Patent Description:
Assembled batteries formed through mutual electrical connection of multiple unit cells are used for instance as high-output power sources for vehicle drive. Examples of unit cells that constitute such an assembled battery include secondary batteries such as lithium ion secondary batteries. This kind of secondary battery has for instance an electrode body that constitutes a power generation element, a battery case that accommodates the electrode body, terminals electrically connected to the electrode body, and external conductive members joined to the terminals outside the battery case. Members may be joined to other members in the production process of the secondary battery.

Japanese Patent Application <CIT> describes projecting energy rays to thereby join, to each other, members that make up a secondary battery. European Patent Application <CIT>, which is prior art under Art. <NUM>(<NUM>) EPC, discloses a secondary battery similar to that of claim <NUM> without, however, an annular recess that has a tapered inner wall surface that widens from a bottom surface of the recess towards the upper surface of the external conductive member. Another secondary battery and method for manufacturing the same is known from <CIT>, forming the basis for the preamble of claim <NUM>.

In an assembled battery, for instance two adjacent unit cells are connected to each other through bridging, via bus bars, of the external conductive members of the two unit cells. The inventors aspire herein to achieve more stable joining of external conductive members and bus bars.

The art disclosed herein provides a method for producing a secondary battery that has: an electrode body including a positive electrode and a negative electrode; a battery case that accommodates the electrode body; a terminal electrically connected to the positive electrode or the negative electrode, and attached to the battery case; and an external conductive member having a through-hole, and joined to the terminal outside the battery case. The above production method has: an attachment step of attaching the terminal to the battery case; an arrangement step of arranging part of the terminal, attached to the battery case, within the through-hole of the external conductive member; a covering step of, after the arrangement step, covering at least part of an upper surface of the external conductive member with a cover member; and a joining step of, after the covering step, joining the external conductive member and the terminal through irradiation of energy rays. The external conductive member has a substantially annular recess, sunk from the upper surface of the external conductive member, around the through-hole; in a plan view, a shortest distance from a peripheral edge of the through-hole up to the outer peripheral edge of the recess is <NUM> or larger; and in the joining step, the external conductive member and the terminal are joined in a state where an edge portion of the cover member is disposed between a planned joint portion of the external conductive member and the terminal, and an outer peripheral edge of the recess, in a cross-sectional view along a direction of penetration into the through-hole.

A production method having such features adhesion of spatter to the upper surface of the external conductive member can be suppressed, since the external conductive member and the terminal are joined to each other in a state where the upper surface of the external conductive member around the through-hole is covered with the cover member. The external conductive member and the bus bar can be joined more stably as a result.

In a preferred implementation of the production method disclosed herein, the cover member has an opening; and the inner diameter of the opening is smaller than the outer diameter of the recess. The effect of the art disclosed herein can be realized yet better by using a cover member having such a configuration.

In another preferred implementation of the production method disclosed herein, a region of overlap of the cover member and the recess, in a plan view, has an annular shape. Such a configuration yet better allows realizing the effect of the art disclosed herein.

In another preferred implementation of the production method disclosed herein, an inner wall surface of the recess is a tapered surface that widens from a bottom surface of the recess towards the upper surface of the external conductive member. In addition to the above effects, such a configuration allows suppressing deformation of the external conductive member at the time of formation of the recess.

In another preferred implementation of the production method disclosed herein, the cover member having an opening is used in the covering step. The upper surface of the external conductive member is covered by the cover member so that an inner edge of the opening overlaps the tapered surface. In addition to the effect of stabilizing joining of the external conductive member and the bus bar, such a configuration allows eliciting also the effect of suppressing deformation of the external conductive member at the time of formation of the recess.

In another preferred implementation of the production method disclosed herein, a ratio (W2/W1) of the shortest distance W1 and a shortest distance W2 from a boundary of the tapered surface and the bottom surface, in a plan view, up to the outer peripheral edge of the recess, is <NUM> or higher. Such a configuration allows bringing out both the above joining stabilization effect and the above deformation suppression effect.

The art disclosed herein provides also a method for producing an assembled battery in which multiple unit cells are connected to each other with a bus bar. The method for producing an assembled battery includes producing a secondary battery as the unit cell, in accordance with the above method for producing a secondary battery, and arranging the bus bar on the upper surface of the external conductive member, and connecting the external conductive member and the bus bar. An assembled battery production method having such features allows joining bus bars to external conductive members more stably.

The art disclosed herein provides also a secondary battery that has: an electrode body including a positive electrode and a negative electrode; a battery case that accommodates the electrode body; a terminal electrically connected to the positive electrode or the negative electrode, and attached to the battery case; and an external conductive member joined to the terminal outside the battery case. In this secondary battery the external conductive member has a through-hole, and part of the terminal is disposed within the through-hole. Around the through-hole there are provided a joint portion of the external conductive member and the terminal, and a substantially annular recess, sunk from the upper surface of the external conductive member, wherein an inner wall surface of the recess is a tapered surface that widens from a bottom surface of the recess towards the upper surface of the external conductive member. A shortest distance W1 from a peripheral edge of the through-hole up to the outer peripheral edge of the recess, in a plan view, is <NUM> or larger.

