Secondary battery

Abstract

According to an embodiment, a secondary battery comprises an electrode body accommodated within an exterior container. The electrode body includes: an electrode group including a plurality of stacked positive electrode plates, negative electrode plates, and separators; a positive electrode current collecting tab group including a plurality of stacked positive electrode current collecting tabs, the positive electrode current collecting tab group extending in one direction from the electrode group; and a negative electrode current collecting tab group including a plurality of stacked negative electrode current collecting tabs, the negative electrode current collecting tab group extending in another direction from the electrode group. At least a portion of the positive electrode current collecting tab group constitutes a binding part in which the plurality of positive electrode current collecting tabs are collected in the thickness direction by a binding member. The thickness of the separator is 4-6 µm. The ratio (WS / W3) of the separator width WS to the coating width W3 of an active material layer having the greater coating width, among an active material layer of the positive electrode plates and an active material layer of the negative electrode plates, is 1.01 < WS / W3 < 1.06. The ratio (T / d2) of the thickness T of the electrode group at the position of the binding part to the difference d2 between the winding-axis-direction length W2 of the positive electrode current collecting tabs and the winding-axis-direction length d1 of the binding member is 0.865 < T / d2 < 2.

Description

secondary battery

[0001] FIELD An embodiment of the present invention relates to a secondary battery.

[0002] In recent years, high-energy-density secondary batteries, such as nonaqueous electrolyte secondary batteries, have been widely used as power sources for electronic devices and electric vehicles. Such secondary batteries include an outer container and an electrode assembly housed in the container together with a nonaqueous electrolyte. In one example, the electrode assembly is configured by stacking or winding a positive electrode, a negative electrode, and a separator. Positive and negative electrode terminals provided on the outer container are connected to the positive and negative electrode current collecting tabs of the electrode assembly via positive and negative electrode leads, respectively.

[0003] JP 2020-95797 A JP 2014-203659 A JP 2021-89857 A

[0004] In the secondary battery described above, a thinner separator can be used to achieve higher power output. However, if the separator is made thinner, the separator may tear near the binding portion when the current collecting tab is joined, causing contact between the electrode end and the current collecting tab, resulting in poor insulation. Furthermore, there is a problem that the separator may shrink at high temperatures, causing contact between the positive electrode and the negative electrode, resulting in a short circuit. An object of the present invention is to provide a secondary battery that can achieve high power output while maintaining insulation and heat resistance.

[0005] According to the embodiment, the secondary battery includes an outer container and an electrode assembly housed in the outer container. The electrode assembly is configured by winding a positive electrode plate having a foil-shaped positive electrode current collector, an active material layer coated on the positive electrode current collector, and a positive electrode current collector tab formed at one side edge portion in the width direction of the positive electrode current collector, a negative electrode plate having a foil-shaped negative electrode current collector, an active material layer coated on the negative electrode current collector, and a negative electrode current collector tab formed at one side edge portion in the width direction of the negative electrode current collector, and a sheet-like separator disposed between the positive electrode plate and the negative electrode plate and facing the active material layer, around a winding central axis, and includes an electrode group including a stacked plurality of layers of the positive electrode plate, the negative electrode plate, and the separator, a positive electrode current collector tab group including a stacked plurality of layers of the positive electrode current collector tabs and extending from the electrode group in one direction in the direction of the winding central axis, and a negative electrode current collector tab group including a stacked plurality of layers of the negative electrode current collector tabs and extending from the electrode group in the other direction in the direction of the winding central axis. At least a portion of the positive electrode current collecting tab group constitutes a bundling section in which multiple layers of positive electrode current collecting tabs are bundled in the thickness direction by a bundling member, the thickness of the separator is 4 μm or more and 6 μm or less, the ratio (WS / W3) of a coating width W3 of one of the active material layers of the positive electrode plate and the active material layer of the negative electrode plate, which has a wider coating width, to a width WS of the separator is 1.01 < WS / W3 < 1.06, and the ratio (T / d2) of a thickness T of the electrode group at the bundling section to a difference d2 between a length W2 of the positive electrode current collecting tab in the direction of the winding central axis and a length d1 of the bundling member in the direction of the winding central axis is 0.865 < T / d2 < 2.

[0006] Fig. 1 is a side view of a secondary battery according to an embodiment, showing the outer case of the secondary battery cut away; Fig. 2 is a perspective view of an electrode body of the secondary battery according to an embodiment, showing a part of the electrode body in a developed state; Fig. 3 is a cross-sectional view of the electrode body at the tab binding portion taken along line A-A in Fig. 1;

[0007] Hereinafter, a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that are easily conceivable by those skilled in the art while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals, and detailed descriptions may be appropriately simplified or omitted.

[0008] 1 is a side view of a secondary battery according to an embodiment, showing the outer container of the secondary battery cut away. As shown in the figure, the secondary battery 10 is a non-aqueous electrolyte secondary battery such as a lithium ion battery, and includes a flat, approximately rectangular outer container 12 and an electrode assembly 30 housed together with a non-aqueous electrolyte solution in the outer container 12. The outer container 12 is an outer can (battery case) formed of a metal plate such as aluminum, an aluminum alloy, iron, or stainless steel.

[0009] The outer container 12 has a container body 16 with an open top end and a rectangular plate-shaped lid 14 that is welded to the container body 16 and closes the opening of the container body 16, forming an airtight interior. The lid 14 is provided with a pair of output terminals, a positive electrode terminal 20 and a negative electrode terminal 21, a pressure release valve (safety valve) not shown, and an injection port. The injection port is sealed with a disk-shaped sealing lid 22. Here, the longitudinal direction of the lid 14 and container body 16 is defined as X, the thickness direction of the lid 14 and container body 16 that is perpendicular to the longitudinal direction X is defined as Y, and the height direction of the container body 16 is defined as Z.

