Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery includes: a flat electrode body (60) in which a positive electrode (30) to which a positive electrode tab (22) is connected and a negative electrode (40) to which a negative electrode tab is connected are wound via a separator (70); and an exterior body (12). In the exterior body, a laminate sheet including an adhesive resin layer is folded back along a bottom portion, the peripheral edge portions of two sheet elements facing each other are joined, and each sheet element is provided with a housing portion (13) for housing the electrode body and an exterior body flat portion (15) for sealing the opening of the housing portion. When the outermost periphery of the positive electrode is divided into two, the exterior body flat part side and the bottom end side of the housing portion, the positive electrode tab (22) is attached to the exterior body flat portion side and is led out from the top portion of the exterior body. The negative electrode tab 24 is attached to an intermediate periphery between the innermost periphery and outermost periphery of the negative electrode and is led out from the top portion.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and in particular to improving safety in the event of a drop impact and reducing internal resistance.

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion batteries have been used as power sources for electronic devices such as smartphones, tablet terminals, notebook PCs, etc. In these cases, there is a particular demand for the secondary batteries to be lightweight and thin.

[0003] For this reason, it is conceivable to use a secondary battery having a flat exterior body formed by folding a laminate sheet such as an aluminum laminate film, as described in Patent Document 1, as a power source for an electronic device. An electrode body is housed inside the exterior body. The electrode body has a positive electrode connected to a positive electrode tab and a negative electrode connected to a negative electrode tab, and the positive electrode and negative electrode are wound in a flat shape with a separator interposed between them. The positive electrode tab and the negative electrode tab are each led out from a top portion, which is opposite to a bottom portion, which is a folded portion of the exterior body.

[0004] In the configuration described in Patent Document 1, the exterior body includes a housing portion that houses the electrode assembly and a flat portion that closes the opening of the housing portion. In addition, a positive electrode tab is attached to an intermediate periphery between the innermost and outermost peripheries of the positive electrode, and a negative electrode tab is attached to an intermediate periphery between the innermost and outermost peripheries of the negative electrode.

[0005] International Publication No. 2022 / 138625

[0006] The configuration described in Patent Document 1 leaves room for improvement in terms of improving safety in the event of a drop impact. Specifically, in the configuration described in Patent Document 1, inside the exterior housing, a portion of the positive electrode tab extending from the electrode assembly toward the sealing portion of the top section may be significantly bent toward the flat portion of the exterior housing, and this portion may ride up on the separator. As a result, when a drop impact occurs in which an external force is applied to the electrode assembly from the leading side of the positive electrode tab of the exterior housing, the positive electrode tab may be pressed strongly against the negative electrode via the separator, potentially causing a short circuit.

[0007] On the other hand, it is possible to attach the positive electrode tab and the negative electrode tab to the outermost flat portion of the exterior body of the positive electrode and the negative electrode, respectively. However, in this case, the negative electrode tab is provided near the end of the negative electrode in the longitudinal direction of the electrode plate. This reduces the current collection efficiency through the negative electrode tab of the negative electrode, increasing the electrical resistance of the negative electrode and causing an increase in the internal resistance of the secondary battery.

[0008] Therefore, an object of the present disclosure is to improve safety when subjected to a drop impact and reduce internal resistance in a nonaqueous electrolyte secondary battery having an exterior body formed by folding a laminate sheet.

[0009] The nonaqueous electrolyte secondary battery according to the present disclosure comprises: a flat-shaped electrode body in which a positive electrode connected to a positive electrode tab and a negative electrode connected to a negative electrode tab are wound with a separator interposed therebetween; and an exterior body in which a laminate sheet including an adhesive resin layer is folded along a bottom portion, and the peripheral portions of two opposing sheet elements are joined together, and each of the two sheet elements is provided with a cup-shaped housing portion that houses the electrode body and an exterior body flat portion that closes the opening of the housing portion, when the outermost periphery of the positive electrode is divided into two, the exterior body flat portion side and the bottom end side of the housing portion, the positive electrode tab is attached to the exterior body flat portion side and extends from the top portion opposite the bottom portion of the exterior body, and the negative electrode tab is attached to an intermediate periphery between the innermost and outermost peripheries of the negative electrode and extends from the top portion.

[0010] The nonaqueous electrolyte secondary battery according to the present disclosure, which includes an exterior body formed by folding a laminate sheet, can improve safety when subjected to a drop impact and reduce internal resistance.

[0011] 1 is a perspective view of a nonaqueous electrolyte secondary battery according to an embodiment; FIG. 2 is a schematic partial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment, taken along a cross section passing through a positive electrode tab and including a direction parallel to the thickness direction and the winding axis direction of the electrode body; FIG. 3 is a schematic cross-sectional view of an electrode body constituting a nonaqueous electrolyte secondary battery according to an embodiment, perpendicular to the winding axis direction; FIG. 4 is an enlarged view of part A in FIG. 3; and FIG. 5 is an enlarged view of part B in FIG. 4. FIG. 5 is a view of a positive electrode constituting a nonaqueous electrolyte secondary battery according to an embodiment in a developed state, as viewed from the outer side of the winding, which is one side in the thickness direction, and FIG. 6 is a view of a negative ..., as viewed from the inner side of the winding, which is the other side in the thickness direction. FIG. 6 is a schematic partial cross-sectional view of a nonaqueous electrolyte secondary battery according to a comparative example, taken along a cross section passing through a positive electrode tab and including a direction parallel to the thickness direction and the winding axis direction. (a) is a schematic cross-sectional view perpendicular to the winding axis direction of an electrode body constituting a nonaqueous electrolyte secondary battery of a comparative example, (b) is an enlarged view of portion C in (a), and (c) is an enlarged view of portion D in (a). (a) is a view of a positive electrode constituting a nonaqueous electrolyte secondary battery of a comparative example in a developed state, as seen from the outer side of the winding, which is one side in the thickness direction, and (b) is a view of a negative ... inner side of the winding, which is the other side in the thickness direction.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments do not limit the present disclosure, and configurations formed by selectively combining multiple examples are also included in the present disclosure.

