Secondary batteries

Abstract

To provide a secondary battery capable of constantly discharging gas from a container while preventing moisture intrusion into the container, and restraining rise of inner pressure of the container.SOLUTION: A secondary battery includes a metal container 13 in which electrode body to which an electrode terminal is electrically connected is accommodated and an electrolytic solution is enclosed. The container 13 has a thin part 15, which is thinner than the rest of the container, located above liquid level of the electrolytic solution. A micropore 19 is formed in the thin part 15 formed to penetrate through inside and outside of the container 13. The micropore 19 has a pore diameter of 1 μm to 20 μm and a length R of 0.8 times to 5 times larger than the pore diameter.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a secondary battery in which an electrode body having electrode terminals electrically connected thereto is housed inside a metal container and an electrolytic solution is enclosed.

Background Art

[0002] Conventionally, in electric vehicles using a motor such as an electric vehicle or a hybrid vehicle as a drive source, secondary batteries such as nickel-metal hydride storage batteries and lithium-ion storage batteries are used as power sources. In this type of secondary battery, when the pressure inside the battery case rises due to smoking or the like caused by an internal short circuit, there is a risk of problems such as the battery case bursting. Therefore, conventionally, secondary batteries are provided with an explosion-proof valve (safety valve) for preventing the bursting of the battery case when the internal pressure rises.

[0003] For example, Patent Document 1 discloses a secondary battery including a metal lid, a metal case whose interior is sealed by the lid and houses a power generation element or the like therein, and a safety valve formed in a part of the lid that breaks when the internal pressure of the case sealed by the lid rises above a predetermined value. In this secondary battery, when the internal pressure of the case rises above a predetermined value, the safety valve opens and gas is discharged to the outside of the case, so problems such as bursting of the case are unlikely to occur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the secondary battery described in Patent Document 1, since both the lid and the case are made of metal, even if gas is generated inside the case during use, the generated gas is not discharged to the outside through the lid or case. In other words, in the secondary battery described in Patent Document 1, once the gas is generated, it is not discharged to the outside of the case but accumulates inside the case, so as the total amount of gas generated increases, the internal pressure of the case rises, and once the internal pressure of the case rises, it is easy to maintain it without changing significantly until the safety valve opens.

[0006] Therefore, the increase in internal pressure within the case places stress on the safety valve and the joint between the lid and the case. This leads to problems such as the safety valve's performance degrading, preventing it from maintaining stable opening pressure performance until the end of the secondary battery's lifespan, and the need to increase the strength of the welded joints by increasing the welding cycle time to prevent damage to the welded joints.

[0007] Thus, in the secondary battery described in Patent Document 1, it is not possible to constantly discharge the gas inside the case, and therefore the rise in internal pressure of the case cannot be suppressed, resulting in various problems arising from this internal pressure.

[0008] If holes are provided in the case that penetrate from the inside to the outside in order to allow gas inside the case to be constantly expelled, external moisture can enter the case through these holes, causing a decrease in the performance of the secondary battery.

[0009] This invention has been made in view of the above circumstances, and aims to provide a secondary battery that can suppress the intrusion of moisture into the container, while continuously discharging gas from inside the container, and can suppress the rise in internal pressure of the container. [Means for solving the problem]

[0010] The characteristic configuration of the secondary battery according to the present invention for achieving the above objective is: A secondary battery in which an electrode body with electrically connected electrode terminals is housed inside a metal container, and an electrolyte is sealed inside, The container has a thin-walled section above the liquid level of the electrolyte, which is thinner than the rest of the container, and micropores are formed in this thin-walled section so as to penetrate the inside and outside of the container. The aforementioned micropores have a pore diameter of 1 μm or more and 20 μm or less, and a length of 0.8 times or more and 5 times or less the pore diameter.

[0011] According to the above-described configuration, the formation of micropores allows for the constant discharge of gas from inside the container through these micropores, even if gas is generated inside the container, thereby suppressing an increase in the internal pressure of the container. Furthermore, the pore diameter of the micropores is between 1 μm and 20 μm, and the length is between 0.8 and 5 times the pore diameter, thereby suppressing the amount of moisture entering the container through the micropores. In other words, according to the above-described configuration, it is possible to suppress the intrusion of moisture into the container while constantly discharging gas from inside the container, thereby suppressing the rise in internal pressure of the container.

