Coin cell

Abstract

The present invention suppresses a decrease in the pulse discharge characteristics of a coin lithium primary cell near the end of discharge. A coin lithium primary cell according to the present invention is provided with: a case (1) having a bottom plate section (1a), an annular bent section (A), and an annular outer wall section (1b); a sealing plate (2) having a top plate section (2a), an annular bent section (B), and an annular inner wall section (2b); a gasket (3); and a power generating element. The bent section (B) has a first bent section (B1) that is continuous with the peripheral edge of the top plate section (2a) and that is bent in a first direction directed toward the bottom plate section (1a). The power generating element is provided with: a positive electrode (4) electrically connected to the bottom plate section (1a); a negative electrode (5) electrically connected to the top plate section (2a); a separator (6); and an electrolyte solution. The negative electrode (5) includes a Li alloy containing Mg by the content of 0.10-5.0 mass%. The Vickers hardness (HVb0) of the top plate section (2a) is 150-250 HV. The ratio of the difference (ΔHVb) between the Vickers hardness (HVb1) of the first bent section (B1) and the Vickers hardness (HVb0) of the top plate section (2a) to the Vickers hardness (HVb0) of the top plate section (2a) is 30-60%.

Description

coin cell battery

[0001] This disclosure relates to coin-type batteries.

[0002] Patent Document 1 describes a method for manufacturing a flat-shaped battery comprising a battery container having an outer can, a sealing body, and a gasket disposed between the outer can and the sealing body, in which a positive electrode, a negative electrode, and an electrolyte are housed, wherein a metal can is used, which is formed by drawing an austenitic or austenitic-ferritic stainless steel material to have a bottom portion, a side portion having an opening on one side, and a bent portion connecting the bottom portion and the side portion, with a cross section that is substantially U-shaped, and the thickness of the side portion being 0.1 to 0.3 mm, and the Vickers bearing of the bottom portion, the bent portion and the side portion of the metal can is used. The present invention proposes a method for manufacturing a flat-shaped battery, comprising: (A) a step of manufacturing the outer can in which the hardness is set to 140 to 320 (HV), and the difference in Vickers hardness between the bent portion and the bottom portion, and the difference in Vickers hardness between the side portion and the bottom portion, are each within 15% of the Vickers hardness of the bottom portion; and (B) a step of crimping the opening side of the side portion of the outer can inward, so that the difference in Vickers hardness between the bent portion and the bottom portion is 90 (HV) or less, and the difference in Vickers hardness between the vicinity of the opening of the side portion and the bent portion is 50 (HV) or more.

[0003] Patent Document 2 proposes a non-aqueous electrolyte coin-type battery in which a power generation element, in which a positive electrode and a negative electrode are arranged opposite each other with a separator, is sealed together with a non-aqueous electrolyte in an exterior component consisting of a positive electrode case made of a metal material, a sealing plate, and a gasket made of resin, characterized in that the sealing plate is made of a clad material in which a nickel plate is clad on at least the outer surface of a steel substrate, and the non-aqueous electrolyte coin-type battery is characterized in that the Vickers hardness of the clad material is 160 to 240 HV.

[0004] Patent Document 3 proposes a lithium primary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains manganese dioxide, the negative electrode contains a lithium alloy, the lithium alloy contains magnesium, and the magnesium content in the lithium alloy is 10% by mass or less.

[0005] Japanese Unexamined Patent Application Publication No. 2017-45551, Japanese Unexamined Patent Application Publication No. 2013-37796, International Publication No. 2024 / 43273

[0006] In a coin-type primary lithium battery, the negative electrode is not consumed uniformly during discharge, and lithium is preferentially consumed from portions where the battery reaction is prone to proceed. Specifically, there is a bias in lithium consumption between the peripheral portion and the central portion of the negative electrode. Since the battery reaction is more likely to proceed in the central portion of the negative electrode than in the peripheral portion, lithium consumption tends to be faster in the central portion. As a result, at the end of discharge, the negative electrode becomes donut-shaped, the reaction area decreases, the internal resistance increases, and the pulse discharge characteristics deteriorate. That is, it becomes difficult to achieve a sufficient lifespan corresponding to the capacity.

[0007] One aspect of the present disclosure provides a coin-type primary lithium battery comprising: a case having a bottom plate portion, an annular bent portion A continuous with a peripheral edge of the bottom plate portion, and an annular outer wall portion rising from the bent portion A; a sealing plate having a top plate portion, a bent portion B continuous with a peripheral edge of the top plate portion, and an annular inner wall portion extending from the bent portion B in a first direction toward the bottom plate portion; a gasket compressed between the outer wall portion and the inner wall portion; and a power generation element sealed by the case and the sealing plate, wherein the bent portion B has a first bent portion continuous with the peripheral edge of the top plate portion and bent in the first direction, the power generation element comprises: a positive electrode electrically connected to the bottom plate portion of the case; a negative electrode electrically connected to the top plate portion of the sealing plate; a separator disposed between the positive electrode and the negative electrode; and an electrolytic solution, the negative electrode includes a Li alloy containing Mg at a content of 0.10% by mass to 5.0% by mass, the Vickers hardness of the top plate portion (HVb0) is 150 HV to 250 HV, and the ratio of a difference (ΔHVb) between the Vickers hardness of the first bent portion (HVb1) and the Vickers hardness of the top plate portion (HVb0) to the Vickers hardness of the top plate portion (HVb0) is 30% to 60%.