[0010] The container body 16 of the outer container 12 has a pair of long side walls 16a that are spaced apart and parallel to each other, a pair of short side walls 16c that are spaced apart and parallel to each other, and a bottom wall 16d. A rectangular top opening is defined by the upper edges of the pair of long side walls 16a and the pair of short side walls 16c. The lid 14 is formed as a rectangular plate approximately the same size as the top opening. The outer periphery of the lid 14 is welded to the upper periphery of the container body 16, and the lid 14 is fixed to the container body 16 while closing the top opening. The lid 14 is preferably laser welded to the container body 16 or bonded with a sealing material such as an adhesive resin. The container body 16 can be made of aluminum, an aluminum alloy, iron, stainless steel, or the like. The lid 14 and the container body 16 are preferably made of the same type of metal. The thickness of the container body 16 is preferably 0.5 mm or less.

[0011] A pair of sealing materials, e.g., gaskets 18, made of an insulator such as synthetic resin or glass, are disposed on the outer surface of the lid 14. A positive terminal 20 is placed on one of the gaskets 18. The positive terminal 20 has a connecting rod 20a that penetrates the gasket 18 and the lid 14 and extends into the container body 16. A negative terminal 21 is placed on the other gasket 18. The negative terminal 21 has a connecting rod 21a that penetrates the gasket 18 and the lid 14 and extends into the container body 16. The positive terminal 20 and the negative terminal 21 are formed of a conductive material such as aluminum, an aluminum alloy, copper, or a copper alloy.

[0012] The positive electrode terminal 20 is electrically connected to the positive electrode current collector tab group 32A of the electrode assembly 30 via a positive electrode lead 24 disposed within the container body 16. The positive electrode lead 24 is formed of a metal plate and integrally includes a rectangular plate-shaped first joint portion 24a and an elongated rectangular plate-shaped second joint portion 24b perpendicular to the first joint portion 24a. The first joint portion 24a abuts against the inner surface of the lid 14 via an insulator 27 and is joined to the connection rod 20b of the positive electrode terminal 20. The second joint portion 24b is positioned opposite the positive electrode current collector tab group 32A and is joined to the positive electrode current collector tab group 32A via a backup lead BR1 (described later). The positive electrode lead 24 and the backup lead BR1 are formed of a conductive material such as aluminum or an aluminum alloy.

[0013] The negative electrode terminal 21 is electrically connected to the negative electrode current collector tab group 33A of the electrode assembly 30 via a negative electrode lead 26 disposed within the container body 16. The negative electrode lead 26 is formed of a metal plate and integrally includes a rectangular plate-shaped first joint portion 26a and an elongated rectangular plate-shaped second joint portion 26b perpendicular to the first joint portion 26a. The first joint portion 26a abuts against the inner surface of the lid 14 via an insulator 27 and is joined to the connection rod 21a of the negative electrode terminal 21. The second joint portion 26b is positioned opposite the negative electrode current collector tab 33 and is joined to the negative electrode current collector tab group 33A via a backup lead BR2 (described later). The negative electrode lead 26 and the backup lead BR2 are formed of a conductive material such as aluminum or an aluminum alloy.

[0014] Insulating members 28a and 28b are provided within the container body 16, providing electrical insulation between the container body 16 and the positive electrode current collector tab group 32A and between the container body 16 and the negative electrode current collector tab group 33A, respectively. In one example, the insulating members 28a and 28b are each formed in a sheet or plate shape having a predetermined thickness from an insulating material such as synthetic resin. The insulating member 28a is attached to the inner surface of the container body 16 on the side of one sidewall 16c and covers the periphery of the positive electrode current collector tab group 32A. The insulating member 28b is attached to the inner surface of the container body 16 on the side of the other sidewall 16c and covers the periphery of the negative electrode current collector tab group 33A. The nonaqueous electrolyte solution contained in the outer container 12 includes a nonaqueous electrolyte and a nonaqueous electrolyte solution. Examples of the nonaqueous electrolyte include a nonaqueous electrolyte solution, a gel electrolyte, and a solid electrolyte. The non-aqueous electrolyte is a solution containing an electrolyte salt and a non-aqueous solvent.

[0015] Next, the configuration of the electrode assembly 30 will be described. FIG. 2 is a perspective view of the electrode assembly, partially exploded. In this embodiment, a so-called horizontal tab-type wound electrode assembly is used as an example of the electrode assembly 30, in which a positive electrode current collector tab and a negative electrode current collector tab extend in opposite directions from the electrode assembly. As shown in FIG. 2 , the electrode assembly 30 includes, for example, a sheet-like positive electrode plate 50 and a sheet-like negative electrode plate 60, which are spirally wound around a central winding axis C with a sheet-like separator 70 interposed therebetween, and further compressed radially to form a flattened rectangular electrode assembly 54 whose cross-sectional shape is substantially the same as that of the outer container 12. The separator 70 is disposed on the outermost layer (outermost periphery) of the electrode assembly 54. The electrode assembly 54 is held in its wound state by an insulating stop tape (not shown) or the like.