[0012] Furthermore, a further characteristic configuration of the secondary battery according to the present invention is: The aforementioned container is A housing having an opening at the top, The facility comprises a lid that seals the opening, The key feature is that the thin-walled portion is formed on the lid, and the micro-holes are formed in the thin-walled portion so as to penetrate both the front and back surfaces of the lid.

[0013] With the above-described configuration, compared to cases where micropores are formed in the side walls of the housing, gases that have accumulated above the liquid surface of the electrolyte inside the container can be efficiently exhausted through the micropores. Therefore, with the above-described configuration, it is easier to suppress the rise in internal pressure of the container.

[0014] Furthermore, a further characteristic configuration of the secondary battery according to the present invention is: The aforementioned micropores are formed in the central part when viewed in a direction perpendicular to the surface of the lid.

[0015] When the internal pressure of the container increases and the container expands, the lid may deform into a mountain shape with the central part as the top. According to the above characteristic configuration, a micropore is provided in the central part of the lid. Therefore, when the lid deforms into a mountain shape with the central part as the top, the gas in the container easily flows toward the micropore, and the exhaust efficiency of the gas through the micropore is improved. Therefore, according to the above characteristic configuration, it is possible to cope with an increase in the internal pressure of the container accompanied by deformation of the lid.

[0016] Furthermore, a further characteristic configuration of the secondary battery according to the present invention is that the thin portion is an explosion-proof valve portion that opens due to an increase in pressure inside the container.

[0017] Generally, above the explosion-proof valve portion, an exhaust path for sending the gas discharged from the container to a desired place when the explosion-proof valve portion opens is provided. According to the above characteristic configuration, micropores are formed in the explosion-proof valve portion. Therefore, the gas discharged through the micropores can be sent to a desired place through the exhaust path. That is, according to the above characteristic configuration, the exhaust path can be shared between normal times (when the explosion-proof valve portion is not open and gas is not discharged from the container through the micropores) and abnormal times (when the explosion-proof valve portion is open).

Effects of the Invention

[0018] As described above, according to the sealing body and the secondary battery provided with the same according to the present invention, it is possible to always discharge the gas inside the container while suppressing the intrusion of moisture into the container, and to suppress an increase in the internal pressure of the container.

Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view of a secondary battery according to an embodiment. [Figure 2] It is a cross-sectional view showing a schematic configuration of a secondary battery according to an embodiment. [Figure 3] It is an enlarged cross-sectional view showing part A (near the explosion-proof valve portion) of FIG. 2. [Figure 4] It is a plan view showing the vicinity of the explosion-proof valve portion of the sealing plate. [Figure 5] It is a graph showing the relationship between the pore diameter of the micropores and the amount of water intrusion. [Figure 6] It is a graph showing the relationship between the length of the pores (length / pore diameter) with respect to the pore diameter of the micropores and the amount of water intrusion. [Figure 7] It is a diagram showing the state where the internal pressure of the battery case has risen. [Figure 8] It is an enlarged cross-sectional view showing the vicinity of the explosion-proof valve portion in the secondary battery according to another embodiment.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In the following, a mode in which the secondary battery is a lithium-ion secondary battery will be described as an example. Also, in the following, for the sake of clarity, each description and each drawing are appropriately simplified.

[0021] 〔Configuration of Secondary Battery 1〕 Referring to FIGS. 1 and 2, the outline of the secondary battery 1 of the present embodiment will be described. FIG. 1 is a perspective view of the secondary battery 1 according to the present embodiment. Also, FIG. 2 is a cross-sectional view showing the schematic configuration of the secondary battery 1 according to the present embodiment. In the following description, the direction parallel to the height direction of the secondary battery 1 is taken as the Z-axis direction, the direction parallel to the longitudinal direction of the electrode body 20 described later is taken as the X-axis direction, and the direction parallel to the thickness direction of the electrode body 20 is taken as the Y-axis direction. The Z-axis direction is a direction parallel to the vertical direction, the X-axis direction and the Y-axis direction are orthogonal to each other, and are directions parallel to the horizontal direction.

