Sealed battery

Abstract

To provide a sealed battery that can prevent an excessive temperature increase even when a safety valve is clogged with discharged substances.SOLUTION: A sealed battery according to the present disclosure comprises: a case that accommodates an electrode body; a safety valve that is provided on a top face of the case and is released when the pressure inside the case becomes equal to or more than a first reference value (first release pressure value); and a gas exhaust valve that is provided in a side face of the case and is released when the pressure inside the case becomes a second reference value (second release pressure value) higher than the first reference value (first release pressure value).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to sealed batteries. [Background technology]

[0002] Sealed batteries such as lithium-ion batteries are widely used as power sources for vehicles or for personal computers, mobile devices, etc. Sealed batteries are provided with an internal pressure release mechanism that releases internal pressure when the internal pressure of the case rises excessively due to overcharging or the like. As an example of an internal pressure release mechanism, Patent Document 1 discloses a safety valve that is formed in a part of the case with a thin wall that is thinner than the other parts, and that breaks (opens) to release the internal pressure when the internal pressure of the case reaches or exceeds a predetermined value (release pressure). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-282850 Summary of the Invention [Problem to be solved by the invention]

[0004] One safety evaluation test to check the resistance of a battery to internal short circuits is the nail penetration test, in which a nail is inserted into a battery to simulate an internal short circuit, and the degree of heat generated by the battery is examined to check the safety of the battery. If a battery cell goes into thermal runaway due to the insertion of a nail into the battery cell, emissions are generated inside the battery cell.

[0005] A battery pack is generally made up of multiple battery cells connected together. If one battery cell in a battery pack is intentionally made to generate heat during testing, and if the safety valve becomes clogged with discharged material, the temperature of that battery cell will rise, and the heat will spread to adjacent battery cells, leading to thermal runaway and possible explosion or other accidents.

[0006] The present invention has been made in consideration of such problems, and an object of the present invention is to provide a sealed battery that can suppress excessive temperature rise even when the safety valve is clogged with discharged material. [Means for solving the problem]

[0007] The sealed battery according to the present disclosure comprises a case that houses an electrode assembly, a safety valve provided on the top surface of the case that opens when the internal pressure of the case reaches a first reference value or higher, and a gas release valve provided on a side surface of the case that opens when the internal pressure of the case reaches a second reference value that is higher than the first reference value. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sealed battery that can suppress excessive temperature rise even when the safety valve is clogged with discharged matter. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the external shape of a sealed battery according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating the internal configuration of the sealed battery of FIG. [Figure 3] 3 is a diagram showing the shapes of a safety valve and a gas exhaust valve in FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are not intended to limit the technology disclosed herein. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. The dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Furthermore, in each drawing, the same elements are given the same reference numerals, and duplicate explanations will be omitted as necessary.

[0011] The embodiments relate to a sealed secondary battery used, for example, as a driving power source for electric vehicles and the like. In this specification, the term "secondary battery" refers generally to an electricity storage device that can be repeatedly charged and discharged, and includes so-called storage batteries, electric double layer capacitors, and other electricity storage elements. Here, a lithium-ion battery in which a wound electrode body and an electrolyte are housed in a flat, rectangular case is used as an example. The term "lithium-ion battery" refers to a secondary battery that uses lithium ions as a charge carrier and achieves charging and discharging by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

[0012] Fig. 1 is a diagram showing the external shape of a lithium-ion battery 10 according to an embodiment. Fig. 2 is a diagram illustrating the internal configuration of the lithium-ion battery 10 of Fig. 1. As shown in Fig. 2, the lithium-ion battery 10 has a structure in which a wound electrode body 20 and an electrolyte (not shown) are housed in a battery case 11. A battery cell stack in which multiple lithium-ion batteries 10 are stacked is housed in a battery pack case (not shown) to form a "battery pack."