[0016] The positive electrode plate 50 includes, for example, a strip-shaped positive electrode current collector 50a made of metal foil and a positive electrode active material layer 50b coated on at least one side (both sides in this embodiment) of the positive electrode current collector 50a. The positive electrode active material layer 50b has a coating width W1 that is smaller than the width of the positive electrode current collector 50a. One side edge of the positive electrode active material layer 50b is aligned with one side edge of the positive electrode current collector 50a, and the other side edge extends parallel to the other side edge of the positive electrode current collector 50a at a fixed interval. The uncoated portion of the positive electrode current collector 50a that does not support the positive electrode active material layer 50b forms a positive electrode current collector tab 32 of the positive electrode plate 50. The positive electrode current collector tab 32 has a fixed width (tab length) W2 in a direction parallel to the winding central axis C and extends continuously along the other side edge of the positive electrode current collector 50a.

[0017] The positive electrode current collector 50a is a conductive thin film, and may be a non-porous metal foil, a punched metal with many holes, or a metal mesh formed from thin metal wires. The positive electrode current collector 50a may be, for example, a metal foil or an alloy foil. Examples of metal foils include aluminum foil, copper foil, and nickel foil. Examples of alloy foils include aluminum alloys, copper alloys, and nickel alloys. The thickness of the positive electrode current collector 50a is preferably, for example, 5 μm to 20 μm.

[0018] The positive electrode active material layer 50b contains a lithium-containing metal oxide as an example of an active material, and may optionally contain a binder and a conductive agent. The positive electrode active material is preferably a lithium-nickel-cobalt-manganese composite oxide, a lithium-manganese composite oxide, or a lithium-cobalt composite oxide. The positive electrode active material may be primary particles or secondary particles formed by agglomeration of primary particles.

[0019] Any binder commonly used in nonaqueous electrolyte batteries can be used. For example, electrochemically stable polyvinylidene fluoride (PVdF), polytetrafluoroethylene, etc. can be used. The type of binder can be one or more types. The conductive agent can be any material that has appropriate conductivity. For example, carbon black such as acetylene black, or carbon such as graphite can be used. The type of conductive agent can be one or more types. An example of a conductive agent in the form of secondary particles is acetylene black.

[0020] The negative electrode plate 60 includes a strip-shaped negative electrode current collector 60a made of metal foil and a strip-shaped negative electrode active material layer 60b coated on at least one surface (both surfaces in this embodiment) of the negative electrode current collector 60a. The negative electrode active material layer 60b has a coating width W3 that is smaller than the width of the negative electrode current collector 60a. In one example, the coating width W3 is set larger than the coating width W1 of the positive electrode active material layer 50b (W3 > W1). One side edge of the negative electrode active material layer 60b is aligned with one side edge of the negative electrode current collector 60a, and the other side edge extends parallel to the other side edge of the negative electrode current collector 60a at a fixed interval. The uncoated portion of the negative electrode current collector 60a that does not support the negative electrode active material layer 60b forms the negative electrode current collector tab 33 of the negative electrode plate 60. The negative electrode current collector tab 33 has a constant width (tab length) W4 in a direction parallel to the winding central axis C, and extends continuously along the other side edge of the negative electrode current collector 60a.

[0021] The negative electrode current collector 60a is a conductive thin film, and the same material as the positive electrode current collector 50a can be used. The negative electrode active material layer 60b includes, as examples of active materials, metal composite oxides, carbonaceous materials, metal compounds, etc., and may optionally include a binder and a conductive agent. Examples of metal composite oxides include titanium-containing oxides. Examples of carbonaceous materials include natural graphite, artificial graphite, coke, vapor-grown carbon fiber, mesophase pitch-based carbon fiber, spherical carbon, and resin-baked carbon. More preferred carbonaceous materials include vapor-grown carbon fiber, mesophase pitch-based carbon fiber, and spherical carbon. Examples of metal compounds that can be used include metal sulfides and metal nitrides.

[0022] The conductive agent can be any material that has suitable conductivity. For example, carbon black such as acetylene black, or carbon such as graphite can be used. The conductive agent can be one type or two or more types. The binder can be any type commonly used in non-aqueous electrolyte batteries. Electrochemically stable materials such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, carboxymethyl cellulose, styrene butadiene rubber, and mixtures thereof are preferably used. The binder can be one type or two or more types.

[0023] The negative electrode plate 60 is disposed offset by a predetermined distance from the positive electrode plate 50 in one direction parallel to the winding central axis C. As a result, the negative electrode active material layer 60b of the negative electrode plate 60 is aligned and faces the positive electrode active material layer 50b of the positive electrode plate 50, and the negative electrode current collector tab 33 does not overlap the positive electrode plate 50 and extends in the opposite direction from the positive electrode current collector tab 32. Similarly, the positive electrode current collector tab 32 of the positive electrode plate 50 does not overlap the negative electrode plate 60 and extends in the opposite direction from the negative electrode current collector tab 33.

[0024] Each separator 70 has a width WS slightly larger than the width W1 of the positive electrode active material layer 50b and the width W3 of the negative electrode active material layer 60b. Each separator 70 faces the entire surface of the positive electrode active material layer 50b and the negative electrode active material layer 60b. One side edge of each separator 70 is aligned with each other and extends parallel to and spaced from one side edge of the positive electrode active material layer 50b and one side edge of the negative electrode active material layer 60b. This allows one side edge of each separator 70 to overlap a portion of the positive electrode current collector tab 32. The other side edges of each separator 70 are aligned with each other and extend parallel to and spaced from the other side edges of the positive electrode active material layer 50b and the other side edges of the negative electrode active material layer 60b. This allows the other side edge of each separator 70 to overlap a portion of the negative electrode current collector tab 33.