[0008] According to the present disclosure, the deterioration of pulse discharge characteristics at the end of discharge of a coin-type primary lithium battery is suppressed.

[0009] This is a longitudinal cross-sectional view of a coin-type lithium primary battery according to one embodiment of the present disclosure. This is an enlarged view of an example of the bent portions A and B of a coin-type lithium primary battery according to one embodiment of the present disclosure.

[0010] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit.

[0011] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0012] The coin-type lithium primary battery (hereinafter also referred to as "lithium primary battery (LB)") relating to this disclosure comprises a case, a sealing plate, a gasket, and a power generation element.

[0013] The term "coin-type battery" also includes "button-type batteries." That is, the shape and diameter of a coin-type lithium primary battery are not particularly limited. For example, a button-type battery whose thickness is greater than its diameter is also included in the definition of a coin-type battery.

[0014] The case has a bottom plate, an annular bent portion A continuous with the periphery of the bottom plate, and an annular outer wall portion rising from the bent portion A in the direction from the bottom plate toward the top plate. The end of the outer wall portion corresponding to the open end of the case is bent toward the center of the case. The bottom plate is usually circular, but may be close to a circular shape (e.g., elliptical). The diameter D of the bottom plate is, for example, 9 mm ≤ D ≤ 24.5 mm, but is not particularly limited. The thickness of the case material is, for example, 0.1 mm to 0.3 mm, and may be 0.15 mm to 0.25 mm.

[0015] The case is made of, for example, stainless steel that is corrosion-resistant at the positive potential. Preferred stainless steels include SUS430, SUS444, and SUS329J.

[0016] The sealing plate has a top plate portion, an annular bent portion B continuous with the periphery of the top plate portion, and an annular inner wall portion extending from the bent portion B in a first direction. The bent portion B has an annular first bent portion that is continuous with the periphery of the top plate portion and bends in the first direction. The first direction is the direction from the top plate portion toward the bottom plate portion. When the direction perpendicular to the first direction is taken as the second direction (the radial direction of the top plate portion), the bent portion B may extend not only in the first direction but also outward in the second direction and toward the inner circumferential surface of the outer wall portion. The top plate portion corresponds to the shape of the bottom plate portion and is usually a circle with a smaller diameter than the bottom plate portion. The thickness of the sealing plate material is usually greater than the thickness of the case material, for example, 0.15 mm to 0.35 mm, and may be 0.2 mm to 0.3 mm.

[0017] The sealing plate is made of, for example, a stainless steel that is stable against lithium metal. Preferred stainless steels include SUS304, SUS316, and SUS430. The sealing plate may also be made of ordinary steel or carbon steel.

[0018] The thickness T of a lithium primary battery (LB) is usually smaller than the diameter D of the base plate (T < D), for example, 1.2 mm ≤ T ≤ 5.0 mm. The thickness T is the distance between the outer surface of the center of the base plate and the outer surface of the center of the top plate.

[0019] In the sealing plate, the bent portion B may further have an annular second bent portion that is continuous with the first bent portion and positioned outward from the first bent portion in a second direction. The region outward from the second bent portion in a second direction is bent such that the inclination from the top plate portion to the bottom plate portion is smaller than that of the region between the first bent portion and the second bent portion. The first bent portion and the second bent portion form a stepped portion or flange-like portion of the sealing plate at a position closer to the bottom plate portion than the opening end of the case.

[0020] The bent portion B may further have a third bent portion located outward from the second bent portion in the second direction. The region on the outer peripheral end side of the sealing plate from the third bent portion is bent such that the inclination from the top plate portion to the bottom plate portion is greater than that of the region between the second bent portion and the third bent portion. The inner wall portion is the portion that extends from the third bent portion toward the bottom plate portion of the case. The inner wall portion may be folded back at the position closest to the bottom plate portion of the case and overlapped in a double layer.

[0021] The gasket is compressed between the outer and inner walls. The gasket serves to seal the space enclosed by the sealing plate and the case. The open end of the case (the end of the outer wall) is pressed against the bent portion B of the sealing plate (for example, a stepped portion or a flange-like portion) via the gasket. This forms a crimped sealing structure.

[0022] The power generation element is sealed by a case and a sealing plate. The power generation element comprises a positive electrode electrically connected to the bottom plate of the case, a negative electrode electrically connected to the top plate of the sealing plate, a separator placed between the positive and negative electrodes, and an electrolyte. The positive and negative electrodes are layered with predetermined thicknesses, and the separator is a sheet with predetermined thicknesses. The positive and negative electrodes are stacked along their respective thickness directions with the separator in between. Here, the stacking direction of the positive and negative electrodes is the direction in which the bottom plate of the case and the top plate of the sealing plate are aligned.

[0023] Here, the sealing plate satisfies the following conditions (A) and (B).

[0024] Condition (A): The Vickers hardness (HVb0) of the top plate is between 150HV and 250HV.

