Lithium battery

Abstract

To realize a high-performance lithium battery.SOLUTION: A lithium battery includes a battery element 20 housed in a cylindrical outer can. The battery element 20 is composed of a positive electrode 22 and a negative electrode 21 containing lithium, wound with a separator 23 interposed therebetween. In the battery element 20, a first end 21a of a negative electrode 21 in a winding direction D1 from a center C1 of the battery element is located on the side in a direction D2 that is opposite the winding direction D1, relative to a second end 22a of the positive electrode 22 in the winding direction D1. The distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 is expressed as 2×pi×thickness of the negative electrode 21×number of turns of the positive electrode 22×α, and is set in the range of 0<α<0.5.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to lithium batteries. [Background technology]

[0002] One type of battery known is a lithium battery (also called a "lithium primary battery") that uses a lithium-containing negative electrode. For example, a spiral-type lithium battery is known, in which a strip-shaped positive electrode plate and a negative electrode plate are spirally wound with a separator interposed therebetween and the resulting electrode roll is housed in an outer can (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-325989 Summary of the Invention [Problem to be solved by the invention]

[0004] In lithium batteries in which a battery element, in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, is housed in a cylindrical outer can, there have been cases in which the winding state or relative arrangement of the negative electrode and positive electrode of the battery element has caused uneven wear of the negative electrode, deterioration of discharge capacity, short-circuiting between the positive and negative electrodes, and the like, resulting in a decrease in battery performance.

[0005] In one aspect, the present invention aims to realize a high-performance lithium battery. [Means for solving the problem]

[0006] In one embodiment, there is provided a lithium battery including: a cylindrical outer can; and a battery element housed in the outer can, the battery element including a positive electrode and a lithium-containing negative electrode wound with a separator interposed therebetween; a first end of the negative electrode in a winding direction from a center of the battery element is located on the opposite side of the winding direction from a second end of the positive electrode in the winding direction; and a distance between the first end and the second end is expressed as 2 × pi × thickness of the negative electrode × number of turns of the positive electrode × α, where α is in the range of 0<α<0.5. [Effects of the Invention]

[0007] In one aspect, it will be possible to realize high-performance lithium batteries. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram (part 1) illustrating an example of the configuration of a lithium battery. [Figure 2] FIG. 2 is a diagram (part 2) illustrating an example of the configuration of a lithium battery. [Figure 3] FIG. 10 is a diagram illustrating the distance between the terminal ends of the negative electrode and the positive electrode. [Figure 4] FIG. 10 is a diagram illustrating an example of the relationship between discharge capacity and voltage. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1 and 2 are diagrams illustrating an example of the configuration of a lithium battery. FIG. 1 shows a schematic cross-sectional view of a main part of an example of a lithium battery. FIG. 2 shows a schematic cross-sectional view of a main part of an example of a battery element provided in the lithium battery. FIG. 2 is a schematic cross-sectional view of a main part of a battery element when a lithium battery having the configuration shown in FIG. 1 is cut at the position of line II. Note that an outer can as shown in FIG. 1 is not shown in FIG. 2.

[0010] As an example, the lithium battery 1 shown in FIG. 1 includes an outer can 10, a battery element 20, an insulating plate 30, an insulating plate 40, an electrolyte 50, a sealing plate 60, and a gasket 70. As shown in FIG. 1 , the outer can 10 is a cylindrical, conductive container with a bottom and one open end. The outer can 10 is made of a material such as stainless steel, steel, or nickel-plated steel. For example, as shown in FIG. 1 , the open end of the outer can 10 is subjected to drawing and crimping, and a conductive sealing plate 60 provided with a positive electrode terminal 61 is fixed via a gasket 70. The sealing plate 60 is made of a material such as stainless steel, steel, or nickel-plated steel. The outer can 10 is sealed by the gasket 70 and the sealing plate 60.

[0011] The battery element 20 is an example of a power generating element housed in the outer can 10. As shown in FIGS. 1 and 2 , the battery element 20 includes a sheet-shaped positive electrode 22, a sheet-shaped negative electrode 21, and a sheet-shaped separator 23. The battery element 20 has a configuration in which the positive electrode 22 and the negative electrode 21 are spirally wound from a center C1 with the separator 23 interposed therebetween. For example, in a lithium battery 1, the battery element 20 is wound such that the outermost periphery of the negative electrode 21 is positioned outside the outermost periphery of the positive electrode 22. The battery element 20 in which the positive electrode 22 and the negative electrode 21 are spirally wound with the separator 23 interposed therebetween is also referred to as a "wound body."

[0012] The positive electrode 22 of the battery element 20 uses a positive electrode material containing a positive electrode active material. The positive electrode active material may be, for example, manganese dioxide. The positive electrode material may include, in addition to the positive electrode active material, a conductive material such as a carbon material, and organic components such as a binder and a solvent. Such materials may be kneaded with the positive electrode active material to form a positive electrode material (also referred to as a "positive electrode mixture"). The positive electrode 22 may include a core 22d (FIG. 2) such as a stainless steel expanded metal that functions as a current collector, with the positive electrode material laminated thereon. For example, the positive electrode 22 is formed by applying a slurry-like positive electrode material to the core 22d, drying it, and rolling it. A metal positive electrode tab 22c is connected to the positive electrode 22 at a predetermined position for external connection.