[0013] "Overall Configuration of Non-Aqueous Electrolyte Secondary Battery" Fig. 1 is a perspective view showing the general shape of a non-aqueous electrolyte secondary battery 10 according to an embodiment. Fig. 2 is a schematic partial cross-sectional view of the non-aqueous electrolyte secondary battery 10 taken along a plane that passes through the positive electrode tab 22 and includes a direction parallel to the thickness direction of the electrode body 60 and the direction of the winding axis O1. Hereinafter, the non-aqueous electrolyte secondary battery 10 will be referred to as a secondary battery 10.

[0014] The secondary battery 10 has a thin rectangular parallelepiped shape overall, and includes an electrode assembly 60, an exterior body 12 that houses the electrode assembly 60 and a non-aqueous electrolyte, a positive electrode tab 22, and a negative electrode tab 24. In this example, the secondary battery 10 is a lithium-ion secondary battery. The non-aqueous electrolyte secondary battery of the present disclosure is not limited to a lithium-ion secondary battery, and may be any non-aqueous electrolyte secondary battery that can have the configuration of the present disclosure.

[0015] In the following description and drawings, the X direction indicates a first direction, which is the thickness direction of the secondary battery 10, the Y direction indicates a second direction, which is the left-right direction of the secondary battery 10, and the Z direction indicates a third direction, which is the height direction of the secondary battery 10. The X direction, Y direction, and Z direction are perpendicular to one another. Furthermore, the α direction indicates the longitudinal direction of the positive electrode 30, and the β direction indicates the lateral direction of the positive electrode 30. The γ direction indicates the longitudinal direction of the negative electrode 40, and the δ direction indicates the lateral direction of the negative electrode 40. The α direction and the β direction are perpendicular to one another, and the γ direction and the δ direction are also perpendicular to one another.

[0016] The exterior body 12 is formed by folding a film-like laminate sheet 11 containing an adhesive resin layer in half along the bottom portion 17, and a wound electrode body 60 is housed in a cup-shaped housing portion 13.

[0017] The laminate sheet 11 is a metal layer made of, for example, aluminum or an aluminum alloy, with an inner resin layer, which is an adhesive resin layer, provided on the surface that will be on the inside when the laminate sheet 11 is folded in half and stacked. The inner resin layer is made of, for example, polypropylene. The metal layer and the inner resin layer can be adhered together using, for example, carboxylic acid-modified polypropylene, in which carboxyl groups are added to polypropylene. The electrode body 60 is then wrapped in the folded laminate sheet 11, and the remaining three sides of the laminate sheet 11 are sealed.

[0018] 1 , the exterior body 12 has a top portion 16 on the upper side, a bottom portion 17 on the lower side, a first side portion 18 on the left side, and a second side portion 20 on the right side. The top portion 16 and the first and second side portions 18, 20 are each formed by overlapping the laminate sheet 11, and a sealing portion is formed in each. The first and second side portions 18, 20 are then folded back in the thickness direction of the laminate sheet 11, so that they overlap the side walls of the storage portion 13.

[0019] The top portion 16 is the end portion opposite the bottom portion 17 of the exterior body 12, and at the overlapping portion of the outer periphery of the folded laminate sheet 11, both ends in the longitudinal direction are overlapped, and a positive electrode tab 22 and a negative electrode tab 24 are led out. The positive electrode tab 22 is connected to the positive electrode 30 of the electrode body 60. The negative electrode tab 24 is connected to the negative electrode 40 of the electrode body 60. In addition, welding resins 26, 28 described below are fixed to the positive electrode tab 22 and the negative electrode tab 24.

[0020] The secondary battery 10 equipped with such an exterior body 12 is electrically connected to an external load by the positive electrode tab 22 and the negative electrode tab 24 .

[0021] The bottom portion 17 is a folded portion of the laminate sheet 11 in the exterior body 12. The first side portion 18 and the second side portion 20 are arranged along the third direction Z at the overlapping portion of the outer periphery of the laminate sheet 11 folded in half.

[0022] In the top portion 16 and each side portion 18, 20, the opposing portions of the folded laminate sheet 11 are overlapped with their inner resin layers in contact, and the outer peripheries of the two opposing sheet elements 11a, 11b are welded by heat and pressure. A storage section 13 for storing an electrode body 60 is provided inside the overlapping portion of the sheet element 11a. A flat exterior portion 15 for closing the opening of the storage section 13 is provided on the sheet element 11b.

[0023] The electrode assembly 60 has an elongated positive electrode 30 connected to a positive electrode tab 22, and an elongated negative electrode 40 connected to a negative electrode tab 24. The positive electrode 30 and the negative electrode 40 are wound with a separator 70 interposed therebetween to form a wound electrode assembly, which is then press-molded into a flat shape. The positive electrode tab 22 is joined to the positive electrode 30 by ultrasonic welding, spot welding, or the like. The negative electrode tab 24 is joined to the negative electrode 40 by ultrasonic welding, spot welding, or the like.