In a secondary battery having such a configuration the external conductive member and the terminal disposed within the through-hole that, in turn provided within the recess sunk from the upper surface of the external conductive member, are joined to each other in the periphery of the through-hole. The terminal and the external conductive member can be joined to each other at the portion recessed from the upper surface of the external conductive member. There is a distance of <NUM> or more from the peripheral edge of the through-hole to the outer peripheral edge of the recess, in a plan view. The upper surface can be kept removed from the joint site of the terminal and the external conductive member, and adhesion of spatter to the upper surface can be suppressed at the time of joining. The external conductive member and the bus bar can be joined more stably as a result.

In addition to the effect of stabilizing joining of the external conductive member and the bus bar, such a configuration allows eliciting the effect of suppressing deformation of the external conductive member at the time of formation of the recess, and the effect of suppressing generation of heat at the time of energization.

In another preferred implementation of the secondary battery disclosed herein, a ratio (W2/W1) of the shortest distance W1 and a shortest distance W2 from a boundary of the tapered surface and the bottom surface, in a plan view, up to the outer peripheral edge of the recess, is <NUM> or higher. Such a configuration allows yet better bringing out the above effects.

In another preferred implementation of the secondary battery disclosed herein, the secondary battery has a current collector member that electrically connects the positive electrode or the negative electrode, and the terminal. A fuse portion is formed in the current collector member. The fuse portion is configured to fuse when a current of <NUM> A or more flows in the secondary battery. In addition to the above effects, such a configuration also further enhances safety.

The art disclosed herein further provides an assembled battery in which multiple unit cells are connected to each other by way of a bus bar. The assembled battery has the above secondary battery, as the unit cell. The bus bar is disposed on the upper surface of the external conductive member, and the unit cells are connected to each other by way of the bus bar. In an assembled battery having such a configuration the bus bar is joined more stably to the external conductive member.

In a preferred implementation of the assembled battery disclosed herein, the bus bar covers the through-hole and the recess. In addition to the above effects, such a configuration allows bringing out the effect of suppressing generation of heat at the time of energization.

Preferred embodiments of the art disclosed herein will be explained next with reference to accompanying drawings. Needless to say, the embodiments described explained herein are not meant to limit the present invention in any particular way. The drawings are drawn schematically, and do not necessarily reflect actual items. Members and portions eliciting identical effects are denoted by identical reference symbols, and a recurrent explanation thereof will be omitted. Any features other than the matter specifically set forth in the present specification and that may be necessary for carrying out the art disclosed herein (for instance general configurations and production processes of batteries secondary batteries and not being characterizing features of the art disclosed herein) can be grasped as instances of design matter for a person skilled in the art based on known art in the relevant technical field. The art disclosed herein can be realized on the basis of the disclosure of the present specification and common technical knowledge in the relevant technical field. In the present specification a numerical value range notated as "A to B" denotes values "equal to or larger than A and equal to or smaller than B", and may encompass instances of values being greater than A and smaller than B.

In the present specification, the term "secondary battery" denotes a power storage device in general capable of being repeatedly charged and discharged, and encompasses conceptually so-called storage batteries (chemical batteries) such as lithium ion secondary batteries and nickel-metal hydride batteries, as well as capacitors such as electrical double layer capacitors.

The reference symbol X in the reference drawings of the present specification denotes a "depth direction", the reference symbol Y denotes a "width direction", and the reference symbol Z denotes a "height direction". Further, F in the depth direction X denotes "front" and Rr denotes "rear". Similarly, L in the width direction Y denotes "left" and R denotes "right". Further, U in the height direction Z denotes "up (top)" and D denotes "down (bottom)". However, the foregoing are merely directions for convenience of explanation, and are not meant to limit in any way the manner in which a secondary battery is installed, or the manner in which an assembled battery is installed.

<FIG> is a perspective-view diagram illustrating schematically a secondary battery according to an embodiment. <FIG> is a cross-sectional diagram along line II-II of <FIG>. As illustrated in <FIG>, the secondary battery <NUM> has a battery case <NUM>, an electrode body <NUM>, a positive electrode terminal <NUM>, a negative electrode terminal <NUM>, external conductive members <NUM>, <NUM>, a positive electrode current collector member <NUM>, a negative electrode current collector member <NUM>, insulators <NUM>, gaskets <NUM> and external insulating members <NUM>. Although explained in detail further on, the positive electrode current collector member <NUM> has a first collector portion <NUM> and second collector portions <NUM>. The negative electrode current collector member <NUM> has a first collector portion <NUM> and second collector portions <NUM>. In the present embodiment the secondary battery <NUM> is a lithium ion secondary battery. Although not illustrated in the figures, the secondary battery <NUM> further includes an electrolyte solution. Electrolyte solutions used in various lithium ion secondary batteries may be used, without particular limitations, as the electrolyte solution. The electrolyte solution is not a characterizing feature of the art disclosed herein, and hence a detailed explanation thereof will be omitted.

