Secondary battery

Abstract

To provide a secondary battery with an efficient and well-formed battery case.SOLUTION: A secondary battery includes a case body 31. The case body 31 accommodates a power generating element inside. The case body 31 includes a first member 32 and a second member 33. The first member 32 has a cylindrical shape with a bottom and is formed from one metal plate by drawing. The second member 33 has a cylindrical shape. The second member 33 is joined to the cylindrical portion of the first member 32 in a fitted state.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a secondary battery in which a power generating element is housed inside a rigid battery case. [Background technology]

[0002] Secondary batteries are widely used as portable power sources for personal computers, mobile terminals, etc., or as power sources for driving vehicles such as EVs (electric vehicles), HVs (hybrid vehicles), and PHVs (plug-in hybrid vehicles). As battery cases for secondary batteries, flexible laminated battery cases and rigid rectangular and cylindrical battery cases are known. Rigid battery cases have the advantages of being highly resistant to external impacts and being less susceptible to damage from needle-shaped members, for example.

[0003] For example, in the secondary battery described in Patent Document 1, two members having the same shape and rigidity are joined by laser welding in an opposing state to form a bottomed, cylindrical or tubular case member having an opening. A lid member (cap plate) is joined to the opening of the formed case member to seal the opening. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-532715 Summary of the Invention [Problem to be solved by the invention]

[0005] In the secondary battery described in Patent Document 1, if the joints between the members constituting the case are not firmly joined without gaps, problems such as electrolyte leakage may occur. However, with the technology described in Patent Document 1, it is very difficult to firmly join the joints by laser welding without gaps while accurately aligning the ends of multiple members against each other.

[0006] Also, drawing (deep drawing) is known as a method for forming a bottomed tubular member. In drawing, a bottomed tubular member is formed by applying pressure to a single metal plate to draw it. Therefore, since there are no seams in the member formed by drawing, problems such as a decrease in bonding strength are unlikely to occur. However, drawing is likely to produce portions (unused portions) of the metal plate material that cannot be used as a battery case and are discarded or the like. The deeper the bottomed tubular member to be formed, the higher the proportion of the unused portions in the metal plate material. Therefore, it has been difficult to efficiently form a bottomed tubular battery case that is deep enough to accommodate a power generating element of a secondary battery by conventional drawing.

[0007] A typical object of the present invention is to provide a secondary battery including a battery case that is efficiently and appropriately formed. [Means for solving the problem]

[0008] One embodiment of a secondary battery disclosed herein is a secondary battery comprising a bottomed, cylindrical case body that houses a power generating element therein, and is characterized in that the case body comprises a bottomed, cylindrical first member and a cylindrical second member formed from a single metal plate by drawing, and the second member is joined in a state where it is fitted into the cylindrical portion of the first member.

[0009] In the secondary battery according to the present disclosure, a cylindrical case body with a bottom is formed by joining a cylindrical second member to a cylindrical first member formed by drawing. That is, regardless of the depth of the cylindrical first member with a bottom, the cylindrical second member is joined to the first member, so that the overall depth of the cylindrical case body with a bottom is sufficiently secured. Therefore, by making the depth of the first member shallow, the ratio of unused parts in the material of the metal plate when forming the first member by drawing can be reduced. Furthermore, the cylindrical second member is joined in a state of being fitted into the cylindrical part of the first member. Therefore, the first member and the second member are easily joined firmly without gaps compared to a case where the ends of the two members are simply joined in a state of contact with each other. Therefore, the battery case of the secondary battery according to the present disclosure can be efficiently and firmly formed.

[0010] The term "cylindrical with bottom" only indicates the shape of the first member and the case body, and does not specify the orientation of the first member and the case body. In other words, the bottoms of the first member and the case body do not need to be located at the bottom of the secondary battery, and may be located at the top or side of the secondary battery.

[0011] In one effective aspect of the secondary battery disclosed herein, the second member is formed into a seamless, continuous tubular shape by extrusion. In this case, no seams are formed at both annular ends of the tubular second member. Therefore, unlike a case where a metal plate is deformed into an annular shape and joined to form the second member, when the lid member is joined to the open end of the second member, the joining strength of the lid member is not reduced by the seam. Therefore, the strength of the battery case is more appropriately ensured.

[0012] In one effective aspect of the secondary battery disclosed herein, the second member is joined by ultrasonic bonding in a state where it is fitted into a cylindrical portion of the first member. In this case, unlike the case where the first member and the second member are joined by laser welding, deterioration of battery performance due to leakage or the like that occurs during joining is unlikely to occur. In addition, since ultrasonic bonding is performed in a state where the fitting portion of the first member and the second member is pressed, gaps are unlikely to occur in the joint portion compared to the case where laser welding or the like is used. Therefore, the battery case is formed more efficiently and appropriately.