[0013] The battery case 11 is a rectangular container having an internal space and an external shape of a roughly rectangular parallelepiped. For example, a lightweight metal material with good thermal conductivity, such as aluminum or stainless steel (SUS), is used for the battery case 11. The battery case 11 includes a main body 12 having an opening that opens upward, and a lid 13 that closes the opening. The periphery of the opening of the main body 12 and the outer edge of the lid 13 are laser welded together, sealing the battery case 11.

[0014] The lid 13 of the battery case 11 is provided with a positive electrode terminal 14 and a negative electrode terminal 15 for external connection. The overall external shape of the lid 13 is a roughly rectangular plate, and terminal pull-out holes (not shown) are formed at both longitudinal ends thereof, through which the positive electrode terminal 14 and the negative electrode terminal 15 pass. One end (outer end) of the positive electrode terminal 14 and the negative electrode terminal 15 protrudes outward from the battery case 11. As shown in FIG. 2 , the other ends (inner ends) of the positive electrode terminal 14 and the negative electrode terminal 15 are electrically connected to the positive electrode 16 and the negative electrode 17 of the wound electrode body 20, respectively, inside the battery case 11.

[0015] A safety valve 30 is provided in the approximate center of the portion of the lid 13 located between the positive electrode terminal 14 and the negative electrode terminal 15. That is, the safety valve 30 is provided on the upper surface of the battery case 11. The safety valve 30 is configured to release the internal pressure when the internal pressure of the battery case 11 rises to or exceeds a predetermined first reference value (for example, approximately 0.3 to 1.0 MPa).

[0016] Gas release valves 31 are provided below two opposing short-side surfaces of the main body 12. The gas release valves 31 are configured to open when the internal pressure of the battery case 11 rises to or exceeds a second reference value that is higher than a first reference value at which the safety valve 30 releases. The gas release valves 31 are configured to release gas from inside the battery case 11 when the safety valve 30 clogs after it releases and the internal pressure of the battery case 11 rises again. The structures of the safety valve 30 and the gas release valve 31 will be described later.

[0017] The wound electrode body 20 is housed in a space surrounded by the main body 12 and the lid body 13. Similar to the wound electrode body of a normal lithium-ion battery, the wound electrode body 20 includes a strip-shaped positive electrode (positive electrode sheet) 16, a negative electrode (negative electrode sheet) 17, and two strip-shaped separators (not shown). The positive electrode 16 and the negative electrode 17 are stacked with the separator sandwiched between them, wound in the longitudinal direction, and then crushed from the side, to produce the wound electrode body 20.

[0018] The positive electrode 16 includes a positive electrode current collector foil and a positive electrode active material layer. The positive electrode current collector foil is a support member for the positive electrode active material layer and is a conductive member such as aluminum (including aluminum alloy) foil for extracting electric charge from the positive electrode active material layer. A positive electrode exposed portion is provided in an area along one long side of the strip-shaped positive electrode current collector foil. The positive electrode active material layer is formed in an area on the positive electrode current collector foil excluding the positive electrode exposed portion.

[0019] The negative electrode 17 includes a negative electrode current collector and a negative electrode active material layer 41. The negative electrode current collector foil is a support member for the negative electrode active material layer and is a conductive member such as copper foil for extracting charge from the negative electrode active material layer. A negative electrode exposed portion is provided in an area along one long side of the strip-shaped negative electrode current collector foil. The negative electrode active material layer is formed in an area on the negative electrode current collector foil excluding the negative electrode exposed portion.

[0020] The positive electrode 16 and the negative electrode 17 are wound in a stacked state with their positions shifted in the longitudinal direction so that the positive electrode exposed portion and the negative electrode exposed portion protrude from one end and the other end of the separator, respectively. The positive electrode terminal 14 and the negative electrode terminal 15 are connected to the positive electrode exposed portion and the negative electrode exposed portion protruding from the core portion of the wound electrode body 20, in which the positive electrode 16, the negative electrode 17, and the separator are tightly wound.

