Patent Description:
<CIT> describes a dissimilar metal joined body (laser joined body) including a copper material, an aluminum material, and a melted mixture part formed in a manner that a part of the aluminum material is melted and flows into the copper material, in which the melted mixture part satisfies predetermined width and depth.

<CIT> and <CIT> disclose dissimilar metal joined conductors including a copper material and an aluminium material, which are both joined by laser welding.

According to the present inventors' examination, when the aforementioned technique is applied to an electrode terminal of a power storage device that is used for a power source for vehicle driving or the like, for example, there is still room for improvement. That is to say, in the application to the power source for vehicle driving or the like, when the power storage device is used, force of vibration, impact, or the like may be applied from the outside. In the technique according to <CIT>, however, since the strength of a border part between a melted part and a non-melted part is low, a metal melted part is broken at the application of the external force, which may result in instable conductive connection of terminals or connection failure. Thus, it has been desired to improve the conduction reliability.

The present disclosure has been made in view of the above circumstances, and an object is to provide a power storage device including a terminal (dissimilar metal joined body) with improved conduction reliability.

A power storage device according to the present disclosure includes an electrode body that includes a first electrode and a second electrode, a battery case that accommodates the electrode body and includes a first surface where a penetration hole is provided, and a first electrode terminal that penetrates the penetration hole of the battery case and is electrically connected to the first electrode. The first electrode terminal includes a first conductive member in which a first metal occupies a maximum ratio on a mass basis, a second conductive member in which a second metal that is different from the first metal occupies a maximum ratio on a mass basis, the second conductive member having a shaft part disposed in the penetration hole, and a metal joined part where the first conductive member and the second conductive member are joined. The metal joined part includes, at a cross section being perpendicular to the first surface, passing an axial center of the shaft part, and extending in a radial direction of the shaft part, a first region in which the first metal occupies <NUM> mass% or more and a second region in which the second metal occupies <NUM> mass% or more, and when a surface passing a border part where the first conductive member and the second conductive member are in contact with each other around the metal joined part is a border surface, the first region includes a region that exists on a side of the first conductive member relative to the border surface and a first protrusion region that protrudes toward the second conductive member relative to the border surface, and the second region includes a region that exists on a side of the second conductive member relative to the border surface and a second protrusion region that protrudes toward the first conductive member relative to the border surface.

In the metal joined part, the first region includes the first protrusion region and the second region includes the second protrusion region; thus, a border between the first region and the second region has an uneven shape in a cross-sectional view. Therefore, the first conductive member and the second conductive member are mechanically engaged with each other and accordingly, the joining strength at the border part can be improved. Additionally, by bending the border part, the distance of the border can be extended; thus, even in the occurrence of a crack in the metal joined part, the development of the crack can be slowed down. As a result, according to the art disclosed herein, even if force of vibration, impact, or the like is applied from the outside during the use, the close contact state between the first conductive member and the second conductive member can be kept easily and the conductive connection between the first conductive member and the second conductive member can be kept stably. Accordingly, the power storage device including the terminal in which the conduction reliability of the metal joined part is improved can be achieved.

The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

Hereinafter, some preferred embodiments of the art disclosed herein will be described with reference to the drawings. Incidentally, matters other than matters particularly mentioned in the present specification and necessary for the implementation of the present disclosure (for example, the general configuration and manufacturing process of a power storage device and a power storage module that do not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the conventional art in the relevant field. The present disclosure can be implemented based on the contents disclosed in the present specification and the technical common sense in the relevant field.

Note that in the drawings below, the members and parts with the same operation are denoted by the same reference sign and the overlapping description may be omitted or simplified. Moreover, in the present specification, the notation "X to Y" for a range signifies a value more than or equal to X and less than or equal to Y, and is meant to encompass also the meaning of being "more than X" and "less than Y".

<FIG> is a perspective view schematically illustrating a power storage module <NUM> according to an embodiment. The power storage module <NUM> includes a plurality of power storage devices <NUM> that are disposed along an arrangement direction X and a plurality of busbars <NUM> that electrically connect the plurality of power storage devices <NUM> to each other. In this case, the power storage module <NUM> further includes a restriction mechanism <NUM>. In the following description, reference signs L, R, F, Rr, U, and D in the drawings respectively denote left, right, front, rear, up, and down, and reference signs X, Y, and Z in the drawings respectively denote a thickness direction of the power storage device <NUM>, a long side direction that is orthogonal to the thickness direction, and an up-down direction that is orthogonal to the thickness direction and the long side direction. The thickness direction X also corresponds to the arrangement direction of the power storage devices <NUM>. These directions are defined however for convenience of explanation, and do not limit the manner in which the power storage module <NUM> is disposed.

The restriction mechanism <NUM> is configured to apply prescribed restriction pressure on the plurality of power storage devices <NUM> from the arrangement direction X. The restriction mechanism <NUM> here includes a pair of end plates <NUM>, a pair of side plates <NUM>, and a plurality of screws <NUM>. The pair of end plates <NUM> are disposed at both ends of the plurality of power storage devices <NUM> in the arrangement direction X. The pair of end plates <NUM> hold the plurality of power storage devices <NUM> therebetween in the arrangement direction X. The pair of end plates <NUM> are preferably made of metal.

The pair of side plates <NUM> link between the pair of end plates <NUM>. The pair of side plates <NUM> are preferably made of metal. The pair of side plates <NUM> are fixed to the end plates <NUM> by the plurality of screws <NUM> so that a restriction load is generally about <NUM> to <NUM> kN, for example. Thus, the restriction load is applied on the plurality of power storage devices <NUM> from the arrangement direction X and accordingly, the power storage module <NUM> is held integrally. The structure of the restriction mechanism is, however, not limited to this example. In another example, the restriction mechanism <NUM> may alternatively include a plurality of restriction bands, bind bars, or the like instead of the side plates <NUM>.

The busbar <NUM> is a conductive member and electrically connects the plurality of power storage devices <NUM> to each other. The busbar <NUM> is formed of, for example, a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The busbar <NUM> is preferably formed of aluminum or an aluminum alloy. In <FIG>, the busbar <NUM> is provided to link between a positive electrode terminal <NUM> (see <FIG>, specifically a positive electrode first conductive member <NUM>) and a negative electrode terminal <NUM> (see <FIG>, specifically a negative electrode first conductive member <NUM>), which will be described below, of the power storage devices <NUM> that are adjacent in the arrangement direction X. The busbar <NUM> is attached to each of the positive electrode terminal <NUM> and the negative electrode terminal <NUM> by welding such as laser welding, for example.

The power storage device <NUM> is a device that can store electric power and is capable of being charged and discharged repeatedly. Note that in the present specification, the term "power storage device" refers to a concept encompassing so-called secondary batteries such as lithium ion secondary batteries and nickel-hydrogen batteries and capacitors such as lithium ion capacitors and electrical double-layer capacitors.

As illustrated in <FIG>, the plurality of power storage devices <NUM> are arranged along the arrangement direction X (in other words, the thickness direction X of the power storage device <NUM>) between the pair of end plates <NUM>. The shape, the size, the number, the arrangement, and the like of the plurality of power storage devices <NUM> included in the power storage module <NUM> are not limited to the aspect disclosed herein, and can be changed as appropriate. Between the power storage devices <NUM> that are adjacent in the arrangement direction X, a different member such as a spacer can exist. Here, the plurality of power storage devices <NUM> are connected to each other in series. However, the connection method between the plurality of power storage devices <NUM> is not limited to the series connection and may be, for example, parallel connection, multiple series-multiple parallel connection, or the like.