[0013] In one effective aspect of the secondary battery disclosed herein, the power generating element includes an electrolyte, and the cylindrical portion of the first member is fitted to the outer periphery of the cylindrical second member. In this case, it is easier to increase the volume of the first member, which is a bottomed cylindrical member, compared to when the cylindrical portion of the first member is fitted to the inside of the second member. Therefore, by disposing the first member at the bottom of the secondary battery, the electrolyte is more likely to appropriately accumulate at the bottom of the first member.

[0014] In one effective embodiment of the secondary battery disclosed herein, the power generating element includes a wound electrode body. The wound electrode body is formed by winding a sheet-shaped positive electrode and a negative electrode with a separator interposed therebetween. The wound electrode body has a pair of R parts that are curved parts of the wound positive electrode, negative electrode, and separator. One of the pair of R parts in the wound electrode body is disposed at the position of the annular open end located opposite the bottom of the first member, or at a position closer to the bottom than the open end. In this case, the depth of the first member, which is a bottomed cylindrical shape, is ensured so that the cylindrical part of the first member is sufficiently fitted with the second member. This makes it easier to ensure the bonding strength between the first member and the second member. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view that illustrates a schematic structure of a secondary battery 1 of the present embodiment. [Diagram 2] FIG. 2 is a perspective view of the electrode body 20. [Diagram 3] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, one of the typical embodiments of the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in this specification and necessary for implementation can be understood as design matters of a person skilled in the art based on the prior art in the field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field. In the following drawings, members and parts that perform the same function are described with the same reference numerals. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

[0017] In this specification, the term "battery" refers to a general power storage device capable of extracting electric energy, and is a concept that includes primary batteries and secondary batteries. The term "secondary battery" refers to a general power storage device that can be repeatedly charged and discharged, and includes so-called storage batteries (i.e., chemical batteries) such as lithium ion secondary batteries, nickel metal hydride batteries, and nickel cadmium batteries, as well as capacitors (i.e., physical batteries) such as electric double layer capacitors. The secondary battery according to the present disclosure will be described in detail below, taking as an example a flat rectangular lithium ion secondary battery, which is a type of secondary battery. However, it is not intended that the secondary battery according to the present disclosure be limited to those described in the following embodiments.

[0018] <Structure of secondary battery> The secondary battery 1 shown in FIG. 1 is a sealed lithium ion secondary battery including an electrode assembly 20, an electrolyte (non-aqueous electrolyte in this embodiment) 10, and a battery case 30. The electrode assembly 20 and the electrolyte are power generating elements of the secondary battery 1. The battery case 30 accommodates the electrode assembly 20 and the electrolyte 10 in a sealed state therein. The shape of the battery case 30 in this embodiment is a flattened rectangular shape. However, the shape of the battery case 30 may be other shapes (for example, a cylindrical shape, etc.).

[0019] The battery case 30 includes a bottomed cylindrical case body 31 having an opening at one end (the upper end in this embodiment) and a plate-shaped lid member 35 that closes the opening of the case body. The details of the configuration of the case body 31 will be described later. The battery case 30 (specifically, the lid member 35 of the battery case 30) is provided with a positive electrode external terminal 42 and a negative electrode external terminal 44 for external connection, and a safety valve 36. The safety valve 36 releases the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher. The battery case 30 is also provided with an injection port 37 for injecting the electrolyte 10 into the battery case 30. The material of the battery case 30 is preferably a material that is lightweight, has good thermal conductivity, and has appropriate rigidity. As an example, the battery case 30 of this embodiment is made of aluminum.

[0020] In the electrode body 20 of this embodiment, a long positive electrode (positive electrode sheet) 50, a long first separator 71, a long negative electrode (negative electrode sheet) 60, and a long second separator 72 are overlapped and wound. That is, the electrode body 20 of this embodiment is a wound electrode body formed by winding the positive electrode 50 and the negative electrode 60 with the first separator 71 and the second separator 72 interposed therebetween.

[0021] As shown in Fig. 2, the electrode body 20 of this embodiment has a pair of R portions 21 formed at the upper and lower ends. The R portions 21 are portions where the wound positive electrode 50, first separator 71, negative electrode 60, and second separator 72 are curved. In order to accommodate the electrode body 20 in the case main body 31 (see Fig. 1), the central portion in the vertical direction of the electrode body 20 is formed into a flat shape.