[0024] The positive electrode tab 22 is led to the outside of the battery via a sealing portion 29 provided at the top of the exterior body 12, forming a positive electrode lead-out portion 22a. The negative electrode tab 24 is led to the outside of the battery via a sealing portion provided at the top of the exterior body 12, forming a negative electrode lead-out portion 24a. In FIG. 1 , the positive electrode lead-out portion 22a and the negative electrode lead-out portion 24a are spaced apart in the second direction Y and extend in the third direction Z. Each sealing portion 29 is formed by thermally welding two sheet elements 11a and 11b, with the positive electrode tab 22 and the negative electrode tab 24 sandwiched therebetween, to seal the space between the sheet elements 11a and 11b. Welding resins 26 and 28 are fixed around the peripheries of each tab 22 and 24. The welding resins 26 and 28 may be made of an insulating resin material, such as modified polyolefin, polyester, or polyvinylidene fluoride.

[0025] The laminate sheet 11 may have an outer resin layer on the surface that faces outward from the metal layer when the laminate sheet 11 is folded in half. The outer resin layer may be made of, for example, nylon. The metal layer and the outer resin layer may be bonded together using, for example, a dry laminating adhesive.

[0026] The nonaqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The nonaqueous electrolyte secondary battery 10 is preferably a lithium ion battery. The electrolyte salt may be, for example, LiBF ４ , LiPF ６Examples of the non-aqueous solvent include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0027] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). From the viewpoint of suppressing a decrease in the charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery or improving input characteristics, the nonaqueous electrolyte preferably contains 5% by mass or more of FEC, and more preferably 5% by mass to 15% by mass of FEC, relative to the mass of the nonaqueous electrolyte.

[0028] 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.).

[0029] "Configuration of electrode assembly and arrangement of electrode tabs" The configuration of the electrode assembly 60 and the arrangement of the electrode tabs, that is, the positive electrode tab 22 and the negative electrode tab 24, in the electrode assembly 60 will be described in detail using the above-mentioned Figure 2 and Figures 3 to 5. Figure 3(a) is a schematic cross-sectional view perpendicular to the direction of the winding axis O1 of the electrode assembly 60 that constitutes the secondary battery 10. Figure 3(b) is an enlarged view of part A in Figure 3(a), and Figure 3(c) is an enlarged view of part B in Figure 3(a).

[0030] As shown in Figures 2 and 3, the electrode assembly 60 is formed by winding a long positive electrode 30 and a long negative electrode 40 in a flat shape with a separator 70 interposed therebetween. In Figure 3, the positive electrode 30 is represented by a shape in which a thick solid line and a thin solid line are connected. The negative electrode 40 is represented by a dashed line. The separator is not shown in Figure 3.

[0031] Furthermore, the thick line portion of the positive electrode 30 indicates a portion where a positive electrode mixture layer 32 ( FIG. 3 ) is formed on at least one surface of the positive electrode core 31, and the thin line portion indicates a portion where a positive electrode mixture layer is not formed on either surface of the positive electrode core 31. In the inner peripheral portion of the electrode body 60, the negative electrode 40 extends from the winding start end of the positive electrode 30 toward the winding start side. On the other hand, in the outer peripheral portion of the electrode body 60, the positive electrode 30 extends from the winding end end of the negative electrode 40 toward the winding end side. In this manner, the positive electrode 30 is disposed on the outermost periphery of the electrode body 60, and the winding end end of the positive electrode 30 is fixed by a winding stop tape 55 attached to the outermost peripheral surface of the positive electrode 30 across the winding end end of the positive electrode 30.

[0032] When the outermost periphery of the positive electrode 30 is divided into two halves, one on the side of the exterior body flat portion 15 ( FIG. 2 ) and the other on the side of the bottom end 13a of the housing portion 13, by a plane Q1 that is perpendicular to the thickness direction and passes through the winding axis O1, the positive electrode tab 22 is attached to the side of the exterior body flat portion 15. More specifically, as shown in FIG. 3 , when the electrode body 60 is cut along a cross section perpendicular to the winding axis O1, the cross-sectional shape of the electrode body 60 includes two arc portions R1 and R2 and two connecting portions T1 and T2 that connect one end of the two arc portions R1 and R2 to each other and the other end of the two arc portions R1 and R2 to each other. In this case, the positive electrode tab 22 is joined to a core exposed portion 31a that constitutes the connecting portion T1 on the exterior body flat portion 15 side of the outermost periphery 35 of the positive electrode 30 and is provided on the inner side of the winding of the outermost periphery 35 on the arc portion R1 side. As a result, the positive electrode tab 22 is attached to the outermost periphery 35 of the positive electrode 30 on the side of the exterior body flat portion 15. The core exposed portion 31a of the positive electrode 30 and the portion of the positive electrode tab 22 that overlaps with the core exposed portion 31a are covered with insulating tape 50. The insulating tape 50 is made of an insulating material such as polyimide. A portion of the insulating tape 50 may be attached to the surface of the positive electrode mixture layer. The positive electrode tab 22 may be joined to a core exposed portion provided on the winding outer side of a portion of the positive electrode 30 that constitutes the connecting portion T1 on the exterior body flat portion 15 side.