<FIG> is a perspective view of the power storage device <NUM>. <FIG> is a schematic longitudinal cross-sectional view taken along line III-III in <FIG>. As illustrated in <FIG>, the power storage device <NUM> includes a battery case <NUM>, an electrode body <NUM>, the positive electrode terminal <NUM>, the negative electrode terminal <NUM>, a positive electrode current collecting member <NUM>, and a negative electrode current collecting member <NUM>. Although not illustrated, the power storage device <NUM> further includes a nonaqueous electrolyte solution (not illustrated) here. The nonaqueous electrolyte solution may be similar to the conventional nonaqueous electrolyte solution, without particular limitations. The power storage device <NUM> is a lithium ion secondary battery here. The power storage device <NUM> is characterized by including the positive electrode terminal <NUM> and/or the negative electrode terminal <NUM> disclosed herein, and the other configurations may be similar to those in the related art.

The battery case <NUM> is a housing that accommodates the electrode body <NUM> and the nonaqueous electrolyte solution. As illustrated in <FIG>, the external shape of the battery case <NUM> is a flat and bottomed cuboid shape (rectangular shape) here. A conventionally used material can be used for the battery case <NUM>, without particular limitations. The battery case <NUM> is preferably made of metal, for example, more preferably made of aluminum, an aluminum alloy, iron, an iron alloy, or the like, and particularly preferably made of aluminum or an aluminum alloy. As illustrated in <FIG>, the battery case <NUM> includes an exterior body <NUM> including an opening <NUM> and a sealing plate (lid body) <NUM> that seals the opening <NUM>. The battery case <NUM> preferably includes the exterior body <NUM> and the sealing plate <NUM>.

As illustrated in <FIG>, the exterior body <NUM> includes a bottom wall 12a with a substantially rectangular shape facing the opening <NUM> (see <FIG>), a pair of long side walls 12b extending from long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from short sides of the bottom wall 12a and facing each other. The long side wall 12b is larger in area than the short side wall 12c. Note that in the present specification, the term "substantially rectangular shape" encompasses, in addition to a perfect rectangular shape (rectangle), for example, a shape whose corner connecting a long side and a short side of the rectangular shape is rounded, a shape whose corner includes a notch, and the like.

The sealing plate <NUM> is a plate-shaped member expanding along an XY plane in <FIG>. The sealing plate <NUM> is one example of "first surface". As illustrated in <FIG>, the sealing plate <NUM> is attached to the exterior body <NUM> so as to cover the opening <NUM>. The sealing plate <NUM> faces the bottom wall 12a of the exterior body <NUM>. The sealing plate <NUM> here is substantially rectangular in shape. It is preferable that the sealing plate <NUM> be substantially rectangular in shape. The battery case <NUM> is unified in a manner that the sealing plate <NUM> is joined (preferably, joined by welding) to a periphery of the opening <NUM> of the exterior body <NUM>. The battery case <NUM> is hermetically sealed (closed).

As illustrated in <FIG>, a liquid injection hole <NUM>, a discharge valve <NUM>, and two terminal extraction holes <NUM> and <NUM> are provided in the sealing plate <NUM>. The liquid injection hole <NUM> is provided for the purpose of injecting the nonaqueous electrolyte solution after the sealing plate <NUM> is assembled to the exterior body <NUM>. The liquid injection hole <NUM> is sealed by a sealing member <NUM>. The discharge valve <NUM> is configured to break when the pressure in the battery case <NUM> becomes more than or equal to a predetermined value so as to discharge the gas out of the battery case <NUM>.

As illustrated in <FIG>, the terminal extraction holes <NUM> and <NUM> penetrate the sealing plate <NUM> in the up-down direction Z. The terminal extraction holes <NUM> and <NUM> are one example of "penetration hole" provided to the sealing plate <NUM> (first surface). In a plan view, the terminal extraction holes <NUM> and <NUM> are formed in an annular shape (for example, circular shape). The terminal extraction hole <NUM> has the inner diameter that enables a shaft column part <NUM> of the positive electrode terminal <NUM> to be described below before a caulking process (before being attached to the sealing plate <NUM>) to pass therethrough. The terminal extraction hole <NUM> has the inner diameter that enables a shaft column part <NUM> of the negative electrode terminal <NUM> to be described below before the caulking process (before being attached to the sealing plate <NUM>) to pass therethrough.

As illustrated in <FIG>, the electrode body <NUM> is accommodated inside the battery case <NUM> (in detail, the exterior body <NUM>). Although not illustrated, the electrode body <NUM> includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode current collector, and a positive electrode mixture layer fixed on the positive electrode current collector and including a positive electrode active material. The negative electrode includes a negative electrode current collector, and a negative electrode mixture layer fixed on the negative electrode current collector and including a negative electrode active material. One of the positive electrode and the negative electrode is one example of "first electrode" and the other is one example of "second electrode". In the present embodiment, the first electrode is the negative electrode and the second electrode is the positive electrode. The first electrode is preferably the negative electrode and the second electrode is preferably the positive electrode.

The structure of the electrode body <NUM> may be similar to the conventional structure thereof, without particular limitations. The electrode body <NUM> here is a wound electrode body with a flat shape in which the positive electrode with a band shape and the negative electrode with a band shape are stacked via a separator in an insulated state and wound using a winding axis as a center. In another embodiment, the electrode body <NUM> may be a stack type electrode body formed in a manner that a plurality of square positive electrodes and a plurality of square negative electrodes are stacked in the insulated state. The number of electrode bodies <NUM> to be disposed in one battery case <NUM> is not limited in particular and may be one or plural.

As illustrated in <FIG>, a positive electrode current collecting part <NUM> is provided at one end part of the electrode body <NUM> in a winding axis direction (the long side direction Y in <FIG>) (left end part in <FIG>). The positive electrode current collecting part <NUM> is an exposed part of the positive electrode current collector in this case, and is formed of, for example, a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. To the positive electrode current collecting part <NUM>, a second part <NUM> of the positive electrode current collecting member <NUM> to be described below is attached. A negative electrode current collecting part <NUM> is provided at the other end part of the electrode body <NUM> in the winding axis direction (right end part in <FIG>). The negative electrode current collecting part <NUM> is an exposed part of the negative electrode current collector in this case, and is formed of, for example, a conductive metal such as copper, a copper alloy, nickel, or stainless steel. To the negative electrode current collecting part <NUM>, a second part <NUM> of the negative electrode current collecting member <NUM> to be described below is attached.

The positive electrode current collecting member <NUM> constitutes a conductive path that electrically connects the positive electrode terminal <NUM> and the positive electrode (second electrode) of the electrode body <NUM>. The positive electrode current collecting member <NUM> is preferably formed of the same metal species as the positive electrode current collecting part <NUM>, for example, a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. As illustrated in <FIG>, the positive electrode current collecting member <NUM> includes a first part <NUM> with a substantially L-like shape, and the second part <NUM> electrically connected to the first part <NUM> and extending along the short side wall 12c of the exterior body <NUM>. The first part <NUM> is attached to an inner surface of the sealing plate <NUM> by the caulking process in an insulated state through an internal insulating member <NUM>. The first part <NUM> is electrically connected to the positive electrode terminal <NUM>. The second part <NUM> is attached to the positive electrode current collecting part <NUM>.