[0022] As shown in FIG. 1, in the positive electrode 50, a positive electrode active material layer 54 is applied along the longitudinal direction on one or both sides (both sides in this embodiment) of a long positive electrode collector 52. In the negative electrode 60, a negative electrode active material layer 64 is applied along the longitudinal direction on one or both sides (both sides in this embodiment) of a long negative electrode collector 62. The uncoated portions 52A, 62A are located at both ends of the electrode body 20 in the direction of the winding axis. The uncoated portion 52A is a portion where the positive electrode collector 52 is exposed without being coated with the positive electrode active material layer 54. The positive electrode collector terminal 43 is joined to the uncoated portion 52A. The positive electrode external terminal 42 is electrically connected to the positive electrode collector terminal 43. The uncoated portion 62A is a portion where the negative electrode collector 62 is exposed without being coated with the negative electrode active material layer 64. A negative electrode current collector terminal 45 is joined to the uncoated portion 62A. A negative electrode external terminal 44 is electrically connected to the negative electrode current collector terminal 45. The materials constituting the positive and negative electrodes and separators of the electrode body 20 and the materials constituting the electrolyte 10 can be the same as those used in conventional general secondary batteries without any restrictions.

[0023] <Case body> The case body 31 included in the battery case 30 will be described in detail with reference to FIG. 1 and FIG. 3. As described above, the case body 31 is formed in a bottomed cylindrical shape. The electrode body 20 and the electrolyte 10 (see FIG. 1), which are power generating elements, are accommodated inside the case body 31. In this embodiment, the bottom of the case body 31 (bottom 321 of the first member 32 described later) is located at the bottom of the secondary battery 1. However, the bottom of the case body 31 does not have to be located at the bottom of the secondary battery 1. In other words, the term "bottomed cylindrical" is merely a term indicating the shape of the case body 31, and does not specify the direction of the case body 31. The case body 31 includes a first member 32 and a second member 33. Both the first member 32 and the second member 33 have appropriate rigidity and are formed of a lightweight metal material (aluminum in this embodiment).

[0024] The first member 32 will be described. As shown in FIG. 3, the first member 32 has a cylindrical shape with a bottom. The first member 32 in this embodiment includes a bottom 321 and a tubular portion 322. The bottom 321 closes the side of the case body 31 opposite to the opening closed by the lid member 35 (see FIG. 1). The tubular portion 322 extends in a tubular shape from the outer periphery of the bottom 321. Therefore, the end of the tubular portion 322 opposite to the bottom 321 (the upper end in FIG. 3) becomes an annular open end 323.

[0025] The first member 32 is formed by drawing (sometimes called deep drawing). Drawing is a processing method for forming a member of a desired shape (a cylindrical shape with a bottom in this embodiment) by applying pressure to a single metal plate to draw it. The first member 32 formed by drawing does not have any joints. Therefore, leakage of the electrolyte 10 from the joints of the first member 32 is suppressed.

[0026] The second member 33 has a cylindrical shape. The shape of the outer periphery of at least the end portion (the lower end portion in this embodiment) of the cylindrical second member 33 on the first member 32 side corresponds to (substantially coincides with) the shape of the inner periphery of the open end 323 of the tubular portion 322 of the first member 32. It is also possible to make the shape of the inner periphery of at least the end portion of the second member 33 on the first member 32 side correspond to the shape of the outer periphery of the open end 323 of the tubular portion 322.

[0027] The cylindrical second member 33 is joined in a fitted state to the cylindrical portion 322 of the first member 32 to form the bottomed cylindrical case body 31. In other words, regardless of the depth of the bottomed cylindrical first member 32, the cylindrical second member 33 is joined to the first member 32, so that the overall depth of the bottomed cylindrical case body 31 (in this embodiment, the distance from the bottom portion 321 to the opening 333 (see FIG. 3) to which the lid member 35 is joined) is sufficiently ensured. Therefore, by making the depth of the first member 32 shallow, the proportion of unused portions of the metal plate material can be reduced when the first member 32 is formed by drawing.

[0028] Moreover, the cylindrical second member 33 is joined in a state of being fitted into the cylindrical portion 322 of the first member 32. Therefore, the first member 32 and the second member 33 can be joined firmly without any gaps, compared to a case in which the end portion (the upper end portion in this embodiment) of the cylindrical portion 322 of the first member 32 and the end portion (the lower end portion in this embodiment) of the second member 33 are joined together in a state in which the two are simply brought into contact with each other.