[0025] The current collectors and current collecting tabs of the positive electrode plate 50 and the negative electrode plate 60 may be formed, for example, by punching metal foil. The thickness of the metal foil, i.e., the thickness of each current collecting tab, is preferably 5 μm or more and 50 μm or less. A thickness of 5 μm or more prevents breakage of the current collectors and current collecting tabs during manufacturing and enables high current collection efficiency. It also prevents dissolution of the current collecting tabs when a large current flows. Furthermore, a thickness of 50 μm or less allows the number of turns (windings) of the electrode plates constituting the electrode assembly to be increased while suppressing an increase in the thickness of the electrode assembly. Preferably, the thickness of the metal foil is 10 μm or more and 20 μm or less. The material of the metal foil varies depending on the type of active material used in the positive and negative electrodes, but may be, for example, aluminum, an aluminum alloy, copper, or a copper alloy.

[0026] The separator 70 preferably has ion permeability and electrical insulation properties. The separator 70 can be a porous film or nonwoven fabric made of a polymer such as polyolefin, cellulose, polyethylene terephthalate, or vinylon. The separator may be made of one type of material or a combination of two or more types of materials. According to this embodiment, the separator 70 is made of polyolefin. Examples of polyolefins include polyethylene and polypropylene. The separator 70 may be a single layer. The separator 70 may also be a multilayer formed by stacking two or more layers. The separator 70 may have an inorganic particle layer or the like formed on its surface. Preferably, one surface of the separator 70 is in physical contact with the positive electrode active material layer 50b, and the other surface is in physical contact with the negative electrode active material layer 60b.

[0027] The thickness of the separator 70 is preferably 4 μm or more and 6 μm or less. Setting the thickness to 4 μm or more makes it possible to prevent the separator 70 from breaking during manufacturing. Setting the thickness to 6 μm or less makes it possible to increase the number of windings (number of windings) of the electrode plates constituting the electrode assembly while suppressing an increase in the thickness of the electrode assembly 30. This increases the overlapping area between the positive electrode plate 50 and the negative electrode plate 60, making it possible to improve the output of the secondary battery 10. In one example, the number of windings of the positive electrode plate 50 and the negative electrode plate 60 is preferably 30 to 100. Furthermore, the installation density of the electrode plates in the thickness direction of the electrode assembly 30 (number of stacked plates / thickness of the electrode group) is preferably set to 3 to 10.

[0028] By overlapping and winding the positive electrode plate 50, separator 70, and negative electrode plate 60, the positive electrode current collector tab 32 is also wound around the winding central axis C and sequentially stacked in the thickness direction to form an annular positive electrode current collector tab group 32A. The positive electrode current collector tab group 32A extends from one axial end of the electrode group 54 in a direction parallel to the winding central axis C. In this embodiment, the positive electrode current collector tab group 32A is formed in a flat track shape including a pair of opposing straight strip portions SL1, SL2. Similarly, the negative electrode current collector tab 33 is wound around the winding central axis C and sequentially stacked in the thickness direction to form an annular negative electrode current collector tab group 33A. The negative electrode current collector tab group 33A extends from the other axial end of the electrode group 54 in another direction parallel to the winding central axis C, that is, in the opposite direction to the extension direction of the positive electrode current collector tab group 32A. In this embodiment, the negative electrode current collector tab group 33A is formed in a flat track shape including a pair of straight line portions SL1, SL2 facing each other.

[0029] 1 , the electrode assembly 30 is housed in the container body 16 with the winding central axis C coinciding with the longitudinal direction X of the outer container 12, and with the positive electrode current collector tab group 32A and the negative electrode current collector tab group 33A each extending in the height direction Z. The positive electrode current collector tab group 32A is disposed on the positive electrode terminal 20 side, and the negative electrode current collector tab group 33A is disposed on the negative electrode terminal 21 side. The positive electrode current collector tab group 32A has a bundling portion 34A that is positioned, for example, shifted toward the positive electrode terminal 20 side in the height direction Z from the winding central axis C. At the bundling portion 34A, the positive electrode current collector tab group 32A is sandwiched from both sides in the thickness direction by a backup lead BR1 formed by bending a rectangular plate material into a U-shape, and is compressed and bundled in the thickness direction. That is, in the bundling portion 34A, the multiple layers of positive electrode current collecting tabs 32 are bundled in the thickness direction by the backup lead BR1 as a bundling member and held in close contact with each other. The second joint portion 24b of the positive electrode lead 24 is joined to the backup lead BR1, for example, by laser welding, and is electrically connected to the positive electrode current collecting tab group 32A via this backup lead BR1. As a result, the positive electrode terminal 20 is electrically connected to the positive electrode of the electrode body 30 via the positive electrode lead 24 and the backup lead BR1.

[0030] The negative electrode current collector tab group 33A has a bundling portion 36A at a position offset toward the negative electrode terminal 21 from the winding central axis C in the height direction Z, for example. The negative electrode current collector tab group 33A is sandwiched from both sides in the thickness direction by a backup lead BR2 formed by bending a rectangular plate material into a U-shape at the bundling portion 36A, and is compressed and bundled in the thickness direction. That is, in the bundling portion 36A, the multiple layers of negative electrode current collector tabs 33 are bundled in the thickness direction by the backup lead BR2 as a bundling member and held in close contact with each other. The second joint portion 26b of the negative electrode lead 26 is joined to the backup lead BR2, for example, by laser welding, and electrically connected to the negative electrode current collector tab group 33A via the backup lead BR2. As a result, the negative electrode terminal 21 is electrically connected to the positive electrode of the electrode assembly 30 via the positive electrode lead 24 and the backup lead BR1.

