Cylindrical secondary battery

Abstract

This battery includes: an electrode body in which a positive electrode (11) having a positive electrode current collector (41) and a positive electrode mixture layer (42) disposed on the positive electrode current collector (41), and a negative electrode (12) having a negative current collector (51) and a negative mixture layer (52) disposed on the negative current collector (51) are wound with a separator interposed therebetween; and a negative electrode lead (21) joined to the negative current collector (51). The negative electrode mixture layer (52) contains a silicon-containing material as a negative electrode active material. The length in the negative electrode width direction of a portion of the negative electrode lead (21) that overlaps the negative current collector (51) in the negative electrode thickness direction is 10-50% of the length in the negative electrode width direction. The weight ratio of the silicon element in the negative electrode mixture layer (52) is 7 mass% or more.

Description

Cylindrical secondary battery

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

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an outer can housing the electrode assembly. The positive electrode includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector. Patent Document 1 describes that the negative electrode active material can be a carbon material, lithium metal or a lithium metal compound, silicon or a silicon compound, or tin or a tin compound.

[0003] Special Publication No. 2024-518360

[0004] The present inventors have discovered the following new problem: When the negative electrode active material contains a silicon-containing material, it becomes easier to achieve high capacity. However, the volume change of the negative electrode mixture layer during charge and discharge increases, which increases the stress acting on the electrodes and other components within the electrode body during charge and discharge. In light of this, in a cylindrical secondary battery, if the weight percentage of silicon in the negative electrode mixture layer is less than 5 mass%, it is likely that long-term reliability will also be good.

[0005] However, when the weight percentage of silicon in the negative electrode mixture layer is gradually increased from less than 5% by mass to several percent by mass or more in order to produce a high-capacity cylindrical secondary battery with the current cylindrical secondary battery structure, the volume change of the negative electrode mixture layer during charging and discharging increases, which makes the electrode more susceptible to damage such as deformation when the battery is used over a long period of time, resulting in insufficient long-term reliability. In other words, the effect of achieving high capacity and the effect of achieving good long-term reliability are in a trade-off relationship. The object of the present disclosure is to provide a cylindrical secondary battery that is easy to achieve high capacity, easy to achieve sufficient long-term reliability, and easy to reduce electrical resistance.

[0006] In order to solve the above problems, the cylindrical secondary battery according to the present disclosure includes an electrode assembly in which a positive electrode having a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, a negative electrode having a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector are wound with a separator interposed therebetween, an electrolyte, an outer can that accommodates the electrode assembly and the electrolyte, and a negative electrode lead joined to the negative electrode current collector, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the length in the negative electrode width direction of a portion of the negative electrode lead that overlaps the negative electrode current collector in the negative electrode thickness direction is 10% or more and 50% or less of the length in the negative electrode width direction, and the weight percentage of silicon in the negative electrode mixture layer is 7% by mass or more.

[0007] The cylindrical secondary battery according to the present disclosure is easy to achieve high capacity, easy to achieve sufficient long-term reliability, and easy to reduce electrical resistance.

[0008] 1 is an axial cross-sectional view of a cylindrical cylindrical secondary battery according to an embodiment of the present disclosure; FIG. 2 is a perspective view showing an example of an electrode body of the cylindrical secondary battery; FIG. 3 is a schematic view showing an example of the structure of a negative electrode mixture layer of the cylindrical secondary battery; (a) is a plan view showing the outer winding surface of a positive electrode developed into a long shape, a portion of a positive electrode lead, and an insulating tape; (b) is a plan view showing the inner winding surface of a positive electrode developed into a long shape, a portion of a positive electrode lead, and an insulating tape; (c) is a plan view showing the outer winding surface of a negative electrode developed into a long shape, a portion of a negative electrode lead, and an insulating tape; (d) is a plan view showing the inner winding surface of a negative electrode developed into a long shape, a portion of a negative electrode lead, and an insulating tape; (a) is a plan view showing the outer winding surface of a positive electrode developed into a long shape, a portion of a positive electrode lead, and an insulating tape in a battery of Example 8; (b) is a plan view showing the inner winding surface of a positive electrode developed into a long shape, a portion of a positive electrode lead, and an insulating tape in a battery of Example 8. 15A and 15B are plan views showing the outer surface of the negative electrode wound in a lengthwise manner, a portion of the negative electrode lead, and the insulating tape in the battery of Example 8, and FIG. 15D is a plan view showing the inner surface of the negative electrode wound in a lengthwise manner, a portion of the negative electrode lead, and the insulating tape in the battery of Example 8. An enlarged schematic cross-sectional view of the periphery of the negative electrode lead in a cross section perpendicular to the height direction of the electrode body of the battery of Example 8 and passing through the negative electrode lead. FIG. 15A is a plan view showing the outer surface of the positive electrode wound in a lengthwise manner, a portion of the positive electrode lead, and the insulating tape in the battery of Example 15, and FIG. 15B is a plan view showing the inner surface of the positive electrode wound in a lengthwise manner, a portion of the positive electrode lead, and the insulating tape in the battery of Example 15. FIG. 15C is a plan view showing the outer surface of the negative electrode wound in a lengthwise manner, and a portion of the negative electrode lead in the battery of Example 15, and FIG. 15D is a plan view showing the inner surface of the negative electrode wound in a lengthwise manner, and a portion of the negative electrode lead in the battery of Example 15. FIG. 10 is a diagram illustrating the bending angle of an electrode.

[0009] Hereinafter, with reference to the drawings, an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail. It is anticipated from the beginning that new embodiments will be constructed by appropriately combining the characteristic portions of the embodiments and variations described below. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations will be omitted. Furthermore, multiple drawings include schematic views, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match.

[0010] The cylindrical secondary battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical lithium-ion secondary battery including a non-aqueous electrolyte is exemplified as the cylindrical secondary battery 10 according to one embodiment, but the battery according to the present disclosure is not limited to this and may be any cylindrical secondary battery.

[0011] In the following description, the term "substantially the same" in the case of the exposed negative electrode current collector portion provided in substantially the same region in the negative electrode longitudinal direction on both the outer surface and the inner surface of the negative electrode winding is intended to allow for manufacturing errors (manufacturing variations) that occur when the exposed negative electrode current collector portion is provided in the same region in the negative electrode longitudinal direction on both the outer surface and the inner surface of the negative electrode winding. The requirement that the exposed negative electrode current collector portion be provided in substantially the same region in the negative electrode longitudinal direction on both the outer surface and the inner surface of the negative electrode winding is satisfied when a portion of the exposed negative electrode current collector portion provided on the outer surface of the negative electrode winding and a portion of the exposed negative electrode current collector portion provided on the inner surface of the negative electrode winding are provided in the same region in the negative electrode longitudinal direction.

[0012] The term "substantially the same" in the case of the exposed positive electrode current collector portions provided in substantially the same region in the longitudinal direction of the positive electrode on both the outer surface and the inner surface of the positive electrode winding is intended to allow for manufacturing errors (manufacturing variations) that occur when the exposed positive electrode current collector portions are provided in the same region in the longitudinal direction of the positive electrode on both the outer surface and the inner surface of the positive electrode winding. The requirement that the exposed positive electrode current collector portions be provided in substantially the same region in the longitudinal direction of the positive electrode on both the outer surface and the inner surface of the positive electrode winding is satisfied when a portion of the exposed positive electrode current collector portion provided on the outer surface of the positive electrode winding and a portion of the exposed positive electrode current collector portion provided on the inner surface of the positive electrode winding are provided in the same longitudinal direction of the positive electrode.