[0025] Condition (B): The ratio of the difference between the Vickers hardness of the first bent section (HVb1) and the Vickers hardness of the top plate (HVb0) (ΔHVb = HVb1 - HVb0) to the Vickers hardness of the top plate (HVb0) is 30% to 60%.

[0026] The bent portion B is usually formed by press working. Since press working increases the Vickers hardness, the Vickers hardness of the bent portion B is higher than that of the top plate (HVb0 < HVb1).

[0027] The negative electrode has a Li alloy containing Mg in a content of 0.10% to 5.0% by mass (hereinafter also referred to as "Li-Mg alloy (N)"). The Li-Mg alloy (N) is less prone to uneven lithium consumption during discharge. That is, the negative electrode is less likely to become donut-shaped at the end of discharge, and the deterioration of pulse discharge characteristics is easily suppressed. In other words, the proportion of Li that can contribute to the discharge reaction at the end of discharge is increased, resulting in a long-life lithium primary battery (LB). Such effects are particularly pronounced when the sealing plate satisfies both conditions (A) and (B).

[0028] Because Mg has high dispersibility in metallic Li and high conductivity (low resistance), it is thought that the current collection performance of the negative electrode is improved, and the negative electrode is consumed more uniformly. In addition, Mg remains in the alloy even after Li is consumed, and the concentration of Mg gradually increases. As a result, holes are less likely to form in the center of the negative electrode, and a difference in Li concentration is created between the center and the outer periphery of the negative electrode. Such a concentration difference is thought to promote the consumption of Li in the outer periphery of the negative electrode. As a result, the utilization rate of the negative electrode is significantly increased.

[0029] If the Mg content of the Li-Mg alloy (N) is less than 0.1 mass%, the effect of Mg will not be fully realized, and the pulse discharge characteristics may deteriorate at the end of discharge due to the negative electrode. Even if the Mg content exceeds 5.0 mass%, no further improvement in pulse discharge performance can be expected. If the Mg content is too high, the proportion of Li in the Li-Mg alloy decreases, making it difficult for lithium primary batteries to achieve high capacity.

[0030] From the viewpoint of more reliably increasing the amount of Li that can contribute to the discharge reaction at the end of the discharge, the Mg content in the Li-Mg alloy (N) may be 0.2 mass% or more, or 0.5 mass% or more. Also, from the viewpoint of ensuring a larger proportion of Li contained in the negative electrode, the Mg content in the Li-Mg alloy (N) may be 4 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less.

[0031] The Li-Mg alloy (N) may further contain aluminum. Hereinafter, the Li-Mg alloy (N) containing Mg and Al will also be referred to as "Li-Mg-Al alloy (N)". Since Al has even higher conductivity than Mg, it is thought that the current collection performance of the negative electrode will be further improved and the negative electrode will be consumed more uniformly. In addition, since Al remains in the alloy even after Li is consumed, it exhibits the same effects as Mg, and the desired effect is enhanced.

[0032] Furthermore, when a lithium alloy contains Al alone, non-uniformity in Li consumption can occur due to Al segregation. On the other hand, when a Li alloy containing Mg also contains Al, such a phenomenon is suppressed. Al's dispersibility in the Li alloy is enhanced by its coexistence with Mg.

[0033] The Al content in the Li-Mg-Al alloy (N) is preferably, for example, 0.10 mass% to 5.0 mass%. From the viewpoint of more reliably increasing the effect of Al, the Al content in the Li-Mg-Al alloy (N) may be 0.2 mass% or more, or 0.5 mass% or more. Furthermore, from the viewpoint of ensuring a larger proportion of Li contained in the negative electrode, the Al content in the Li-Mg-Al alloy (N) may be 4 mass% or less, 3 mass% or less, 2 mass% or less, or 1 mass% or less.

[0034] The total content of Mg and Al in the Li-Mg-Al alloy (N) is preferably 5.1% by mass or less, and more preferably 5.0% by mass or less. This makes it possible for the lithium primary battery (LB) to maintain a high capacity. The total content of Mg and Al in the Li-Mg-Al alloy (N) may be, for example, 0.2% to 4% by mass, 0.3% to 3% by mass, 0.3% to 2% by mass, or 0.3% to 1.0% by mass.

[0035] The mass ratio of Mg to Al (Mg / Al ratio) in the Li-Mg-Al alloy (N) is preferably, for example, 0.2 to 50. Furthermore, the Al content is preferably lower than the Mg content. The Mg / Al ratio may be greater than 1, 50 or less, or between 1.5 and 50.

[0036] Lithium alloys may contain one or more metallic elements capable of alloying with lithium, in addition to Mg and Al. Examples of metallic elements capable of alloying with lithium include Na, Ca, Sn, Ni, Pb, In, K, Fe, and Si, but are not particularly limited. However, from the viewpoint of ensuring capacity, the total content of metallic elements other than lithium in the lithium alloy is preferably 15% by mass or less, or 11% by mass or less. That is, the Li content in the lithium alloy used for the negative electrode is preferably 85% by mass or more, or 89% by mass or more, and more preferably 95% by mass or more.

[0037] The composition of lithium alloys can be determined by inductively coupled plasma (ICP) emission spectrometry or atomic absorption spectrometry (AAS).