[0013] The negative electrode 21 of the battery element 20 uses a negative electrode material containing a negative electrode active material. The negative electrode active material is lithium, for example, metallic lithium, or a lithium alloy containing lithium as a component. The lithium alloy is, for example, a lithium-aluminum alloy. The negative electrode 21 may include a copper foil or the like that functions as a current collector, on which a negative electrode material containing lithium is laminated. For example, the negative electrode 21 is formed by attaching a lithium foil or lithium alloy foil, which is the negative electrode material, to a copper foil or the like. A metal negative electrode tab 21c is connected to the negative electrode 21 at a predetermined position for external connection.

[0014] The negative electrode tab 21c connected to the negative electrode 21 is also referred to as a "first tab," and the positive electrode tab 22c connected to the positive electrode 22 is also referred to as a "second tab." 1 and 2, the positive electrode 22 and the negative electrode 21 are wound with a separator 23 interposed therebetween. The positive electrode 22 and the negative electrode 21 are separated by the separator 23. The separator 23 may be a polyolefin-based or cellulose-based porous film, a woven fabric, a nonwoven fabric, or the like.

[0015] 1, a non-aqueous organic electrolyte solution in which a lithium electrolyte salt is dissolved in an organic solvent is used as the electrolyte solution 50. For example, lithium trifluoromethanesulfonate is used as the lithium electrolyte salt. For example, ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, etc. are used as the organic solvent.

[0016] As shown in FIG. 1, an insulating plate 30 and an insulating plate 40 are provided inside the exterior can 10, for example, on the bottom thereof and on the top of the battery element 20 housed therein, respectively. The positive electrode 22 of the battery element 20 housed in the outer can 10 is electrically connected to a positive electrode terminal 61 of a sealing plate 60 that is insulated from the outer can 10 via a gasket 70 and seals the open end side of the outer can 10, using a positive electrode tab 22c that penetrates the insulating plate 40. The negative electrode 21 of the battery element 20 housed in the outer can 10 is electrically connected to the inner wall of the outer can 10, which is insulated from the sealing plate 60 that has the positive electrode terminal 61 via a gasket 70, using a negative electrode tab 21c. The outer can 10 (for example, a part of its bottom surface) functions as a negative electrode terminal.

[0017] The lithium battery 1 having the above-described configuration is manufactured, for example, using the following method. A bottomed cylindrical outer can 10, a sheet-like positive electrode 22, a sheet-like negative electrode 21, and a sheet-like separator 23 are prepared. The prepared positive electrode 22, negative electrode 21, and separator 23 are used to fabricate a battery element 20. In fabricating the battery element 20, the positive electrode 22 and the negative electrode 21 are spirally wound from a center C1 with the separator 23 interposed therebetween. At this time, for example, the winding is performed so that the outermost periphery of the negative electrode 21 is positioned outside the outermost periphery of the positive electrode 22. In this manner, the cylindrical battery element 20 is fabricated.

[0018] The fabricated battery element 20 is inserted and housed in the outer can 10. Before the battery element 20 is housed, an insulating plate 30 is provided on the bottom inside the outer can 10. After the battery element 20 is housed, an insulating plate 40 is provided on the top of the battery element 20 inside the outer can 10. Furthermore, a drawing process is applied to the open end side of the outer can 10, and a drawn portion (beading portion) is formed.

[0019] A predetermined electrolyte solution 50 is then poured into the exterior can 10 housing the battery element 20. Thereafter, using the drawn portion of the exterior can 10 formed by drawing as a seat, a sealing plate 60 connected to the positive electrode 22 of the battery element 20 by a positive electrode tab 22c, i.e., a sealing plate 60 equipped with a positive electrode terminal 61, is placed so that a gasket 70 is provided on its outer edge, and further, the open edge of the exterior can 10 is crimped. As a result, the sealing plate 60 is fixed to the exterior can 10 via the gasket 70, and a sealed structure is realized by the exterior can 10, the gasket 70, and the sealing plate 60.

[0020] For example, a lithium battery 1 is manufactured using this method. Although FIG. 1 illustrates a lithium battery 1 in which the sealing plate 60 is fixed to the outer can 10 via the gasket 70 to seal the battery, it is also possible to employ a configuration in which a sealed structure is achieved by laser welding a sealing plate provided with a positive electrode terminal to the open end of the outer can 10 via a gasket.

[0021] When the lithium battery 1 is discharged, lithium is taken up by ion conduction from the lithium-containing negative electrode 21 through the separator 23 to the positive electrode 22. In the lithium battery 1, the discharge operation is realized by such ion conduction of lithium.

[0022] Here, the battery element 20 of the lithium battery 1 as described above will be further described with reference to FIG. 2 above and FIG. 3 shown below. As shown in FIG. 2 , the battery element 20 of the lithium battery 1 is formed by winding a positive electrode 22 and a negative electrode 21 with a separator 23 interposed therebetween. For example, the negative electrode 21 is wound so that the outermost periphery of the negative electrode 21 is positioned outside the outermost periphery of the positive electrode 22. In such a battery element 20, the negative electrode 21 includes a negative electrode portion that faces the positive electrode 22 only on the inner surface, and a negative electrode portion that faces the positive electrode 22 on both the inner and outer surfaces. In the negative electrode portion that faces the positive electrode 22 on both the inner and outer surfaces, the consumption of lithium contained in the negative electrode 21 during discharge may be relatively large. If the lithium in the negative electrode 21 is not consumed uniformly during discharge, this may result in the negative electrode 21 being broken, the discharge capacity of the lithium battery 1 being reduced, or the like.