[0013] In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as the "upper" side, and the bottom 68 side of the outer casing 16 in the axial direction is referred to as the "lower" side. Of the components described below, components that are not recited in the independent claims that represent the highest concept are optional components and are not essential components.

[0014] 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 showing an example of an electrode assembly 14 of the cylindrical secondary battery 10. As shown in Fig. 1, the cylindrical secondary battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), a metal outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte, and a sealing body 17 that closes an opening on the upper axial side of the outer can 16. In the example shown in Fig. 1, the outer can 16 has a cylindrical shape with a bottom, but the outer can may also have a cylindrical shape, and the battery may have a structure in which both axial openings of the outer can are sealed.

[0015] 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 negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal direction and width direction (short direction). The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example. The negative electrode 12 may form the winding start end of the electrode assembly 14. However, typically, the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

[0016] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0017] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0018] The positive electrode 11 has a positive electrode current collector 41 (see FIGS. 4( a) and 4(b)) and positive electrode mixture layers 42 (see FIGS. 4(a) and 4(b)) disposed on both sides of the positive electrode current collector 41. The positive electrode current collector 41 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 having such a metal disposed on its surface. The positive electrode mixture layer 42 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, 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 current collector 41, drying the coating, and then compressing it to form the positive electrode mixture layers 42 on both sides of the positive electrode current collector 41.

[0019] The positive electrode active material is mainly composed of a lithium-containing composite oxide. Examples of metal elements contained in the lithium-containing composite oxide (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 composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. The lithium-containing composite oxide may have a spinel structure or an olivine structure. However, since this makes it easier to prepare a positive electrode with a large discharge capacity, it is preferable that the lithium-containing composite oxide have a layered rock salt structure.

[0020] Examples of the conductive agent contained in the positive electrode mixture layer 42 include carbon black such as acetylene black and ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 42 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.

[0021] The negative electrode 12 has a negative electrode current collector 51 (see FIGS. 4(c) and 4(d)) and a negative electrode mixture layer 52 (see FIGS. 4(c) and 4(d)) disposed on both sides of the negative electrode current collector 51. The negative electrode current collector 51 may be 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 having such a metal disposed on its surface. The negative electrode mixture layer 52 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode current collector 51, drying the coating, and then compressing it to dispose the negative electrode mixture layer 52 on both sides of the negative electrode current collector 51.

[0022] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. In order to effectively increase the discharge capacity of the negative electrode mixture layer 52, the negative electrode mixture layer 52 contains a silicon-containing material containing silicon (Si) as the negative electrode active material.

[0023] FIG. 3 is a schematic diagram showing an example of the structure of the negative electrode mixture layer 52. As shown in FIG. 3, the negative electrode mixture layer 52 includes graphite 60 and a silicon-containing material 70. The silicon-containing material 70 includes, for example, an ion-conducting phase 71 and an Si phase 72 dispersed in the ion-conducting phase 71. The weight ratio of the Si phase 72 in the silicon-containing material 70 is preferably 30 mass% or more because this increases the discharge capacity and tends to result in high output for the battery 10. Furthermore, the weight ratio of the Si phase 72 in the silicon-containing material 70 is preferably 60 mass% or less because this reduces the volume change of the negative electrode mixture layer 52 during charging and discharging, thereby suppressing the expansion and contraction of the electrode body 14 during charging and discharging, and thus tends to result in excellent durability for the battery 10. The ion-conducting phase 71 may be composed of, for example, an amorphous carbon phase, a lithium silicate phase, a silicon oxide phase, a titanium oxide phase, a zirconium oxide phase, or the like. In order to suppress volumetric changes in the negative electrode active material during charge and discharge and to increase charge and discharge efficiency, it is preferable that the ion-conducting phase 71 contains an amorphous carbon phase.

[0024] The weight ratio of elemental silicon to the anode mixture layer 52 is 7 mass% or more because this increases the discharge capacity and results in high output for the battery 10. To further increase battery output, the weight ratio of elemental silicon to the anode mixture layer 52 is preferably 12 mass% or more. Furthermore, the weight ratio of elemental silicon to the anode mixture layer 52 is preferably 50 mass% or less because this reduces volumetric change in the anode mixture layer 52 during charging and discharging, thereby suppressing expansion and contraction of the electrode body 14 during charging and discharging, and thus tends to improve the durability (long-term reliability) of the battery 10. The mass of elemental silicon may be approximately the same as the mass of the Si phase 72. That is, the weight ratio of the Si phase 72 to the anode mixture layer 52 may be 7 mass% or more and 50 mass% or less. The anode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, a compound containing such a metal, or the like.

[0025] 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 52, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer 52 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0026] 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 disposed on the surface of the separator 13.

[0027] As shown in FIG. 1 , a positive electrode lead 20 is joined to the positive electrode 11, and a negative electrode lead 21 is joined to the end of the negative electrode 12 at the winding start side in the longitudinal direction. The battery 10 has an insulating plate 18 above the electrode body 14 and an insulating plate 19 below the electrode body 14. The positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes through a through hole in the insulating plate 19 and extends toward the bottom 68 of the outer can 16. The positive electrode lead 20 is connected to the underside of the sealing plate 23 of the sealing body 17 by welding or the like. A terminal cap 27 constituting the top plate of the sealing body 17 is electrically connected to the sealing plate 23, and the terminal cap 27 serves as a positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the metal outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0028] Fig. 4(a) is a plan view showing the outer winding surface 11a of the positive electrode 11 developed into a long shape, a portion of the positive electrode lead 20, and the insulating tape 60, Fig. 4(b) is a plan view showing the inner winding surface 11b of the positive electrode 11 developed into a long shape, a portion of the positive electrode lead 20, and the insulating tape 60. Fig. 4(c) is a plan view showing the outer winding surface 12a of the negative electrode 12 developed into a long shape, a portion of the negative electrode lead 21, and the insulating tape 75, and Fig. 4(d) is a plan view showing the inner winding surface 12b of the negative electrode 12 developed into a long shape, a portion of the negative electrode lead 21, and the insulating tape 75.

[0029] In Figures 4(a) and 4(b), the α direction indicates the longitudinal direction of the positive electrode 11 when the positive electrode 11 is developed into a long shape, and the β direction indicates the width direction of the positive electrode when the positive electrode 11 is developed into a long shape. In Figures 4(c) and 4(d), the γ direction indicates the longitudinal direction of the negative electrode 12 when the negative electrode 12 is developed into a long shape, and the δ direction indicates the width direction of the negative electrode when the negative electrode 12 is developed into a long shape. In Figures 4(a) and 4(b), the hatched area indicates the positive electrode mixture layer 42, and in Figures 4(c) and 4(d), the hatched area indicates the negative electrode mixture layer 52.