[0031] FIG. 3 is a cross-sectional view of the electrode assembly including the bundling portion taken along line A-A in FIG. 1. As shown, in the bundling portion 34A, the tip ends (outer edge portions) of the positive electrode current collector tab group 32A are sandwiched from both sides in the thickness direction Y by the backup lead BR1 and are compressed and bundled in the central portion in the thickness direction Y. This holds the multiple layers of positive electrode current collector tabs 32 in close contact with each other. The backup lead BR1 is fixed to the positive electrode current collector tab group 32A by, for example, ultrasonic bonding. The portion of the positive electrode current collector tab 32 between the base end on the positive electrode active material layer 50b side and the backup lead BR1 extends from the electrode group 54 to the backup lead BR1 at an inclination with respect to the thickness direction Y. The more distant the positive electrode current collector tab 32 is from the center in the thickness direction Y, the greater the inclination angle. Note that the positive electrode current collector tab 32 located in the central portion in the thickness direction Y extends in a substantially straight line without inclination. Although not shown, in the bundling portion 36A, the tip portions (outer edge portions) of the negative electrode current collecting tab group 33A are sandwiched from both sides in the thickness direction Y by the backup lead BR2 and are compressed and bundled at the center in the thickness direction Y. This holds the tip portions of the multiple layers of negative electrode current collecting tabs 33 in close contact with each other. Note that as an example of the backup leads BR1 and BR2, aluminum backup leads with a thickness of 0.1 mm, a height of 25 mm, and a width of 3.2 mm are used. The current collecting tabs are bundled using the backup leads and ultrasonically welded.

[0032] 3 , T denotes the thickness in the thickness direction Y of the electrode group 54 with backup leads BR1 and BR2 attached, W2 denotes the length in the longitudinal direction X (tab length) of the positive electrode current collector tab 32, d1 denotes the length in the longitudinal direction X of the backup lead BR1 (lead length), d2 denotes the length in the longitudinal direction X of the base end of the positive electrode current collector tab 32 (the portion between the base end on the positive electrode active material layer 50b side and the backup lead BR1) (tab length W2 − lead length d1), W3 denotes the coating width in the longitudinal direction X of the negative electrode active material layer 60b, WS denotes the width in the longitudinal direction X of the separator 70 (see FIG. 2 ), and α denotes the angle formed between the positive electrode current collector tab 32 on one end side in the thickness direction Y and the positive electrode current collector tab 32 on the other end side in the thickness direction Y, between the backup leads and the electrode group 54.

[0033] The thickness T of the electrode assembly 54 when the bundling portions 34A, 36A of the current collecting tab assembly are bound with backup leads BR1, BR2 can be determined as follows. The electrode assembly 30 is removed from the outer packaging, washed with ethyl methyl carbonate (EMC), and dried. After drying, the electrode assembly 30 is disassembled, and the number of stacked positive and negative current collecting tabs and separators sandwiched between the backup leads BR1, BR2 is counted. The thicknesses of the positive and negative electrode plates are measured using a 5 mm diameter probe of a constant-pressure height measuring instrument. The thicknesses of the positive and negative electrode plates are measured by sampling 5 cm x 5 cm areas from the center of the flat portions located at the outermost and innermost positions of the electrode assembly 54. The thickness of each of the outermost and innermost sample rings is measured five times, and the thicknesses of the positive and negative electrode plates are obtained by averaging the total of 10 measurements. The separator thickness is measured by sampling five separator layers, counting from the outermost and innermost layers, of an electrode group in which the electrode current collecting tabs are clamped by backup leads. The sampling positions are in a 5 cm x 5 cm area from the center of the flat portion of the electrode group. The 10 sampled separators are stacked and the thickness is measured five times, and the measured values ​​are averaged to obtain the thickness per separator. The thickness T of the electrode group 54 in which the electrode current collecting tabs are clamped by backup leads is obtained from the thicknesses and number of stacks of the positive electrode plate, negative electrode plate, and separator.

[0034] The tab length W2 of the positive electrode current collector tab 32, which is one end portion parallel to the long side of the positive electrode current collector, can be obtained by measuring the tab length at five locations on the positive electrode current collector tab with digital calipers and averaging the measured values. The lead length d1 of the backup lead BR1 can be obtained by measuring the lead length at five locations on the backup lead with digital calipers and averaging the measured values. The difference between the obtained tab length W2 and the lead length d1 is defined as d2. The coating width W3 of the negative electrode active material layer and the separator width WS can be determined as follows. The coating width W3 can be obtained by measuring the coating width W3 with digital calipers at five locations corresponding to the locations where the tab length of the electrode current collector tab was measured and averaging the measured values. The separator width WS can be obtained by measuring the width of the portion of the separator located opposite the location where the coating width W3 was measured with digital calipers and averaging the measured values.