[0021] The components and materials constituting the lithium ion battery 10 are not particularly limited and may be the same as those used in widely known lithium ion secondary batteries. Examples of the components and materials constituting the lithium ion battery 10 are shown below.

[0022] Examples of the positive electrode active material contained in the positive electrode active material layer include lithium transition metal oxides and lithium transition metal phosphate compounds. The positive electrode active material layer may contain, in addition to the positive electrode active material, a conductive material, a binder, and the like. Examples of the negative electrode active material contained in the negative electrode active material layer 41 include carbon materials such as graphite. The negative electrode active material layer may contain, in addition to the negative electrode active material, a binder, a thickener, and the like.

[0023] The separator insulates the positive electrode 16 from the negative electrode 17 and provides a path for charge carrier movement between the positive electrode active material layer and the negative electrode active material layer. As the separator, a porous sheet (film) made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used.

[0024] The electrolyte typically contains a non-aqueous solvent and a supporting salt. Known non-aqueous solvents used in electrolytes for lithium ion secondary batteries can be used as the non-aqueous solvent. Examples of non-aqueous solvents include ethylene carbonate (EC) and propylene carbonate (PC). Examples of supporting salts include lithium salts such as LiPF6 and LiBF4.

[0025] Fig. 3 is a diagram showing the surface shapes of the safety valve 30 and the gas release valve 31 in Fig. 2. The safety valve 30 and the gas release valve 31 may have, for example, the same structure. In Fig. 3, the reference numeral of the gas release valve 31 provided in the main body 12 is written in parentheses. However, as described above, the gas release valve 31 opens when the internal pressure of the battery case 11 rises to or exceeds a second reference value that is higher than the first reference value at which the safety valve 30 opens.

[0026] The safety valve 30 includes a thinned portion 32 and a rupture groove 33. When the internal pressure of the battery case 11 reaches or exceeds a predetermined first reference value (first release pressure value), the rupture groove 33 of the safety valve 30 ruptures due to the internal pressure. The thinned portion 32 is an oval-shaped portion that is thinner than the other portions of the lid 13. The oval shape is a shape in which semicircular arcs are connected to both ends of two parallel straight lines of the same length. For example, the thickness of the lid 13 is 0.5 mm to 1 mm, and the thickness of the thinned portion 32 is 0.1 mm to 0.3 mm.

[0027] The fracture groove 33 is formed in the thin-walled portion 32. The fracture groove 33 may include, for example, a central groove 34 that extends linearly in the longitudinal direction of the thin-walled portion 32 in the central portion of the thin-walled portion 32, and side grooves 35 that branch off from both sides of the central groove 34. Each of the side grooves 35 is connected by a peripheral groove 36 that runs along the semicircular arc of the fracture groove 33. That is, the side grooves 35 and the peripheral groove 36 form a fan-like loop. The cross-sectional shape of the fracture groove 33 is a V-shape that opens to the surface of the thin-walled portion 32.

[0028] The central groove 34, side grooves 35, and peripheral grooves 36 that make up the rupture groove 33 may each have a different depth. The depth of each groove can be changed as appropriate depending on the pressure setting to be released depending on the shape and application of the battery. In the lithium-ion battery 10, when the internal pressure of the battery case 11 reaches or exceeds a first reference value, the safety valve 30 opens efficiently, allowing gas generated inside the battery case 11 to be quickly released.

[0029] The gas release valve 31 may have a similar configuration to the safety valve 30. Like the safety valve 30, the gas release valve 31 may also have a thin-walled portion 32 and a breaking groove 33. The thin-walled portion 32 of the gas release valve 31 is an oval-shaped portion that is thinner than the other portions of the main body 12. For example, the thickness of the main body 12 is 0.5 mm to 1 mm, and the thickness of the thin-walled portion 32 is 0.1 mm to 0.3 mm.