The negative electrode current collecting member <NUM> constitutes a conductive path that electrically connects the negative electrode terminal <NUM> and the negative electrode (first electrode) of the electrode body <NUM>. The negative electrode current collecting member <NUM> is preferably formed of the same metal species as the negative electrode current collecting part <NUM>, for example, a conductive metal such as copper, a copper alloy, nickel, or stainless steel. As illustrated in <FIG>, the negative electrode current collecting member <NUM> includes a first part <NUM> with a substantially L-like shape, and the second part <NUM> electrically connected to the first part <NUM> and extending along the short side wall 12c of the exterior body <NUM>. The first part <NUM> is attached to the inner surface of the sealing plate <NUM> by the caulking process in the insulated state through the internal insulating member <NUM>. The first part <NUM> is electrically connected to the negative electrode terminal <NUM>. The second part <NUM> is attached to the negative electrode current collecting part <NUM>.

<FIG> is a perspective view schematically illustrating a united object in which the positive electrode terminal <NUM>, the negative electrode terminal <NUM>, the first part <NUM> of the positive electrode current collecting member <NUM>, and the first part <NUM> of the negative electrode current collecting member <NUM> are attached to a sealing plate assembly, that is, the sealing plate <NUM>. The positive electrode terminal <NUM> and the negative electrode terminal <NUM> are preferably attached to the sealing plate <NUM>.

The positive electrode terminal <NUM> is disposed at an end part of the sealing plate <NUM> on one side in the long side direction Y (left end part in <FIG>). As illustrated in <FIG>, the positive electrode terminal <NUM> is electrically connected to the positive electrode (second electrode) of the electrode body <NUM> through the positive electrode current collecting member <NUM>. The positive electrode terminal <NUM> includes two kinds of conductive members, that is, the positive electrode first conductive member <NUM> and a positive electrode second conductive member <NUM>. The positive electrode first conductive member <NUM> and the positive electrode second conductive member <NUM> are integrated and electrically connected to each other. The positive electrode first conductive member <NUM> is disposed outside the battery case <NUM>. The positive electrode first conductive member <NUM> here has a plate shape. The positive electrode first conductive member <NUM> is insulated from an outer surface of the sealing plate <NUM> (upper surface in <FIG>) by an external insulating member <NUM>. When the power storage module <NUM> (see <FIG>) is manufactured, the busbar <NUM> is attached to the positive electrode first conductive member <NUM>.

The positive electrode second conductive member <NUM> penetrates the terminal extraction hole <NUM> and extends from inside to outside of the battery case <NUM>. The positive electrode second conductive member <NUM> includes the shaft column part <NUM> that is disposed in the terminal extraction hole <NUM>. The positive electrode second conductive member <NUM> is insulated from the sealing plate <NUM> by the internal insulating member <NUM> and a gasket <NUM>. The gasket <NUM> insulates the sealing plate <NUM> and the positive electrode second conductive member <NUM> and moreover, has a function that closes the terminal extraction hole <NUM>. In this case, the positive electrode second conductive member <NUM> is fixed by caulking to a peripheral part of the sealing plate <NUM> that surrounds the terminal extraction hole <NUM> in the state of being insulated from the sealing plate <NUM> by the caulking process. A caulking part 30c is formed at an end part of the positive electrode second conductive member <NUM> on the exterior body <NUM> side (lower end part in <FIG>). The positive electrode second conductive member <NUM> is fixed to the sealing plate <NUM> by the caulking process and moreover, electrically connected to the first part <NUM>.

The negative electrode terminal <NUM> is disposed at an end part of the sealing plate <NUM> on the other side in the long side direction Y (right end part in <FIG>). As illustrated in <FIG>, the negative electrode terminal <NUM> is electrically connected to the negative electrode (first electrode) of the electrode body <NUM> through the negative electrode current collecting member <NUM>. In the present embodiment, the negative electrode terminal <NUM> is one example of "first electrode terminal that is electrically connected to the negative electrode (first electrode)". The first electrode terminal is preferably the negative electrode terminal <NUM>. Hereinafter, a structure is explained in detail about the case where the first electrode terminal is the negative electrode terminal <NUM>. In another embodiment, however, the first electrode terminal may be the positive electrode terminal <NUM>. In that case, "negative electrode" can be replaced by "positive electrode" as appropriate in the description below.

<FIG> is a plan view schematically illustrating a vicinity of the negative electrode terminal <NUM> in <FIG>. <FIG> is a schematic longitudinal cross-sectional view taken along line VI-VI in <FIG>. <FIG> is a schematic longitudinal cross-sectional view illustrating only the negative electrode terminal <NUM> in <FIG>. As illustrated in <FIG>, the negative electrode terminal <NUM> includes two kinds of conductive members, that is, the negative electrode first conductive member <NUM> and a negative electrode second conductive member <NUM>. The negative electrode first conductive member <NUM> is one example of "first conductive member". The negative electrode second conductive member <NUM> is one example of "second conductive member". The negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> are integrated by a fastening part <NUM> and a metal joined part <NUM>, which will be described below, so as to be connected electrically to each other. However, the fastening part <NUM> is not essential and may be omitted in another embodiment.

The negative electrode first conductive member <NUM> is formed of, for example a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The negative electrode first conductive member <NUM> preferably contains aluminum or an aluminum alloy. The negative electrode first conductive member <NUM> is preferably formed of aluminum or an aluminum alloy at least in the vicinity of the metal joined part <NUM>. The negative electrode first conductive member <NUM> is preferably formed of aluminum or an aluminum alloy. In the present embodiment, the negative electrode first conductive member <NUM> is mainly formed of a first metal. In other words, the first metal occupies the maximum ratio on the mass basis. The first metal occupies preferably <NUM> mass% or more, more preferably <NUM> mass% or more, and particularly preferably <NUM> mass% or more of the entire negative electrode first conductive member <NUM> (however, excluding a part where the metal joined part <NUM> is formed). The first metal is preferably aluminum. The first metal is preferably the same metal species as the busbar <NUM>.

The negative electrode first conductive member <NUM> is disposed outside the battery case <NUM>. The negative electrode first conductive member <NUM> has a plate shape here. As illustrated in <FIG>, the negative electrode first conductive member <NUM> is insulated from the outer surface (upper surface in <FIG>) of the sealing plate <NUM> by the external insulating member <NUM>. Between the negative electrode first conductive member <NUM> and the sealing plate <NUM>, the external insulating member <NUM> is preferably disposed. The external insulating member <NUM> is preferably a resin member.

As illustrated in <FIG>, the negative electrode first conductive member <NUM> has a substantially rectangular shape here. The negative electrode first conductive member <NUM> has two parts sectioned in the long side direction Y: a connection part 41a electrically connected to the negative electrode second conductive member <NUM>; and an extension part 41b disposed on one side of the connection part 41a in the long side direction Y (on the left in <FIG>). The extension part 41b is a part where the busbar <NUM> is disposed when the power storage module <NUM> (see <FIG>) is manufactured. The extension part 41b is one example of "busbar connection region". By the provision of the extension part 41b, the contact area with the busbar <NUM> can be secured sufficiently and the conduction reliability of the power storage module <NUM> can be improved. Note that in <FIG> and <FIG>, the busbar <NUM> and a welding part W between the busbar <NUM> and the negative electrode first conductive member <NUM> are expressed with imaginary lines (two-dot chain lines).

As illustrated in <FIG>, the negative electrode first conductive member <NUM> has a flat plate shape and includes a lower surface 41d and an upper surface 41u here. The lower surface 41d is in contact with the negative electrode second conductive member <NUM>. As can be seen from <FIG>, the lower surface 41d is a surface that faces the battery case <NUM> (specifically, sealing plate <NUM>). The upper surface 41u is a surface apart from the battery case <NUM> and the negative electrode second conductive member <NUM>. As illustrated in <FIG>, the negative electrode first conductive member <NUM> includes a thin part 41t that is depressed from the upper surface 41u to be thinner than the extension part 41b, a penetration hole <NUM> penetrating in the up-down direction Z, and a concave part 41r depressed from the lower surface 41d.