[0038] If the sealing plate satisfies both conditions (A) and (B), the top plate portion has a predetermined elasticity (in other words, a reaction force that presses the negative electrode) suitable for holding and pressing the negative electrode. When the top plate portion is subjected to pressure from the power generation element, the position of the center portion of the top plate portion is slightly displaced. The bend B of the sealing plate is an annular portion that is continuous with the periphery of the top plate portion. Because the top plate portion is surrounded by the annular bend B, the displacement of the center portion of the top plate portion when the top plate portion is subjected to pressure is strongly influenced by the strength of the bend B. If conditions (A) and (B) are satisfied, the displacement of the center portion of the top plate portion is controlled to a range that can enhance the power generation capacity of the Li-Mg alloy (N) which is the negative electrode.

[0039] If only condition (A) is met, the elasticity of the top plate will be excessive or insufficient, making it difficult to sufficiently enhance the power generation capacity of the Li-Mg alloy (N). On the other hand, if only condition (B) is met, the strength of the top plate will be excessive or insufficient, resulting in an excessive or insufficient elasticity of the top plate.

[0040] Even when using Li-Mg alloy (N) for the negative electrode, if conditions (A) and (B) are not met, the elasticity of the top plate may be excessive or insufficient. Even with a negative electrode made of Li-Mg alloy (N), if the negative electrode is subjected to excessive pressure, it may become donut-shaped at the end of the discharge. In that case, the utilization rate of the negative electrode cannot be sufficiently increased. On the other hand, if the pressure applied to the negative electrode is insufficient, poor contact may occur at the end of the discharge, and the pulse discharge characteristics may deteriorate. Therefore, it is important to control the range of the Vickers hardness (HVb0) of the top plate and the Vickers hardness (HVb1) of the first bend so that the Li-Mg alloy (N) can exhibit sufficiently high performance.

[0041] The lithium primary battery (LB) is further preferably satisfied with at least one of the following conditions (C) and (D), and more preferably satisfied with both conditions (C) and (D).

[0042] Condition (C): The Vickers hardness (HVa0) of the base plate is between 130HV and 230HV.

[0043] Condition (D): The ratio of the difference (ΔHVa) between the Vickers hardness (HVa) of the bent portion A and the Vickers hardness (HVa0) of the bottom plate portion to the Vickers hardness (HVa0) of the bottom plate portion is 30% to 50%.

[0044] When both conditions (C) and (D) are satisfied, the bottom plate portion of the case has predetermined elasticity suitable for holding and pressing the positive electrode. When the bottom plate portion receives pressure from the power generation element, the position of the central portion of the bottom plate portion is slightly displaced. The bent portion A of the case is an annular portion continuous with the peripheral edge of the bottom plate portion. Since the bottom plate portion is surrounded by the annular bent portion A, the displacement of the central portion of the bottom plate portion when the bottom plate portion receives pressure is strongly influenced by the strength of the bent portion A. When at least one of conditions (C) and (D) is satisfied, the displacement of the central portion of the bottom plate portion is controlled within a range that can enhance the performance of the positive electrode as a power generation element, and further controlled within a range that can further enhance the performance of the Li-Mg alloy (N) serving as the negative electrode as a power generation element.

[0045] When condition (C) is satisfied, the bottom plate portion can have sufficient strength, so that appropriate pressure is easily applied to the entire power generation element. On the other hand, since the bottom plate portion does not have excessive strength, the bottom plate portion can be flexibly displaced, so that excessive pressure is less likely to be applied to the power generation element. Further, when condition (D) is satisfied, it is considered that the bottom plate portion can be displaced more flexibly in accordance with the expansion of the positive electrode.

[0046] (Method for measuring Vickers hardness) Vickers hardness is measured on the obtained cut surface after cutting the sealing plate or the case along an arbitrary diameter thereof in a direction parallel to the thickness direction of the sealing plate or the case. The cut surface is polished with #400 abrasive paper, and then the cross-section is mirror-finished by buff polishing using #2000 abrasive paper. Vickers hardness is measured at a predetermined position of the polished cross-section by the Vickers hardness test method in accordance with JIS Z 2244:2009. The set test force is 150 mN, and the holding time is 10 seconds. As the Vickers hardness tester, for example, Dynamic Ultra Micro Hardness Tester DUH-210 manufactured by Shimadzu Corporation can be used.

[0047] The Vickers hardness of the top plate portion of the sealing plate is measured at a plurality of points (for example, 3 or more points) within a range from the center of the top plate portion to a distance equal to 0.5 times the radius r1 of the top plate portion (range from 0r1 (center) to 0.5r1), and the average value of the measured values is obtained.

[0048] The Vickers hardness of the bottom plate portion of the case is measured at a plurality of points (for example, 3 or more points) within a range from the center of the bottom plate portion to a distance equal to 0.5 times the radius r2 of the bottom plate portion (range from 0r2 (center) to 0.5r2), and the average value of the measured values is obtained.