[0030] The rupture groove 33 is formed in the thin-walled portion 32. When the internal pressure of the battery case 11 reaches or exceeds a second reference value (second opening pressure value) that is higher than the first reference value, the rupture groove 33 of the gas release valve 31 is ruptured by the internal pressure.

[0031] When a nail penetration test is conducted as a safety evaluation test for batteries, in which a nail is inserted into a battery to simulate an internal short circuit, the battery cell experiences thermal runaway, generating emissions from the battery cell, including fragments of the positive and negative electrodes and separators, electrolyte, and high-temperature, high-pressure gases generated by reactions.

[0032] A battery pack is composed of multiple lithium-ion batteries 10 connected together as battery cells. In this battery pack nail penetration test, one of the multiple lithium-ion batteries 10 constituting the battery pack is used as a trigger cell, and a nail is inserted into the trigger cell to cause thermal runaway. During this test, the safety valve 30 of the trigger cell may become clogged with discharged material, preventing sufficient discharge and resulting in the discharged material remaining inside the trigger cell. Because the discharged material due to thermal runaway is extremely hot, the temperature of the trigger cell may rise, increasing the heat transfer to other adjacent battery cells and potentially causing thermal runaway in the adjacent cells.

[0033] In the embodiment, the lithium-ion battery 10 is provided with a plurality of gas release valves 31 in addition to the safety valve 30. Even if the safety valve 30 becomes clogged with discharged material after the internal pressure reaches or exceeds a first reference value and the safety valve 30 opens, the gas release valve 31 opens when the internal pressure of the battery case 11 rises again and reaches or exceeds a second reference value. This allows the high-temperature discharged material to be released to the outside of the battery case 11, suppressing a temperature rise in the lithium-ion battery 10 that serves as the trigger cell and making it possible to suppress heat propagation to adjacent battery cells.

[0034] <Test example> A thermal chain reaction test using a nail was conducted on a five-cell battery pack using five lithium-ion batteries 10 according to the embodiment. Of the five stacked lithium-ion batteries 10, the lithium-ion battery 10 located in the center was used as the trigger cell for the nail to penetrate. The nail had a diameter of 6 mm and a tip angle of 60 degrees. The nail was pushed in at a speed of 2 mm / s, and the battery pack's state of charge (SOC) was 100%. As a comparative example, a comparative battery pack was fabricated using five sealed batteries without a gas release valve 31, and a similar test was conducted.

[0035] In the embodiment, the gas exhaust valve 31 is opened, and the exhaust is released to the outside of the battery case 11. Therefore, when comparing the embodiment with the comparative example, it was confirmed that the weight of the trigger cell was reduced by 10% and the temperature of the battery cell adjacent to the trigger cell was reduced by 9%.

[0036] The present invention is not limited to the above-described embodiment and can be modified as appropriate without departing from the spirit and scope of the invention. The shapes of the safety valve 30 and the gas release valve 31 described above are examples, and are not limited to these, and various shapes can be included in the present invention. The number and arrangement of the gas release valves 31 are also examples. More than two gas release valves 31 may be used, and the arrangement of the gas release valves 31 may be changed as appropriate. The type of battery is not limited to the lithium ion battery described above, and various types of batteries with different electrode body materials and electrolytes may be used. [Explanation of symbols]

[0037] 3 positive electrode plate 4 negative plates 10. Lithium-ion battery 11 Battery case 12 Main Unit 13 Lid 14 Positive terminal 15 Negative terminal 16 positive electrode 17 Negative electrode 20 Wound electrode body 30 Safety valve 31 Gas exhaust valve 32 Thin-walled section 33 Breaking groove 34 Central groove 35 Side groove 36 Peripheral groove

Claims

[Claim 1] a case that houses the electrode body; a safety valve provided on the upper surface of the case and opening when the internal pressure of the case reaches or exceeds a first reference value; a gas release valve provided on a side surface of the case, the gas release valve opening when the internal pressure of the case reaches a second reference value higher than the first reference value; Equipped with Sealed battery.

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