[0023] For example, in the battery element 20, as shown in FIG. 2, the positive electrode 22 has a region AR1 that faces the negative electrode 21 only on its inner surface, not on its outer surface. During discharge, the amount of lithium absorbed from the negative electrode 21 into the positive electrode 22 in this region AR1 may be less than the amount of lithium absorbed from the negative electrode 21 into the positive electrode 22 near the region AR1 on both the inner and outer surfaces thereof. Therefore, lithium absorption from the negative electrode 21 on the inner surface side of the region AR1 that faces the positive electrode 22 may be more rapid than in other regions. Furthermore, lithium absorbed from the negative electrode 21 may migrate to other regions of the positive electrode 22, such as those near the region AR1, into the positive electrode 22 in the region AR1. Lithium absorption from the negative electrode 21 on the opposing inner and outer surfaces of the positive electrode 22 may further progress into the other regions of the positive electrode 22 where lithium has migrated to the region AR1. This phenomenon may occur more easily as the region AR1 becomes larger. Therefore, if the area AR1 becomes large, the lithium in the negative electrode 21 may be unevenly consumed, which may easily cause breakage or the like.

[0024] Therefore, the battery element 20 is configured such that the first end 21a of the negative electrode 21 in the winding direction D1 (clockwise in FIG. 2) from the center C1 is located in a direction D2 opposite to the winding direction D1 (counterclockwise in FIG. 2) relative to the second end 22a of the positive electrode 22 in the winding direction D1. Furthermore, the battery element 20 is configured such that the distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 is expressed as 2 × pi × thickness of the negative electrode 21 × number of turns of the positive electrode 22 × α, where the coefficient α is in the range of 0 < α < 0.5.

[0025] By adopting this configuration in the battery element 20, as described below, the area of ​​the region AR1 of the positive electrode 22, where the outer surface does not face the negative electrode 21 but faces the negative electrode 21 only on the inner surface, is reduced. This reduces the amount of lithium absorbed into the positive electrode 22 in region AR1 from the negative electrode 21, which faces the positive electrode 22 on the inner surface. Furthermore, the amount of lithium absorbed from the negative electrode 21 in other regions of the positive electrode 22, such as near region AR1, that migrates to region AR1 is also reduced. By reducing the amount of lithium absorbed in the positive electrode 22 that migrates to region AR1, a certain amount of lithium remains in the region of the positive electrode 22 outside region AR1, thereby suppressing the progress of lithium absorption by the positive electrode 22 in that region from the negative electrode 21, which faces the positive electrode 22 on both the inner and outer surfaces. As a result, uneven consumption of lithium in the negative electrode 21 is suppressed, and the disconnection of the negative electrode 21 and the deterioration of the discharge capacity of the lithium battery 1 are suppressed.

[0026] Furthermore, in the battery element 20, if the positions of the first terminal end 21a of the negative electrode 21 and the second terminal end 22a of the positive electrode 22 are aligned in the winding direction D1, or if the first terminal end 21a of the negative electrode 21 is positioned closer to the winding direction D1 than the second terminal end 22a of the positive electrode 22, it becomes possible to make the area AR1 smaller or to eliminate it, but the following concerns arise.

[0027] That is, the positive electrode 22 is fabricated, for example, by rolling and cutting a metal core 22d coated with a positive electrode mixture. In this case, the metal core 22d is exposed at the second end 22a of the positive electrode 22 due to cutting when fabricating the positive electrode 22. If the core 22d exposed at the second end 22a of the positive electrode 22 has a chipped or protruding portion due to cutting, this portion is more likely to break through the separator 23 and come into contact with the negative electrode 21, increasing the possibility of a short circuit.

[0028] Therefore, the battery element 20 is configured such that the first terminal end 21a of the negative electrode 21 is located closer to the second terminal end 22a of the positive electrode 22 in the direction D2 opposite to the winding direction D1. However, when the distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 exceeds a certain distance, as described above, the area of ​​the region AR1 where the outer surface of the positive electrode 22 does not face the negative electrode 21 but only the inner surface faces the negative electrode 21 increases, which may lead to uneven consumption of lithium in the negative electrode 21. Such uneven consumption of lithium may lead to breakage of the negative electrode 21 and a deterioration in the discharge capacity of the lithium battery 1.

[0029] Therefore, the battery element 20 is configured so that the distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 in the winding direction D1 is a constant value, that is, expressed as 2 × pi × thickness of the negative electrode 21 × number of windings of the positive electrode 22 × α, where the coefficient α is in the range of 0 < α < 0.5.

[0030] Here, the distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 in the winding direction D1 will be further described with reference to FIG. FIG. 3 is a diagram illustrating the distance between the negative and positive electrode terminals.