[0033] On the other hand, the negative electrode tab 24 is attached to an intermediate periphery 45 between the innermost and outermost peripheries of the negative electrode 40, on the side of the exterior body flat portion 15 when the electrode assembly 60 is divided in two by a plane Q1 perpendicular to the thickness direction. More specifically, in the above-described cross-sectional shape obtained by cutting the electrode assembly 60 along a cross section perpendicular to the winding axis O1, the negative electrode tab 24 is joined to a core exposed portion 41a that constitutes the connecting portion T1 on the exterior body flat portion 15 side of the intermediate periphery 45 of the negative electrode 40 and is provided on the inner side of the winding on the arc portion R2 side of the intermediate periphery 45. As a result, the negative electrode tab 24 is attached to the exterior body flat portion 15 side of the intermediate periphery 45 of the negative electrode 40. As described below, this improves safety in the event of a drop impact and reduces internal resistance in the secondary battery 10.

[0034] The attachment portion of the negative electrode tab 24 on the negative electrode 40 is preferably provided in the central 1 / 3 range between the innermost and outermost surfaces of the electrode body 60 in the thickness direction of the electrode body 60, which coincides with the first direction X in Figure 3, of the connecting portion T1 on the outer body flat portion 15 side of the electrode body 60.

[0035] The exposed core portion 41 a of the negative electrode 40 and the portion of the negative electrode tab 24 that overlaps with the exposed core portion 41 a are covered with insulating tape 50. A portion of the insulating tape 50 may be attached to the surface of the negative electrode mixture layer. The negative electrode tab 24 may be joined to the exposed core portion of the negative electrode 40 that is provided on the wound outer side of the portion that constitutes the connecting portion T1 on the exterior body flat portion 15 side.

[0036] 4(a) is a view of the positive electrode 30 in an expanded state as seen from the outer side of the winding, which is one side in the thickness direction, and FIG. 4(b) is a view as seen from the inner side of the winding, which is the other side in the thickness direction. The up-down direction of the positive electrode 30 is reversed in FIG. 4(a) and FIG. 4(b). In FIG. 4, the left edge of the positive electrode 30 on the paper surface is the winding start end. In FIG. 4, the length of the positive electrode 30 in the longitudinal direction of the electrode plate is shown shorter than it actually is.

[0037] The positive electrode 30 includes a positive electrode core 31 and a positive electrode mixture layer 32 provided on both sides of the positive electrode core 31. In FIG. 4 , the positive electrode core 31 is shown as a coarse sandy area, and the positive electrode mixture layer 32 is shown as a fine sandy area. The positive electrode mixture layer 32 provided on the inner surface of the positive electrode core 31 shown in FIG. 4( b) includes an extension 36 that extends toward the end of the winding beyond the end of the positive electrode mixture layer 32 provided on the outer surface of the positive electrode core 31 shown in FIG. 4( a). The positive electrode tab 22 is attached to the core exposed portion 31 a by joining, by ultrasonic welding or the like, to the core exposed portion 31 a sandwiched between two positive electrode mixture layer 32-forming portions A1 and A2 spaced apart in the longitudinal direction of the positive electrode 30, which is the winding direction of the extension 36. The core exposed portion 31a is an exposed portion of the surface of the metal constituting the positive electrode core 31 that is not covered by the positive electrode mixture layer 32. The core exposed portion 31a is formed only in a portion including one end of the positive electrode 30 in the direction of the winding axis O1 of the electrode body 60 (the upper end in FIG. 4A and the lower end in FIG. 4B).

[0038] In this way, the positive electrode tab 22 is attached to the core exposed portion 31a sandwiched between the two positive electrode mixture layer 32 formation portions A1, A2 spaced apart in the winding direction of the positive electrode 30, thereby increasing the rigidity of the positive electrode 30 around the attachment portion of the positive electrode tab 22. This makes it difficult for the attachment portion of the positive electrode 30 to deform. This further improves the safety of the secondary battery 10 in the event of a drop impact, as described below. Furthermore, the capacity of the secondary battery 10 can be increased.

[0039] 4 , among longitudinal portions of the positive electrode mixture layer 32 on the inside and outside of the positive electrode 30, a core exposed portion 31a is formed only in a portion in the winding axis direction of the electrode body 60, and no positive electrode tab is attached to this core exposed portion 31a, which is covered with insulating tape 50. The core exposed portion 31a to which no positive electrode tab is attached is provided to prevent the positive electrode mixture layer 32 from facing, via the separator 70, a portion facing a core exposed portion or a negative electrode tab 24 provided on both sides of the negative electrode 40 described below, when the electrode body 60 is formed. This makes it possible to suppress Li deposition on the negative electrode 40 during charging.

[0040] In addition, an insulating tape 51 is attached to the boundary between the positive electrode core 31 and the positive electrode mixture layer 32. A step occurs depending on whether or not the positive electrode mixture layer 32 is present. When an external force is applied to the secondary battery, for example, when the secondary battery is accidentally dropped, the positive electrode mixture may slide off near this boundary, and the fallen positive electrode mixture may cause a short circuit. The insulating tape 51 is provided to prevent such a short circuit.

[0041] Figure 5(a) is a view of the negative electrode 40 in an unfolded state as seen from the outer side of the winding, which is one side in the thickness direction, and Figure 5(b) is a view as seen from the inner side of the winding, which is the other side in the thickness direction. The up-down direction of the negative electrode 40 is reversed in Figures 5(a) and 5(b). In Figure 5, the left edge of the negative electrode 40 on the paper surface is the winding start end. In Figure 5, the longitudinal length of the negative electrode 40 is shown shorter than it actually is.