[0029] The cylindrical second member 33 is formed into a continuous cylindrical shape without joints by extrusion. Therefore, no joint is formed at the opening 333 of the second member 33 to which the lid member 35 (see FIG. 1) is joined. Therefore, when the lid member 35 is joined to the opening 333 of the second member 33, the joint strength is not reduced by the joint. However, in cases where the joint strength of the lid member 35 to the opening is unlikely to decrease, the cylindrical second member may be formed by deforming a plate-like member into a ring shape and joining both ends.

[0030] The second member 33 is joined by ultrasonic bonding in a state where it is fitted into the tubular portion 322 of the first member 32. Therefore, unlike the case where the first member 32 and the second member 33 are joined by laser welding or the like, deterioration of battery performance due to leakage or the like occurring during joining is unlikely to occur. In addition, ultrasonic bonding is performed while pressing the fitting portion of the first member 32 and the second member 33 with the ultrasonic horn and the anvil (receiving jig) in a state where one of them is placed inside the case body 31 and the other is placed outside the case body 31. Therefore, the possibility of a gap occurring in the joint portion of the first member 32 and the second member 33 is further reduced. Note that, in the fitting portion of the first member 32 and the second member 33, ultrasonic bonding is performed in a state where an anvil that matches the curved shape is placed in the portion where the members are curved. Therefore, the curved portion of the members is also appropriately joined.

[0031] As described above, the shape of the outer periphery of at least the end (lower end in this embodiment) of the cylindrical second member 33 on the first member 32 side corresponds to the shape of the inner periphery of the open end 323 of the cylindrical portion 322 of the first member 32. As a result, the cylindrical portion 322 of the first member 32 fits into the outer periphery of the second member 33. Therefore, it is easier to increase the volume of the bottomed cylindrical first member 32 compared to the case where the outer periphery of the cylindrical portion 322 of the first member 32 is fitted into the inner periphery of the second member 33. Therefore, the electrolyte 10 is more likely to be appropriately accumulated in the first member 32. However, when the influence of the ease of accumulation of the electrolyte 10 is small, the two may be joined in a state where the outer periphery of the cylindrical portion 322 of the first member 32 is fitted into the inner periphery of the second member 33.

[0032] As shown in FIG. 2, the electrode body 20 of this embodiment has a pair of R portions 21 formed by curving the wound electrodes, etc., at each of a pair of opposing ends (upper and lower ends in this embodiment). As shown in FIG. 1, one of the pair of R portions 21 in the electrode body 20 (the lower R portion 21 in this embodiment) is disposed at the position of the annular open end 323 located opposite the bottom 321 of the first member 32, or on the bottom 321 side of the open end 323. Therefore, the depth of the bottomed cylindrical first member 32 is ensured so that the cylindrical portion 322 in the first member 32 is sufficiently fitted with the second member 33. This makes it easier to ensure the bonding strength between the first member 32 and the second member 33.

[0033] Although the detailed description has been given above with reference to specific embodiments, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the above-described embodiments. [Explanation of symbols]

[0034] 1 Secondary battery 10 Electrolyte 20 Electrode body 21 R section 30 Battery case 31 Case body 32 First member 321 Bottom 322 Cylinder part 323 Open end 33 Second member 35 Lid member

Claims

1. A secondary battery having a bottomed cylindrical case body that houses a power generating element therein, The power generating element includes an electrolyte, The case body includes: A first member is formed from a single metal plate by drawing, has a bottomed cylindrical shape, and is composed of a flat bottom and a surface perpendicular to the bottom; A cylindrical second member; Equipped with The second member is joined in a state where it is fitted into a cylindrical portion of the first member, The fitting portion between the second member and the cylindrical portion of the first member includes a curved portion, a joint portion between an outer periphery of the second member and an inner periphery of a cylindrical portion of the first member is formed in the fitted portion including the curved portion, the power generating element is a wound electrode body in which sheet-shaped positive and negative electrodes are wound with a separator interposed therebetween, the wound electrode body having a pair of R portions which are curved portions of the wound positive electrode, the wound negative electrode, and the wound separator; The wound electrode body is housed in the case body such that a winding axis direction of the wound electrode body is parallel to a bottom portion of the first member, an entirety of one of the pair of R portions in the wound electrode body is disposed at a position closer to the bottom than an annular open end located on the opposite side to the bottom of the first member, Secondary battery.

2. The secondary battery according to claim 1 , wherein the second member is formed into a seamless, continuous cylindrical shape by extrusion.

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