As illustrated in <FIG>, the thin part 41t is formed in an annular shape (for example, circular shape) so as to surround the penetration hole <NUM> in a plan view. In the thin part 41t, the metal joined part <NUM> is provided. The penetration hole <NUM> is formed at a center part of the thin part 41t in a plan view. The penetration hole <NUM> can function as an escape route of distortion by gas or heat generated at welding. The penetration hole <NUM> is formed to be circular in a plan view. The penetration hole <NUM> is provided on an inner peripheral side relative to the fastening part <NUM> and the metal joined part <NUM>. From the penetration hole <NUM>, the negative electrode second conductive member <NUM> (specifically, a flange part 42f to be described below) is exposed.

As illustrated in <FIG>, the concave part 41r is provided on an outer peripheral side relative to the metal joined part <NUM>. Although not illustrated, the concave part 41r is formed in an annular shape (for example, circular shape) in a plan view. The concave part 41r is formed in a tapered shape whose diameter reduces toward the lower surface 41d of the negative electrode first conductive member <NUM> (in other words, toward the negative electrode second conductive member <NUM>) here. In the concave part 41r, the fastening part <NUM> is provided. In the concave part 41r, a constriction part 42n of the negative electrode second conductive member <NUM>, which is described below, is inserted.

The negative electrode second conductive member <NUM> is formed of, for example, a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode second conductive member <NUM> preferably contains copper or a copper alloy. The negative electrode second conductive member <NUM> is preferably formed of copper or a copper alloy at least in the vicinity of the metal joined part <NUM>. The negative electrode second conductive member <NUM> is preferably formed of copper or a copper alloy. In the present embodiment, the negative electrode second conductive member <NUM> is mainly formed of a second metal. In other words, the second metal occupies the maximum ratio on the mass basis. The second metal occupies preferably <NUM> mass% or more, more preferably <NUM> mass% or more, and particularly preferably <NUM> mass% or more of the entire negative electrode second conductive member <NUM> (however, excluding a part where the metal joined part <NUM> is formed). The second metal is particularly preferably copper. The second metal is preferably a metal with higher hardness (for example, Vickers hardness (HV)) than the first metal. The second metal is preferably the same metal species as the negative electrode current collecting part <NUM> and/or the negative electrode current collecting member <NUM>. The negative electrode second conductive member <NUM> may include a metal covered part that is formed of copper or a copper alloy mainly and has a surface thereof partially or entirely covered with metal such as Ni. Thus, the resistance against an electrolyte can be increased and the corrosion resistance can be improved.

As illustrated in <FIG>, the negative electrode second conductive member <NUM> penetrates the terminal extraction hole <NUM> and extends from inside to outside of the battery case <NUM>. The negative electrode second conductive member <NUM> is insulated from the sealing plate <NUM> by the internal insulating member <NUM> and the gasket <NUM>. The gasket <NUM> insulates the sealing plate <NUM> and the negative electrode second conductive member <NUM> and moreover, has a function that closes the terminal extraction hole <NUM>. In this case, the negative electrode second conductive member <NUM> is fixed by caulking to a peripheral part of the sealing plate <NUM> that surrounds the terminal extraction hole <NUM> in the state of being insulated from the sealing plate <NUM> by the caulking process. A caulking part 40c is formed at an end part of the negative electrode second conductive member <NUM> on the exterior body <NUM> side (lower end part in <FIG>). The negative electrode second conductive member <NUM> is fixed to the sealing plate <NUM> by the caulking process and moreover, electrically connected to the first part <NUM>.

The negative electrode second conductive member <NUM> has a substantially cylindrical columnar shape here. The negative electrode second conductive member <NUM> preferably has a columnar shape. As illustrated in <FIG>, the negative electrode second conductive member <NUM> has an axial center C. The negative electrode second conductive member <NUM> includes the flange part 42f electrically connected to the negative electrode first conductive member <NUM>, and the shaft column part <NUM> coupled to a lower end part of the flange part 42f. The negative electrode second conductive member <NUM> preferably has the flange part 42f on an upper part and the shaft column part <NUM> below the flange part 42f.

The flange part 42f is a part that protrudes from the terminal extraction hole <NUM> of the sealing plate <NUM> to the outside of the battery case <NUM> as illustrated in <FIG>. The flange part 42f has a larger outer shape than the shaft column part <NUM>. Although not illustrated, the outer shape of the flange part 42f is substantially cylindrical columnar here. The outer shape of the flange part 42f is larger than that of the terminal extraction hole <NUM> of the sealing plate <NUM>. As illustrated in <FIG>, an axial center of the flange part 42f coincides with the axial center C of the negative electrode second conductive member <NUM>. The flange part 42f includes a lower surface 42d, a side surface (outer peripheral surface) 42o extending upward from the lower surface 42d, the constriction part 42n in which a part of the side surface 42o is constricted, and an upper surface 42u. The upper surface 42u is in contact with the concave part 41r of the negative electrode first conductive member <NUM>. On the upper surface 42u, the metal joined part <NUM> is provided.

The constriction part 42n is provided continuously or intermittently in a part of the side surface 42o of the flange part 42f as illustrated in <FIG>. Although not illustrated, the constriction part 42n is formed in an annular shape (for example, circular shape) in a plan view. When the constriction part 42n is formed in the annular shape, the fastening part <NUM> with high strength can be formed. The constriction part 42n is formed axially symmetrically about the axial center C of the flange part 42f. The constriction part 42n is formed in an inverted tapered shape whose diameter increases toward the upper surface 41u (in other words, away from the shaft column part <NUM>). The fastening part <NUM> is provided in the constriction part 42n. The constriction part 42n is inserted into the concave part 41r of the negative electrode first conductive member <NUM>. The constriction part 42n is fitted into the concave part 41r of the negative electrode first conductive member <NUM> and engaged with the concave part 41r here.

As illustrated in <FIG>, the shaft column part <NUM> extends downward from the lower end part of the flange part 42f. The shaft column part <NUM> is one example of "shaft part". Although not illustrated, the shaft column part <NUM> has a cylindrical shape here. An axial center of the shaft column part <NUM> coincides with the axial center C of the flange part 42f. Before the caulking process, the lower end part of the shaft column part <NUM>, that is, an end part on the opposite side of the flange part 42f is hollow. As illustrated in <FIG>, the shaft column part <NUM> is disposed in the terminal extraction hole <NUM> of the sealing plate <NUM>. The lower end part of the shaft column part <NUM> is spread by the caulking process to form the caulking part 40c. The shaft column part <NUM> is electrically connected to the first part <NUM> of the negative electrode current collecting member <NUM> by the caulking process.

The fastening part <NUM> is a mechanical fixing part for the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM>. Here, the fastening part <NUM> is a mechanical fixing part for the concave part 41r and the flange part 42f (specifically, constriction part 42n). By the provision of the fastening part <NUM> in addition to the metal joined part <NUM>, the conduction reliability of the negative electrode terminal <NUM> can be improved further. A formation method for the fastening part <NUM> is not limited in particular as long as mechanical joining with mechanical energy is used, and may be, for example, press-fitting, caulking, shrink-fitting, riveting, folding, bolt joining, or the like.

In the present embodiment, the fastening part <NUM> is provided at the lower surface 41d of the negative electrode first conductive member <NUM> as illustrated in <FIG>. The fastening part <NUM> is an engagement part where the concave part 41r of the negative electrode first conductive member <NUM> and the constriction part 42n of the negative electrode second conductive member <NUM> are engaged here. Specifically, the fastening part <NUM> is a press-fitting engagement part where the constriction part 42n of the negative electrode second conductive member <NUM> is engaged with the concave part 41r of the negative electrode first conductive member <NUM> by press-fitting. The fastening part <NUM> is configured in a manner that an inner wall of the concave part 41r of the negative electrode first conductive member <NUM> is fixed (for example, fixed by pressure) with the constriction part 42n of the negative electrode second conductive member <NUM>. Thus, even when the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> are formed of dissimilar metal for example, these can be fixed suitably.