[0042] The negative electrode 40 includes a negative electrode core 41 and a negative electrode mixture layer 42 provided on both sides of the negative electrode core 41. In FIG. 5 , the negative electrode core 41 is shown as a coarse sandy area, and the negative electrode mixture layer 42 is shown as a fine sandy area. The negative electrode mixture layer 42 provided on the outer surface of the negative electrode core 41 shown in FIG. 5( a) extends further toward the winding start side than the winding start end of the negative electrode mixture layer 42 provided on the inner surface of the negative electrode core 41 shown in FIG. 5( b). The negative electrode tab 24 is joined by ultrasonic welding or the like to a core exposed portion 41 a sandwiched between two longitudinally separated negative electrode mixture layer 42 formation portions B1 and B2 on the inner side of the winding in the middle portion of the longitudinal direction (the winding direction) of the negative electrode 40. This allows the negative electrode tab 24 to be attached to the core exposed portion 41 a. At this time, similar to the core exposed portion 31a, the core exposed portion 41a is formed only in a portion including one end of the negative electrode 40 in the direction of the winding axis of the electrode body 60. This also further improves the safety of the secondary battery in the event of a drop impact.

[0043] According to the secondary battery 10 described above, the positive electrode tab 22 is attached to the outermost periphery 35 of the positive electrode 30, closer to the flat portion 15 of the exterior body. As a result, as shown in FIG. 2 , within the exterior body 12, the portion of the positive electrode tab 22 extending from the electrode assembly 60 toward the sealing portion 29 can extend substantially along the third direction Z toward the sealing portion 29 without being significantly bent toward the flat portion 15 of the exterior body. Therefore, the significantly bent portion of the positive electrode tab 22 does not ride up onto the edge of the separator on the top portion 16 side. Therefore, even if the battery 10 is dropped with the leading portions 22 a, 24 a of the tabs 22, 24 facing downwards, and an external force is applied from the leading side of the positive electrode tab 22 of the exterior body 12 toward the electrode assembly 60, the positive electrode tab 22 is prevented from being strongly pressed against the negative electrode via the separator. This prevents short-circuiting of the secondary battery 10, thereby improving the safety of the secondary battery 10.

[0044] Furthermore, when the positive electrode tab 22 is led out through the sealing portion 29 in the top portion 16 of the exterior body 12, the length between the lead-out start point from the electrode body 60 and the sealing portion 29 can be reduced. This reduces the variation in the path length of the positive electrode tab 22 between them, making it easier to position the positive electrode tab 22. This makes it easier to weld the positive electrode tab 22 to the exterior body, improving the reliability of the sealing portion 29.

[0045] Furthermore, the negative electrode tab 24 is attached to an intermediate periphery 45 between the innermost and outermost peripheries of the negative electrode 40. As a result, the attachment position of the negative electrode tab 24 on the negative electrode 40 is closer to the center in the longitudinal direction of the negative electrode 40 compared to when the negative electrode tab 24 is attached to the outermost periphery of the negative electrode 40. This improves the current collection efficiency through the negative electrode tab 24 of the negative electrode 40, thereby reducing the electrical resistance of the negative electrode 40 and the internal resistance of the secondary battery 10.

[0046] Furthermore, by attaching the negative electrode tab 24 to the intermediate circumference 45 of the negative electrode 40, the positive electrode tab 22 and the negative electrode tab 24 are spaced apart in the thickness direction of the electrode assembly 60. The positive electrode tab 22 and the negative electrode tab 24 are spaced apart on one side of the arc portion R1 and the other side of the arc portion R2 in the cross-sectional shape of the electrode assembly 60 perpendicular to the winding axis O1 direction. Therefore, even if the above-mentioned drop impact occurs, deformation of the connection portions between the positive electrode tab 22 and the negative electrode tab 24 and the electrode assembly 60 can be prevented from causing concentrated high pressure on the positive electrode 30 and the negative electrode 40. For example, because a circumferential portion of at least one of the positive electrode 30 and the negative electrode 40 is interposed between the respective connection portions, the deformation of the respective connection portions is less likely to cause an interaction that leads to the above-mentioned high pressure. This further suppresses short-circuiting of the secondary battery 10, thereby further improving safety in the event of a drop impact.

[0047] Furthermore, in each of the positive electrode 30 and the negative electrode 40, the core exposed portions 31a, 41a are formed only in a portion of the winding axis direction, thereby increasing the proportion of the positive electrode mixture layer 32 and the negative electrode mixture layer 42 in the positive electrode 30 and the negative electrode 40, respectively. This increases the capacity of the secondary battery 10. Furthermore, the periphery of the attachment portion of the positive electrode tab 22 in the positive electrode core 31 is surrounded by the positive electrode mixture layer 32, and the periphery of the attachment portion of the negative electrode tab 24 in the negative electrode core 41 is surrounded by the negative electrode mixture layer 42. This increases the rigidity around the attachment portions of the tabs 22, 24, making the attachment portions of the positive electrode tab 22 and the negative electrode tab 24 in the positive electrode 30 and the negative electrode 40 less likely to deform. This further reduces the high compression when the above-mentioned drop impact occurs, thereby further improving safety.

[0048] Furthermore, because the negative electrode tab 24 is attached to the intermediate periphery 45 of the negative electrode 40, a bent portion is formed inside the exterior housing 12 at the portion of the negative electrode tab 24 extending from the electrode assembly 60 toward the sealing portion 29, where the bent portion is bent significantly toward the exterior housing flat portion 15. This may cause this bent portion to ride up onto the end of the separator 70 on the top portion 16 side. However, as shown in FIG. 2 , in the electrode assembly 60, the height of the negative electrode 40 along the winding axis O1 is generally greater than the height of the positive electrode 30. This makes it less likely for a short circuit to occur even if the bent portion of the negative electrode tab 24 is bent toward the electrode assembly 60 upon the above-described drop impact.