[0049] The Vickers hardness of the first bent portion of the bent portion B of the sealing plate is obtained by specifying the location with the highest curvature of the first bent portion (first pole point) on the outer surface of the sealing plate, then measuring at a plurality of points (for example, 3 or more points) within a circumference centered on the first pole point and having a radius equal to the thickness T1 of the top plate portion (within a circumference on a virtual plane including the cross-section after polishing), and calculating the average value of the measured values. Here, when one electrode of a positive electrode or a negative electrode is disposed on the inner surface of one exterior member of the top plate portion and the bottom plate portion, at least one projection protruding toward the electrode may be formed in a region of the inner surface overlapping with the electrode. A region of the outer surface overlapping with the inner surface where the projection is formed may be deformed to form a depression. When such a depression is formed in the exterior member, the Vickers hardness at a location of the exterior member excluding the depression is used as the measured value.

[0050] The Vickers hardness of the bent portion A of the case is obtained by specifying the location with the highest curvature of the bent portion A (second pole point) on the outer surface of the case, then measuring at a plurality of points (for example, 3 or more points) within a circumference centered on the second pole point and having a radius equal to the thickness T2 of the bottom plate portion (within a circumference on a virtual plane including the cross-section after polishing), and calculating the average value of the measured values.

[0051] Hereinafter, a coin-type battery according to an embodiment of the present disclosure will be described with reference to the drawings. However, the following embodiment does not limit the technical scope of the present disclosure.

[0052] Figure 1 is a cross-sectional view of an example of a coin-type lithium primary battery (LB) (hereinafter referred to as "coin-type battery 10"). The coin-type battery 10 includes an exterior body configured of a case, a sealing plate, and a gasket. Figure 2 is an enlarged view of an example of bent portions A and B of the coin-type battery 10.

[0053] Case 1 has a bottom plate portion 1a, a bent portion A that is continuous with the periphery of the bottom plate portion 1a, and an outer wall portion 1b that rises from the bent portion A. Case 1 is a cylindrical, shallow battery can. The end of the outer wall portion 1b is bent inward to form part of a crimped sealing structure.

[0054] The sealing plate 2 has a top plate portion 2a, a bent portion B that is continuous with the periphery of the top plate portion 2a, and an inner wall portion 2b that extends from the bent portion B inward to the outer wall portion 1b. The bent portion B comprises a first bent portion B1, a second bent portion B2, a third bent portion B3, and a folded portion B4.

[0055] The first bent portion B1 is continuous with the periphery of the top plate portion 2a. The first bent portion B1 is bent in a direction toward the inside of the outer wall portion 1b (first direction).

[0056] The second bend B2 is continuous with the first bend B1 and bends in a second direction. The second direction is the radial direction of the top plate and is away from the center of the top plate 2a. The first bend B1 and the second bend B2 form a stepped portion Bf (flange-shaped portion) of the sealing plate 2 at a position closer to the bottom plate 1a than the opening end of the case 1 (the end of the outer wall portion 1b).

[0057] The third bent portion B3 is continuous with the second bent portion B2 and the inner wall portion 2b, and is bent in the first direction. The inner wall portion 2b extends from the third bent portion B3 toward the bottom plate portion 1a of the case 1, and the folded portion B4 is formed by folding the end of the inner wall portion 2b outward.

[0058] The Vickers hardness of the first bent portion B1 is measured at multiple points within a dashed circle centered on the first pole P1 with the highest curvature on the outer surface of the first bent portion B1, and with a radius equal to the thickness T1 of the top plate portion 2a, and then averaged.

[0059] The Vickers hardness of the bent portion A is measured at multiple points within a dashed circle centered at the second pole P2, which has the highest curvature of the bent portion A, and with a radius equal to the thickness T2 of the base plate portion 1a, and then averaged.

[0060] A portion of the gasket 3 is interposed between the outer wall 1b of the case 1 and the inner wall 2b of the sealing plate 2, thereby sealing the gap between the case 1 and the sealing plate 2. The gasket 3 may be pre-installed on the inner wall 2b of the sealing plate 2 before battery assembly. Examples of materials that can be used for the gasket 3 include polypropylene (PP), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK).

[0061] The power generation element is housed inside the outer casing. The power generation element includes a positive electrode 4, a negative electrode 5 positioned opposite the positive electrode 4, a separator 6 interposed between the positive electrode 4 and the negative electrode 5, and an electrolyte (not shown). In the illustrated example, the positive electrode 4 is positioned opposite the bottom plate portion 1a of the case 1. The case 1 functions as a positive electrode terminal. On the other hand, the negative electrode 5 is positioned opposite the top plate portion 2a of the sealing plate 2. The sealing plate 2 functions as a negative electrode terminal.

[0062] In the illustrated example, the circumferential surface of the positive electrode 4 is surrounded by a conductive ring 8. The conductive ring 8 is not essential. When such a conductive ring is used, current can be collected not only from the bottom surface of the positive electrode 4 but also from the circumferential surface, thereby improving the current collection efficiency from the positive electrode 4. Furthermore, by using the conductive ring 8, the positive electrode can be stably held within the case 1. The material of the conductive ring 8 is not particularly limited, but stainless steel is preferred. It is preferable that the conductive ring 8 be made of the same material as the case.

[0063] The positive electrode 4 is formed by pressure molding the positive electrode mixture into a coin shape. The positive electrode mixture contains a positive electrode active material. The type of positive electrode active material is not particularly limited, but for example, it contains manganese dioxide. The thickness T of the positive electrode 4 may be, for example, 400 μm or more and 2000 μm or less.