The fastening part <NUM> is provided on an outer peripheral side of the flange part 42f relative to the metal joined part <NUM> here. Although not illustrated, the fastening part <NUM> is formed in an annular shape (for example, circular shape) in a plan view. The fastening part <NUM> is formed continuously here. Thus, the strength of the fastening part <NUM> can be increased and the conduction reliability of the negative electrode terminal <NUM> can be improved further.

The metal joined part <NUM> is a metallurgic joined part between the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM>. The metal joined part <NUM> is a joined part between the thin part 41t and the flange part 42f here. The metal joined part <NUM> includes a fused and solidified part, which is formed in a manner that the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> are melted by irradiation with an energy beam, fused, and solidified. The fused and solidified part can be formed by using, for example, light energy, electron energy, thermal energy, or the like. In particular, welding is preferable. The welding can achieve the metal joined part <NUM> with high strength relatively easily and stably. A method of the welding is not limited in particular and may be, for example, laser welding, electron beam welding, ultrasonic welding, resistance welding, tungsten inert gas (TIG) welding, or the like. The metal joined part <NUM> is preferably a laser welding part formed by laser welding. Note that a suitable condition of the laser welding will be discussed in a manufacturing method below.

As illustrated in <FIG>, in the present embodiment, the metal joined part <NUM> is provided on the upper surface 41u of the negative electrode first conductive member <NUM>. The metal joined part <NUM> is provided at a position apart from the penetration hole <NUM>. The metal joined part <NUM> is provided on an outer peripheral side of the penetration hole <NUM>. The metal joined part <NUM> is provided at a position apart from the fastening part <NUM>. Thus, the thermal influence on the fastening part <NUM> and the like can be reduced. The metal joined part <NUM> can be a joined part with relatively higher stiffness than the fastening part <NUM>, for example.

The metal joined part <NUM> is provided on the inner peripheral side (on a center side of the flange part 42f) relative to the fastening part <NUM> in a plan view here. In other words, the metal joined part <NUM> is provided closer to a center 42c of the negative electrode second conductive member <NUM>. The metal joined part <NUM> can be a joined part with relatively lower strength (fragile) than the fastening part <NUM>. By arranging the aforementioned metal joined part <NUM> on the inner peripheral side of the fastening part <NUM>, the metal joined part <NUM> can be maintained stably and the conduction reliability of the negative electrode terminal <NUM> can be increased for a long time.

The metal joined part <NUM> is provided in the thin part 41t here. Thus, the energy at the joining can be saved and the weldability can be improved. The metal joined part <NUM> is formed continuously or intermittently. The metal joined part <NUM> is formed axially symmetrically about the axial center C of the flange part 42f. Thus, the strength of the metal joined part <NUM> can be increased and the conduction reliability of the negative electrode terminal <NUM> can be improved further.

As illustrated in <FIG>, the metal joined part <NUM> is formed in an annular shape (for example, circular shape) in a plan view. Thus, the strength (for example, tensile strength) of the metal joined part <NUM> can be increased and the conduction reliability of the negative electrode terminal <NUM> can be improved further. The metal joined part <NUM> is provided so as to surround the center 42c of the flange part 42f along the entire circumference here. As illustrated in <FIG>, the metal joined part <NUM> is provided so as to surround an outer edge of the penetration hole <NUM> using the axial center C of the flange part 42f as a center. By providing the metal joined part <NUM> at a periphery of the penetration hole <NUM>, the distortion or deformation due to heat at the welding can be released, so that the influence on the fastening part <NUM> and the like can be reduced. In the cross-sectional view in <FIG>, the metal joined part <NUM> is distinguished as follows: a metal joined part 45A on a side closer to the extension part 41b (on the left side in <FIG>); and a metal joined part 45B on a side farther from the extension part 41b (on the right side in <FIG>).

<FIG> is a magnified view schematically illustrating the vicinity of the metal joined part 45A on the side closer to the extension part 41b in <FIG> (on the left side in <FIG>). As illustrated in <FIG>, at a cross section being perpendicular to the sealing plate <NUM> (first surface), passing the axial center C of the shaft column part <NUM>, and extending in a radial direction of the shaft column part <NUM>, the metal joined part <NUM> includes a first region <NUM> and a second region <NUM>. As indicated by a dashed line in <FIG>, the negative electrode terminal <NUM> includes a border surface B passing a border part where the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> are in contact with each other around the metal joined part <NUM>. The border surface B extends in a direction parallel to the sealing plate <NUM> (specifically, the outer surface of the sealing plate <NUM> or the inner surface of the sealing plate <NUM>). In <FIG>, the border surface B passes the metal joined part <NUM>. The border surface B roughly divides the metal joined part <NUM> into the negative electrode first conductive member <NUM> side (upper side in <FIG>) and the negative electrode second conductive member <NUM> side (lower side in <FIG>).

In the present embodiment, the cross section is a first cross section (cross section taken along line VI-VI in <FIG>) passing the axial center C of the negative electrode second conductive member <NUM> and extending along the long side direction Y of the sealing plate <NUM> (first surface). However, for example, in a case where the metal joined part <NUM> has a shape other than the annular shape and the metal joined part <NUM> is not formed in this first cross section, the aforementioned cross section may be a second cross section with the smallest angle with the first cross section among the cross sections passing the axial center C of the negative electrode second conductive member <NUM> and extending in the radial direction of the negative electrode second conductive member <NUM>.

The first region <NUM> is a region where the first metal (here, Al) occupies <NUM> mass% or more. The first region <NUM> can be a region where the metal (mainly, second metal) included in the negative electrode second conductive member <NUM> is melted in the negative electrode first conductive member <NUM>. By suppressing the melting of the metal other than the first metal in the first region <NUM> to be less than <NUM> mass%, generation of a fragile intermetallic compound can be suppressed and the strength (for example, tensile strength) can be increased. The first region <NUM> exists mostly on the negative electrode first conductive member <NUM> side (upper side in <FIG>) relative to the border surface B and partially protrudes toward the negative electrode second conductive member <NUM> (lower side in <FIG>). The first region <NUM> includes a region A1 existing on the negative electrode first conductive member <NUM> side (upper side in <FIG>) relative to the border surface B and a first protrusion region P1 protruding toward the negative electrode second conductive member <NUM> (lower side in <FIG>) relative to the border surface B.

The second region <NUM> is a region where the second metal (here, Cu) occupies <NUM> mass% or more. The second region <NUM> can be a region where the metal (mainly, first metal) included in the negative electrode first conductive member <NUM> is melted in the negative electrode second conductive member <NUM>. By suppressing the melting of the metal other than the second metal in the second region <NUM> to be less than <NUM> mass%, the generation of the fragile intermetallic compound can be suppressed and the strength (for example, tensile strength) can be increased. In contrast to the first region <NUM>, the second region <NUM> exists mostly on the negative electrode second conductive member <NUM> side (lower side in <FIG>) relative to the border surface B and partially protrudes toward the negative electrode first conductive member <NUM> (upper side in <FIG>). The second region <NUM> includes a region A2 existing on the negative electrode second conductive member <NUM> side (lower side in <FIG>) relative to the border surface B and a second protrusion region P2 protruding toward the negative electrode first conductive member <NUM> (upper side in <FIG>) relative to the border surface B.

