Cylindrical lithium primary battery

Abstract

To prevent a short circuit at the tab of a cylindrical lithium primary battery even when the battery is deformed by a strong external force or impact.SOLUTION: A cylindrical lithium primary battery includes an outer casing, and a wound electrode body disposed within the outer casing, in which a positive electrode 5 and a negative electrode are wound around each other with a separator interposed between them. The positive electrode 5 includes a core 5a having a recess 5a3 recessed from face 5a1 toward face 5a2 opposite face 5a1, composite layers 5b, 5c provided on faces 5a1, 5a2 of the core 5a, and a positive electrode tab 16 connected to the recess 5a3 of the core 5a.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a cylindrical lithium primary battery. [Background technology]

[0002] There is a cylindrical lithium (Li) primary battery in which a positive electrode and a negative electrode are wound with a separator interposed therebetween and disposed in a cylindrical exterior body (see, for example, Patent Document 1). The positive electrode has a configuration in which a composite material containing an active material is applied to a metal material that serves as a core body.

[0003] Metal tabs are used to electrically connect the positive electrode and negative electrode to the exterior body, sealing body, etc. In cylindrical lithium primary batteries, the positive electrode tab is generally connected to the core body. In addition, batteries are required to be highly safe, and not to explode or catch fire even if the exterior body is deformed by a strong external force or impact. If the tab of one of the positive and negative electrodes is deformed when the battery is deformed, the hard tab may break through the separator and come into contact with the other electrode, which may lead to explosion or fire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-122592 A Summary of the Invention [Problem to be solved by the invention]

[0005] One aspect of the present invention aims to suppress the occurrence of a short circuit at the tabs in a cylindrical lithium primary battery, even when the battery is deformed by a strong external force or impact. [Means for solving the problem]

[0006] In one embodiment, a cylindrical lithium primary battery is provided, comprising an outer casing, and a wound electrode body disposed within the outer casing, in which a positive electrode and a negative electrode are wound around each other with a separator interposed between them, wherein the positive electrode comprises a core body having a recess extending from a first surface toward a second surface opposite the first surface, a composite layer provided on the first surface and the second surface of the core body, and a tab connected to the recess of the core body. Effect of the Invention

[0007] In one aspect, even when the battery is deformed due to a strong external force or impact, the occurrence of a short circuit at the tab can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a cylindrical lithium primary battery. [Diagram 2] FIG. 2 is a plan view showing an example of a positive electrode according to the present embodiment. [Diagram 3] FIG. 2 is a cross-sectional view showing an example of a positive electrode according to the present embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a positive electrode according to the present embodiment after winding. [Diagram 5] FIG. 2 is a cross-sectional view showing an example of a positive electrode of a first comparative example. [Figure 6] FIG. 11 is a diagram showing an example in which a short circuit occurs when the positive electrode of the first comparative example is used. [Figure 7] FIG. 11 is a plan view showing an example of a positive electrode of a second comparative example. [Figure 8] FIG. 4 is a cross-sectional view showing an example of a positive electrode of a second comparative example. [Figure 9] FIG. 11 is a cross-sectional view showing an example of a positive electrode of a second comparative example after winding. [Figure 10] FIG. 13 is a diagram showing an example of a test result. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a cylindrical lithium primary battery. The cylindrical lithium primary battery 1 includes a cylindrical exterior body 2 with a bottom, and a wound electrode body 10 disposed within the exterior body 2 and wound around a negative electrode 4 and a positive electrode 5 with a separator 6 interposed between them. The wound electrode body 10 is disposed within the exterior body 2 together with a nonaqueous electrolyte 3.

[0010] The wound electrode body 10 is wound in a spiral shape around the cylindrical axis 2a of the exterior body 2 as the winding axis. The non-aqueous electrolyte 3 is a non-aqueous solvent to which an additive has been added. As the non-aqueous solvent, for example, a mixture of PC (propylene carbonate), EC (ethylene carbonate), and DME (1,2-dimethoxyethane) in a weight ratio of PC:EC:DME=10:10:80 can be used. As the additive, for example, lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ) can be used as a supporting salt.