[0022] As shown in FIGS. 1 and 2, the secondary battery 1 of the present embodiment includes a battery case 10 composed of a case body 11 and a sealing plate 13, electrode terminals composed of external terminals 25, 26 and current collecting terminals 27, 28, an electrode body 20, an electrolytic solution L, etc. The secondary battery 1 is a sealed secondary battery in which the electrode body 20, the current collecting terminals 27, 28, etc. are housed inside the case body 11, the opening of the case body 11 is sealed with the sealing plate 13, and then the electrolytic solution L is injected into the case body

[0023] [Configuration of battery case 10] As shown in Figures 1 and 2, the battery case 10 of this embodiment consists of a case body 11 with a roughly rectangular parallelepiped shape and an open top, and a sealing plate 13 that seals the opening of the case body 11. In this embodiment, both the case body 11 and the sealing plate 13 are made of aluminum, but are not limited to this, and various metals and alloys can be used as materials for the case body 11 and the sealing plate 13. In this embodiment, the battery case 10 corresponds to a "container," and the case body 11 corresponds to a "housing."

[0024] In this embodiment, the sealing plate 13 has a shape corresponding to the shape of the opening of the case body 11 and is configured to seal the opening of the case body 11. The sealing plate 13 in this embodiment is made of a substantially rectangular flat plate member, with a positive electrode terminal PS consisting of a positive electrode external terminal 25 and a positive electrode current collector terminal 27 disposed on one end in the longitudinal direction (X-axis direction), and a negative electrode terminal NS consisting of a negative electrode external terminal 26 and a negative electrode current collector terminal 28 disposed on the other end. In this embodiment, the sealing plate 13 corresponds to the "lid," and the positive electrode terminal PS and negative electrode terminal NS correspond to the "electrode terminals."

[0025] As will be described in more detail later, the sealing plate 13 of this embodiment has an explosion-proof valve portion 15 formed between the positive electrode terminal PS and the negative electrode terminal NS, which opens when the pressure inside the battery case 10 increases, and micro-pores 19 are formed in the explosion-proof valve portion 15. Furthermore, in this embodiment, the sealing plate 13 has an injection portion 14 formed between the explosion-proof valve portion 15 and the positive electrode terminal PS for injecting electrolyte L into the inside of the battery case 10.

[0026] [Configuration of electrode body 20] In this embodiment, the electrode body 20 is composed of a wound body formed by winding together long strip-shaped positive electrode material and negative electrode material, laminated with a strip-shaped separator, and then compressing it into a flattened shape. As shown in Figures 1 and 2, the electrode body 20 of this embodiment is substantially rectangular in thickness direction (Y-axis direction), with a positive electrode terminal joint portion 21 formed on one end in the longitudinal direction (X-axis direction) of the thickness direction, where the positive electrode material is concentrated, and a negative electrode terminal joint portion 22 formed on the other end, where the negative electrode material is concentrated. The structure of the electrode body 20 is not particularly limited, and various structures used in general sealed secondary batteries can be adopted. Furthermore, the materials used for the positive electrode material and negative electrode material are not particularly limited, but in this embodiment, aluminum is used for the positive electrode material and copper is used for the negative electrode material.

[0027] In this embodiment, the electrode body 20 is housed inside the case body 11 in a position where its thickness and longitudinal directions are parallel to the horizontal direction, while covered with an insulating film. Furthermore, the electrode body 20 and the case body 11 are insulated from each other by an insulating film (not shown).

[0028] [Configuration of the positive and negative electrodes] In this embodiment, the secondary battery 1 is equipped with a positive electrode external terminal 25 and a negative electrode external terminal 26 as external terminals, and a positive electrode current collector terminal 27 and a negative electrode current collector terminal 28 as current collector terminals. Furthermore, the secondary battery 1 of this embodiment is equipped with a positive electrode insulating member 29, a negative electrode insulating member 30, a positive electrode gasket 31, and a negative electrode gasket 32.

[0029] The positive external terminal 25 and the negative external terminal 26 are terminals for external connection and are located on the surface 13a (top surface) of the sealing plate 13, in other words, outside the case body 11. In this embodiment, each external terminal 25 and 26 has a plate-like portion 25a, 26a, etc., which is approximately rectangular in plan view. In this embodiment, the positive external terminal 25 is made of aluminum and the negative external terminal 26 is made of copper, but the material of each external terminal 25 and 26 is not particularly limited, and various metals and alloys with good conductivity can be used.

[0030] The positive electrode gasket 31 and the negative electrode gasket 32 ​​are components made of an insulating material. In this embodiment, both the positive electrode gasket 31 and the negative electrode gasket 32 ​​are made of PFA resin. In this embodiment, the positive electrode gasket 31 and the negative electrode gasket 32 ​​have a shape in which side wall portions 31a and 32a extend upward from the outer surface edge of a plate-shaped base portion (not shown), and the positive electrode external terminal 25 and the negative electrode external terminal 26 are arranged such that the plate-shaped portions 25a and 26a are located within the space surrounded by the side wall portions 31a and 32a.