[0030] As shown in Fig. 4(a), the outer winding surface 11a of the positive electrode 11 has a positive electrode current collector exposed portion 41a located at a distance in the positive electrode longitudinal direction from both ends in the positive electrode longitudinal direction. The positive electrode current collector exposed portion 41a is provided so as to be sandwiched between positive electrode mixture layers 42 in the positive electrode longitudinal direction. Furthermore, as shown in Fig. 4(b), the inner winding surface 11b of the positive electrode 11 has a positive electrode current collector exposed portion 41b located at a distance in the positive electrode longitudinal direction from both ends in the positive electrode longitudinal direction. The positive electrode current collector exposed portion 41b is provided so as to be sandwiched between positive electrode mixture layers 42 in the positive electrode longitudinal direction.

[0031] The positive electrode current collector exposed portion 41a and the positive electrode current collector exposed portion 41b are provided in approximately the same region in the longitudinal direction of the positive electrode. The positive electrode lead 20 is joined to the positive electrode current collector exposed portion 41b by ultrasonic welding or the like. Briefly, the positive electrode 11 has the positive electrode current collector exposed portion 41b, where the positive electrode current collector 41 is exposed, in an intermediate portion, such as the center portion, in the winding direction, and the positive electrode lead 20 is electrically connected to the positive electrode current collector exposed portion 41b.

[0032] 4( c), the outer winding surface 12a of the negative electrode 12 has a first negative electrode current collector exposed portion 51a where the negative electrode current collector 51 is exposed at the end on the winding start side in the longitudinal direction of the negative electrode, and a second negative electrode current collector exposed portion 51b where the negative electrode current collector 51 is exposed at the end on the winding end side in the longitudinal direction of the negative electrode. As shown in FIG. 4( d), the inner winding surface 12b of the negative electrode 12 has a first negative electrode current collector exposed portion 51c where the negative electrode current collector 51 is exposed at the end on the winding start side in the longitudinal direction of the negative electrode, and a second negative electrode current collector exposed portion 51d where the negative electrode current collector 51 is exposed at the end on the winding end side in the longitudinal direction of the negative electrode.

[0033] In the examples shown in Figures 4(c) and 4(d), the first negative electrode current collector exposed portion 51a and the first negative electrode current collector exposed portion 51c are provided in approximately the same region in the negative electrode longitudinal direction. However, the length of the first negative electrode current collector exposed portion 51a in the negative electrode longitudinal direction may be longer than the length of the first negative electrode current collector exposed portion 51c in the negative electrode longitudinal direction. Also, in the examples shown in Figures 4(c) and 4(d), the second negative electrode current collector exposed portion 51b and the second negative electrode current collector exposed portion 51d are provided in approximately the same region in the negative electrode longitudinal direction. However, the length of the second negative electrode current collector exposed portion 51b in the negative electrode longitudinal direction may be longer than the length of the second negative electrode current collector exposed portion 51d in the negative electrode longitudinal direction. The second negative electrode current collector exposed portion 51b has a portion that is included in the outermost peripheral surface of the electrode body 14 and includes a portion that contacts the inner peripheral surface of the outer can 16. The negative electrode lead 21 is joined to the first negative electrode current collector exposed portion 51a by ultrasonic welding or the like. The negative electrode width direction length t1 of the negative electrode lead 21 at a portion overlapping the negative electrode current collector 51 in the negative electrode thickness direction is 10% to 50% of the negative electrode width direction length t2. The negative electrode lead 21 may be joined to the first negative electrode current collector exposed portion 51a at one location. However, because this tends to lower electrical resistance and facilitates the production of a highly energy-efficient battery 10, it is preferable that the negative electrode lead 21 be joined to the first negative electrode current collector exposed portion 51a at multiple locations spaced apart from one another. In this embodiment, both the winding start side and the winding end side of the negative electrode 12 are electrically connected to the negative electrode terminal, thereby reducing the current path on the negative electrode side and reducing electrical resistance.

[0034] As shown in Figures 4(a) and 4(b), insulating tape 60 is attached to each of the positive electrode current collector exposed portion 41a and the positive electrode current collector exposed portion 41b in a manner that covers the positive electrode mixture layer 42 located on both sides in the α direction. Furthermore, as shown in Figures 4(c) and 4(d), insulating tape 75 is also attached to the first negative electrode current collector exposed portion 51a in a manner that covers at least the negative electrode lead 21. The insulating tapes 60 and 75 are provided for the purposes of preventing short circuits and preventing the active material from falling off. The insulating tapes 60 and 75 may be formed, for example, of a tape having a base material made of polyimide film and an adhesive material made of silicone. However, the insulating tapes may be formed of any material that is insulating and can be applied.

[0035] Referring again to FIG. 1 , the battery 10 further includes a resin gasket 28 disposed between the exterior can 16 and the sealing body 17. The sealing body 17 is fixed to the opening of the exterior can 16 by crimping via the gasket 28. This seals the internal space of the battery 10. The gasket 28 is sandwiched between the exterior can 16 and the sealing body 17, and insulates the sealing body 17 from the exterior can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the exterior can 16 and the sealing body 17.

[0036] The outer can 16 has a cylindrical portion 30 and a bottom portion 68. The cylindrical portion 30 includes an annular shoulder portion 38 and an annular grooved portion 34. The grooved portion 34 is formed, for example, by spinning a portion of the side surface of the outer can 16 radially inward along the entire circumferential direction to form an annular recess radially inward. The shoulder portion 38 is formed by bending the upper end of the outer can 16 inward along the entire circumferential direction toward the peripheral edge portion 45 of the sealing body 17 when the sealing body 17 is crimped to the outer can 16.

[0037] The sealing body 17 has a structure in which, in order from the electrode body 14 side, a sealing plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The sealing plate 23 has at least one through-hole 23a. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheral edges.

[0038] When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the terminal cap 27, cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks and gas is released from the through-hole 27a of the terminal cap 27. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the battery 10.

[0039] In the above description, the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and a convex terminal cap 27 that covers the rupture plate. However, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in this order from the electrode body side. Alternatively, the sealing body may not have a rupture plate, and the bottom of the outer can may have a thin, easily breakable portion that breaks when the battery generates abnormal heat.

[0040] Next, the effects of the battery 10 will be described. When the negative electrode active material contains a silicon-containing material, it becomes easier to achieve a high capacity. However, the volume change of the negative electrode mixture layer during charging and discharging increases, which increases the stress acting on the electrodes and other components within the electrode body during charging and discharging. In this context, in a cylindrical secondary battery, if the weight percentage of silicon in the negative electrode mixture layer is less than 5 mass %, it is likely that long-term reliability will also be good.

[0041] However, when the weight percentage of silicon element in the negative electrode mixture layer is gradually increased from less than 5% by mass to several% by mass or more in order to produce a high-capacity cylindrical secondary battery with the current cylindrical secondary battery structure, the volume change of the negative electrode mixture layer due to charge and discharge increases, and as a result, damage such as deformation of the electrode is likely to occur when the battery is used over a long period of time, and long-term reliability is likely to be insufficient. In other words, there is a trade-off between the effect of realizing high capacity and the effect of realizing good long-term reliability.