[0011] The negative electrode 4 contains lithium. For example, the negative electrode 4 is a sheet of lithium metal or a lithium alloy. Examples of the lithium alloy that can be used include a lithium-aluminum (Al) alloy, a lithium-magnesium (Mg) alloy, a lithium-tin (Sn) alloy, a lithium-zinc alloy, a lithium-antimony (Sb) alloy, and a lithium-silicon (Si) alloy.

[0012] A metal that alloys with lithium may be disposed on the surface of the negative electrode 4 to form an alloyed layer. For example, aluminum foil may be disposed on the surface of the negative electrode 4 to be alloyed with lithium. The metal disposed on the surface of the negative electrode 4 is not particularly limited as long as it is an element that alloys with lithium, and for example, magnesium, tin, zinc, silicon, etc. may be used. The material disposed on the surface of the negative electrode 4 is not limited to metal foil, and may be a plate, powder, or a processed version of the same.

[0013] The positive electrode 5 is an electrode plate including a core body that functions as a current collector and a composite layer that covers the core body. As described later, a part of the core body is exposed, and a positive electrode tab 16 is connected to the exposed part.

[0014] As the core, for example, a lath plate, a plain woven wire mesh, an expanded metal, a punched metal, a metal foil, or the like can be used. The positive electrode 5 according to the present embodiment is particularly suitable for a core such as a lath plate, a plain woven wire mesh, an expanded metal, or a punched metal, which is difficult to deform due to its thickness. When such a core is used, since it is difficult to deform, if unevenness occurs in the portion of the positive electrode tab 16 as in the positive electrode 20 of Comparative Example 1 (see FIG. 5) described later, winding becomes even more difficult.

[0015] The core is preferably made of stainless steel that is resistant to corrosion against the positive electrode potential. For example, the material of the core may be SUS (Steel Use Stainless) 316, SUS 444, etc., but is not limited to these materials.

[0016] The composite layer contains, for example, manganese dioxide as a positive electrode active material. An example of a positive electrode active material containing manganese dioxide is EMD (Electrolytic Manganese Dioxide). The composite layer contains, for example, carbon as a conductive material. Examples of conductive materials containing carbon include Ketjen Black (KB) and graphite (Gr). The composite layer further contains a binder. For example, a fluorine-based resin is used as the binder. The composite layer may contain other additives as components. The composite layer is produced, for example, by applying a slurry containing an active material, a conductive material, a binder, and the like to a core body and rolling the applied film.

[0017] The separator 6 is, for example, a microporous film made of polyolefin. The separator 6 may be a laminate of a microporous film made of polyolefin and a nonwoven fabric (for example, a sheet-shaped resin nonwoven fabric (such as a polypropylene nonwoven fabric)). The microporous film preferably has a shutdown function.

[0018] The cylindrical lithium primary battery 1 shown in FIG. 1 further includes a sealing plate 11, a positive electrode terminal 12, a metal washer 13, a resin gasket 14, a negative electrode tab 15, and a positive electrode tab 16.

[0019] The sealing plate 11 has a disk-shaped portion with an opening in the center, and the edge of the disk-shaped portion is bent upward. The positive electrode terminal 12 and the washer 13 are crimped via a gasket 14. The edge of the sealing plate 11 and the upper edge of the exterior body 2 are welded by laser welding or the like. This seals the can opening of the battery can, which is the exterior body 2, and seals the inside of the exterior body 2.

[0020] The negative electrode 4 and the inner surface of the exterior body 2 are electrically connected via a negative electrode tab 15. In addition, the positive electrode 5 and the lower surface of the positive electrode terminal 12 are electrically connected via a positive electrode tab 16. Fig. 2 is a plan view showing an example of a positive electrode according to the present embodiment. Fig. 3 is a cross-sectional view showing an example of a positive electrode according to the present embodiment. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Figs. 2 and 3 show the positive electrode 5 before being wound.