[0064] Manganese dioxide is preferably electrolytic manganese dioxide. Electrolytic manganese dioxide preferably contains many β-type crystal structures, which have excellent structural stability, but may also contain crystal structures other than β-type. For example, manganese dioxide may contain α-type, γ-type, δ-type, ε-type, η-type, λ-type, or ramsdellite-type crystal structures.

[0065] The positive electrode mixture may further contain a binder. Examples of binders include fluororesins, rubber particles, and acrylic resins. The positive electrode mixture may contain, for example, 1% to 5% by mass of the binder.

[0066] The positive electrode mixture may contain graphite. The graphite functions as a conductive additive. The inclusion of graphite in the positive electrode mixture ensures sufficient electron conduction pathways within the positive electrode. The graphite may also contain expanded graphite. The particles of expanded graphite have a flattened shape. Expanded graphite can be formed, for example, by widening the gap between basal planes (interlayer expansion) by inserting a chemical such as sulfuric acid or an organic acid between the basal planes of graphite. Expanded graphite has a large interplanar spacing in the c-axis direction perpendicular to the basal plane and is easily peeled off, making it prone to becoming flattened. The interplanar spacing (d200) of the (002) plane of expanded graphite may be, for example, 3.37 Å or more. The crystallite size Lc(002) in the c-axis direction may be, for example, 500 Å or less. The interplanar spacing (d002) and crystallite size Lc(002) can be obtained by analyzing data obtained by powder X-ray diffraction using CuKα rays.

[0067] The positive electrode mixture may contain 1% to 10% by mass of graphite, or 1% to 5% by mass. The graphite may contain 80% or more by mass of expanded graphite, or 90% or more by mass. Alternatively, the graphite may contain 100% by mass of expanded graphite.

[0068] The negative electrode 5 is a coin-shaped Li-Mg alloy (N). The diameter dn of the negative electrode may be larger than the diameter dp of the positive electrode. The ratio of dp to dn (dp / dn ratio) may be, for example, 0.85 to 0.98.

[0069] The electrolyte contains a non-aqueous solvent and a solute (salt) that dissolves therein. The solute concentration in the electrolyte is preferably 0.3 to 2.0 mol / L. As the non-aqueous solvent, cyclic carbonate esters, linear carbonate esters, linear ethers, cyclic ethers, etc., can be used. These may be used individually or in mixtures of two or more. As the solute, LiBF4, LiPF6, LiClO4, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, etc., can be used.

[0070] The separator 6 can be made of any material that can prevent a short circuit between the positive electrode 4 and the negative electrode 5. Examples include woven fabrics, nonwoven fabrics, and microporous films made of polyolefins, polyesters, etc.

[0071] [Note] The above description of embodiments discloses the following technologies.

[0072] (Technical 1) A case having a bottom plate, an annular bent portion A continuous with the periphery of the bottom plate, and an annular outer wall portion rising from the bent portion A; a sealing plate having a top plate, an annular bent portion B continuous with the periphery of the top plate, and an annular inner wall portion extending in a first direction toward the bottom plate from the bent portion B; a gasket compressed between the outer wall portion and the inner wall portion; and a power generation element sealed by the case and the sealing plate, wherein the bent portion B is continuous with the periphery of the top plate and has a first bent portion that bends in the first direction; the power generation element comprises a positive electrode electrically connected to the bottom plate of the case, a negative electrode electrically connected to the top plate of the sealing plate, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; the negative electrode has a Li alloy containing Mg at a content of 0.10% to 5.0% by mass. A coin-type lithium primary battery, wherein the Vickers hardness (HVb0) of the top plate portion is 150HV to 250HV, and the ratio of the difference (ΔHVb) between the Vickers hardness (HVb1) of the first bent portion and the Vickers hardness (HVb0) of the top plate portion to the Vickers hardness (HVb0) of the top plate portion is 30% to 60%.

[0073] (Technical 2) The coin-type lithium primary battery according to Technical 1, wherein the bent portion B further comprises a second bent portion that is continuous with the first bent portion and bends outward in a second direction intersecting the first direction, and a third bent portion that is continuous with the second bent portion and the inner wall portion and bends in the first direction.

[0074] (Technology 3) The coin-type lithium primary battery according to Technology 1 or 2, wherein the Vickers hardness (HVa0) of the bottom plate portion is 130HV to 230HV, and the ratio of the difference (ΔHVa) between the Vickers hardness (HVa) of the bent portion A and the Vickers hardness (HVa0) of the bottom plate portion to the Vickers hardness (HVa0) of the bottom plate portion is 30% to 50%.

[0075] (Technology 4) The coin-type battery according to any one of Technologies 1 to 3, wherein the Li alloy further contains Al in a content of 0.10% to 5.0% by mass, and the total content of Mg and Al in the Li alloy is 5.1% by mass or less.

[0076] Next, the present disclosure will be described in detail based on examples. However, the following examples do not limit the configuration of the coin-type battery of the present disclosure.