[0042] In contrast, as will be explained in detail later, the present inventors have confirmed that, as long as the negative electrode width direction length t1 (see FIG. 4( a)) of the portion of the negative electrode lead 21 overlapping the negative electrode current collector 51 in the negative electrode thickness direction is short and t1 is 50% or less of the negative electrode width direction length t2 (see FIG. 4( a)), the long-term reliability of the battery can be improved even when the weight percentage of silicon in the negative electrode mixture layer 52 is increased from less than 5% by mass to several percent by mass or more, i.e., 7% by mass or more. The weight percentage of silicon was measured by disassembling the fabricated battery and using ICP (Inductively Coupled Plasma). ICP is a type of optical emission spectroscopy. When plasma energy is applied to an analysis sample from an external source, the contained component elements (atoms) are excited. In ICP, emission lines (spectral lines) emitted by the excited atoms as they return to a lower energy level are measured, and the content of the component elements (atoms) is determined based on the measured emission lines.

[0043] The reason why the long-term reliability of the battery is increased is presumably because, if t1 is 50% or less of the negative electrode width direction length t2, the dimension of the portion in the height direction of the electrode body 14 where the negative electrode lead 21 is not present becomes long, and therefore, even if charging and discharging are repeated many times, the circularity of the hollow portion 14a (see Figure 1) of the electrode body 14 is likely to be maintained at a high level, and deformation, etc., is less likely to occur.

[0044] The present inventors have also confirmed that electrical resistance is easily reduced when t1 is 10% or more of t2. Furthermore, when t1 is 10% or more of t2, the bonding strength of the negative electrode lead 21 is easily sufficient. Therefore, according to the battery 10, since the weight percentage of silicon element in the negative electrode mixture layer 52 is 7% by mass or more and t1 is 10% to 50% of t2, not only can the effects of realizing high capacity and good long-term reliability, which are in a trade-off relationship, be achieved, but electrical resistance is also easily reduced and the bonding strength of the negative electrode lead 21 is easily sufficient. The quantitative values ​​of t1 and t2 can be derived by disassembling the battery, unfolding the leads and electrode plates, and measuring their lengths. Measurements can be made, for example, using a vernier caliper in millimeters.

[0045] It is preferable that t1 be 40% or less of t2, as this tends to improve the long-term reliability of the battery 10. It is also preferable that t1 be 20% or more of t2, as this tends to reduce the electrical resistance and improve the bonding strength of the negative electrode lead 21 to the negative electrode current collector 51. It is also preferable that the negative electrode lead 21 be bonded to the negative electrode current collector 51 at two or more locations spaced apart from each other, as this tends to reduce the electrical resistance and improve the bonding strength of the negative electrode lead 21 to the negative electrode current collector 51.

[0046] The expansion ratio of the negative electrode mixture layer 52 may be 10% or more. When the expansion and contraction of the negative electrode mixture layer 52 is large, such that the expansion ratio of the negative electrode mixture layer 52 is 10% or more, setting t1 to 50% or less of t2 is effective in achieving good long-term reliability. The expansion ratio is calculated as follows: First, the battery is disassembled after full charge, and the negative electrode plate is cleaned and then cross-sectioned using CP processing or ion milling. The thickness of the mixture is measured using a scanning electron microscope at an acceleration voltage of 2 kV and a magnification of 500x. After discharge, the battery is disassembled, and the negative electrode plate is cleaned and then cross-sectioned using CP processing. The thickness of the mixture is measured using a scanning electron microscope at an acceleration voltage of 2 kV and a magnification of 500x. Five points were measured for the cross-sectional mixture thickness in the observation area, and the average value of three points was used, excluding the upper and lower limit values.

[0047] The swelling ratio is then calculated by [(fully charged thickness - thickness after discharge) / thickness after discharge]. The thickness of the core material is not taken into consideration when calculating the swelling ratio. Specific examples of the charge / discharge method for full charge and discharge in the calculation include charging in an air-cooled environment at 25°C, at a constant current of 0.3 C, after which the voltage reaches 4.2 V, constant voltage charging at a voltage of 4.2 V until the current value reaches 0.02 C, and discharging at a constant current of 0.2 C until the battery voltage reaches 2.5 V.

[0048] The inventors of the present invention conducted tests to confirm the capacitance, resistance, and reliability of Examples 1 to 15 and Comparative Examples 1 to 3. Next, the configurations, test contents, and test results of Examples 1 to 15 and Comparative Examples 1 to 3 will be described.

[0049] 1 to 4, the negative electrode lead had a widthwise length t1 (hereinafter simply referred to as t1) of a portion that overlapped the negative electrode current collector in the thickness direction of the negative electrode, which was 25% of the widthwise length t2 (hereinafter simply referred to as t2). The weight percentage of silicon in the negative electrode mixture layer was 21% by mass.

[0050] Example 2 A battery was fabricated that was different from the battery of Example 1 in that t1 was 40% of t2.

[0051] Example 3 A battery was fabricated that was different from the battery of Example 1 in that the weight percentage of silicon element in the negative electrode mixture layer was 35 mass %.

[0052] Example 4 A battery was fabricated that was different from the battery of Example 1 in that the weight percentage of silicon element in the negative electrode mixture layer was 50 mass %.

[0053] Example 5 A battery was fabricated that was different from the battery of Example 1 in that t1 was 13% of t2.

[0054] Example 6 A battery was fabricated that was different from the battery of Example 1 in that t1 was 50% of t2.

[0055] Example 7 A battery was fabricated that was different from the battery of Example 1 in that t1 was 50% of t2 and the weight percentage of silicon element in the negative electrode mixture layer was 10 mass %.

[0056] Example 8 A cylindrical secondary battery (hereinafter simply referred to as battery) was fabricated in which the current path on the positive electrode side and the current path on the negative electrode side were different from those of the batteries of Examples 1-7. FIG. 5 is a schematic development view showing the structure of the positive electrode 111 and the structure of the negative electrode 112 in the battery of Example 8. In detail, FIG. 5( a) is a plan view showing the outer winding surface 111a of the positive electrode 111 developed into a long shape, a part of the positive electrode lead 120, and the insulating tape 160, and FIG. 5( b) is a plan view showing the inner winding surface 111b of the positive electrode 111 developed into a long shape, a part of the positive electrode lead 120, and the insulating tape 160. 5(c) is a plan view showing the outer winding surface 112a of the negative electrode 112 unfolded into a long shape, a part of the negative electrode lead 121, and the insulating tape 175, and FIG. 5(d) is a plan view showing the inner winding surface 112b of the negative electrode 112 unfolded into a long shape, a part of the negative electrode lead 121, and the insulating tape 175.

[0057] 5( a) and 5(b), the α' direction indicates the longitudinal direction of the positive electrode 111 when the positive electrode 111 is developed into a long strip, and the β' direction indicates the width direction of the positive electrode when the positive electrode 111 is developed into a long strip. Also, in FIGS. 5(c) and 5(d), the γ' direction indicates the longitudinal direction of the negative electrode 112 when the negative electrode 112 is developed into a long strip, and the δ' direction indicates the width direction of the negative electrode when the negative electrode 112 is developed into a long strip. In FIGS. 5(a) and 5(b), the hatched region indicates the positive electrode mixture layer 142, and in FIGS. 5(c) and 5(d), the hatched region indicates the negative electrode mixture layer 152.