[0031] The positive electrode current collector terminal 27 and the negative electrode current collector terminal 28 are terminals for inputting and outputting power from the electrode body 20, and are located on the back surface 13b (bottom surface) of the sealing plate 13, in other words, inside the case body 11. In this embodiment, the positive electrode current collector terminal 27 is made of aluminum and the negative electrode current collector terminal 28 is made of copper, but the material of each current collector terminal 27, 28 is not particularly limited, and various metals and alloys with good conductivity can be used.

[0032] The positive electrode current collector terminal 27 and the negative electrode current collector terminal 28 of this embodiment are elongated plate-shaped members that extend along the height direction (Z-axis direction) of the secondary battery 1. The lower end of each current collector terminal 27, 28 has electrode connection portions 27a, 28a that are connected to the terminal joint portions (positive electrode terminal joint portion 21 and negative electrode terminal joint portion 22) of the electrode body 20. On the other hand, the upper end of each current collector terminal 27, 28 has terminal connection portions 27b, 28b that are electrically connected to the respective external terminals 25, 26.

[0033] The positive electrode insulating member 29 and the negative electrode insulating member 30 are plate-shaped members made of an insulating material. In this embodiment, both the positive electrode insulating member 29 and the negative electrode insulating member 30 are made of PFA resin.

[0034] In this embodiment, on the positive electrode side, a positive electrode gasket 31 is disposed on the surface 13a of one end of the sealing plate 13 in the longitudinal direction, and a positive electrode external terminal 25 is disposed on the positive electrode gasket 31. On the other hand, a positive electrode insulating member 29 is disposed on the back surface 13b of one end of the sealing plate 13 in the longitudinal direction, and a positive electrode current collector terminal 27 is disposed below the positive electrode insulating member 29, with the electrode connection portion 27a of the positive electrode current collector terminal 27 being joined to the positive electrode terminal joint portion 21 of the electrode body 20. In this embodiment, the positive electrode external terminal 25 and the sealing plate 13 are insulated by the positive electrode gasket 31, and the positive electrode current collector terminal 27 and the sealing plate 13 are insulated by the positive electrode insulating member 29.

[0035] In this embodiment, a shaft portion is formed on the lower surface of the plate-shaped portion 25a of the positive electrode external terminal 25. The shaft portion of the positive electrode external terminal 25 is inserted through through holes formed in the positive electrode gasket 31, the sealing plate 13, the positive electrode insulating member 29, and the terminal connection portion 27b of the positive electrode current collector terminal 27. The lower end (crimped portion) of the shaft portion protruding from the terminal connection portion 27b is crimped, thereby joining the positive electrode external terminal 25 and the positive electrode current collector terminal 27. The space between the shaft portion of the positive electrode external terminal 25 and the through hole formed in the sealing plate 13 is kept airtight by the positive electrode gasket 31.

[0036] Although a detailed explanation will be omitted, the secondary battery 1 of this embodiment has a similar configuration on the negative electrode side.

[0037] [Electrolyte L] After joining the case body 11 and the sealing plate 13, any excess electrolyte L beyond the amount that can be held by the electrode body 20 through impregnation is injected into the battery case 10 from the injection section 14. The excess amount of injected electrolyte L accumulates in the battery case 10. Specifically, in this embodiment, electrolyte L is injected into the battery case 10 so that the liquid level of electrolyte L does not exceed the maximum liquid level height LHmax. The maximum liquid level height LHmax is the height from the bottom inner surface of the battery case 10 (specifically the case body 11) to a position arbitrarily set between the upper end of the electrode body 20 and the back surface of the sealing plate 13. When the electrode body 20 is sufficiently held by electrolyte L, the excess amount of electrolyte L accumulates in the battery case 10. In this embodiment, the liquid level height LH of the excess amount of electrolyte L accumulated in the battery case 10 is the height from the bottom inner surface of the battery case 10 (specifically the case body 11) to approximately the midpoint in the height direction of the secondary battery 1. Furthermore, the liquid level height LH of the electrolyte L is the liquid level of the electrolyte L under normal operating conditions (with the external terminals 25 and 26 facing upwards).