[0021] The positive electrode 5 has a core body 5a, mixture layers 5b and 5c, and a positive electrode tab 16. The core body 5a has a recess 5a3 recessed from a surface 5a1 toward a surface 5a2 opposite to the surface 5a1.

[0022] The mixture layers 5b and 5c are provided on the surfaces 5a1 and 5a2 of the core body 5a. In the example of Fig. 2 and Fig. 3, parts of the mixture layers 5b and 5c are removed to expose the recesses 5a3. The positive electrode tab 16 is connected to the recess 5a3 of the core body 5a. In order to obtain a cylindrical lithium primary battery 1 with high output characteristics, it is desirable that the cross-sectional area of ​​the positive electrode tab 16 is relatively large. However, if the width of the positive electrode tab 16 is increased, the area to be peeled off the composite layers 5b and 5c increases, and the battery capacity decreases. For this reason, it is desirable to increase the thickness of the positive electrode tab 16. For example, the positive electrode tab 16 is thicker than the thickness of the core body 5a and the composite layers 5b and 5c.

[0023] The positive electrode tab 16 is connected to the core body 5a at a welding point 16b1 by welding, as shown in Fig. 3. The welding can be performed by, for example, resistance welding. If the attachment position of the positive electrode tab 16 in the longitudinal direction of the core body 5a is too close to the end of the winding shaft side where the curvature becomes large when the core body 5a is wound, winding may become difficult due to the influence of the hard and thick positive electrode tab 16. Although not particularly limited, the attachment position of the positive electrode tab 16 in the longitudinal direction of the core body 5a is, for example, a position about 2 / 5 of the longitudinal length of the core body 5a from the end of the winding shaft side.

[0024] The recesses 5a3 are formed, for example, at the same time that parts of the composite layers 5b and 5c are peeled off from the core body 5a. The recesses 5a3 may be formed by pressure applied when the positive electrode tab 16 is welded. Alternatively, the recesses 5a3 may be formed by applying pressure to the part of the core body 5a where the positive electrode tab 16 is to be connected, before the composite layers 5b and 5c are formed.

[0025] The recess 5a3 is formed at a depth such that, when the positive electrode 5 is wound, the surface 16a of the positive electrode tab 16 opposite the core body 5a does not protrude from the surface 5b1 of the composite layer 5b provided on the surface 5a1 opposite the core body 5a.

[0026] Furthermore, recess 5a3 is preferably formed to a depth such that, when positive electrode 5 is wound, recess 5a3 does not protrude from surface 5c1 of mixture layer 5c provided on surface 5a2 on the side opposite to core body 5a. Although not shown in the figure, an insulating film may be attached to the composite layers 5b, 5c to cover the exposed portion of the core body 5a and the portion of the positive electrode tab 16 connected to the recess 5a3 in order to prevent short circuits.

[0027] FIG. 4 is a cross-sectional view showing an example of the positive electrode according to the present embodiment after winding. The wound positive electrode 5 included in the wound electrode body 10 as shown in Fig. 1 is in a bent state as shown in Fig. 4. As shown in Fig. 4, in the wound positive electrode 5, the surface 16a of the positive electrode tab 16 opposite the core body 5a does not protrude from the surface 5b1 of the mixture layer 5b provided on the surface 5a1 opposite the core body 5a.

[0028] Further, recess 5a3 does not protrude from surface 5c1 of mixture layer 5c provided on surface 5a2, the surface being opposite to core body 5a. In the example of Figure 4, the positive electrode tab 16 is provided on the part of the core 5a that is not covered with the composite layers 5b, 5c, on the side of the rotating shaft of the winding (inner side of the winding), but it may be provided on the part opposite the rotating shaft side of the winding (outer side of the winding).

[0029] Before describing the effect of using such a positive electrode 5, the following comparative example will be described. Fig. 5 is a cross-sectional view showing an example of a positive electrode of the first comparative example. In Fig. 5, the same elements as those of the positive electrode 5 shown in Fig. 3 are denoted by the same reference numerals. Note that a plan view of the positive electrode 20 of the first comparative example is omitted because it is the same as that shown in Fig. 2. Also, Fig. 5 shows the positive electrode 20 before being wound.