[0049] In the embodiment, the negative electrode tab 24 is positioned closer to the exterior flat portion 15 than the center of the thickness direction of the electrode assembly 60. The negative electrode tab 24 can be formed using a tab forming device (not shown). The tab forming device includes a receiving jig, a bending jig that moves relative to the receiving jig, and a drive device that moves the bending jig. The negative electrode tab 24 is formed into a shape having a bent portion by sandwiching and pressing a linearly extending negative electrode tab before processing between the receiving jig and the bending jig. At this time, a protrusion that protrudes in a direction perpendicular to the extension direction of the negative electrode tab before processing is formed on the forming surface of the receiving jig. The tip of the protrusion is abutted against the negative electrode tab before processing to form a starting point for the bent portion. As described above, when the negative electrode tab 24 is positioned closer to the exterior flat portion 15 than the center of the thickness direction of the electrode assembly 60, the amount of bending of the bent portion can be reduced, and the height of the protrusion of the receiving jig can also be reduced. This allows the negative electrode tab 24 to be bent with high precision. This makes it possible to suppress variations in the position of the welding resin 28 fixed to the negative electrode tab 24, and to weld the sealing portion 29 with higher precision. This makes it possible to improve the reliability of the sealing portion 29.

[0050] FIG. 6 is a schematic partial cross-sectional view of a comparative example secondary battery 10a taken along a plane passing through the positive electrode tab 22 and including a direction parallel to the thickness direction and the winding axis O2. FIG. 7(a) is a schematic cross-sectional view of the electrode body 60a constituting the secondary battery 10a, perpendicular to the winding axis O2. FIG. 7(b) is an enlarged view of portion C in FIG. 7(a), and FIG. 7(c) is an enlarged view of portion D in FIG. 7(a). FIG. 8(a) is a view of the positive electrode 30a constituting the secondary battery 10a in a deployed state, as seen from the outer side of the winding, which is one side in the thickness direction, and FIG. 8(b) is a view of the negative electrode 40a constituting the secondary battery 10a in a deployed state, as seen from the outer side of the winding, which is one side in the thickness direction, and FIG. 8(b) is a view of the negative electrode 40a constituting the secondary battery 10a in a deployed state, as seen from the inner side of the winding, which is the other side in the thickness direction.

[0051] As shown in Figures 6 to 9, in the secondary battery 10a of the comparative example, unlike the secondary battery 10 of the embodiment shown in Figures 1 to 5, the positive electrode tab 22 is attached not to the outermost periphery of the positive electrode 30a but to an intermediate periphery 37 (Figure 7) between the innermost and outermost peripheries of the positive electrode 30a, and is attached to the side of the exterior body flat portion 15 (upper side in Figure 7(a)) when the electrode body 60 is divided into two by a plane Q2 perpendicular to the thickness direction.

[0052] 8, when the positive electrode 30a is in an expanded state, the positive electrode tab 22 is joined to a core exposed portion 31b provided in the longitudinal middle portion of the positive electrode 30a near the winding start end. The core exposed portion 31b extends over the entire direction of the winding axis O2 of the positive electrode 30a (direction β in FIG. 8).

[0053] 9 , in the developed state of the negative electrode 40a, the negative electrode tab 24 is joined to a core exposed portion 41b provided toward the winding end of a longitudinally intermediate portion of the negative electrode 40. Similar to the core exposed portion 31a, the core exposed portion 41b also extends over the entire negative electrode 40 in the direction of the winding axis O2.

[0054] In this comparative example, a portion of the positive electrode tab 22 extending from the electrode assembly 60 toward the sealing portion 29 forms a bent portion 38 that is bent significantly toward the flat portion 15 of the exterior housing. Therefore, as shown in the area surrounded by a dashed-dotted line frame E in FIG. 6 , a portion of the positive electrode tab 22 rides up onto the end of the separator 70 on the top portion 16 side. Therefore, if the battery is dropped with the respective leading portions 22a of the positive electrode tab 22 and the negative electrode tab 24 facing downwards, and an external force is applied to the electrode assembly 60 from the sealing portion 29 side of the exterior housing 12, a drop impact occurs. This may cause the positive electrode tab 22 to be pressed strongly against the negative electrode 40 via the separator 70, resulting in a short circuit. This leaves room for improvement in the comparative example in terms of improving safety during a drop impact.

[0055] 1 to 5, as shown in Fig. 2, the positive electrode tab 22 is attached to the outermost periphery of the positive electrode 30 on the side of the flat portion 15 of the exterior body. This prevents the positive electrode tab from climbing up onto the separator as in the comparative example, even if a drop impact occurs in which an external force is input to the electrode body 60 from the sealing portion 29 side of the exterior body 12, thereby suppressing a short circuit.

[0056] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples.

[0057] Example [Fabrication of Secondary Battery] A wound electrode assembly 60 was fabricated by spirally winding a positive electrode 30 and a negative electrode 40 with a separator 70 interposed therebetween, and then press-molded into a flat shape. The electrode assembly 60 was then housed in the housing portion 13 of the exterior body 12 so that both end surfaces of the electrode assembly 60 in the direction of the winding axis faced the bottom portion 17 and the top portion 16, respectively. The positive electrode tab 22 connected to the positive electrode 30 and the negative electrode tab 24 connected to the negative electrode 40 of the electrode assembly 60 were led out from the top portion 16 of the exterior body 12. As in the embodiment shown in FIGS. 1 to 5 , the positive electrode tab 22 was attached to the exterior body flat portion 15 at the outermost periphery of the positive electrode 30, and the negative electrode tab 24 was attached to the exterior body flat portion 15 at the intermediate periphery 45 between the innermost and outermost peripheries of the negative electrode 40. A liquid electrolyte (non-aqueous electrolyte solution) was injected into the laminate sheet 11 housing the electrode assembly 60 and sealed. In this way, the secondary battery 10 of Example 1 was fabricated.