[0038] The electrolyte can be a solution in which an electrolyte that functions as a charge carrier is dissolved in a solvent, and may contain additives. The type of electrolyte is not particularly limited, but in this embodiment, for example, one or more lithium salts such as LiPF6 can be used. Furthermore, the type of solvent included in the electrolyte is not particularly limited, but in this embodiment, for example, one or more non-aqueous solvents such as carbonates can be used.

[0039] [Configuration of explosion-proof valve section 15] Next, the configuration of the explosion-proof valve section 15 will be described in detail with reference to the drawings. Figure 3 is an enlarged cross-sectional view showing section A of Figure 2 (near the explosion-proof valve section 15). Figure 4 is a plan view showing the vicinity of the explosion-proof valve section 15 of the sealing plate 13.

[0040] As shown in Figures 1 to 4, the sealing plate 13 has an explosion-proof valve portion 15 formed in its longitudinal center. Specifically, in this embodiment, the explosion-proof valve portion 15 is formed such that the back surface 13b of the sealing plate 13 is recessed toward the front surface 13a, and the front surface 13a is recessed toward the back surface 13b such that it is relatively shallower in depth than the recess of the back surface 13b. In other words, the explosion-proof valve portion 15 is formed as a thin-walled portion that is thinner than the other parts of the sealing plate 13, in the center when viewed in a direction perpendicular to the front surface 13a of the sealing plate 13. The thickness of the explosion-proof valve portion 15 can be appropriately set according to the required valve opening pressure, but for example, it is 0.1 mm to 0.2 mm.

[0041] Furthermore, as shown in Figures 3 and 4, in this embodiment, the explosion-proof valve portion 15 has a fracture initiation point portion 16 formed therein, which serves as an initiation point for rupture at an internal pressure level that does not cause the battery case to rupture due to increased pressure inside the battery case 10. Specifically, in this embodiment, the fracture initiation point portion 16 is composed of two fracture grooves 17a, 17b, 18a, and 18b with a concave cross-section formed on the surface 15a and back surface 15b of the explosion-proof valve portion 15, respectively. The two fracture grooves 17a and 17b formed on the surface 15a of the explosion-proof valve portion 15 intersect in a plan view, and the two fracture grooves 18a and 18b formed on the back surface 15b intersect in a bottom view. In other words, the fracture initiation point portion 16 is formed as a thin-walled portion that is thinner than the other parts of the explosion-proof valve portion 15. The thickness of the fracture initiation point 16 can be set appropriately according to the required valve opening pressure, but for example, it is 0.02 mm to 0.08 mm. In addition, the number of fracture grooves and the cross-sectional shape of the fracture initiation point 16 can also be changed appropriately according to the required valve opening pressure.

[0042] In a sealed secondary battery like the secondary battery 1 of this embodiment, where both the case body 11 and the sealing plate 13 are made of metal, in other words, the battery case 10 is made of metal, there is an advantage in that moisture can be prevented from entering the battery case 10 and electrolyte L can be prevented from leaking out of the battery case 10. On the other hand, in a sealed secondary battery with a metal battery case 10, even if gas is generated inside the battery case 10 during use, such as due to smoke generation from an internal short circuit, the generated gas cannot be discharged to the outside of the battery case 10. Therefore, the rise in internal pressure of the battery case 10 cannot be suppressed, and there is a risk that various problems may arise due to the internal pressure of the battery case 10.

[0043] Therefore, in the secondary battery 1 of this embodiment, measures are taken to form micropores 19 in the battery case 10 in order to expel gas from inside the battery case 10 and suppress the rise in internal pressure of the battery case 10.

[0044] As shown in Figures 3 and 4, the micropores 19 in this embodiment are formed in the explosion-proof valve portion 15 formed in the sealing plate 13 located above the liquid level height LH and the maximum liquid level height LHmax of the electrolyte L, so as to penetrate both the front and back surfaces. More specifically, the micropores 19 are formed in the center of the fracture initiation point portion 16 formed in the explosion-proof valve portion 15 (the intersection of the two fracture groove portions 17a and 17b) in a plan view, so as to penetrate both the front and back surfaces. In other words, the micropores 19 are formed in the thin-walled portion formed above the liquid level height LH and the maximum liquid level height LHmax of the electrolyte L, so as to penetrate both the inside and outside of the battery case 10.

[0045] In this case, if micropores 19 are formed in the secondary battery 1, it is necessary to suppress the intrusion of moisture into the battery case 10 through the micropores 19 in order to suppress the deterioration of the performance of the secondary battery 1.

