 can be performed, for example, by contacting only the first region 38 with a high-temperature roller. For example, the heat treatment temperature and heat treatment time can be adjusted by adjusting the temperature and rotation speed of the roller. To change the surface hardness values ​​of the 1-1 region 38a and the 1-2 region 38b, the 1-1 region 38a and the 1-2 region 38b can be heat treated under different conditions. The heat treatment of the positive electrode substrate exposed portion 34 may be performed before or after the positive electrode mixture layer 32 is formed on the surface of the positive electrode substrate 30. The surface hardness of the negative electrode substrate exposed portion 44 can also be adjusted by heat treatment, similar to the surface hardness of the positive electrode substrate exposed portion 34 described above.

[0044] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0045] Example 1 Preparation of Positive Electrode A strip of aluminum foil having a surface hardness of 100 GPa and a thickness of 15 μm was prepared. A portion of this aluminum foil on one side in the strip width direction corresponding to H1 was heat-treated by contacting it with a roller at 150°C for 10 seconds. Separately, 100 parts by mass of the positive electrode active material, 1 part by mass of acetylene black (AB), 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. The positive electrode active material was LiNi 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 that positive electrode substrate exposed portions H1 and H2 were formed. 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 substrate. The axial lengths of H1 and H2 formed in the positive electrode substrate exposed portions were each 3 mm.

[0046] [Preparation of Negative Electrode] A strip of copper foil with a surface hardness of 300 GPa and a thickness of 8 μm was prepared. A portion of this copper foil corresponding to H3 on one side of the strip width direction was heat-treated by contacting it with a roller at 150 ° C for 10 seconds. Separately, 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 that negative electrode core exposed portions H3 and H4 were formed. This coating was dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode core. The lengths of H3 and H4 formed in the negative electrode core exposed portions were each 3 mm.

[0047] [Preparation of non-aqueous electrolyte] 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 at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0048] [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 core portion extending from the top end of the electrode assembly and the exposed negative electrode core portion extending from the bottom end 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. The negative electrode current collector was welded to the bottom of the bottomed cylindrical outer can, and the positive electrode current collector and the sealing plate 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 sealing plate via a gasket to prepare a cylindrical test cell.

[0049] [Evaluation of welding defect rate] For 100 test cells, the connection state between the positive electrode current collector plate and the exposed portion of the positive electrode substrate, and the connection state between the negative electrode current collector plate and the exposed portion of the negative electrode substrate were checked. If there was a portion where the current collector plate and the end of the substrate were not in contact and welding was not completed at the non-contact portion when welding was performed, it was determined that a welding defect had occurred.

[0050] [Evaluation of Poor Elongation Rate] 100 test cells were prepared, and each test cell was subjected to 500 cycles of the following charge-discharge cycle. The cross section of each test cell after the charge-discharge cycle was observed using an X-ray CT device (Shimadzu Corporation, SMX-225CT FPD HR). Poor elongation was determined to have occurred when the end of the negative electrode mixture layer at the top of the electrode body stretched due to the charge-discharge cycle and came into contact with the exposed portion of the positive electrode substrate, and when the end of the positive electrode mixture layer at the bottom of the electrode body stretched due to the charge-discharge cycle and came into contact with the exposed portion of the negative electrode substrate. [Charge-Discharge Cycle] At an ambient temperature of 25°C, the test cell was charged at a constant current of 0.3 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 0.01 C. Subsequently, the test cell was discharged at a constant current of 0.5 C to 2.5 V, and this charge-discharge cycle was considered one cycle.

[0051] Example 2 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 30 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 30 seconds for heat treatment. The compressive strengths of H1, H2, H3, and H4 were 70 GPa, 100 GPa, 210 GPa, and 300 GPa, respectively.

[0052] Example 3 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 25 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 20 seconds for heat treatment. H1, H2, H3, and H4 were 40 GPa, 100 GPa, 120 GPa, and 300 GPa, respectively.

[0053] Example 4 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 30 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 8 seconds for heat treatment. H1, H2, H3, and H4 were 40 GPa, 100 GPa, 240 GPa, and 300 GPa, respectively.

[0054] Example 5 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 15 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 30 seconds for heat treatment. H1, H2, H3, and H4 were 60 GPa, 100 GPa, 90 GPa, and 300 GPa, respectively.