[0058] 5( a) and 5(b), the positive electrode 11 has two double-sided positive current collector exposed portions 145a, 145b where the positive electrode current collector 141 is exposed in approximately the same region in the positive electrode longitudinal direction (α' direction) on both the outer winding surface 111a and the inner winding surface 111b, and does not have a portion where the positive electrode current collector is exposed on only one surface. The two double-sided positive current collector exposed portions 145a, 145b are provided at both the winding start end and the winding end of the positive electrode 111 at positions spaced apart in the α' direction and are spaced apart from each other in the α' direction. The two double-sided positive current collector exposed portions 145a, 145b have a fixed-lead exposed portion 145a to which the positive electrode lead 120 is fixed and a non-fixed-lead exposed portion 145b located at a distance in the α' direction from the positive electrode lead 120 and to which the positive electrode lead 120 is not fixed.

[0059] The negative electrode 112 has a double-sided negative electrode current collector exposed portion 155a where the negative electrode current collector 151 is exposed in substantially the same region in the negative electrode longitudinal direction (γ' direction shown in Figures 5(c) and 5(d)) on both the outer winding surface 112a and the inner winding surface 112b. The double-sided negative electrode current collector exposed portion 155a is provided between the γ' direction of two double-sided negative electrode mixture layer arranged portions 156a and 156b in the negative electrode 112, where the negative electrode mixture layer 152 is present on both the outer winding surface 112a and the inner winding surface 112b.

[0060] 6 is an enlarged schematic cross-sectional view of the periphery of the negative electrode lead 121 in a cross section perpendicular to the height direction of the electrode body 114 of the battery of Example 8 and passing through the negative electrode lead 121. As shown in Fig. 6, the double-sided negative electrode current collector exposed portion 155a faces the double-sided positive electrode current collector exposed portions 145a, 145b, with the separator 113 interposed between them. The unfixed lead exposed portion 145b is located closer to the start of winding than the fixed lead exposed portion 145a. The outer-side unfixed lead exposed portion 147b of the unfixed lead exposed portion 145b, which is located on the outer side of the winding, faces the inner-side negative electrode current collector exposed portion 157b of the double-sided negative electrode current collector exposed portion 155a, which is located on the inner side of the winding, with the separator 113 interposed between them.

[0061] The positive electrode lead 120 is fixed to the inside-side lead fixing exposed portion 148a of the lead fixing exposed portion 145a, which is located on the inside side of the winding, and the negative electrode lead 121 is fixed to the outside-side negative electrode current collector exposed portion 157a of the double-sided negative electrode current collector exposed portion 155a, which is located on the outside side of the winding. The outside-side negative electrode current collector exposed portion 157a is located at a distance in the negative electrode longitudinal direction from both ends in the negative electrode longitudinal direction, and is joined to the negative electrode lead 121, and is an example of an intermediate negative electrode current collector exposed portion. The outside-side negative electrode current collector exposed portion 157a faces the inside-side lead fixing exposed portion 148a with the separator 113 interposed therebetween.

[0062] The positive electrode lead 120 protrudes to a first side in the height direction (upper side in the height direction), and the negative electrode lead 121 protrudes to a second side in the height direction (lower side in the height direction). At least a portion of the positive electrode lead 120 is fixed to a position where the positive electrode lead 121 overlaps with the negative electrode lead facing position on the positive electrode 111, which faces the negative electrode lead 121 with the separator 113 interposed therebetween, in the positive electrode width direction. The positive electrode lead 120 and the negative electrode lead 121 are fixed to the electrode body 114 at different height positions.

[0063] As shown in FIGS. 5( c) and 5(d) , the outer winding surface 112a of the negative electrode 112 has an outermost negative electrode current collector exposed portion 158 where the negative electrode current collector 151 is exposed at the end on the winding end side in the γ′ direction, and the inner winding surface 112b of the negative electrode 112 also has an outermost negative electrode current collector exposed portion 159 where the negative electrode current collector 151 is exposed at the end on the winding end side in the γ′ direction.

[0064] The outermost negative electrode current collector exposed portion 158 includes a portion located on the outermost surface of the electrode assembly. The outermost negative electrode current collector exposed portion 158 contacts the inner circumferential surface of the battery's outer can and is electrically connected to the inner circumferential surface of the outer can. By fixing the negative electrode lead 121 to the radially intermediate portion of the electrode assembly and contacting the outermost negative electrode current collector exposed portion 158 with the inner circumferential surface of the battery's outer can, both the longitudinal intermediate portion and the end portion of the negative electrode 112 on the winding end side are electrically connected to the negative electrode terminal. This shortens the current path through which current flows and reduces electrical resistance. Note that a configuration different from that of Example 8 may be adopted, such as by disposing a separator on the outermost periphery of the electrode assembly, or by not contacting the outer can with the negative electrode current collector exposed portion provided at the end portion of the negative electrode on the winding end side in the longitudinal direction of the negative electrode.

[0065] 5( a) and 5(b), insulating tape 160 is applied to each of the double-sided positive electrode current collector exposed portions 145a, 145b on both the outer winding surface 111a and the inner winding surface 111b in a manner that covers the positive electrode mixture layer 142 located on both sides in the α' direction. Furthermore, as shown in FIGS. 5(c) and 5(d), insulating tape 175 is also applied to the outer winding negative electrode current collector exposed portion 157a to which the negative electrode lead 121 is fixed, in a manner that covers at least the negative electrode lead.

[0066] In Example 8, the insulating tape 175 is applied without covering the negative electrode mixture layers 152 located on both sides in the γ' direction. The insulating tape may be applied to the inner-side negative electrode current collector exposed portion 157 b, or may be applied so as to cover the boundary between the negative electrode mixture layer 152 and the outer-side negative electrode current collector exposed portion 157 a.

[0067] The insulating tapes 160 and 175 are provided to prevent short circuits and the active material from falling off. The insulating tapes 160 and 175 can be, for example, tapes with a polyimide film base and a silicon adhesive, but any insulating and adhesive tape may be used. In Example 8, the negative electrode width direction length t1 of the portion of the negative electrode lead 121 that overlaps the negative electrode current collector 151 in the negative electrode thickness direction is 25% of the negative electrode width direction length t2. Furthermore, the weight percentage of silicon in the negative electrode mixture layer 152 is 21% by mass.

[0068] Example 9 A battery was fabricated in comparison with Example 8, except that t1 was 40% of t2.

[0069] Example 10 In comparison with Example 8, a battery was fabricated, which differed in that the weight percentage of silicon element in the negative electrode mixture layer was 35 mass %.

[0070] Example 11 In comparison with Example 8, a battery was fabricated, which differed in that the weight percentage of silicon element in the negative electrode mixture layer was 50 mass %.

[0071] Example 12 A battery was fabricated in comparison with Example 8, except that t1 was 13% of t2.

[0072] Example 13 A battery was fabricated in comparison with Example 8, except that t1 was 50% of t2.

[0073] Example 14 A battery was fabricated that was different from the battery of Example 8 in that t1 was 50% of t2 and the weight percentage of silicon element in the negative electrode mixture layer was 10 mass %.