[0031] In FIG. 3, both the negative electrode 21 and the positive electrode 22 are shown as circular rings to simplify the battery element 20, which is wound so that the outermost periphery of the negative electrode 21 is positioned outside the outermost periphery of the positive electrode 22. However, for convenience, the outermost negative electrode 21 is shown as half of the circular ring-shaped negative electrode 21. The thicknesses of the negative electrode 21 and the positive electrode 22 are both set to a constant value of thickness t. FIG. 3 shows an example in which the number of turns of the positive electrode 22 is 2. Hereinafter, the thickness of the negative electrode 21 will also be referred to as the "negative electrode thickness," the thickness of the positive electrode 22 will also be referred to as the "positive electrode thickness," and the number of turns of the positive electrode 22 will also be referred to as the "number of turns of the positive electrode." The battery element 20 will also be referred to as a "wound body."

[0032] If pi is the constant of the circumference of a circle, then the circumferential length of the positive electrode 22 in the first turn wound around the center C1 of the battery element 20 from the reference S1 (position where the number of turns = 0) is 2 × π × positive electrode thickness. The circumferential length of the negative electrode 21 in the first turn is 2 × π × (positive electrode thickness + negative electrode thickness). The circumferential length of the positive electrode 22 in the second turn is 2 × π × (positive electrode thickness + negative electrode thickness + positive electrode thickness). The circumferential length of the negative electrode 21 in the second turn is 2 × π × (positive electrode thickness + negative electrode thickness + positive electrode thickness + negative electrode thickness).

[0033] Therefore, if the distance L1 between the ends of the negative electrode 21 and the positive electrode 22 is considered to be the difference between the sum of the circumferences of the negative electrode 21 and the sum of the circumferences of the positive electrode 22, the distance L1 is expressed by the following equation (1). Distance L1 = {2 × π × (positive electrode thickness + negative electrode thickness)} + {2 × π × (positive electrode thickness + negative electrode thickness + positive electrode thickness + negative electrode thickness)} - {2 × π × positive electrode thickness} - {2 × π × (positive electrode thickness + negative electrode thickness + positive electrode thickness)} = {2 × π × negative electrode thickness} + {2 × π × negative electrode thickness} (1) Now, since the number of positive turns is 2, equation (1) can be rewritten as the following equation (2).

[0034] Distance L1 = {2 × π × negative electrode thickness} × 2 = {2 × π × negative electrode thickness} × number of positive electrode turns (2) As shown in this equation (2), the distance L1 between the ends of the negative electrode 21 and the positive electrode 22 can be expressed as the product of {2 × π × negative electrode thickness} and the number of turns of the positive electrode. The length corresponding to the distance L1 shown in equation (2) is shown in Figure 3. In the simplified example shown in Figure 3, this length corresponds to half the circumferential length of the negative electrode 21 arranged on the second turn of the outermost circumference (the part of the arc indicated by the double-headed arrow).

[0035] While an example in which the number of positive electrode windings is two is shown here, the same approach can be adopted when the number of positive electrode windings is one or three or more. In either case, distance L1 can be expressed according to the number of positive electrode windings using the above formula (2), i.e., {2 × π × negative electrode thickness} × number of positive electrode windings. That is, when the number of positive electrode windings is one, if the difference between the sum of the circumferences of the negative electrode 21 and the positive electrode 22 is defined as distance L1 using the above approach, distance L1 = {2 × π × negative electrode thickness} × 1. When the number of positive electrode windings is three, if the difference between the sum of the circumferences of the negative electrode 21 and the positive electrode 22 is defined as distance L1 using the above approach, distance L1 = {2 × π × negative electrode thickness} × 3. The same applies when the number of positive electrode windings is four or more. In this way, distance L1 is expressed as the product of {2 × π × negative electrode thickness} and the number of positive electrode windings. Based on the above concept, in the simplified example shown in Figure 3, the product of {2 x π x negative electrode thickness} and the number of positive electrode turns corresponds to half the circumferential length of the negative electrode 21 located at the outermost periphery.

[0036] The above formula (2) can be further expressed as the following formula (3) using a coefficient α. Distance L1 = 2 × π × negative electrode thickness × positive electrode turns × α (3) In the simplified example shown in Figure 3, the distance L1 (= 2 x π x negative electrode thickness x number of positive electrode turns) shown in the above equation (2) is a length equivalent to half the circumferential length of the negative electrode 21 located at the outermost periphery, so when the coefficient α in equation (3) is α = 1 (Figure 3), it is a length equivalent to half the circumferential length.

[0037] On the other hand, in Equation (3), when the coefficient α is α=0 ( FIG. 3 ), the distance L1=0, i.e., the terminal positions of the negative electrode 21 and the positive electrode 22 are aligned. However, as described above, when the terminal positions of the negative electrode 21 and the positive electrode 22 (the first terminal 21a and the second terminal 22a in FIG. 2 ) are aligned, a short circuit between the negative electrode 21 and the positive electrode 22 may occur, so α=0 is excluded. From the viewpoint of suppressing uneven consumption of lithium in the negative electrode 21, resulting in disconnection of the negative electrode 21, and deterioration of the discharge capacity of the lithium battery 1, it is preferable to move the terminal end of the negative electrode 21 closer to the terminal end of the positive electrode 22 (reducing the area of ​​region AR1 in FIG. 2 ), i.e., to set the coefficient α in Equation (3) to a value other than 0 and close to 0. Here, as an example, the upper limit is set to α=0.5 ( FIG. 3 ), and the coefficient α in Equation (3) is set to a range of 0<α<0.5.