[0030] The core 20a of the positive electrode 20 of the first comparative example does not have a recess 5a3 as shown in Fig. 3. The positive electrode tab 16 is connected to the exposed portion of the core 20a, but the surface 16a opposite to the core 20a side protrudes from the surface 5b1 of the mixture layer 5b opposite to the core 20a side.

[0031] When such a positive electrode 20 of the first comparative example is used, the following problems may occur. FIG. 6 is a diagram showing an example in which a short circuit occurs when the positive electrode of the first comparative example is used.

[0032] Even when positive electrode 20 of the first comparative example is wound, surface 16a of positive electrode tab 16 protrudes from surface 5b1 of mixture layer 5b. When a force in the direction of the arrow 30 is applied from the outside of the cylindrical lithium primary battery, the positive electrode tab 16 is pushed out. In the example of FIG. 6, the positive electrode tab 16 breaks through the separator 6, resulting in a portion 31 in close proximity to the negative electrode 4. In this case, a short circuit occurs, which may lead to an explosion or fire. Even if an insulating film is attached so as to cover the exposed portion of the core body 20a and the portion of the positive electrode tab 16 connected to the core body 20a, the same problem may occur.

[0033] Furthermore, when a wound electrode body is formed using the positive electrode 20 of the first comparative example, unevenness occurs at the positive electrode tab 16, and the roundness of the wound electrode body deteriorates. This makes it easier for excess space to be generated within the exterior body 2. The stainless steel core body 20a is difficult to wind because of its hardness, but when a positive electrode tab 16 thicker than the core body 20a is used, the occurrence of the above-mentioned unevenness makes winding even more difficult.

[0034] In contrast, in the positive electrode 5 according to the present embodiment as shown in Fig. 3, the positive electrode tab 16 is connected to the recess 5a3 of the core body 5a. Therefore, the surface 16a of the positive electrode tab 16 is prevented from protruding from the surface 5b1 of the composite layer 5b, as compared to the case where the positive electrode 20 of the first comparative example is used, and the occurrence of a short circuit as shown in Fig. 6 is prevented. Therefore, the safety of the battery can be ensured.

[0035] 1 is formed using the positive electrode 5 as shown in Fig. 3, the positive electrode tab 16 is prevented from protruding from the surface 5b1 of the composite layer 5b. This prevents the occurrence of irregularities in the portion of the positive electrode tab 16, and prevents the roundness of the wound electrode body from deteriorating even when a stainless steel core 20a is used.

[0036] Further, recess 5a3 is formed at a depth not to protrude from surface 5c1 of mixture layer 5c provided on surface 5a2 opposite to core body 5a, thereby preventing core body 5a from breaking through adjacent separator 6 and coming into contact with negative electrode 4 due to an external force.

[0037] Fig. 7 is a plan view showing an example of a positive electrode of the second comparative example. Fig. 8 is a cross-sectional view showing an example of a positive electrode of the second comparative example. Fig. 8 is a cross-sectional view taken along line VIII-VIII in Fig. 7. Figs. 7 and 8 show positive electrode 40 before being wound.

[0038] FIG. 9 is a cross-sectional view showing an example of a positive electrode of the second comparative example after winding. The positive electrode 40 of the second comparative example has a core body 40a, composite layers 40b and 40c, and a positive electrode tab 41.

[0039] The core body 40a is different from the core body 5a of the positive electrode 5 shown in FIG. 3 in that no recess is formed. The mixture layers 40b, 40c are provided on the surfaces 40a1, 40a2 of the core body 40a. In the example of Fig. 7 to Fig. 9, parts of the mixture layers 40b, 40c are removed to expose part of the core body 40a.