[0035] According to this embodiment, the thickness of the separator 70 is 4 μm or more and 6 μm or less. The ratio (WS / W3) of the coating width W3 of the negative electrode active material layer 60b, which has the widest coating width among the active material layers of the positive electrode plate 50 and the negative electrode plate 60, to the width WS of the separator 70 is set to a range of 1.01 < WS / W3 < 1.06. Furthermore, the ratio (T / d2) of the thickness T of the electrode group 54 to the difference d2 between the length (tab length) W2 of the positive electrode current collector tab 32 in the longitudinal direction X and the length (lead length) d1 of the backup lead BR1 (tab length W2 - lead length d1) is set to a range of 0.865 < T / d2 < 2. The inventors discovered that this configuration maintains the insulation and heat resistance of the electrode plate when the current collector tab is joined, thereby providing a high-power secondary battery. This ensures insulation and safety when the current collector tab is joined, and enables the secondary battery to achieve high power output. The tensile strength of the separator 70 in the longitudinal direction X (direction TD) is 100 kg / cm ２ Above, 130kg / cm ２ It is desirable that the angle α of the positive electrode current collector tab 32 extending between the bundling portion 34A and the electrode group 54 is 100°≦α<120°. Although not shown, the bundling portion 36A of the negative electrode current collector tab group 33A has the same configuration and dimensional ratio as the bundling portion 34A of the positive electrode current collector tab group 32A described above.

[0036] The effects of the secondary battery according to the above-described embodiment will be verified based on various examples and comparative examples described below. Table 1 shows a comparison of the dimensions, dimensional ratios, resistance, and output characteristics of each part for Examples 1 to 6 and Comparative Examples 1 to 4.

[0037] (Example 1) (Preparation of Positive Electrode) In the secondary battery according to Example 1, a spinel-type lithium manganese composite oxide LiMn2O4 and a layered rock salt-type lithium cobalt composite oxide LiCoO2 as positive electrode active materials, PVdF as a binder, and graphite as a conductive agent were suspended in N-methylpyrrolidone to obtain a slurry for preparing a positive electrode. The mixing ratios of LiMn2O4, LiCoO2, PVdF, and graphite in N-methylpyrrolidone were 85 wt%, 15 wt%, 2 wt%, and 3 wt%, respectively.

[0038] A 12 μm thick aluminum foil was used as the positive electrode current collector. The positive electrode current collector had a band shape extending in a first direction (longitudinal direction) and having a width in a second direction (winding central axis direction X) perpendicular to the first direction. The positive electrode slurry prepared by the above procedure was applied to both sides of the positive electrode current collector and dried. When applying the positive electrode slurry, a 10 mm band-shaped portion extending in the first direction (longitudinal direction X) was left uncoated on a portion of the surface of the positive electrode current collector, forming a positive electrode current collector tab. After drying, the active material-containing layer (positive electrode active material layer) on the positive electrode current collector was cut to a width of 90 mm. After cutting, the electrode was rolled under a constant load to produce a positive electrode plate.

[0039] (Preparation of negative electrode) Spinel-type lithium titanium composite oxide Li4Ti5O as negative electrode active material 12A slurry for preparing a negative electrode was obtained by suspending PVdF as a binder and graphite as a conductive agent in N-methylpyrrolidone. The mixing ratios of lithium titanate, PVdF, and graphite added to N-methylpyrrolidone were 95 wt %, 2 wt %, and 3 wt %, respectively. A 12 μm-thick aluminum foil was used as the negative electrode current collector. The negative electrode current collector had a band shape extending in a first direction (longitudinal direction) and having a width in a second direction (winding central axis direction X) perpendicular to the first direction. The negative electrode slurry prepared by the above procedure was applied to both sides of the negative electrode current collector and dried. When applying the negative electrode slurry, a band-shaped portion extending in the first direction (longitudinal direction) and uncoated with the slurry was left 10 mm long on a portion of the surface of the negative electrode current collector, forming a negative electrode current collector tab. After drying, the active material layer on the negative electrode current collector was cut to a coating width of 95 mm. After cutting, the electrode was rolled under a constant load to prepare a negative electrode plate.

[0040] (Preparation of Electrode Assembly) A microporous membrane made of polypropylene (PP) with a thickness of 5 μm and a width of 97 mm was prepared as a separator. The prepared positive electrode plate and negative electrode plate were wound around a central winding axis extending in the width direction of the positive electrode plate and negative electrode plate with a separator sandwiched between them. At this time, the positive electrode active material layer and negative electrode active material layer were wound while adjusting their positions so that the surface of the positive electrode active material layer faced the surface of the negative electrode active material layer, i.e., so that the surface of the positive electrode active material layer did not protrude from the surface of the negative electrode active material layer. The electrode assembly was pressed radially to adjust the thickness so that the thickness of the electrode assembly was 9.75 mm. A 50 μm thick insulating tape was attached to the surface of the negative electrode active material layer at the outermost periphery of the electrode assembly to fix the electrode assembly. The electrode assembly prepared by winding as described above was pressed for 60 seconds under a load of 90 kN at a temperature of 25°C to obtain an electrode assembly including a positive electrode current collecting tab group, an electrode assembly, and a negative electrode current collecting tab group. At the bundling portion of the positive electrode current collecting tab group, the positive electrode current collecting tabs were bundled with an aluminum backup lead having a thickness of 0.1 mm, a height of 25 mm, and a width of 3.2 mm, and ultrasonically welded. At the bundling portion of the negative electrode current collecting tab group, the negative electrode current collecting tabs were bundled with an aluminum backup lead having a thickness of 0.1 mm, a height of 25 mm, and a width of 3.2 mm, and ultrasonically welded.

[0041] (Strength Measurement) The tensile strength of the separator in the winding central axis direction (TD direction) of the produced electrode assembly (see FIG. 3) was measured. The tensile strength was the limit tensile force (kg / cm) at which the separator was torn. ２ In Example 1, the separator strength (TD direction) corresponds to 125 kg / cm ２ there were.