[0058] The fabricated secondary battery 10 had a height of 69 mm in the third direction Z, a thickness of 4.9 mm in the first direction X, and a width of 56 mm in the second direction Y, excluding the lead-out portions of the positive electrode tab 22 and the negative electrode tab 24. The rated capacity of the secondary battery 10 was 3150 mAh.

[0059] [Drop Test] As a configuration simulating a battery pack including the secondary battery 10, a test was made in which the secondary battery 10 was sandwiched between two acrylic resin plates, and the test was performed in which the test specimen was dropped from a height of 1 m with the lead-out portions of the positive electrode tab 22 and the negative electrode tab 24 facing downward, 10 times for each of five test specimens, and the presence or absence of a voltage drop due to a short circuit was confirmed.

[0060] [Measurement of Internal Resistance] The internal resistance of the fabricated secondary battery 10 was measured. The internal resistance was measured for 30 secondary batteries, and the average value of the internal resistances was calculated.

[0061] Comparative Example 1 A secondary battery 10a of Comparative Example 1 was fabricated having a configuration similar to that of the comparative examples shown in FIGS. 6 to 9 . A drop test was conducted using a test sample simulating a battery pack including the fabricated secondary battery 10a to check for voltage drop and to measure the internal resistance of the secondary battery 10a in the same manner as in the examples. Other configurations of Comparative Example 1 were the same as those of the examples. In Comparative Example 1, the positive electrode tab 22 was attached to the intermediate periphery between the innermost and outermost peripheries of the positive electrode 30a, and the negative electrode tab 24 was attached to the intermediate periphery between the innermost and outermost peripheries of the negative electrode 40a.

[0062] 1 to 5, the negative electrode tab was attached to the outermost flat portion of the exterior body of the negative electrode. The negative electrode tab and the positive electrode tab were arranged apart in the second direction Y of the electrode body. In Comparative Example 2, the configuration other than the arrangement of the negative electrode tab was the same as in the Example. In Comparative Example 2, only the internal resistance was measured in the same manner as in the Example.

[0063] <Test Results> Table 1 shows the results of the drop test for the secondary batteries 10 and 10a according to the example and comparative example 1.

[0064]

[0065] In Table 1, for each of the five test samples (N=5), it was confirmed whether a voltage drop was confirmed at least once in ten drop tests. "5 / 5 No voltage drop" in the Example column indicates that no voltage drop was confirmed in any of the five test samples. "3 / 5 Voltage drop" in the Comparative Example 1 column indicates that a voltage drop was confirmed in three of the five test samples.

[0066] As can be seen from the results shown in Table 1, in the examples, no voltage drop was confirmed in any of the test samples, and no short circuits occurred. This is thought to be because, in the examples, there were no large bends in the positive electrode tab 22 inside the test samples, and the positive electrode tab 22 did not climb onto the separator 70. Therefore, even when an external force was applied due to a drop impact, a short circuit in which the positive electrode tab 22 came into contact with the negative electrode 40 was unlikely to occur. As a result, it was confirmed that the examples could improve safety in the event of a drop impact.

[0067] On the other hand, a voltage drop was observed in some of the test samples in Comparative Example 1. The reason for this is thought to be that in Comparative Example 1, the test sample had a large bent portion 38 in the positive electrode tab 22 inside, causing the positive electrode tab 22 to climb up onto the separator 70, and therefore, when an external force was applied due to a drop impact, a short circuit occurred in which the positive electrode tab 22 came into contact with the negative electrode 40a.

[0068] Table 2 shows the measurement results of the internal resistance of the secondary batteries 10 and 10a according to the example, comparative example 1, and comparative example 2.

[0069]

[0070] In Table 2, the internal resistance was measured for each of the 30 test samples, and the average value of the internal resistances was expressed as an index. The index is expressed as a relative value of the internal resistance of Example 1 and Comparative Example 1, with the internal resistance of Comparative Example 2 set at 100.

[0071] As can be seen from the results shown in Table 2, the internal resistance of Comparative Example 1 is approximately half that of Comparative Example 2. This is because, in Comparative Example 2, the positive electrode tab and the negative electrode tab are attached to the outermost periphery of the positive electrode and the negative electrode, respectively, and the positive electrode tab and the negative electrode tab are attached near the longitudinal winding end of the positive electrode and the negative electrode, respectively. In this case, the length from each positive electrode tab and each negative electrode tab to the longitudinal winding start end of the electrode plate increases, and the current collection efficiency through the positive electrode tab and the negative electrode tab decreases. This is thought to have increased the electrical resistance of the positive electrode and the negative electrode.

[0072] On the other hand, in Comparative Example 1, the positive electrode tab 22 and the negative electrode tab 24 are attached to the intermediate periphery between the outermost and innermost peripheries of the positive electrode 30a and the negative electrode 40a, respectively. This allows the positive electrode tab 22 and the negative electrode tab 24 to be attached at positions significantly removed from the longitudinal winding end of the positive electrode 30a and the negative electrode 40a, respectively. Therefore, the attachment portion of the positive electrode tab 22 can be positioned closer to the longitudinal center of the positive electrode, and the attachment portion of the negative electrode tab 24 can be positioned closer to the longitudinal center of the negative electrode. This improves the current collection efficiency through the positive electrode tab 22 and the negative electrode tab 24, reducing the electrical resistance of the positive electrode 30a and the negative electrode 40a. It is believed that the internal resistance of the secondary battery 10a was reduced to approximately half that of Comparative Example 2.