[0046] Therefore, after diligent research, the inventor discovered that by adjusting the diameter of the micropores 19 and the ratio of the length of the pores to the diameter of the pores to a predetermined range, it is possible to enable the discharge of gas from inside the battery case 10 while suppressing the intrusion of moisture into the battery case 10.

[0047] Specifically, the inventors fabricated secondary batteries 1 in which micropores with different pore diameters and pore length-to-pore diameter ratios were formed, and measured the amount of moisture that entered the battery case 10 of each secondary battery 1. More precisely, a thin-walled section with a thickness of 15 μm was formed in the battery case 10 of each secondary battery 1, and micropores with diameters of 1 μm, 5 μm, 10 μm, 20 μm, and 30 μm were formed in the thin-walled section, and the amount of moisture that entered the battery case 10 was measured. Figures 5 and 6 are graphs summarizing the results; Figure 5 is a graph showing the relationship between the pore diameter of the micropores and the amount of moisture that entered, and Figure 6 is a graph showing the relationship between the pore length-to-pore diameter ratio (length / pore diameter) and the amount of moisture that entered.

[0048] As can be seen from Figure 5, if the pore diameter of the micropores is between 1 μm and 20 μm, the amount of water penetration can be suppressed. On the other hand, as can be seen from Figure 6, if the ratio of the length of the pore to the diameter (length / pore diameter) is between 0.8 and 5, in other words, if the length is between 0.8 and 5 times the diameter of the pore, the amount of water penetration can be suppressed. Thus, it is presumed that when the pore diameter is between 1 μm and 20 μm and the length is between 0.8 and 5 times the diameter of the pore, gas can be discharged while suppressing the amount of water penetration because the pore diameter is large enough to allow gas to pass through but not water, which has a smaller molecular size and higher viscosity than the gas, and because the diffusion of water within the pores is suppressed.

[0049] Therefore, in the secondary battery 1 of this embodiment, the micropores 19 have a pore diameter R of 1 μm or more and 20 μm or less, and a length T1 of 0.8 times or more and 5 times the pore diameter. In this embodiment, the pore diameter R refers to the diameter of the circle circumscribing the opening edge of the micropore. Also, in this embodiment, the length T1 is synonymous with the plate thickness of the fracture initiation point 16.

[0050] As an example of a method for manufacturing the sealing plate 13 in this embodiment, one can be described as a method in which a plate material such as aluminum is subjected to press working or cutting to form the explosion-proof valve portion 15 and the fracture initiation point portion 16, and then micropores 19 are formed using a known method capable of processing on the micron order, such as focused ion beam method.

[0051] The effects of the secondary battery 1 having the above configuration will now be explained. Figure 7 shows the state in which the internal pressure of the battery case 10 has increased, and the thick arrows in the figure represent the flow of gas.

[0052] According to the secondary battery 1 of this embodiment, while suppressing the amount of moisture entering the battery case 10 through the micropores 19, gas generated inside the battery case 10 can be constantly discharged through the micropores 19, thereby suppressing the rise in internal pressure of the battery case 10.

[0053] Therefore, according to the secondary battery 1 of this embodiment, it is possible to reduce the surplus space that was reserved to lower the internal pressure of the battery case 10, and increase the area occupied by battery elements such as the electrode body 20 that are involved in power generation, thereby improving the battery capacity.

[0054] Furthermore, according to the secondary battery 1 of this embodiment, the rise in internal pressure of the battery case 10 can be suppressed, thereby reducing damage to the explosion-proof valve section 15 and the rupture initiation point 16, and maintaining stable valve opening pressure performance until the end of the battery's lifespan.

[0055] Furthermore, in the secondary battery 1 of this embodiment, the rise in internal pressure of the battery case 10 can be suppressed, thereby reducing damage to the welded area between the case body 11 and the sealing plate 13. Consequently, the penetration depth during welding can be reduced, and the welding cycle time and welding energy can be reduced.