[0077] Examples 1-8, Comparative Examples 1-8: Coin-type batteries A1-A8 of Examples 1-8 and coin-type batteries C1-C8 of Comparative Examples 1-8 were manufactured using the following procedure, with a base plate diameter D = 20 mm, thickness T = 3.2 mm, and electrical capacity of 225 mAh.

[0078] (i) A case having a bottom plate, a bent portion A, and an outer wall was fabricated from stainless steel (SUS430) with a case thickness of 200 μm by deep drawing. By controlling the conditions of the deep drawing process, the Vickers hardness (HVa0) of the bottom plate and the Vickers hardness (HVa) of the bent portion A were changed as shown in Table 1. A sealant consisting of bron asphalt and mineral oil was applied to the inside of the outer wall of the case.

[0079] (ii) A sealing plate having a top plate portion, a bent portion B, and an inner wall portion was manufactured from stainless steel (SUS430) with a sealing plate thickness of 250 μm by press working. The bent portion B has a first bent portion, a second bent portion, and a third bent portion. By controlling the press working conditions, the Vickers hardness (HVb0) of the top plate portion and the Vickers hardness (HVb1) of the first bent portion were changed as shown in Table 1. A polypropylene gasket was fitted to the inner wall portion.

[0080] (iii) A positive electrode mixture was prepared by mixing 100 parts by mass of manganese dioxide, which is the positive electrode active material of the power generation element, 7 parts by mass of expanded graphite, which is a conductive additive, and 5 parts by mass of polytetrafluoroethylene, which is a binder. The positive electrode mixture was molded into a coin shape with a diameter of 15 mm and a thickness of 2 mm to produce a positive electrode.

[0081] Furthermore, a negative electrode was fabricated by punching out a circular shape from a 0.6 mm thick Li-Mg alloy (N) so that the dp / dn ratio was 0.91. The Mg content in the Li-Mg alloy (N) was 0.5 mass%.

[0082] The electrolyte used was an organic electrolyte prepared by dissolving LiClO4 as a solute at a concentration of 1.0 mol / L in a non-aqueous solvent consisting of a mixture of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 2:1.

[0083] (iv) The positive electrode was placed on the bottom plate of the coin cell assembly case, and a 300 μm thick polypropylene nonwoven fabric was placed on top of it as a separator. Then, the organic electrolyte was poured into the case. The negative electrode was attached to the inside of the top plate of the sealing plate. Next, the sealing plate was positioned to close the opening of the case, and the end of the outer wall of the case was crimped to the bent portion B of the sealing plate via a gasket to complete the coin cell.

[0084] [Evaluation] Ten coin-type batteries were prepared for each example, and their continuous pulse characteristics (10mA, ON for 5 seconds, OFF for 55 seconds) were evaluated. Table 1 shows the maintenance time until the cutoff voltage of 1.8V was reached. When Mg-free Li metal was used as the negative electrode, the maintenance time was 19.8 hours to 20.9 hours, regardless of the Vickers hardness of the sealing plate and case. A maintenance time of 21 hours or more was judged to be a good product. The results are shown in Table 1. The number in the center of the table is the maintenance time (the same applies below).

[0085]

[0086] Examples 9-16, Comparative Examples 9-16: Except for changing the Vickers hardness of each part as shown in Table 2, coin-type batteries A9-A16 of Examples 9-16 and coin-type batteries C9-C16 of Comparative Examples 9-16 were manufactured and evaluated in the same manner as described above. The results are shown in Table 2.

[0087]

[0088] Examples 17-24, Comparative Examples 17-24: Except for changing the Vickers hardness of each part as shown in Table 3, coin-type batteries A17-A24 of Examples 17-24 and coin-type batteries C17-C24 of Comparative Examples 17-24 were manufactured and evaluated in the same manner as described above. The results are shown in Table 3.

[0089]

[0090] Tables 1-3 show that good quality products can be obtained when the Vickers hardness of the sealing plate is (HVb1-HVb0) / HVb0 = 30% to 60%, and even better quality products can be obtained when the Vickers hardness of the case is (HVa-HVa0) / HVa = 30% to 50%.

[0091] Examples 25-36: Except for changing the Vickers hardness of each part as shown in Table 4, coin-type batteries A25-A36 of Examples 25-36 were manufactured and evaluated in the same manner as described above. The results are shown in Table 4.

[0092]

[0093] Table 4 shows that when the Vickers hardness of the top plate of the sealing plate is 150, 200, and 250 HV, (HVb1 - HVb0) / HVb0 = 50%, and the Vickers hardness of the case is (HVa - HVa0) / HVa = 40%, then a good product can be obtained when the Vickers hardness of the bottom plate of the case is between 130 HV and 230 HV.

[0094] Examples 37-44, Comparative Examples 25-32: A negative electrode was prepared by punching out a 0.6 mm thick Li-Mg-Al alloy (N) into a circular shape with a diameter of 16 mm. The Mg content in the Li-Mg-Al alloy (N) was 0.5 mass%, and the Al content was 0.2 mass%. Coin-type batteries A37-A44 of Examples 37-44 and C25-32 of Comparative Examples 25-32 were prepared and evaluated in the same manner as described above, except for the use of the negative electrode. The results are shown in Table 5.