[0073] On the other hand, in the Example, the positive electrode tab 22 is attached to the outermost periphery of the positive electrode 30, which is disadvantageous in terms of electrical resistance compared to Comparative Example 1, but the negative electrode tab 24 is attached to an intermediate winding portion between the outermost and innermost peripheries of the negative electrode 40. As a result, in the Example, the attachment portion of the negative electrode tab 24 can be moved closer to the center in the longitudinal direction of the electrode plate in the negative electrode 40 compared to Comparative Example 2, thereby improving the current collection efficiency through the negative electrode tab 24. For this reason, as shown in Table 1, it is believed that the internal resistance of the secondary battery 10 was able to be reduced to a level equivalent to that of Comparative Example 1.

[0074] As described above, it was confirmed that the embodiment can significantly reduce the internal resistance compared to the comparative example 2, and can improve safety in the event of a drop impact compared to the comparative example 1.

[0075] In the case of Comparative Example 2, the positive electrode tab is attached to the outermost flat portion of the positive electrode exterior, and the negative electrode tab is attached to the outermost flat portion of the negative electrode exterior. This means that the positive electrode tab and the negative electrode tab are positioned at approximately the same position in the thickness direction of the electrode body, and therefore, when an external input is applied to the battery after being dropped and impacted, the space between the positive electrode and the negative electrode is likely to be compressed, which is thought to be disadvantageous in terms of preventing short circuits.

[0076] In this way, the configuration of the present disclosure can improve safety in the event of a drop impact and reduce internal resistance.

[0077] The present disclosure will be further described by the following embodiments. Configuration 1: A nonaqueous electrolyte secondary battery comprising: a flat-shaped electrode assembly in which a positive electrode connected to a positive electrode tab and a negative electrode connected to a negative electrode tab are wound with a separator interposed therebetween; and an exterior housing in which a laminate sheet including an adhesive resin layer is folded along a bottom portion to join the peripheral edges of two opposing sheet elements, and each of the two sheet elements is provided with a cup-shaped housing portion that houses the electrode assembly and a flat housing portion that closes the opening of the housing portion, when the outermost periphery of the positive electrode is divided into two, at the side of the flat housing portion and the side of the bottom end of the housing portion, the positive electrode tab is attached to the side of the flat housing portion and extends from a top portion of the exterior housing opposite the bottom portion, and the negative electrode tab is attached to an intermediate periphery between the innermost and outermost peripheries of the negative electrode and extends from the top portion. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the positive electrode tab is attached to a positive electrode substrate exposed portion located between two positive electrode mixture layers spaced apart in the winding direction in the positive electrode.Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the negative electrode tab is arranged on the outer casing flat portion side with respect to the center in the thickness direction of the electrode body.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the positive electrode tab is attached to a positive electrode substrate exposed portion formed on only a portion of the positive electrode in the winding axis direction of the electrode body, and the negative electrode tab is attached to a negative electrode substrate exposed portion formed on only a portion of the negative electrode in the winding axis direction.

[0078] REFERENCE SIGNS LIST 10, 10a Non-aqueous electrolyte secondary battery (secondary battery), 11 Laminate sheet, 12 Exterior body, 13 Housing portion, 15 Exterior body flat portion, 16 Top portion, 17 Bottom portion, 18 First side portion, 20 Second side portion, 22 Positive electrode tab, 24 Negative electrode tab, 25 Bent portion, 26, 28 Welding resin, 29 Sealing portion, 30, 30a Positive electrode, 31 Positive electrode core, 32 Positive electrode mixture layer, 35 Outermost periphery, 36 Extension portion, 37 Intermediate periphery, 38 Bent portion, 40, 40a Negative electrode, 41 Negative electrode core, 42 Negative electrode mixture layer, 45 Intermediate periphery, 50, 51 Insulating tape, 55 Winding tape, 60, 60a Electrode body, 70 Separator.

Claims

1. A nonaqueous electrolyte secondary battery comprising: a flat electrode assembly in which a positive electrode connected to a positive electrode tab and a negative electrode connected to a negative electrode tab are wound with a separator interposed therebetween; and an exterior body in which a laminate sheet including an adhesive resin layer is folded along a bottom portion, and the peripheral portions of two opposing sheet elements are joined, and each of the two sheet elements is provided with a cup-shaped container portion for accommodating the electrode assembly and a flat container portion for closing the opening of the container portion; wherein, when the outermost periphery of the positive electrode is divided into two, at the side of the flat container portion and the side of the bottom end of the container portion, the positive electrode tab is attached to the side of the flat container portion and extends from the top portion of the exterior body opposite the bottom portion; and the negative electrode tab is attached to an intermediate periphery between the innermost and outermost peripheries of the negative electrode and extends from the top portion.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode tab is attached to an exposed portion of the positive electrode substrate located between two positive electrode mixture layers spaced apart in the winding direction.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode tab is disposed on the flat portion side of the exterior body relative to the center in the thickness direction of the electrode body.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode tab is attached to a positive electrode substrate exposed portion formed on only a portion of the positive electrode in the direction of the winding axis of the electrode body, and the negative electrode tab is attached to a negative electrode substrate exposed portion formed on only a portion of the negative electrode in the direction of the winding axis.

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