In this manner, in the present embodiment, the first region <NUM> includes the first protrusion region P1, the second region <NUM> includes the second protrusion region P2, and a border between the first region <NUM> and the second region <NUM> has an uneven shape. A border part between the first region <NUM> and the second region <NUM> is slippery and has low strength in general; however, when the border part has such an uneven shape and the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> are engaged with each other mechanically, the border part becomes less slippery and the joining strength (for example, tensile strength) can be improved. Additionally, by bending the border part, the distance of the border part can be extended; thus, even in the occurrence of a crack in the metal joined part <NUM>, the development of the crack can be slowed down. As a result, according to the art disclosed herein, even if force of vibration, impact, or the like is applied from the outside during the use, the close contact state between the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> can be kept easily and the conductive connection between the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> can be kept stably.

The metal joined part <NUM> where the first region <NUM> includes the first protrusion region P1 and the second region <NUM> includes the second protrusion region P2 can be achieved by performing circumferential welding (wobbling) at the welding, for example, as illustrated in <FIG>, which will be described in detail below.

Although not limited in particular, as illustrated in <FIG>, at the cross section being perpendicular to the sealing plate <NUM> (first surface), passing the axial center C of the shaft column part <NUM>, and extending in the radial direction of the shaft column part <NUM>, a ratio C1 of the area of the first protrusion region P1 to the total area of the first region <NUM> is preferably <NUM> to <NUM> (<NUM> to <NUM>%) and more preferably <NUM> to <NUM> (<NUM> to <NUM>%). Furthermore, a ratio C2 of the area of the second protrusion region P2 to the total area of the second region <NUM> is preferably <NUM> to <NUM> (<NUM> to <NUM>%) and more preferably <NUM> to <NUM> (<NUM> to <NUM>%). With the ratios in the aforementioned ranges, the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> can be mechanically engaged with each other more firmly. In addition, the development of the crack can be slowed down effectively. Therefore, the effect of the art disclosed herein can be achieved at a higher level. The ratio C2 of the area of the second protrusion region P2 is preferably larger than the ratio C1 of the area of the first protrusion region P1. Note that the aforementioned ratios C1 and C2 of the areas can be achieved by adjusting the conditions of the welding to be described below (for example, output of laser, frequency or width of wobbling, or the like).

As illustrated in <FIG>, at the cross section (here, cross section taken along line VI-VI in <FIG>) being perpendicular to the sealing plate <NUM> (first surface), passing the axial center C of the shaft column part <NUM>, and extending in the radial direction of the shaft column part <NUM>, a part of the border surface B that passes the metal joined part <NUM> is a line LB. At this time, it is preferable that a half (<NUM>%) or more of the line LB cross the second region <NUM>. When the line LB crosses the second region <NUM> containing a large amount of second metal with high hardness (here, Cu) with a probability of <NUM>% or more@@, the strength (for example, tensile strength) or the durability of the metal joined part <NUM> can be improved.

In a case where the negative electrode terminal <NUM> includes the fastening part <NUM>, in at least one of (preferably, both) the two metal joined parts <NUM> (metal joined part 45A and metal joined part 45B) included in the cross section in <FIG>, the second protrusion region P2 is preferably disposed closer to the fastening part <NUM> than the first protrusion region P1 at the cross section (here, cross section taken along line VI-VI in <FIG>) being perpendicular to the sealing plate <NUM> (first surface), passing the axial center C of the shaft column part <NUM>, and extending in the radial direction of the shaft column part <NUM> as illustrated in <FIG>. According to the present inventors' examination, when vibration, impact, or the like is applied to the fastening part <NUM>, the metal joined part <NUM> starts to be broken from the fastening part <NUM> side. Therefore, by arranging the second protrusion region P2 containing a large amount of second metal with relative high hardness (here, Cu) closer to the fastening part <NUM> than the first protrusion region P1 containing a large amount of first metal with relative low hardness (here, Al), the strength (for example, tensile strength) and the durability of the metal joined part <NUM> can be improved. Note that the positional relation between the first protrusion region P1 and the second protrusion region P2 can be adjusted by the condition of the welding (specifically, direction of rotation of wobbling) to be described below.

In the case where the negative electrode terminal <NUM> includes the extension part 41b and the busbar <NUM> is connected to the extension part 41b, in at least one of the metal joined part 45A and the metal joined part 45B (preferably both), it is preferable that the second protrusion region P2 be disposed closer to the extension part 41b (busbar connection region) than the first protrusion region P1 at the cross section being perpendicular to the sealing plate <NUM> (first surface) and extending along the long side direction Y of the sealing plate <NUM> (first surface) as illustrated in <FIG>. In particular, it is preferable that the second protrusion region P2 be disposed closer to the extension part 41b than the first protrusion region P1 in the metal joined part 45A on the side close to the extension part 41b (on the left side in <FIG>).

To the extension part 41b, force of vibration, impact, or the like is applied easily through the busbar <NUM>. When such force is applied to the extension part 41b, the metal joined part <NUM> starts to be broken from the extension part 41b side. Therefore, by arranging the second protrusion region P2 containing a large amount of second metal with relative high hardness (here, Cu) closer to the extension part 41b than the first protrusion region P1 containing a large amount of first metal with relative low hardness (here, Al), the strength (for example, tensile strength) and the durability of the metal joined part <NUM> can be improved. Note that the positional relation between the first protrusion region P1 and the second protrusion region P2 can be adjusted by the condition of the welding (specifically, direction of rotation of wobbling) to be described below.

As illustrated in <FIG>, the metal joined part <NUM> according to this embodiment additionally includes a third region <NUM> at the border between the first region <NUM> and the second region <NUM>. The third region <NUM> is a region where the first metal is contained by <NUM> mass% or more and less than <NUM> mass% and the second metal is contained by <NUM> mass% or more and less than <NUM> mass%. However, the third region <NUM> is not always necessary and can be omitted in another embodiment.

Although not limited in particular, the negative electrode terminal <NUM> as described above can be manufactured by, for example, preparing the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM> as described above and performing a manufacturing method including a fastening step and a welding joining step. Note that the order of the fastening step and the welding joining step is not limited in particular; however, from the viewpoint of suppressing the damage of the metal joined part <NUM> when the fastening part <NUM> is formed, the welding joining step is performed preferably after the fastening step. However, the fastening step may be performed after the welding joining step or both steps may be performed at substantially the same time. The manufacturing method disclosed herein may further include another step at an optional stage.

In the fastening step, the negative electrode first conductive member <NUM> and the flange part 42f of the negative electrode second conductive member <NUM> are mechanically fixed so as to form the fastening part <NUM>. The fastening part <NUM> can be formed in a manner that, for example, the constriction part 42n of the negative electrode second conductive member <NUM> is inserted into the concave part 41r of the negative electrode first conductive member <NUM> and the concave part 41r of the negative electrode first conductive member <NUM> is deformed along the outer shape of the constriction part 42n of the negative electrode second conductive member <NUM>, so that the inner wall of the concave part 41r is fixed by the negative electrode second conductive member <NUM>. Thus, the strength of the fastening part <NUM> can be improved. In some preferred embodiments, the fastening part <NUM> is formed by engaging the concave part 41r of the negative electrode first conductive member <NUM> and the constriction part 42n of the negative electrode second conductive member <NUM>. For example, the fastening part <NUM> can be formed by horizontally press-fitting the constriction part 42n of the negative electrode second conductive member <NUM> into the concave part 41r of the negative electrode first conductive member <NUM>. Thus, the workability of the fastening step can be improved.