[0042] (Battery Assembly) An aluminum lid body was prepared, to which a positive electrode terminal, a negative electrode terminal, an insulator, a positive electrode lead, and a negative electrode lead were attached. The positive electrode lead and the negative electrode lead were laser-welded to the backup lead of the fabricated electrode assembly, and the electrode assembly was then housed in an aluminum outer container body. A lid body was placed to close the opening of the container body, and the periphery of the lid body was welded to the container body. Next, a nonaqueous electrolyte solution was prepared. The nonaqueous electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.2 mol / L in a nonaqueous solvent prepared by mixing propylene carbonate (PC) and methyl ethyl carbonate (MEC) in a 1:1 volume ratio. The nonaqueous electrolyte solution prepared as described above was injected into the outer container through an electrolyte inlet provided in the lid body. Next, a sealing lid was welded to the periphery of the electrolyte inlet to seal the electrolyte inlet, and the battery was assembled.

[0043] (Insulation Resistance Test) Before injecting the non-aqueous electrolyte, a voltage of 50 V was applied between the positive and negative terminals of the secondary battery using a high resistance meter to measure the resistance. In Example 1, the resistance was greater than 1 MG (>1 MG).

[0044] (Heating Test) Before injecting the nonaqueous electrolyte, the secondary battery was left standing in an environment of 100°C for 1 hour. Thereafter, the secondary battery was left standing in an environment of 25°C for 1 hour, and a voltage of 50 V was applied between the positive and negative terminals of the secondary battery using an ultra-high resistance meter to measure the resistance value. In Example 1, the resistance value was greater than 1 MG (>1 MG).

[0045] (Output Test) After injecting the non-aqueous electrolyte, the secondary battery was charged at a constant current / voltage of 1 C up to 2.8 V, and after a 20-minute rest, was discharged at a constant current of 10 C down to 1.8 V. The output at this time was taken as the output characteristics of the secondary battery. The output characteristics of the secondary battery of Example 1 were set to 100.

[0046] As shown in Table 1, in the secondary battery of Example 1 described above, the separator had a thickness of 5 μm, a width WS of 97 mm, a coating width W3 of the negative electrode active material layer of 95 mm, a thickness T of the electrode group of 9.75 mm, and a difference d2 between the tab length and the lead length of 6.8 mm. The measurement methods for each dimension were as described above. Therefore, the ratio of the separator width WS to the coating width W3 (WS / W3) was 1.02, and the ratio of the electrode group thickness T to the difference d2 (T / d2) was 1.434.

[0047] (Example 2) The secondary battery of Example 2 was constructed in the same manner as the secondary battery of Example 1, except that the thickness of the separator was 4 μm and the thickness T of the electrode group was 9.7 mm. In Example 2, the strength (TD) was 107 kg / cm ２ The ratio (T / d2) of the thickness T of the electrode group to the difference d2 is 1.426. The output characteristic of the secondary battery of Example 2 is 101.

[0048] (Example 3) The secondary battery of Example 3 was constructed in the same manner as the secondary battery of Example 1, except that the thickness of the separator was 6 μm and the thickness T of the electrode group was 9.8 mm. In Example 3, the strength (TD) was 140 kg / cm ２ The ratio (T / d2) of the thickness T of the electrode group to the difference d2 is 1.441. The output characteristic of the secondary battery of Example 3 is 99.

[0049] Example 4 The secondary battery of Example 4 has the same configuration as the secondary battery of Example 1, except that the lead length is reduced to 2 mm and the ratio T / d2 is set to 1.219. The output characteristic of the secondary battery of Example 4 indicates 100.

[0050] (Example 5) The secondary battery of Example 5 has the same configuration as the secondary battery of Example 1, except that the lead length is increased to 4.2 mm and the ratio T / d2 is set to 1.681. The output characteristic of the secondary battery of Example 5 indicates 100.

[0051] (Example 6) The secondary battery of Example 6 has the same configuration as the secondary battery of Example 1, except that the thickness of the separator is set to 4 μm and the number of windings is adjusted so that the thickness T of the electrode group is 9.5 mm. In the secondary battery of Example 5, the ratio T / d2 is 1.397, and the output characteristics are 96.

[0052] Comparative Example 1 The secondary battery of Comparative Example 1 was configured similarly to the secondary battery of Example 1, except that the separator width WS was set to 96 mm. In the secondary battery of Comparative Example 1, the ratio WS / W3 was 1.01, and the output characteristics could not be measured.

[0053] (Comparative Example 2) The secondary battery of Comparative Example 2 was configured similarly to the secondary battery of Example 1, except that the separator width WS was 99 mm, the coating width W3 was 90 mm, and the tab length was 15 mm. In the secondary battery of Comparative Example 2, the ratio WS / W3 was 1.10, and the ratio T / d2 was 0.826. The output characteristics showed 90.

[0054] (Comparative Example 3) The secondary battery of Comparative Example 3 has the same configuration as the secondary battery of Example 1, except that the width (lead length) of the backup lead is increased to 5.5 mm. In the secondary battery of Comparative Example 3, the difference d2 is 4.5 mm, and the ratio T / d2 is 2.167. In an insulation resistance test of the secondary battery of Comparative Example 3, the resistance value exceeded the measurement limit (OVL), making it impossible to measure, and the output characteristics also became impossible to measure.