[0074] Example 15 A cylindrical secondary battery (hereinafter simply referred to as battery) was fabricated in which the current path on the positive electrode side and the current path on the negative electrode side were different from those of the batteries of Examples 1-7 and also different from those of the batteries of Examples 8-14. FIG. 7 is a schematic development showing the structure of the positive electrode 11 and the structure of the negative electrode 212 in the battery of Example 15. Specifically, FIG. 7( a) is a plan view showing the outer winding surface 11a of the positive electrode 11 developed into a long shape, a portion of the positive electrode lead 20, and the insulating tape 60. FIG. 7( b) is a plan view showing the inner winding surface 11b of the positive electrode 11 developed into a long shape, a portion of the positive electrode lead 20, and the insulating tape 60. FIG. 7( c) is a plan view showing the outer winding surface 212a of the negative electrode 212 developed into a long shape and a portion of the negative electrode lead 221. FIG. 7( d) is a plan view showing the inner winding surface 212b of the negative electrode 212 developed into a long shape and a portion of the negative electrode lead 221.

[0075] 7( a) and 7(b), the α direction indicates the longitudinal direction of the positive electrode 11 when the positive electrode 11 is developed into a long strip, and the β direction indicates the width direction of the positive electrode when the positive electrode 11 is developed into a long strip. In addition, in FIGS. 7(c) and 7(d), the γ" direction indicates the longitudinal direction of the negative electrode 212 when the negative electrode 212 is developed into a long strip, and the δ" direction indicates the width direction of the negative electrode when the negative electrode 212 is developed into a long strip. In addition, in FIGS. 7(a) and 7(b), the region indicated by diagonal hatching indicates the positive electrode mixture layer 42, and in FIGS. 7(c) and 7(d), the region indicated by diagonal hatching indicates the negative electrode mixture layer 252.

[0076] As shown in Figures 4(a), 4(b), 7(a), and 7(b), the positive electrode 11, positive electrode lead 20, and positive electrode-side insulating tape 60 and its application location in the battery of Example 15 are the same as those in the battery of Example 1. On the other hand, as shown in Figures 7(c) and 7(d), the negative electrode 212 has negative electrode current collector exposed portions 258, 259 at the end on the winding end side in the negative electrode longitudinal direction. In the battery of Example 15, the length in the γ'' direction of the negative electrode current collector exposed portion 258 on the outer winding surface 212a of the negative electrode 212 is approximately the same as the length in the γ'' direction of the negative electrode current collector exposed portion 259 on the inner winding surface 212b of the negative electrode 212.

[0077] One end of the negative electrode lead 221 is joined to the negative electrode current collector exposed portion 258. The other end of the negative electrode lead 221 is joined to the bottom of the outer can. In Example 15, the length t1 in the negative electrode width direction of the portion of the negative electrode lead 221 that overlaps the negative electrode current collector 251 in the negative electrode thickness direction is 50% of the length t2 in the negative electrode width direction. In addition, the weight percentage of silicon in the negative electrode mixture layer 252 is 50 mass%.

[0078] Comparative Example 1 A battery was fabricated that was different from the battery of Example 1 in that t1 was 70% of t2.

[0079] Comparative Example 2 A battery was fabricated that was different from the battery of Example 1 in that t1 was 9% of t2.

[0080] Comparative Example 3 A battery was fabricated in comparison with the battery of Example 1, except that the weight percentage of silicon in the negative electrode mixture layer was 6 mass %.

[0081] (Capacity Measurement) The capacity of each of the batteries of Examples 1-8 and Comparative Examples 1-3 was measured. Specifically, for each of the batteries of Examples 1-8 and Comparative Examples 1-3, in an air-cooled environment at 25°C, the battery in a predetermined state of charge (SOC) was discharged at a constant current rate of 0.2 C to 2.5 V, then charged at a constant current of 0.3 C, and subsequently charged at a constant voltage of 4.2 V to 0.02 C. The battery was then discharged at a constant current rate of 0.2 C to 2.5 V, and the capacity (discharge capacity) was measured. Batteries with a capacity of 5800 mAh or more were rated A, batteries with a capacity of 5600 mAh or more but less than 5800 mAh were rated B, and batteries with a capacity less than 5600 mAh were rated C. Cells with capacities of A and B were deemed acceptable.

[0082] (DC Resistance Measurement) Each of the batteries of Examples 1-5 and Comparative Examples 1 and 2 was charged in a water-cooled environment at 25°C with a constant current of 0.3 C until the battery voltage reached 4.2 V, and then constant-voltage charged at 4.2 V until the current value reached 0.02 C. After a 20-minute pause, the battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.85 V. The battery was then charged at a constant voltage of 4.2 V at a constant current of 0.3 C in a 25°C environment until the battery voltage reached 50% of the initial capacity. The battery was then left to stand in an open circuit for 1 hour, after which it was discharged at a constant current of 0.5 C for 10 seconds. The direct current resistance (DCR), (OCV-CCV) / I10s, was calculated using the open circuit voltage (OCV), the closed circuit voltage (CCV) 10 seconds after discharge, and the current value (I10s) 10 seconds after discharge. A resistance value of 30 mΩ or less was considered acceptable.

[0083] (Electrode Plate Deformation Measurement Test) For each of the batteries of Examples 1-8 and Comparative Examples 1-3, in an air-cooled environment at 45°C, constant voltage charging was performed at a constant current of 0.3 C until the voltage reached 4.2 V, followed by constant voltage charging at a voltage of 4.2 V until the current value reached 0.02 C, and then constant current discharging at a constant current of 0.5 C until the battery voltage reached 2.85 V. This charge-discharge cycle was repeated 300 times. The bending angle of the electrode, which was bent most toward the hollow portion of the electrode body on the inner side of the winding, indicated by θ in FIG. 8, was measured using CT images of a cross section parallel to the radial direction of the electrode body. A was evaluated as A when θ was 170° or greater, B when θ was greater than 150° and less than 170°, and C when θ was 150° or less. The electrode plate deformation amounts of cells A and B were evaluated as passing.

[0084] (Test results)

[0085] The test results are shown in Table 1. In Table 1, the negative electrode lead length ratio indicates the ratio of the length in the negative electrode width direction to the length in the negative electrode width direction at the portion of the negative electrode lead that overlaps the negative electrode current collector (negative electrode) in the negative electrode thickness direction. In addition, with regard to the lead structure, A indicates that the current collection structure of the positive electrode and negative electrode is the structure shown in FIG. 4, B indicates that the current collection structure of the positive electrode and negative electrode is the structure shown in FIG. 5, and C indicates that the current collection structure of the positive electrode and negative electrode is the structure shown in FIG. 7.

[0086] The larger the amount of Si element, the higher the capacity, but the larger the volume change of the negative electrode mixture layer during charge and discharge, which tends to lower reliability. Also, the shorter the negative electrode lead length, the smaller the contact area between the negative electrode current collector and the negative electrode lead, which increases resistance, but on the other hand, the smaller the height range within the electrode body where the negative electrode lead exists, which tends to maintain high circularity and tends to increase reliability.

[0087] In this context, the battery of Comparative Example 3, in which the amount of Si element was 6% by mass, was given a capacity rating of C and was unable to achieve a high capacity, whereas the batteries other than Comparative Example 3, in which the amount of Si element was 10% by mass or more, were given a capacity rating of A or B and were able to achieve a sufficient capacity. The present inventors conducted the above three tests on many prototype batteries in addition to the batteries whose test results are listed in Table 1, and confirmed that if the amount of Si element was 7% by mass or more, the capacity rating was likely to be B or higher and a sufficient capacity was likely to be achieved.