[0055] Example 6 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 25 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 30 seconds for heat treatment. H1, H2, H3, and H4 were 50 GPa, 100 GPa, 120 GPa, and 300 GPa, respectively.

[0056] <Example 7> In the preparation of the positive electrode, the portion corresponding to H1-1 of the positive electrode substrate exposed portion was heat-treated by contacting it with a 150 ° C. roller for 25 seconds, and the portion corresponding to H1-2 of the positive electrode substrate exposed portion was heat-treated by contacting it with a 150 ° C. roller for 10 seconds, and in the preparation of the negative electrode, the roller temperature was changed to 150 ° C. and the roller contact time was changed to 15 seconds. Except for this, a test cell was prepared and evaluated in the same manner as in Example 1. H1-1, H1-2, H2, H3, and H4 were 50 GPa, 70 GPa, 100 GPa, 180 GPa, and 300 GPa, respectively. H1 was 60 GPa, which is the average of H1-1 and H1-2.

[0057] Example 8 Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 25 seconds for heat treatment, and in the preparation of the negative electrode, the roller temperature was changed to 150°C and the roller contact time was changed to 8 seconds for heat treatment. H1, H2, H3, and H4 were 50 GPa, 100 GPa, 240 GPa, and 300 GPa, respectively.

[0058] Example 9 In the preparation of the positive electrode, a portion of the positive electrode substrate exposed portion corresponding to H1-1 was heat-treated by contacting it with a roller at 150 ° C. for 25 seconds, and a portion of the positive electrode substrate exposed portion corresponding to H1-2 was heat-treated by contacting it with a roller at 150 ° C. for 10 seconds. In the preparation of the negative electrode, except that no heat treatment was performed, a test cell was prepared and evaluated in the same manner as in Example 1. H1-1, H1-2, H2, H3, and H4 were 50 GPa, 70 GPa, 100 GPa, 300 GPa, and 300 GPa, respectively. H1 was 60 GPa, which is the average of H1-1 and H1-2.

[0059] Comparative Example 1 Test cells were fabricated and evaluated in the same manner as in Example 1, except that no heat treatment was performed in the fabrication of either the positive electrode or the negative electrode. The compressive strengths of H1, H2, H3, and H4 were 100 GPa, 100 GPa, 300 GPa, and 300 GPa, respectively.

[0060] <Comparative Example 2> Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the entire surface of the aluminum foil was heat-treated by contacting it with a roller at 150°C for 10 seconds, and in the preparation of the negative electrode, the entire surface of the copper foil was heat-treated by contacting it with a roller at 150°C for 10 seconds. The compressive strengths of H1, H2, H3, and H4 were 70 GPa, 70 GPa, 210 GPa, and 210 GPa, respectively.

[0061] <Comparative Example 3> Test cells were prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode, the entire surface of the aluminum foil was heat-treated by contacting it with a roller at 150°C for 30 seconds, and in the preparation of the negative electrode, the entire surface of the copper foil was heat-treated by contacting it with a roller at 150°C for 30 seconds. The compressive strengths of H1, H2, H3, and H4 were 40 GPa, 40 GPa, 120 GPa, and 120 GPa, respectively.

[0062] Table 1 shows the evaluation results of the test cells according to the examples and comparative examples.

[0063]

[0064] As shown in Table 1, both poor welding and poor elongation were suppressed in the test cells of Examples 1 to 9. On the other hand, the test cells of Comparative Examples 1 to 3 were unable to suppress both poor welding and poor elongation.