[0055] (Comparative Example 4) The secondary battery of Comparative Example 4 was configured similarly to the secondary battery of Example 1, except that the separator width WS was 92 mm, the coating width W3 was 90 mm, the tab length was 15 mm, and the lead length of the backup lead was 3 mm. In the secondary battery of Comparative Example 4, the difference d2 was 12 mm, and the ratio T / d2 was 0.813. The output characteristic showed 80.

[0056] As can be seen from Table 1, the secondary batteries of Examples 1 to 6 showed a resistance of 1 MΩ or more in the insulation resistance test before the non-aqueous electrolyte was injected. Furthermore, the secondary batteries of Examples 1 to 6 showed a resistance of 1 MΩ or more even after the heating test. Furthermore, good output characteristics were obtained in the output test. The secondary battery of Example 6 had a separator strength of 92 kg / cm. ２ Therefore, the thickness T of the electrode group was adjusted to 9.5 mm to prevent the separator from tearing and short-circuiting, and therefore the output characteristics were slightly lower than those of Examples 1 to 5. In order to obtain higher output characteristics, the separator strength should be 100 kg / cm ２ It is preferable that this is equal to or greater than this.

[0057] In the secondary battery of Comparative Example 1, insulation failure occurred after the heating test. In the insulation resistance test of the secondary battery of Comparative Example 1 after the heating test, the resistance value exceeded the measurement limit (OVL), making it impossible to measure, and the output characteristics also became impossible to measure. It is believed that because the separator width was narrow compared to the coating width, the separator contracted at high temperatures, causing contact between the positive electrode and the negative electrode. In the secondary battery of Comparative Example 2, no insulation failure occurred in the heating test, but because the separator width was wide compared to the coating width, the output density decreased.

[0058] In the secondary battery of Comparative Example 3, insulation failure occurred in the insulation test. It is believed that the distance to the backup lead (tab length) was short compared to the thickness of the electrode group, and the outermost separator was pulled and torn when the foil was collected by the backup lead, causing the current collecting tab to come into contact with the electrode end, resulting in a short circuit. In the secondary battery of Comparative Example 4, the output characteristics deteriorated. It is believed that this was because the distance to the backup lead (tab length) was long compared to the thickness of the electrode group, reducing the opposing area of ​​the electrodes.

[0059] As described above, in the secondary batteries according to the above-described embodiments and examples, the thickness of the separator 70 is set to 4 μm or more and 6 μm or less. The ratio (WS / W3) of the coating width W3 of the active material layer having the wider coating width to the width WS of the separator 70 of the positive electrode plate 50 and the negative electrode plate 60 is set to satisfy the relationship 1.01 < WS / W3 < 1.06. Furthermore, the ratio (T / d2) of the thickness T of the electrode group 54 to the difference d2 between the length (tab length) W2 of the positive electrode current collector tab 32 in the longitudinal direction X and the length (lead length) d1 of the backup lead (tab length W2 - lead length d1) is set to the range 0.865 < T / d2 < 2. This configuration maintains the insulation and heat resistance of the electrode plate when the current collector tab is joined, thereby providing a high-power secondary battery. Insulation and safety are ensured when the current collector tab is joined, enabling the secondary battery to achieve high power output. As described above, the tensile strength of the separator 70 in the longitudinal direction X (direction TD) is 100 kg / cm ２ Above, 130kg / cm ２ It is desirable that the angle α between the current collecting tabs extending between the binding portion 34A and the electrode group 54 is 100°≦α<120°.

[0060] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope and spirit of the invention, as well as the scope of the invention and its equivalents as set forth in the claims. For example, the electrode assembly housed in the outer container is not limited to a single electrode assembly, but may be multiple electrode assemblies. The materials, shapes, sizes, etc. of the elements constituting the secondary battery are not limited to the above-described embodiments and can be modified as needed.

Claims

1. An outer container; a positive electrode plate having a foil-shaped positive electrode current collector, an active material layer coated on the positive electrode current collector, and a positive electrode current collector tab formed on one side edge in the width direction of the positive electrode current collector; a negative electrode plate having a foil-shaped negative electrode current collector, an active material layer coated on the negative electrode current collector, and a negative electrode current collector tab formed on one side edge in the width direction of the negative electrode current collector; and a sheet-shaped separator disposed between the positive electrode plate and the negative electrode plate and facing the active material layer, all of which are wound around a central axis. an electrode assembly including a plurality of stacked layers of the positive electrode plates, the negative electrode plates, and the separator, configured by being wound together; a positive electrode current collecting tab group including the stacked plurality of layers of positive electrode current collecting tabs and extending from the electrode assembly in one direction along the winding central axis; and a negative electrode current collecting tab group including the stacked plurality of layers of negative electrode current collecting tabs and extending from the electrode assembly in another direction along the winding central axis, the electrode assembly being housed in the outer container; a thickness of the separator is 4 μm or more and 6 μm or less; a ratio (WS / W3) of a coating width W3 of one of the active material layers of the positive electrode plate and the active material layer of the negative electrode plate, which has a wider coating width, to a width WS of the separator is 1.01 < WS / W3 < 1.06; and a ratio (T / d2) of a thickness T of the electrode group at the binding portion to a difference d2 between a length W2 of the positive electrode current collecting tab in the direction of the winding central axis and a length d1 of the binding member in the direction of the winding central axis is 0.865 < T / d2 < 2.

2. The tensile strength of the separator in the direction of the winding central axis is 100 kg / cm ２ Above, 130kg / cm ２ The secondary battery according to claim 1 , wherein:

3. The secondary battery according to claim 1, wherein the separator is made of a polyolefin-based material.

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