[0038] Based on the concept described in FIG. 3, in the battery element 20 of the lithium battery 1 shown in FIG. 2, the distance L1 between the first end 21a of the negative electrode 21 and the second end 22a of the positive electrode 22 in the winding direction D1 is set to 2 × π × negative electrode thickness × number of positive electrode windings × α, where the coefficient α is set to a value in the range of 0 < α < 0.5. This shortens the distance L1 and reduces the area of ​​the region AR1 compared to when the coefficient α is set to a value greater than 0.5. As a result, uneven consumption of lithium in the negative electrode 21, resulting in breakage of the negative electrode 21 and deterioration of the discharge capacity of the lithium battery 1, are effectively suppressed.

[0039] In the battery element 20 shown in FIG. 2 , the value of 2×π×negative electrode thickness×number of positive electrode windings does not necessarily correspond to half the circumferential length of the negative electrode 21 arranged at the outermost periphery, as in the simplified example described in FIG. 3 , due to the thickness of the negative electrode 21 (negative electrode thickness), the thickness of the positive electrode 22 (positive electrode thickness), the thickness of the separator 23 (separator thickness), and the diameter of the center portion C1 (center portion diameter). The distance L1 in the battery element 20 is determined based on the proportion of the thickness of the negative electrode 21 to the total thickness of the negative electrode 21, the thickness of the positive electrode 22, the thickness of the separator 23, and the diameter of the center portion C1. In the battery element 20, which is a wound body, the relationship of total negative electrode thickness:wound body radius={2×π×negative electrode thickness×number of positive electrode windings}:wound body circumferential length holds (as will be described later in Example 4 as an example).

[0040] 2, in the battery element 20, the distance L1 is set to a predetermined value, and an insulating tape 24 is provided so as to cover the inner circumferential surface of the end portion including the second terminal end 22a of the positive electrode 22. The insulating tape 24 not only covers the inner circumferential surface of the end portion including the second terminal end 22a of the positive electrode 22, but may also be provided so as to extend from the second terminal end 22a to the outside of the positive electrode 22, as shown in FIG. 2. The insulating tape 24 is thicker than the separator 23, for example.

[0041] As described above, the metal core 22d is exposed at the second end 22a of the positive electrode 22 due to cutting during fabrication of the positive electrode 22. If this exposed core 22d breaks through the separator 23 and comes into contact with the negative electrode 21, a short circuit will occur between the positive electrode 22 and the negative electrode 21. Therefore, in the battery element 20, as shown in FIG. 2 above, an insulating tape 24 is provided so as to cover the inner circumferential surface of the end including the second end 22a of the positive electrode 22, and the inner circumferential surface of the end and the negative electrode 21 inside it are isolated by the separator 23 and the insulating tape 24. This prevents contact between the core 22d exposed at the second end 22a of the positive electrode 22 and the negative electrode 21, thereby preventing a short circuit between the positive electrode 22 and the negative electrode 21 due to contact.

[0042] Here, the width W1 (FIG. 2) of the insulating tape 24 covering the inner circumferential surface of the end including the second end 22a of the positive electrode 22 from the second end 22a is expressed using a coefficient β as in the following equation (4). Width W1 = 2 × π × negative electrode thickness × positive electrode turns × β (4) In the battery element 20, the width W1 of the insulating tape 24 covering the inner circumferential surface of the end portion including the second end 22a of the positive electrode 22 from the second end 22a is set to a value calculated by 2 × π × negative electrode thickness × number of positive electrode windings × β, where the coefficient β is set to a value in the range of 0.5 < β ≦ 1. If the insulating tape 24 is not provided to cover the inner circumferential surface of the end portion including the second end 22a of the positive electrode 22, i.e., if the coefficient β is β = 0, short circuits due to contact between the core 22d of the positive electrode 22 and the negative electrode 21 may not be prevented. Furthermore, if the insulating tape 24 is not provided with the specified width W1, i.e., if the coefficient β is, for example, β ≦ 0.5 or β > 1, a rapid capacity loss may occur when the lithium battery 1 approaches the relatively final stage of discharge. Therefore, it is preferable that the insulating tape 24 be provided with the specified width W1 on the inner circumferential surface of the end portion including the second end 22a of the positive electrode 22.

[0043] 2, the battery element 20 is configured such that the first starting end 21b of the negative electrode 21 wound from the center C1 is located closer to the winding direction D1 than the second starting end 22b of the positive electrode 22 wound from the center C1, for the following reasons.

[0044] Similar to the second terminal end 22a, a metal core 22d is exposed at the second starting end 22b of the positive electrode 22 by cutting during fabrication of the positive electrode 22. If the exposed core 22d breaks through the separator 23 and comes into contact with the negative electrode 21, a short circuit between the positive electrode 22 and the negative electrode 21 occurs. For this reason, the battery element 20 is configured such that the first starting end 21b of the negative electrode 21 is positioned closer to the winding direction D1 than the second starting end 22b of the positive electrode 22, as shown in FIG. 2 above. This prevents contact between the core 22d exposed at the second starting end 22b of the positive electrode 22 and the negative electrode 21, thereby preventing a short circuit between the positive electrode 22 and the negative electrode 21 due to the contact.