[0065] The present disclosure is further described by the following embodiments. Configuration: 1 A cylindrical secondary battery including an electrode assembly in which a first electrode and a second electrode having opposite polarities are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the first electrode has a first core and a first mixture layer formed on the surface of the first core, a first core exposed portion where the first core is exposed is disposed at one end of the electrode assembly in the winding axis direction, the first core exposed portion has a first bending point and is joined to a first current collector plate, and when the first core exposed portion is divided into a first region on the first current collector plate side from the first bending point and a second region on the first mixture layer side from the first bending point, a surface hardness H1 of the first region and a surface hardness H2 of the second region satisfy the relationship H1 < H2. Configuration 2: The cylindrical secondary battery according to Configuration 1, wherein H1 and H2 satisfy the relationship H1 / H2<0.6.Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, wherein, when the first region is divided in half in the width direction of the electrode body, with the side of the first bending point being a 1-1 region and the side of the first current collector plate being a 1-2 region, the surface hardness H1-1 of the 1-1 region and the surface hardness H1-2 of the 1-2 region satisfy the relationship H1-1<H1-2.Configuration 4: The cylindrical secondary battery according to any one of Configurations 1 to 3, wherein the first electrode is a positive electrode and the second electrode is a negative electrode, and H1 satisfies 20 GPa<H1<100 GPa and H2 satisfies 50 GPa<H1<150 GPa.a second electrode having a second core and a second mixture layer formed on the surface of the second core; a second core exposed portion where the second core is exposed is arranged on the surface of the second electrode, the second core exposed portion being in contact with one end of the second electrode in the width direction and extending in the longitudinal direction of the second electrode with a substantially constant width; the second core exposed portion extending from the end face of the electrode body substantially parallel to the direction of the winding axis of the electrode body, having a second bending point, and being joined to a second current collector plate; and when the second core exposed portion is divided into a third region on the second current collector plate side from the second bending point and a fourth region on the second mixture layer side from the second bending point, a surface hardness H3 of the third region and a surface hardness H4 of the fourth region satisfy the relationship H3<H4. Configuration 6: The cylindrical secondary battery according to Configuration 5, wherein H1 and H3 satisfy the relationship 0.25≦H1 / H3≦1.1. Configuration 7: The cylindrical secondary battery according to Configuration 5 or 6, wherein H1 satisfies 20 GPa

[0066] REFERENCE SIGNS LIST 10 Cylindrical 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 cylindrical secondary battery comprising: an electrode assembly in which a first electrode and a second electrode having mutually different polarities are wound with a separator interposed therebetween; a non-aqueous electrolyte; and a cylindrical outer can with a bottom that accommodates the electrode assembly and the non-aqueous electrolyte, the first electrode has a first core and a first mixture layer formed on a surface of the first core, a first core exposed portion in which the first core is exposed is disposed at one end of the electrode body in the winding axis direction, the first core exposed portion having a first bending point and being joined to a first current collector plate; A cylindrical secondary battery, wherein when the first substrate exposed portion is divided into a first region from the first bending point to the first current collector plate side and a second region from the first bending point to the first mixture layer side, a surface hardness H1 of the first region and a surface hardness H2 of the second region satisfy the relationship H1<H2.

2. The cylindrical secondary battery according to claim 1 , wherein H1 and H2 satisfy a relationship of H1 / H2<0.

6.

3. 2. The cylindrical secondary battery according to claim 1, wherein when the first region is divided in half in the width direction of the electrode body, the side of the first bending point is defined as a 1-1 region, and the side of the first current collector plate is defined as a 1-2 region, a surface hardness H1-1 of the 1-1 region and a surface hardness H1-2 of the 1-2 region satisfy the relationship H1-1<H1-2.

4. The first electrode is a positive electrode and the second electrode is a negative electrode, The cylindrical secondary battery according to claim 1 , wherein H1 satisfies 20 GPa<H1<100 GPa and H2 satisfies 50 GPa<H2<150 GPa.

5. The first electrode is a positive electrode and the second electrode is a negative electrode, the second electrode has a second core and a second mixture layer formed on a surface of the second core, a second core exposed portion in which the second core is exposed is disposed at the other end of the electrode body in the winding axis direction, the second core exposed portion having a second bending point and being joined to a second current collector plate, 2. The cylindrical secondary battery according to claim 1, wherein when the second substrate exposed portion is divided into a third region from the second bending point to the second current collector plate side and a fourth region from the second bending point to the second mixture layer side, a surface hardness H3 of the third region and a surface hardness H4 of the fourth region satisfy the relationship H3<H4.

6. The cylindrical secondary battery according to claim 5 , wherein H1 and H3 satisfy a relationship of 0.25≦H1 / H3≦1.

1.

7. 6. The cylindrical secondary battery according to claim 5, wherein H1 satisfies 20 GPa<H1<100 GPa, H2 satisfies 50 GPa<H2<150 GPa, H3 satisfies 100 GPa<H3<300 GPa, and H4 satisfies 250 GPa<H4<500 GPa.

8. The first electrode is a negative electrode and the second electrode is a positive electrode, The cylindrical secondary battery according to claim 1 , wherein H1 satisfies 100 GPa<H1<300 GPa and H2 satisfies 250 GPa<H2<500 GPa.