[0088] The present inventors conducted the above three tests on many prototype batteries in addition to the batteries whose test results are listed in Table 1, and confirmed that if the amount of Si element is 21 mass % or less, the reliability rating is likely to be A or higher, and the reliability is likely to be excellent. Furthermore, the present inventors conducted the above three tests on many prototype batteries in addition to the batteries whose test results are listed in Table 1, and confirmed that if the amount of Si element is 50 mass % or less, the reliability rating is likely to be B or higher, and the reliability is likely to be high.

[0089] Since the reliability rating of the battery of Comparative Example 2 was C, it was confirmed that reliability decreases when the negative electrode lead length ratio is 70%. On the other hand, the batteries other than Comparative Example 2, which had a negative electrode lead length ratio of 50% or less, were rated A or B in reliability, confirming that sufficient reliability can be achieved. The present inventors conducted the above three tests on many prototype batteries in addition to the batteries whose test results are listed in Table 1, and confirmed that when the negative electrode lead length ratio is 40% or less, the reliability rating is likely to be A and good reliability is likely to be achieved.

[0090] In Comparative Example 2, where the negative electrode lead length ratio was 9%, the resistance exceeded 30 mΩ, whereas in Examples 5 and 12, where the negative electrode lead length ratio was 13%, the resistance was 30 mΩ or less, achieving low resistance. The present inventors conducted the above three tests on numerous prototype batteries in addition to the batteries whose test results are listed in Table 1 and confirmed that a negative electrode lead length ratio of 10% or more easily achieves low resistance of 30 mΩ or less. Furthermore, a negative electrode lead length ratio of 10% or more easily achieves acceptable bonding strength between the negative electrode lead and the negative electrode current collector. Furthermore, the present inventors conducted the above three tests on numerous prototype batteries in addition to the batteries whose test results are listed in Table 1 and confirmed that a negative electrode lead length ratio of 20% or more easily reduces the resistance to 28 mΩ or less, reduces heat generation, and increases energy efficiency.

[0091] From the above test results, when the negative electrode lead length ratio is 10% or more and 50% or less, and the weight ratio of silicon element in the negative electrode mixture layer is 7% by mass or more, it is easy to realize both the effect of easily achieving high capacity and the effect of easily achieving sufficient long-term reliability, which are in a trade-off relationship with each other, and it is easy to realize both the effect of easily achieving high capacity and the effect of easily achieving sufficient long-term reliability, and it is easy to realize low electrical resistance. Furthermore, when the weight ratio of silicon element in the negative electrode mixture layer is 50% by mass or less, it is easy to realize good long-term reliability. Furthermore, when the negative electrode lead length ratio is 20% or more and 40% or less, it is easy to produce a battery that is easy to realize high energy efficiency and good long-term reliability.

[0092] By fabricating a Type A battery in which the positive and negative electrodes have the structure shown in FIG. 4 or a Type B battery in which the positive and negative electrodes have the structure shown in FIG. 5, the current path on the negative electrode side can be shortened, resistance can be reduced, and energy efficiency can be improved. Furthermore, when the expansion and contraction of the negative electrode mixture layer is large, such that the expansion ratio of the negative electrode mixture layer is 10% or more, the effect of achieving good long-term reliability by setting the negative electrode lead length ratio to 50% or less is significant. Furthermore, even if the negative electrode lead length ratio is shortened to 50% or less, electrical resistance tends to be low, making it easier to fabricate a battery with high energy efficiency. Therefore, it is preferable that the negative electrode lead be joined to the negative electrode current collector at multiple locations spaced apart from each other.

[0093] The present disclosure is not limited to the above-described embodiments and their variations, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents. For example, in the above-described embodiments, the battery has been described as having one positive electrode lead, but the battery may have multiple positive electrode leads joined to the positive electrode at intervals in the longitudinal direction of the positive electrode. Furthermore, one axial end of the electrode assembly may be configured as a strip-shaped positive electrode current collector exposed portion, and the positive electrode current collector exposed portion may be joined to a current collector plate electrically connected to a positive electrode terminal.

[0094] The battery may have N sets (N is a natural number of 2 or more) of two sets of double-sided positive electrode current collector exposed portions 145a, 145b, a positive electrode lead 120, a double-sided negative electrode current collector exposed portion 155a, and a negative electrode lead 121 spaced apart in the winding direction of the electrode body, with the relative positional relationship described in detail with reference to Fig. 5. In this way, the current paths in each of the positive electrode and the negative electrode can be further shortened, thereby significantly reducing the resistance of the battery.

[0095] The battery may have a configuration in which one negative electrode lead is electrically connected to the end of the negative electrode current collector at the start of winding in the winding direction without the end of the negative electrode current collector being in contact with the inner surface of the outer can. Also, although the battery has been described as having one negative electrode lead, the battery may have multiple negative electrode leads joined to the negative electrode at intervals in the longitudinal direction of the negative electrode.

[0096] For example, the battery may have two negative electrode leads, one of which is electrically connected to the end of the negative electrode current collector at the start of winding in the winding direction, and the other of which is electrically connected to the end of the negative electrode current collector at the end of winding in the winding direction. Even when the battery has multiple negative electrode leads, if the negative electrode lead length ratio of each negative electrode lead is set to 10% or more and 50% or less, high energy efficiency and good long-term reliability are likely to be achieved.

[0097] The positive electrode lead may be joined to the outer surface of the wound positive electrode or to the inner surface of the wound positive electrode. The positive electrode current collector exposed portion to which the positive electrode lead is joined may be provided over the entire region in the width direction of the positive electrode, or may be provided over only a portion of the region in the width direction of the positive electrode. Providing the positive electrode current collector exposed portion to which the positive electrode lead is joined over only a portion of the region in the width direction of the positive electrode can increase the capacity.

[0098] The negative electrode may be joined to the outer surface of the negative electrode or to the inner surface of the negative electrode. The negative electrode current collector exposed portion to which the negative electrode lead is joined may be provided over the entire region in the width direction of the negative electrode, or may be provided over only a portion of the region in the width direction of the negative electrode. Providing the negative electrode current collector exposed portion to which the negative electrode lead is joined over only a portion of the region in the width direction of the negative electrode can increase the capacity.