[0045] 2, the battery element 20 is configured such that, when the position P1 of the second starting end 22b of the positive electrode 22 wound from the center C1 is defined as 0 degrees, the angle θ of the second end 22a with respect to the winding direction D1 from the second starting end 22b is within a range of 90 degrees or less. Furthermore, as shown in FIG. 2, the battery element 20 is configured such that, when the position P1 of the second starting end 22b of the positive electrode 22 wound from the center C1 is defined as 0 degrees, the angle θ of the negative electrode tab 21c (first tab) connected to the negative electrode 21 and the positive electrode tab 22c (second tab) connected to the positive electrode 22 with respect to the winding direction D1 from the second starting end 22b is within a range of more than 90 degrees and less than 360 degrees.

[0046] The negative electrode tab 21c and the positive electrode tab 22c are made of metal and have a certain thickness to ensure electrical conduction. By configuring the position of the second end 22a of the positive electrode 22 and the positions of the negative electrode tab 21c and the positive electrode tab 22c to fall within the above-mentioned angle θ, the roundness of the spirally wound battery element 20 when viewed from the axial direction of the center C1 is improved. This makes it easier to insert the wound battery element 20 into the cylindrical outer can 10 during the manufacture of the lithium battery 1.

[0047] Examples and comparative examples will be described below. Example 1 A positive electrode mixture containing manganese dioxide was applied to both sides of a stainless steel expanded metal core, followed by drying, rolling, and cutting. A positive electrode tab was attached at a predetermined position to produce a positive electrode. A lithium-aluminum alloy foil was attached to copper foil, and a negative electrode tab was attached at a predetermined position to produce a negative electrode. A polypropylene separator was used as the separator, and the positive and negative electrodes were spirally wound with the separator interposed between them so that the outermost periphery of the negative electrode was positioned outside the outermost periphery of the positive electrode to produce a battery element. The inner circumferential surface of the battery element, including the end of the positive electrode, was covered with insulating tape.

[0048] In fabricating the battery element, the starting end of the negative electrode was positioned closer to the center of the battery element in the winding direction than the starting end of the positive electrode. The starting end of the positive electrode was positioned at 0 degrees, and the ending end of the positive electrode was positioned within a range of 90 degrees or less in the winding direction. The starting end of the positive electrode was positioned at 0 degrees, and the positive and negative electrode tabs were positioned within a range of more than 90 degrees but less than 360 degrees in the winding direction.

[0049] In Example 1, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.1, and the coefficient β in the above formula (4) was 0.7. That is, in Example 1, the coefficient α was 0.1 when the distance between the end of the negative electrode and the end of the positive electrode in the winding direction was expressed as L1 = 2 × π × negative electrode thickness × number of positive electrode turns × α, and the coefficient β was 0.7 when the width of the insulating tape covering the inner peripheral surface from the end of the positive electrode was expressed as W1 = 2 × π × negative electrode thickness × number of positive electrode turns × β. The battery element of Example 1 had a value of 2 × π × negative electrode thickness × number of positive electrode turns of 10.3, the distance L1 calculated from the above formula (3) was 1 mm, and the width W1 calculated from the above formula (4) was 7 mm. The number of turns of the positive electrode is counted to one decimal place, with the position (0 degrees) of the starting point of the positive electrode wound from the center of the battery element as the reference.

[0050] The fabricated battery element was inserted into a cylindrical outer can with a bottom, and an electrolyte was poured into the outer can. The outer can was then electrically connected as required and sealed with a sealing plate, etc., to fabricate a lithium battery with a nominal voltage of 3 V.

[0051] The fabricated lithium batteries were discharged at a constant current of 5 mA to a depth of discharge of 80%, and then discharged at a constant resistance of 5.6 kΩ to evaluate the decrease in discharge capacity and the presence or absence of a sudden decrease in discharge capacity above a certain threshold voltage. The fabricated lithium batteries were also evaluated for the presence or absence of a short circuit (internal short circuit) between the positive electrode core and the negative electrode.

[0052] <Example 2> In Example 2, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.1, and the coefficient β in the above formula (4) was 0.6. For the battery element of Example 2, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 1 mm, and the width W1 calculated from the above formula (4) was 6 mm.

[0053] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. Example 3 In Example 3, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.4, and the coefficient β in the above formula (4) was 1.0. For the battery element of Example 3, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 4 mm, and the width W1 calculated from the above formula (4) was 10 mm.

[0054] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. Example 4 In Example 4, a battery element was fabricated in which the negative electrode thickness was 0.33 mm, the number of positive electrode turns was 5.1 (5 turns + 47 degrees), the coefficient α in the above formula (3) was 0.1, and the coefficient β in the above formula (4) was 0.7. In Example 3, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.6, the distance L1 calculated from the above formula (3) was 1 mm, and the width W1 calculated from the above formula (4) was 7 mm.

[0055] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. Taking the configuration of Example 4 as an example, the battery element has the following configuration: The total negative electrode thickness is 0.33 mm negative electrode thickness × 5.1 positive electrode windings = 1.68 mm. The total positive electrode thickness is 0.67 mm positive electrode thickness × 5.1 positive electrode windings = 3.42 mm. The total separator thickness is 0.055 mm separator thickness × 5.1 positive electrode windings × 2 positive and negative electrode outer surfaces = 0.56 mm. The center diameter is 1.61 mm. Therefore, the radius of the battery element, which is the wound body (winding body radius) is 7.27 mm, and its circumferential length (winding body circumferential length) is 45.7 mm. Therefore, since the total negative electrode thickness is 1.68 mm, the value of 2 × π × negative electrode thickness × number of positive electrode windings is 10.6, the radius of the winding body is 7.27 mm, and the circumferential length of the winding body is 45.7 mm, it can be said that the relationship total negative electrode thickness: winding body radius = {2 × π × negative electrode thickness × number of positive electrode windings}: winding body circumferential length holds.