[0040] The positive electrode tab 41 is welded to the core body 40a at a welding point 41b1 in an exposed portion of the surface 40a1 of the core body 40a. Unlike the positive electrode tab 16 of the positive electrode 5 shown in Fig. 3, the thickness of the positive electrode tab 41 is the same as the thickness of the composite layer 40b provided on the surface 40a1. Therefore, the surface 41a of the positive electrode tab 41 does not protrude from the surface 40b1 of the composite layer 40b.

[0041] However, if the cross-sectional area of ​​the positive electrode tab 41 is made equal to the cross-sectional area of ​​the positive electrode tab 16 of the positive electrode 5 in order to maintain the same output characteristics as when the positive electrode 5 shown in Fig. 3 is used, the width of the positive electrode tab 41 will be wider than the width of the positive electrode tab 16. In this way, if the width of the positive electrode tab 41 is widened, the area from which the composite layers 40b and 40c are peeled off will increase, resulting in a decrease in battery capacity.

[0042] In contrast to the positive electrode 40 of the second comparative example, in the positive electrode 5 shown in FIG. 3, the positive electrode tab 16 is connected to the recess 5a3 of the core body 5a, so that even if the thickness of the positive electrode tab 16 is increased, the surface 16a of the positive electrode tab 16 is prevented from protruding from the surface 5b1 of the composite layer 5b. Therefore, even if the width of the positive electrode tab 16 is relatively narrow, the thickness of the positive electrode tab 16 can be increased, so that high output characteristics can be obtained. In addition, since the width of the positive electrode tab 16 can be relatively narrow, the area of ​​the composite layers 5b and 5c to be peeled off is suppressed, so that a decrease in battery capacity can be prevented.

[0043] (Test Example) Next, the results of tests performed on the battery performance when the positive electrode 5 according to the present embodiment as shown in Figs. 2 and 3 was used, and when the positive electrodes 20 and 40 of the above two comparative examples were used, are shown.

[0044] FIG. 10 is a diagram showing an example of the test results. Comparative Example 1 shows the test results when the positive electrode 20 of the first comparative example as shown in FIG. 5 and FIG. 6 was used.

[0045] Comparative Example 2 shows the test results when the positive electrode 40 of the second comparative example as shown in FIGS. 7 to 9 was used. Example 1 shows the test results when the positive electrode 5 according to the present embodiment as shown in Figs. 2 to 4 was used.

[0046] The composite layers 5b, 5c, 40b, and 40c of the positive electrodes 5, 20, and 40 of Comparative Examples 1 and 2 and Example 1 were prepared by applying a slurry obtained by mixing a positive electrode active material, a conductive material, and a binder in a mass ratio of 90:5:5 to the front and back surfaces of the cores 5a, 20a, and 40a, and rolling the coating film. EMD was used as the positive electrode active material, carbon as the conductive material, and fluorine-based resin as the binder. A lath plate was used as the cores 5a, 20a, and 40a. The thicknesses of the composite layers 5b, 5c, 40b, and 40c (represented as "composite layer one-sided thickness" in FIG. 10) were 0.15 mm.

[0047] Parts of the composite layers 5b, 5c, 40b, and 40c were removed, and the positive electrode tabs 16 and 41 were connected by resistance welding to the exposed portions of the cores 5a, 20a, and 40a. In the positive electrode 5 of Example 1, the recesses 5a3 were formed when the parts of the composite layers 5b and 5c were peeled off from the core 5a, and the positive electrode tab 16 was connected to the recesses 5a3. In FIG. 10, the presence or absence of the formation of such recesses 5a3 is indicated as "presence or absence of core recesses."

[0048] The width (tab width) of the positive electrode tab 16 used in Comparative Example 1 and Example 1 was 3.5 mm, and the thickness (tab thickness) of the positive electrode tab 16 was 0.2 mm. On the other hand, the width of the positive electrode tab 41 used in Comparative Example 2 was 4.65 mm, and the thickness of the positive electrode tab 41 was 0.15 mm.