[0099] Configuration 1: A cylindrical secondary battery comprising: an electrode assembly in which a positive electrode having a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, a negative electrode having a negative electrode current collector and a negative electrode having a negative electrode mixture layer disposed on the negative electrode current collector, and the positive electrode mixture layer is wound with a separator interposed therebetween; an electrolyte; an outer can that accommodates the electrode assembly and the electrolyte; and a negative electrode lead joined to the negative electrode current collector, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, the length in the negative electrode width direction of a portion of the negative electrode lead that overlaps the negative electrode current collector in a negative electrode thickness direction is 10% or more and 50% or less of the length in the negative electrode width direction, and the weight percentage of silicon in the negative electrode mixture layer is 7 mass% or more. The negative electrode has a first negative electrode current collector exposed portion, to which the negative electrode lead is joined, at a winding start end in the negative electrode longitudinal direction, and a second negative electrode current collector exposed portion, to which the negative electrode lead is joined, at a winding end end in the negative electrode longitudinal direction. The negative electrode has one or more intermediate negative electrode current collector exposed portions, which are positioned at intervals in the negative electrode longitudinal direction from both ends in the negative electrode longitudinal direction and to which the negative electrode lead is joined. a cylindrical secondary battery according to Aspect 4, wherein the intermediate negative electrode current collector exposed portion is included in a double-sided negative electrode current collector exposed portion in which the negative electrode current collector is exposed in substantially the same region in the negative electrode longitudinal direction on both the outer surface of the negative electrode winding and the inner surface of the negative electrode winding; the positive electrode has two or more double-sided positive electrode current collector exposed portions in which the negative electrode current collector is exposed in substantially the same region in the positive electrode longitudinal direction on both the outer surface of the positive electrode winding and the inner surface of the positive electrode winding; the two or more double-sided positive electrode current collector exposed portions are positioned at intervals in the positive electrode longitudinal direction from both ends in the positive electrode longitudinal direction and are arranged at intervals from each other in the positive electrode longitudinal direction; the two or more double-sided positive electrode current collector exposed portions include a fixed-lead exposed portion to which a positive electrode lead is joined and a non-fixed-lead exposed portion to which a positive electrode lead is not fixed; and at least a portion of the positive electrode lead is fixed to the negative electrode lead at a position in the positive electrode width direction that overlaps with a position of the positive electrode facing the separator interposed between the negative electrode lead and the positive electrode. Configuration 5: The cylindrical secondary battery according to any one of Configurations 1 to 4, wherein the swelling ratio of the negative electrode mixture layer is 10% or more. Configuration 6: The cylindrical secondary battery according to any one of Configurations 1 to 5, wherein the weight ratio of the silicon element in the negative electrode mixture layer is 50 mass% or less.A cylindrical secondary battery according to any one of Aspects 1 to 6, wherein the length in the negative electrode width direction of the portion of the negative electrode lead that overlaps the negative electrode current collector in the negative electrode thickness direction is 20% to 40% of the length in the negative electrode width direction. A cylindrical secondary battery according to any one of Aspects 1 to 7, wherein the negative electrode lead is joined to the negative electrode current collector at a plurality of locations spaced apart from one another.

[0100] REFERENCE SIGNS LIST 10 Battery, 11,111 Positive electrode, 11a,111a Outer winding surface, 11b,111b Inner winding surface, 12,112,212 Negative electrode, 12a,112a,212a Outer winding surface, 12b,112b,212b Inner winding surface, 13,113 Separator, 14,114 Electrode body, 14a Hollow portion, 16 Outer can, 17 Sealing body, 18,19 Insulating plate, 20,120 Positive electrode lead, 21,121,221 Negative electrode lead, 23 Sealing plate, 23a Through hole, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Terminal cap, 27a Through hole, 28 Gasket, 30 Cylindrical portion, 34 Grooved portion, 38 Shoulder portion, 41, 141 Positive electrode current collector, 41a, 41b Positive electrode current collector exposed portion, 42, 142 Positive electrode mixture layer, 45 Peripheral portion, 51, 151, 251 Negative electrode current collector, 51a, 51c First negative electrode current collector exposed portion, 51b, 51d Second negative electrode current collector exposed portion, 52, 152, 252 Negative electrode mixture layer, 60, 75, 160, 175 Insulating tape, 68 Bottom portion, 70 Silicon-containing material, 71 Ion-conducting phase, 72 Si phase, 145a, 145b Double-sided positive electrode current collector exposed portion, 145a Lead-fixed exposed portion, 145b Lead-unfixed exposed portion, 147b Outer winding lead non-fixed exposed portion, 148a inner winding lead fixed exposed portion, 155a double-sided negative electrode current collector exposed portion, 156a, 156b double-sided negative electrode mixture layer disposed portion, 157a outer winding negative electrode current collector exposed portion, 157b inner winding negative electrode current collector exposed portion, 158 outermost peripheral negative electrode current collector exposed portion, 159, 258, 259 negative electrode current collector exposed portion.

Claims

1. A cylindrical secondary battery comprising: an electrode assembly in which a positive electrode having a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode having a negative electrode mixture layer disposed on the negative electrode current collector are wound with a separator interposed therebetween; an electrolyte; an outer can accommodating the electrode assembly and the electrolyte; and a negative electrode lead joined to the negative electrode current collector, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, the length in the negative electrode width direction of a portion of the negative electrode lead that overlaps the negative electrode current collector in the negative electrode thickness direction is 10% to 50% of the length in the negative electrode width direction, and the weight percentage of silicon in the negative electrode mixture layer is 7 mass% or more.

2. The cylindrical secondary battery according to claim 1, wherein the negative electrode has a first negative electrode current collector exposed portion to which the negative electrode lead is joined at the end of the negative electrode where winding begins in the longitudinal direction, and the negative electrode has a second negative electrode current collector exposed portion in contact with the inner circumferential surface of the outer can at the end of the negative electrode where winding ends in the longitudinal direction.

3. The cylindrical secondary battery according to claim 1, wherein the negative electrode has one or more intermediate negative electrode current collector exposed portions located at intervals in the longitudinal direction of the negative electrode from both ends in the longitudinal direction of the negative electrode and to which the negative electrode lead is joined.

4. The cylindrical secondary battery according to claim 3, wherein the intermediate negative electrode current collector exposed portion is included in a double-sided negative electrode current collector exposed portion in which the negative electrode current collector is exposed in approximately the same region in the negative electrode longitudinal direction on both the outer surface of the negative electrode winding and the inner surface of the negative electrode winding, the positive electrode has two or more double-sided positive electrode current collector exposed portions in which the negative electrode current collector is exposed in approximately the same region in the positive electrode longitudinal direction on both the outer surface of the positive electrode winding and the inner surface of the positive electrode winding, the two or more double-sided positive electrode current collector exposed portions are located at intervals in the positive electrode longitudinal direction from both ends in the positive electrode longitudinal direction and are arranged at intervals from each other in the positive electrode longitudinal direction, the two or more double-sided positive electrode current collector exposed portions include a lead-fixed exposed portion to which a positive electrode lead is joined and a lead-unfixed exposed portion to which a positive electrode lead is not fixed, and at least a portion of the positive electrode lead is fixed to the negative electrode lead at a position in the positive electrode width direction that overlaps with the negative electrode lead opposing position on the positive electrode facing the separator interposed therebetween.

5. A cylindrical secondary battery according to any one of claims 1 to 4, wherein the swelling rate of the negative electrode mixture layer is 10% or more.

6. The cylindrical secondary battery according to any one of claims 1 to 4, wherein the weight ratio of the silicon element in the negative electrode mixture layer is 50 mass % or less.

7. A cylindrical secondary battery according to any one of claims 1 to 4, wherein the length in the negative electrode width direction of the portion of the negative electrode lead that overlaps the negative electrode current collector in the negative electrode thickness direction is 20% to 40% of the length in the negative electrode width direction.

8. A cylindrical secondary battery according to any one of claims 1 to 4, wherein the negative electrode lead is joined to the negative electrode current collector at a plurality of locations spaced apart from one another.

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