[0056] <Comparative Example 1> In Comparative Example 1, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.0, and the coefficient β in the above formula (4) was 0.7. For the battery element of Comparative Example 1, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 0 mm, and the width W1 calculated from the above formula (4) was 7 mm.

[0057] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. <Comparative Example 2> In Comparative Example 2, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.7, and the coefficient β in the above formula (4) was 0.7. For the battery element of Comparative Example 2, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 7 mm, and the width W1 calculated from the above formula (4) was 7 mm.

[0058] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. <Comparative Example 3> In Comparative Example 3, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.7, and the coefficient β in the above formula (4) was 0.9. For the battery element of Comparative Example 3, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 7 mm, and the width W1 calculated from the above formula (4) was 9 mm.

[0059] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. <Comparative Example 4> In Comparative Example 4, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 1.0, and the coefficient β in the above formula (4) was 0.7. For the battery element of Comparative Example 4, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 10 mm, and the width W1 calculated from the above formula (4) was 7 mm.

[0060] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. <Comparative Example 5> In Comparative Example 5, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.4, and the coefficient β in the above formula (4) was 0.4. For the battery element of Comparative Example 5, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 4 mm, and the width W1 calculated from the above formula (4) was 4 mm.

[0061] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. <Comparative Example 6> In Comparative Example 6, a battery element was fabricated in which the negative electrode thickness was 0.2 mm, the number of positive electrode turns was 8.2 (8 turns + 72 degrees), the coefficient α in the above formula (3) was 0.4, and the coefficient β in the above formula (4) was 1.3. For the battery element of Comparative Example 6, the value of 2 × π × negative electrode thickness × number of positive electrode turns was 10.3, the distance L1 calculated from the above formula (3) was 4 mm, and the width W1 calculated from the above formula (4) was 13 mm.

[0062] A lithium battery was fabricated in the same manner as in Example 1, except that such a battery element was fabricated, and its discharge capacity and short circuit were evaluated. Here, the discharge capacity evaluation of the lithium batteries of Examples 1-4 and Comparative Examples 1-6 will be described.

[0063] Fig. 4 is a diagram illustrating an example of the relationship between discharge capacity and voltage, in which the horizontal axis represents discharge capacity [mAh] and the vertical axis represents voltage [V]. When a lithium battery is discharged at a constant current to 80% depth of discharge (80% DOD) and then discharged at a constant resistance, the behavior of the discharge capacity can be roughly classified into three patterns A, B, and C as shown in Figure 4. Pattern A is a pattern in which the decrease in discharge capacity is suppressed in the range from above threshold voltage V1 to below threshold voltage V1 during constant resistance discharge. Pattern B is a pattern in which the decrease in discharge capacity is suppressed in the range above threshold voltage V1 during constant resistance discharge, but a rapid decrease in discharge capacity occurs in the range below threshold voltage V1. Pattern C is a pattern in which the decrease in discharge capacity is suppressed in the range above threshold voltage V1 during constant resistance discharge.

[0064] Here, for each of the lithium batteries in Examples 1-4 and Comparative Examples 1-6, a lithium battery with a nominal voltage V0 of 3 V was prepared. The threshold voltage V1 was set to 2 V, and constant-current discharge was performed at a constant current of 5 mA to a depth of discharge of 80%. After that, a constant resistance discharge of 5.6 kΩ was performed. In other words, an evaluation was made to see whether or not a sudden decrease in discharge capacity occurred above the threshold voltage V1 of 2 V, i.e., whether or not a sudden decrease in discharge capacity occurred above the threshold voltage.

[0065] Furthermore, the lithium batteries of Examples 1-4 and Comparative Examples 1-6 were evaluated for the presence or absence of short circuits between the positive electrode (its core) and the negative electrode based on the energized state. Table 1 shows the configurations and evaluation results of Examples 1-4 and Comparative Examples 1-6.

[0066] [Table 1]

[0067] As can be seen from Table 1, in the lithium batteries of Examples 1-4, in which the coefficient α was in the range of 0<α<0.5 and the coefficient β was in the range of 0.5<β≦1, no sudden decrease in discharge capacity was observed above the threshold voltage V1 during constant resistance discharge after the constant current discharge. However, in the lithium battery of Example 3, a decrease in discharge capacity was observed below the threshold voltage V1 during constant resistance discharge after the constant current discharge. That is, the lithium batteries of Examples 1-2 and 4 exhibited behavior similar to pattern A in FIG. 4, while the lithium battery of Example 3 exhibited behavior similar to pattern B in FIG. 4. No short circuit between the positive electrode and the negative electrode was observed in the lithium batteries of Examples 1-4.