In the welding joining step, the thin part 41t of the negative electrode first conductive member <NUM> and the flange part 42f of the negative electrode second conductive member <NUM> are joined by welding; thus, the metal joined part <NUM> is formed. By performing the welding joining step after the fastening step, the metal joined part <NUM> with the stable shape can be formed with high accuracy. The metal joined part <NUM> can be formed in a manner that, for example, the thin part 41t of the negative electrode first conductive member <NUM> and the flange part 42f of the negative electrode second conductive member <NUM> are stacked, an energy beam is delivered from the negative electrode first conductive member <NUM> (thin part 41t) side, and welding is performed so that the energy reaches at least the upper surface 42u of the flange part 42f through the thin part 41t. The welding is preferably performed by the method as described above, for example the laser welding.

Although not limited in particular, in a preferred embodiment, circumferential welding (wobbling) is performed using a single-mode fiber laser. <FIG> is an explanatory view for describing a method of the laser welding in the case of forming the annular metal joined part <NUM> as illustrated in <FIG>. <FIG> illustrates only a part of the thin part 41t for which the welding is performed in a plan view. Although not limited in particular, the annular metal joined part <NUM> may be formed as follows: welding starts from a welding start point (<NUM>), the whole laser travels clockwise and the rotation of the wobbling progresses counterclockwise, and thus, the laser light is delivered so as to draw an annular trace to a welding end point (<NUM>) while surrounding the outer edge of the penetration hole <NUM> as illustrated in <FIG>.

Note that the conditions of the welding (for example, output of laser, welding speed, conditions of wobbling (frequency or width), and the like) are design matters that can be adjusted as appropriate in accordance with, for example, the materials of the negative electrode first conductive member <NUM> and the negative electrode second conductive member <NUM>, the thickness of the negative electrode first conductive member <NUM>, and the like. In one example, the output of the laser is preferably about <NUM> to <NUM> W, more preferably <NUM> W or less, and still more preferably <NUM> to <NUM> W. Additionally, the welding speed is preferably about <NUM> to <NUM>/s and more preferably <NUM> to <NUM>/s. The frequency of the wobbling is preferably about <NUM> or less, and for example, <NUM> to <NUM>. The width of the wobbling is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>, for example. By such conditions, the negative electrode second conductive member <NUM> (Cu), which is melted less easily relatively, can be melted stably. Moreover, the melting depth can be prevented from becoming too deep and the melting of Cu of the negative electrode second conductive member <NUM> can be suppressed.

<FIG> is a schematic longitudinal cross-sectional view in the vicinity of the metal joined parts 45A and 45B taken along line IXB-IXB in <FIG>. When the laser light is delivered along the entire circumference once so as to surround the outer edge of the penetration hole <NUM> while keeping the direction of the rotation of the wobbling the same as illustrated in <FIG>, the second protrusion region P2 is disposed closer to the extension part 41b than the first protrusion region P1 in the metal joined part 45A on the side close to the extension part 41b at the cross section (cross section taken along line IXB-IXB in <FIG>) being perpendicular to the sealing plate <NUM> (first surface), passing the axial center C of the shaft column part <NUM>, and extending in the radial direction of the shaft column part <NUM>. On the other hand, in the metal joined part 45B on the side far from the extension part 41b, the first protrusion region P1 is disposed closer to the extension part 41b than the second protrusion region P2.

Note that the metal joined part <NUM> is formed on the inner peripheral side relative to the fastening part <NUM> here. Thus, the joined place is displaced less easily and the workability in the welding joining step can be improved. Moreover, the welding place shakes less easily when the metal joined part <NUM> is formed and thus, the weldability can be improved. Furthermore, here, since the thin part 41t is welded, the energy can be saved and the weldability can be improved.

The power storage device <NUM> and the power storage module <NUM> can be used for various applications, and can be suitably used in an application in which an external force such as vibration or impact may be applied during the use thereof and typically, used as a motive power source (driving power source) for a motor mounted on various vehicles such as a passenger car or a truck. Although the type of passenger cars is not particularly limited, examples thereof may include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), a battery electric vehicle (BEV), and the like.

Several Examples relating to the present disclosure will be explained below, but the disclosure is not meant to be limited to these Examples.

First, a first conductive member with a plate shape (material: aluminum (A1050)) and a second conductive member with a cylindrical shape (material: copper (C1100)) were prepared. Next, for each of Example and Comparative Example, the first conductive member and the second conductive member were overlapped and irradiated with the single-mode fiber laser from the first conductive member side; thus, the welding was performed under conditions shown in Table <NUM>. In this manner, the metal joined part was formed.

First, for each of Example and Comparative Example, a part where the metal joined part was formed was cut at the cross section along the center of the metal joined part of the second conductive member and embedded and polished; thus, an observation sample was manufactured. Next, the manufactured observation sample was subjected to an etching process using an etchant (etching solution in which ammonia water diluted to <NUM>% and hydrogen peroxide solution diluted to <NUM>% were mixed at a ratio of <NUM>:<NUM> and stirred) to change the color of the metal joined part, so that the border was made recognizable. Next, in the electron microscope system SU-<NUM> manufactured by Hitachi, the observation sample was photographed using a scanning electron microscope (SEM) and a cross-sectional image was obtained. Note that the measurement conditions were as follows. The SEM observation images are shown in <FIG>. Although not illustrated, the obtained SEM observation images were analyzed using energy dispersive X-ray spectroscopy (EDX), so that the distributions of the metal elements (Al, Cu) were analyzed.

<FIG> illustrates a trace of the laser welding and is a cross-sectional SEM observation image of the metal joined part in Comparative Example, and <FIG> illustrates a trace of the laser welding and is a cross-sectional SEM observation image of the metal joined part in Example. As shown in <FIG>, the metal joined part in Comparative Example in which the linear welding was performed was formed so as to be narrower as getting away from the surface on the welded side (in other words, welding depth becomes deeper). On the other hand, the metal joined part in Example in which the circumferential welding (wobbling) was performed as shown in <FIG> included the first region containing <NUM> mass% or more of Al (first metal) and including the first protrusion region and the second region containing <NUM> mass% or more of Cu (second metal) and including the second protrusion region, with the border part between the first region and the second region bent in an uneven shape as schematically illustrated in <FIG>. Therefore, it has been confirmed that the metal joined part disclosed herein can be suitably formed by, for example, the circumferential welding (wobbling).

In the present test example, the plurality of negative electrode terminals in which the positional relation between the first protrusion region P1 and the second protrusion region P2 of the metal joined part was changed were manufactured by changing the direction of the rotation of the wobbling (clockwise, counterclockwise) in Example of Test Example I. <FIG> is a plan view of the negative electrode terminal schematically illustrating a trace of the laser welding in Example <NUM>, and <FIG> is a plan view of the negative electrode terminal schematically illustrating a trace of the laser welding in Example <NUM>.

That is to say, in Example <NUM>, in the laser welding, the welding started from the welding start point (<NUM>), the whole laser traveled from the lower side to the upper side (clockwise) in <FIG> and the rotation of the wobbling progressed clockwise, and thus, the laser light was delivered so as to draw a trace with a line shape to the welding end point (<NUM>) as illustrated in <FIG>. On the other hand, in Example <NUM>, in the laser welding, the welding started from the welding start point (<NUM>), the whole laser traveled from the lower side to the upper side (clockwise) in <FIG> and the rotation of the wobbling progressed counterclockwise (reverse rotation of Example <NUM>), and thus, the laser light was delivered so as to draw a trace with a line shape to the welding end point (<NUM>) as illustrated in <FIG>. Note that the output of the laser was changed to <NUM> W in Example <NUM> and Example <NUM>.