[0049] In the positive electrodes 5, 20, and 40 of Comparative Examples 1 and 2 and Example 1 produced as described above, the surface 16a of the positive electrode tab 16 protruded from the surface 5b1 of the mixture layer 5b in the positive electrode 20 of Comparative Example 1. In contrast, in the positive electrodes 5 and 40 of Comparative Example 2 and Example 1, the surfaces 16a and 41a of the positive electrode tabs 16 and 41 did not protrude from the surfaces 5b1 and 40b1 of the mixture layers 5b and 40b.

[0050] For other components of the cylindrical primary lithium battery, they are the same as those in Comparative Examples 1 and 2 and Example 1. The non-aqueous electrolyte 3 is a base electrolyte in which PC, EC, and DME are mixed at a weight ratio of PC:EC:DME = 10:10:80, and LiCF 3 SO 3 is added at 0.5 M (=mol / L) and used.

[0051] As the negative electrode 4, a lithium-aluminum alloy was used. Also, as the separator 6, a microporous film made of polyolefin was used. The positive electrodes 5, 20, 40 and the negative electrode 4 were wound in a state of facing each other via the separator 6, and a wound electrode body (when the positive electrode 5 was used, the wound electrode body 10 in FIG. 1) was produced.

[0052] After inserting the obtained wound electrode body together with the non-aqueous electrolyte 3 into the cylindrical outer package 2, the edge of the sealing plate 11 and the upper edge of the outer package 2 were welded by laser welding or the like, and a cylindrical primary lithium battery was produced. The outer diameter of the produced cylindrical primary lithium battery is 17 mm and the height is 500 mm.

[0053] For each of the cylindrical primary lithium batteries of Comparative Examples 1 and 2 and Example 1, continuous discharge was performed at 5 mA, and the battery capacity up to 2 V was measured. Further, an impact test was carried out according to the test conditions of the Impact Test of UL1642. The result of the impact test is represented by the number of ignitions per test number. In FIG. 10, "p" represents the number of cylindrical primary lithium batteries.

[0054] As shown in FIG. 10, when the battery capacity of Example 1 was set to 100%, the battery capacity of Comparative Example 1 was 100%, but in Comparative Example 2, the battery capacity was 99%, and it was found that the battery capacity was lower than that of Comparative Example 1 and Example 1. Also, in Comparative Example 1, the number of ignitions was 2 per 10. In Comparative Example 1, there may have been a short circuit as shown in FIG. 6. In contrast, in Example 1 (and also in Comparative Example 2), the number of ignitions was 0 per 10, and it was confirmed that the safety of the battery was ensured.

[0055] One aspect of the cylindrical lithium primary battery of the present invention has been described above based on the embodiment, but this is merely an example and the present invention is not limited to the above description. [Explanation of symbols]

[0056] 1 Cylindrical lithium primary battery 2 Exterior body 2a cylindrical shaft 3 Nonaqueous electrolyte 4 Negative electrode 5,20,40 positive electrode 5a,20a,40a core 5a1,5a2,40a1,40a2 side 5a3 Recess 5b,5c,40b,40c Composite layer 5b1,5c1,16a,41a,40b1 surface 6 Separator 10 Wound electrode body 11 Sealing plate 12 Positive terminal 13 Washer 14 Gasket 15 Negative tab 16,41 Positive electrode tab 16b1,41b1 Welding point 30 Arrow 31 locations

Claims

1. An exterior body; a wound electrode body disposed within the exterior body, the positive electrode and the negative electrode being wound around each other with a separator interposed between them; having The positive electrode is a core body having a recess recessed from a first surface toward a second surface opposite to the first surface; A composite layer provided on the first surface and the second surface of the core body; a tab connected to the recess of the core; A cylindrical lithium primary battery having a

2. 2. The cylindrical lithium primary battery in accordance with claim 1, wherein said core is made of stainless steel.

3. 2. The cylindrical lithium primary battery according to claim 1, wherein the composite layer contains manganese dioxide and the negative electrode contains lithium.

4. 2 . The cylindrical lithium primary battery according to claim 1 , wherein the recess does not protrude from a surface of the mixture layer provided on the second surface opposite to the substrate side.

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