[0095]

[0096] Examples 45-52, Comparative Examples 33-40: Except for using a Li-Mg-Al alloy (N) with a Mg content of 0.5 mass% and an Al content of 0.2 mass% and changing the Vickers hardness of each part as shown in Table 6, coin-type batteries A46-A52 of Examples 46-52 and coin-type batteries C33-C40 of Comparative Examples 33-40 were prepared and evaluated in the same manner as described above. The results are shown in Table 6.

[0097]

[0098] Examples 53-60, Comparative Examples 41-48: Except for using a Li-Mg-Al alloy (N) with a Mg content of 0.5 mass% and an Al content of 0.2 mass% and changing the Vickers hardness of each part as shown in Table 7, coin-type batteries A53-A60 from Examples 53-60 and C41-C48 from Comparative Examples 41-48 were manufactured and evaluated in the same manner as described above. The results are shown in Table 7.

[0099]

[0100] Tables 5 to 7 show that good quality products can be obtained when the Vickers hardness of the sealing plate is (HVb1 - HVb0) / HVb0 = 30% to 60%, and even better quality products can be obtained when the Vickers hardness of the case is (HVa - HVa0) / HVa = 30% to 50%.

[0101] Examples 61-72: Except for using a Li-Mg-Al alloy (N) with a Mg content of 0.5 mass% and an Al content of 0.2 mass% and changing the Vickers hardness of each part as shown in Table 8, coin-type batteries A61-A72 of Examples 61-72 were manufactured and evaluated in the same manner as above. The results are shown in Table 9.

[0102]

[0103] Table 8 shows that when the Vickers hardness of the top plate of the sealing plate is 150, 200, and 250 HV, (HVb1 - HVb0) / HVb0 = 50%, and the Vickers hardness of the case is (HVa - HVa0) / HVa = 40%, then a good product can be obtained when the Vickers hardness of the bottom plate of the case is between 130 HV and 230 HV.

[0104] In the examples in Tables 1 to 4, a Li-Mg alloy (N) with a Mg content of 0.5 mass% was used, but it was confirmed that similar effects can be obtained even when the Mg content of the Li-Mg alloy (N) is between 0.10 mass% and 5 mass%.

[0105] Furthermore, in each example in Tables 5 to 8, a Li-Mg-Al alloy (N) with an Mg content of 0.5 mass% and an Al content of 0.2 mass% was used. However, it was confirmed that similar effects can be obtained even when the Mg content of the Li-Mg-Al alloy (N) is between 0.10 mass% and 5 mass%, and the Al content is between 0.10 mass% and 5 mass%.

[0106] Furthermore, while the dp / dn ratio was set to 0.91 in each example in Tables 1 to 8, it was confirmed that similar effects can be obtained in the range of dp / dn ratio = 0.85 to 0.98.

[0107] This disclosure is applicable to coin-type lithium primary batteries.

[0108] 1: Case 1a: Bottom plate 1b: Outer wall 2: Sealing plate 2a: Top plate 2b: Inner wall 3: Gasket 4: Positive electrode 5: Negative electrode 6: Separator 8: Conductive ring 10: Coin cell A: Bent part A B: Bent part B1: First bend part B2: Second bend part B3: Third bend part B4: Folded part Bf: Step P1: First pole P2: Second pole

Claims

1. A case having a bottom plate, an annular bent portion A continuous with the periphery of the bottom plate, and an annular outer wall portion rising from the bent portion A; a sealing plate having a top plate, an annular bent portion B continuous with the periphery of the top plate, and an annular inner wall portion extending in a first direction toward the bottom plate from the bent portion B; a gasket compressed between the outer wall portion and the inner wall portion; and a power generation element sealed by the case and the sealing plate, wherein the bent portion B is continuous with the periphery of the top plate and has a first bent portion that bends in the first direction; the power generation element comprises a positive electrode electrically connected to the bottom plate of the case, a negative electrode electrically connected to the top plate of the sealing plate, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; the negative electrode has a Li alloy containing Mg in a content of 0.10% to 5.0% by mass. A coin-type lithium primary battery, wherein the Vickers hardness (HVb0) of the top plate portion is 150HV to 250HV, and the ratio of the difference (ΔHVb) between the Vickers hardness (HVb1) of the first bent portion and the Vickers hardness (HVb0) of the top plate portion to the Vickers hardness (HVb0) of the top plate portion is 30% to 60%.

2. The coin-type lithium primary battery according to claim 1, wherein the bent portion B further comprises a second bent portion that is continuous with the first bent portion and bends outward in a second direction intersecting the first direction, and a third bent portion that is continuous with the second bent portion and the inner wall portion and bends in the first direction.

3. The coin-type lithium primary battery according to claim 1, wherein the Vickers hardness (HVa0) of the bottom plate portion is 130HV to 230HV, and the ratio of the difference (ΔHVa) between the Vickers hardness (HVa) of the bent portion A and the Vickers hardness (HVa0) of the bottom plate portion to the Vickers hardness (HVa0) of the bottom plate portion is 30% to 50%.

4. The coin-type battery according to claim 1, wherein the Li alloy further contains Al in a content of 0.10% to 5.0% by mass, and the total content of Mg and Al in the Li alloy is 5.1% by mass or less.

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