[0056] Furthermore, in the secondary battery 1 of this embodiment, micro-holes 19 are provided at the rupture initiation point 16 of the explosion-proof valve portion 15 formed in the center of the sealing plate 13 in a plan view. As a result, as shown in Figure 7, when gas is generated inside the battery case 10, and the generated gas gathers at the top of the battery case 10, causing the internal pressure of the battery case 10 to rise and the sealing plate 13 to deform into a mountain-like shape with the center as its peak, the gas inside the battery case 10 can easily flow toward the micro-holes 19. Therefore, compared to cases where the micro-holes 19 are formed anywhere other than the center of the sealing plate 13, or where the micro-holes 19 are formed in the case body 11, gas can be efficiently exhausted through the micro-holes 19. In addition, even if the internal pressure inside the battery case 10 rises rapidly and the sealing plate 13 deforms, the internal pressure can be reduced because the gas can be efficiently exhausted through the micro-holes.

[0057] Furthermore, in a typical secondary battery, an exhaust path is provided above the explosion-proof valve 15 to send the gas discharged from inside the battery case 10 when the explosion-proof valve 15 is open to the outside. In the secondary battery 1 of this embodiment, since micropores 19 are formed in the explosion-proof valve 15, it is possible to send the gas discharged from inside the battery case 10 through the micropores 19 to the outside through the exhaust path. In other words, in the secondary battery 1 of this embodiment, the exhaust path can be used in both normal conditions (when the explosion-proof valve 15 is not open) and abnormal conditions (when the explosion-proof valve 15 is open). Therefore, there is no need to provide separate equipment to discharge the gas discharged through the micropores 19 to the outside, and equipment costs can be reduced.

[0058] [Another embodiment] [1] In the above embodiment, a configuration in which micropores 19 are formed in the sealing plate 13 has been described, but the invention is not limited to this configuration. A thin-walled portion may be formed in the case body 11 at a position above the liquid level LH ​​of the electrolyte L, and micropores may be formed in the thin-walled portion. Even in this configuration, the amount of moisture entering the battery case 10 through the micropores can be suppressed, while gas generated inside the battery case 10 can be constantly discharged through the micropores, thereby suppressing the rise in internal pressure of the battery case 10.

[0059] [2] In the above embodiment, a configuration in which micropores 19 are formed in the fracture initiation point portion 16 of the explosion-proof valve portion 15, which is formed as a thin-walled portion in the central part of the sealing plate 13 in a plan view has been described, but the configuration is not limited to this configuration. The micropores 19 may be formed in a thin-walled portion formed in a part of the sealing plate 13 other than the central part in a plan view. Furthermore, regardless of whether or not the fracture initiation point portion 16 is formed in the explosion-proof valve portion 15, as shown in Figure 8, the micropores 19 may be formed in the explosion-proof valve portion 15, in which case the length T2 is synonymous with the plate thickness of the explosion-proof valve portion 15. Even in this configuration, the amount of moisture entering the battery case 10 through the micropores can be suppressed, while gas generated inside the battery case 10 can be constantly discharged through the micropores, thereby suppressing the rise in internal pressure of the battery case 10.

[0060] [3] In the above embodiment, a configuration in which one microhole 19 is formed in the sealing plate 13 has been described, but the embodiment is not limited to this configuration. For example, there may be a configuration in which multiple microholes are formed in the sealing plate 13 and multiple microholes are also formed in the case body 11, in other words, a configuration in which multiple microholes are formed in the battery case 10. In such a configuration as well, the rise in internal pressure of the battery case 10 can be suppressed in the same manner as described above.

[0061] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Explanation of Symbols]

[0062] 1: Secondary battery 10: Battery case (container) 11: Case body (enclosure) 13: Sealing plate (lid body) 15: Explosion-proof valve section (thin-walled section) 16: Fracture initiation point (thin-walled section) 19: Micropore PS: Positive terminal (electrode terminal) NS: Negative terminal (electrode terminal) L: Electrolyte LH: Liquid level R: Hole diameter T1: Length T2: Length

Claims

1. A secondary battery in which an electrode body with electrically connected electrode terminals is housed inside a metal container, and an electrolyte is sealed inside, The aforementioned container is A housing having an opening at the top, The facility comprises a lid that seals the opening, The lid has a thin-walled portion located above the liquid level of the electrolyte, which is thinner than the rest of the lid and serves as an explosion-proof valve that opens when the pressure inside the container increases. Microholes are formed in this thin-walled portion so as to penetrate both the front and back surfaces of the lid. The aforementioned micropores are a secondary battery in which the pore diameter is 1 μm or more and 20 μm or less, and the length is 0.8 times or more and 5 times the pore diameter.

2. The secondary battery according to claim 1, wherein the micropores are formed in the central part when viewed in a direction perpendicular to the surface of the lid.

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