[0068] In contrast, in the lithium batteries of Comparative Examples 1-4, in which the coefficient α was outside the range of 0<α<0.5, a rapid decrease in discharge capacity was observed above the threshold voltage V1 during constant resistance discharge after the constant current discharge. That is, the lithium batteries of Comparative Examples 1-4 exhibited behavior similar to pattern C in FIG. 4. Among the lithium batteries of Comparative Examples 1-4, the lithium batteries of Comparative Examples 2-4 did not exhibit short-circuiting between the positive and negative electrodes, but the lithium battery of Comparative Example 1, in which α=0 and the terminal positions of the positive and negative electrodes were aligned, exhibited short-circuiting between the positive and negative electrodes.

[0069] In addition, in the lithium battery of Comparative Example 5-6, in which the coefficient α was in the range of 0<α<0.5 but the coefficient β was outside the range of 0.5<β≦1, a rapid decrease in discharge capacity was observed above the threshold voltage V1 during constant resistance discharge after the constant current discharge. That is, the lithium battery of Comparative Example 5-6 exhibited behavior similar to pattern C in FIG. 4. No short circuit between the positive electrode and the negative electrode was observed in the lithium battery of Comparative Example 5-6.

[0070] From the above, when the distance between the end of the negative electrode and the end of the positive electrode in the winding direction of the battery element is expressed as L1 = 2 × π × negative electrode thickness × number of positive electrode windings × α, the coefficient α is in the range of 0 < α < 0.5 (Examples 1-4 and Comparative Examples 5-6), short circuits between the positive electrode and the negative electrode are suppressed.

[0071] In lithium batteries (Examples 1-4) in which the coefficient α is in the range of 0<α<0.5 and the coefficient β is in the range of 0.5<β≦1 when the width of the insulating tape from the end of the positive electrode is expressed as W1=2×π×negative electrode thickness×number of turns of positive electrode×β, short circuits between the positive electrode and the negative electrode are suppressed, and a rapid decrease in discharge capacity at threshold voltages V1 and above is also suppressed. On the other hand, in lithium batteries (Comparative Examples 5-6) in which the coefficient α is in the range of 0<α<0.5 and the coefficient β is outside the range of 0.5<β≦1, short circuits between the positive electrode and the negative electrode are suppressed, but a rapid decrease in discharge capacity at threshold voltages V1 and above may occur.

[0072] In lithium batteries (Comparative Examples 1-4) in which the coefficient α is outside the range of 0<α<0.5, even if the coefficient β is in the range of 0.5<β≦1, a short circuit between the positive electrode and the negative electrode or a rapid decrease in discharge capacity at or above the threshold voltage V1 may occur.

[0073] Therefore, it is preferable that the battery element of the lithium battery be configured so that when the distance between the end of the negative electrode and the end of the positive electrode in the winding direction is expressed as L1 = 2 × π × negative electrode thickness × number of turns of positive electrode × α (the above formula (3)), the coefficient α is in the range of 0 < α < 0.5. In addition to this configuration, it is even more preferable that the battery element of the lithium battery be configured so that when the width of the insulating tape from the end of the positive electrode is expressed as W1 = 2 × π × negative electrode thickness × number of turns of positive electrode × β (the above formula (4)), the coefficient β is in the range of 0.5 < β ≦ 1. [Explanation of symbols]

[0074] 1 lithium battery 10 Outer can 20 Battery elements 21 Negative electrode 21a 1st end 21b 1st starting point 21c Negative electrode tab 22 Positive electrode 22a 2nd end 22b 2nd starting point 22c Positive tab 22d Core 23 Separator 24 Electrical tape 30, 40 Insulating plate 50 Electrolyte 60 Sealing plate 61 Positive terminal 70 Gasket AR1 area C1 center D1 Winding direction D2 opposite direction L1 distance P1 position S1 Standard t thickness V0 Nominal voltage V1 threshold voltage W1 width

Claims

1. A cylindrical outer can; a battery element housed in the outer can and including a positive electrode and a negative electrode containing lithium wound together with a separator interposed therebetween; Including, a first end of the negative electrode in a winding direction from a center of the battery element is located on the opposite side of the winding direction from a second end of the positive electrode in the winding direction, a distance between the first end and the second end is expressed as 2×pi×thickness of the negative electrode×number of turns of the positive electrode×α, where α is in the range of 0<α<0.

5.

2. an insulating tape covering an inner circumferential surface of an end portion of the positive electrode, the end portion including the second end portion; 2. The lithium battery according to claim 1, wherein the width of the insulating tape covering the inner circumferential surface from the second end is expressed as 2 × pi × thickness of the negative electrode × number of turns of the positive electrode × β, and β is in the range of 0.5 < β ≦ 1.

3. 2. The lithium battery according to claim 1, wherein a first start end of the negative electrode wound from the center is located closer to the winding direction than a second start end of the positive electrode wound from the center.

4. 2. The lithium battery according to claim 1, wherein when a position of a second starting end of the positive electrode wound from the center is defined as 0 degrees, the second end is located within a range in which the angle of the winding direction from the second starting end is 90 degrees or less.

5. a first tab connected to the negative electrode; a second tab connected to the positive electrode; Including, 2. The lithium battery of claim 1, wherein when the position of a second starting end of the positive electrode wound from the center is defined as 0 degrees, the angle of the winding direction from the second starting end is within a range of more than 90 degrees and less than 360 degrees, and the first tab and the second tab are located within the range of more than 90 degrees and less than 360 degrees.

6. The lithium battery according to claim 1 , wherein the outermost periphery of the negative electrode is disposed outside the outermost periphery of the positive electrode.

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