The SEM observation of the metal joined parts formed in this manner indicates that the first protrusion region P1 existed closer to the busbar connection region (on the left side in <FIG>) than the second protrusion region P2 in Example <NUM> as illustrated in <FIG>. On the other hand, in Example <NUM>, the second protrusion region P2 existed closer to the busbar connection region than the first protrusion region P1. In Example <NUM>, the positional relation between the first protrusion region P1 and the second protrusion region P2 is the same as that of the metal joined part <NUM> in <FIG> described in the aforementioned embodiment. Example <NUM> is an example of the metal joined part obtained by performing mirror inversion in a symmetrical manner on the metal joined part in Example <NUM>.

Next, a busbar was welded to the extension part (busbar connection region) of the negative electrode terminal in each example. Next, a commercial tensile tester was prepared and the second conductive member was held with a clamp of the tensile tester. Then, based on JIS K <NUM>-<NUM> (determination of peel strength of bonded assemblies-part <NUM>: <NUM>° peel), the busbar was pulled in a vertical direction (<NUM>°-direction) so as to peel the busbar from the first conductive member in the tensile tester, and the strength at which the metal joined part was broken was measured as the tensile strength (N). The results are expressed in <FIG>. Note that as the numeral of the tensile strength is higher, it means that the joining strength is higher.

As expressed in <FIG>, the tensile strength was relatively higher in Example <NUM> in which the second protrusion region P2 was disposed close to the busbar connection region than in Example <NUM> in which the first protrusion region P1 was disposed close to the busbar connection region. Therefore, it has been understood that the metal joined part can have higher strength and durability by disposing the second protrusion region P2 on the busbar connection region side.

Although some embodiments of the present disclosure have been described above, these embodiments are just examples. The present disclosure can be implemented in various other modes. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. The techniques described in the scope of claims include those in which the embodiments exemplified above are variously modified and changed. For example, a part of the aforementioned embodiment can be replaced by another modified aspect, and the other modified aspect can be added to the aforementioned embodiment. Additionally, the technical feature may be deleted as appropriate unless such a feature is described as an essential element.

<First modification> For example, in the aforementioned embodiment, the metal joined part <NUM> was formed in the annular shape (for example, circular shape) in a plan view as illustrated in <FIG>. Moreover, the metal joined part <NUM> was formed by delivering the laser so as to draw the annular trace as illustrated in <FIG>. However, the present disclosure is not limited to this example. In a modification, the metal joined part <NUM> may be formed in a C shape, a semi-circular arc shape, a double or more circular shape, a spiral shape, a linear shape, a dashed line shape, or the like in a plan view. The metal joined part <NUM> may be formed by performing the laser welding twice or more.

<FIG> is a diagram corresponding to <FIG> in a first modification. For example, in a case of forming a metal joined part <NUM> with a substantially annular shape including two semi-circular arc shapes, for example, first, the welding may start from the welding start point (<NUM>), the whole laser may travel clockwise and the rotation of the wobbling may progress clockwise, and thus, the laser light may be delivered so as to draw a semi-circular trace to the welding end point (<NUM>) along the outer edge of the penetration hole <NUM> as illustrated in <FIG>. Next, the welding may start from a welding start point (<NUM>), the whole laser may travel clockwise and the rotation of the wobbling may progress counterclockwise (direction of rotation is changed), and the laser light may be delivered so as to draw a semi-circular trace to a welding end point (<NUM>) along the outer edge of the penetration hole <NUM>.

<FIG> is a diagram corresponding to <FIG> in the first modification. If the laser light is delivered by changing the direction of the rotation of the wobbling in the middle as illustrated in <FIG>, the second protrusion region P2 is disposed closer to the extension part 41b than the first protrusion region P1 in both the two metal joined parts <NUM> (metal joined part 145A and metal joined part 145B) at the cross section taken along line XIIIB-XIIIB in <FIG>. Thus, the metal joined part <NUM> can have higher strength and durability than in the aforementioned embodiment.

<Second modification> For example, in the aforementioned embodiment, the negative electrode first conductive member <NUM> is sectioned into the connection part 41a and the extension part 41b in the long side direction Y and the extension part 41b is disposed on one side in the long side direction Y. Moreover, the busbar <NUM> is attached to the extension part 41b, avoiding the connection part 41a. However, the present disclosure is not limited to this example. In the modification, the negative electrode first conductive member <NUM> does not need to be sectioned into the connection part 41a and the extension part 41b in the long side direction Y. In this case, for example, the busbar <NUM> may be attached to a central part of the negative electrode first conductive member <NUM> in the long side direction Y or may be attached to an outer edge part of the negative electrode first conductive member <NUM>.

<FIG> is a diagram corresponding to <FIG> in a second modification. As illustrated in <FIG>, in a negative electrode terminal <NUM> in this modification, a connection part 241a is disposed at a central part of a negative electrode first conductive member <NUM> in the long side direction Y. Moreover, a busbar <NUM> is attached to the central part in the long side direction Y so as to cover an entire thin part 241t from above. In this case, the welding part W between the busbar <NUM> and the negative electrode first conductive member <NUM> is provided at an outer peripheral part of a metal joined part <NUM>. Note that a negative electrode second conductive member <NUM> may be similar to the negative electrode second conductive member <NUM> in the aforementioned embodiment.

<FIG> is a schematic longitudinal cross-sectional view in a vicinity of metal joined parts 245A and 245B taken along line XV-XV in <FIG>. At a cross section taken along line XV-XV in <FIG>, in both the metal joined parts 245A and 245B, the second protrusion region P2 is disposed closer to the welding part W with the busbar <NUM> than the first protrusion region P1. Thus, the metal joined part <NUM> can have higher strength and durability similarly to the first modification. The metal joined part <NUM> as described above can be manufactured similarly to the aforementioned embodiment.

Claim 1:
A power storage device (<NUM>) comprising:
an electrode body (<NUM>) that includes a first electrode and a second electrode;
a battery case (<NUM>) that accommodates the electrode body (<NUM>) and includes a first surface (<NUM>) where a penetration hole (<NUM>) is provided; and
a first electrode terminal (<NUM>) that penetrates the penetration hole (<NUM>) of the battery case (<NUM>) and is electrically connected to the first electrode, wherein
the first electrode terminal (<NUM>) includes a first conductive member (<NUM>) in which a first metal occupies a maximum ratio on a mass basis, a second conductive member (<NUM>) in which a second metal that is different from the first metal occupies a maximum ratio on a mass basis, the second conductive member (<NUM>) having a shaft part (<NUM>) disposed in the penetration hole (<NUM>), and a metal joined part (<NUM>) where the first conductive member (<NUM>) and the second conductive member (<NUM>) are joined,
the metal joined part (<NUM>) includes, at a cross section being perpendicular to the first surface (<NUM>), passing an axial center (C) of the shaft part (<NUM>), and extending in a radial direction of the shaft part (<NUM>), a first region (<NUM>) in which the first metal occupies <NUM> mass% or more and a second region (<NUM>) in which the second metal occupies <NUM> mass% or more, and
when a surface passing a border part where the first conductive member (<NUM>) and the second conductive member (<NUM>) are in contact with each other around the metal joined part (<NUM>) is a border surface (B), the first region (<NUM>) includes a region (A1) that exists on a side of the first conductive member (<NUM>) relative to the border surface (B) and a first protrusion region (P1) that protrudes toward the second conductive member (<NUM>) relative to the border surface (B), and the second region (<NUM>) includes a region (A2) that exists on a side of the second conductive member (<NUM>) relative to the border surface (B) and a second protrusion region (P2) that protrudes toward the first conductive member (<NUM>) relative to the border surface (B).