In the present embodiment the battery case <NUM> is a housing that accommodates the electrode body <NUM> and the electrolyte solution. The battery case <NUM> has herein a flat and bottomed cuboid (square) external shape. The material of the battery case <NUM> is not particularly limited, and may be identical to conventionally used materials. The battery case <NUM> is preferably made of a metal, and is more preferably made up of for instance aluminum, an aluminum alloy, iron, or an iron alloy.

In the present embodiment the battery case <NUM> has an exterior body <NUM> and a sealing plate (lid) <NUM>. As illustrated in <FIG>, the exterior body <NUM> includes a flat rectangular bottom portion 12a, a pair of mutually opposing first side walls 12b extending in the height direction Z from a pair of opposing sides of the bottom portion 12a, and a pair of mutually opposing second side walls 12c extending in the height direction Z from another pair of opposing sides of the bottom portion 12a. In the present embodiment the first side walls 12b are long side walls extending from a pair of opposing long sides of the bottom portion 12a. The second side walls 12c are short side walls extending from a pair of opposing short sides of the bottom portion 12a. In the present embodiment the surface area of the second side walls 12c is smaller than the surface area of the first side walls 12b. A portion facing the bottom portion 12a and surrounded by the pair of first side walls 12b and the pair of second side walls 12c constitutes an opening <NUM>. A sealing plate <NUM> is a member that seals the opening <NUM> of the exterior body <NUM>. The sealing plate <NUM> opposes the bottom portion 12a of the exterior body <NUM>. The sealing plate <NUM> has a substantially rectangular shape in a plan view. The battery case <NUM> is integrated through joining of the sealing plate <NUM> to the peripheral edge of the opening of the exterior body <NUM>. The joining means is for instance welding such as laser welding. The battery case <NUM> is hermetically (air-tight) sealed.

The sealing plate <NUM> has a liquid injection hole <NUM> and a gas discharge valve <NUM>. The purpose of the liquid injection hole <NUM> is to inject an electrolyte solution after assembly of the sealing plate <NUM> to the exterior body <NUM>. The liquid injection hole <NUM> is sealed by a sealing member <NUM>. The gas discharge valve <NUM> is a thin portion configured to break, and release gas to the exterior of the battery case <NUM>, when the pressure within the battery case <NUM> exceeds a predetermined value.

<FIG> is a perspective-view diagram illustrating an electrode body attached to a sealing plate. <FIG> is a perspective-view diagram illustrating an electrode body having second collector portions attached thereto. As illustrated in <FIG>, the secondary battery <NUM> has three electrode assemblies <NUM>. As illustrated in <FIG>, the second collector portions <NUM> of the positive electrode current collector member <NUM> are disposed on one side in a long-side direction Y (left side in <FIG>), and the second collector portions <NUM> of the negative electrode current collector member <NUM> are disposed on the other side (right side in <FIG>), the collector portions of respective polarity being connected in parallel. As illustrated in <FIG>, one or more electrode assemblies <NUM> are disposed inside the exterior body <NUM> while covered with an electrode body holder <NUM> made up of a resin-made sheet of polypropylene (PP) or the like. The number of electrode assemblies <NUM> accommodated in the secondary battery <NUM> is not particularly limited, and may be for instance one or two, or four or more.

Each electrode body <NUM>, which is a power generation element of secondary battery <NUM>, has a positive electrode and a negative electrode. <FIG> is a schematic diagram for explaining the configuration of the electrode body. As illustrated in <FIG>, each electrode body <NUM> has a positive electrode plate <NUM>, a negative electrode plate <NUM>, and a respective separator <NUM> disposed between the positive electrode plate <NUM> and the negative electrode plate <NUM>. As illustrated in <FIG>, the electrode body <NUM> is a wound electrode body in which a strip-shaped positive electrode plate <NUM> and a strip-shaped negative electrode plate <NUM> are laid up on each other via a respective strip-shaped separator <NUM>, with the resulting stack wound in the longitudinal direction. As illustrated in <FIG>, the electrode body <NUM> has a main body 20a, a positive electrode tab group <NUM>, and a negative electrode tab group <NUM>. The main body 20a is a portion at which the positive electrode plate <NUM>, the negative electrode plate <NUM>, and the separators <NUM> are laid up on each other, and has for instance a flat shape.

The width of the main body 20a is for instance <NUM> or larger. The width of the main body 20a may be for instance <NUM> or larger. The width of the main body 20a may be for instance <NUM> or smaller, or <NUM> or smaller. In the present specification the term "width of the main body 20a" denotes (width direction Y in <FIG>) instance the length of the main body 20a in the transverse direction of the negative electrode plate <NUM>.

As illustrated in <FIG> and <FIG>, the electrode body <NUM> is disposed inside the exterior body <NUM> so that a winding axis WL is parallel to the width direction Y. In the present embodiment the electrode body <NUM> is disposed inside the exterior body <NUM> in an orientation such that the winding axis WL is parallel to the bottom portion 12a and perpendicular to the second side walls 12c. The end surfaces of the electrode body <NUM> in the direction along the winding axis WL oppose respective second side walls 12c of the exterior body <NUM>. In the present specification, for convenience of explanation, the end surface of each electrode body <NUM> (for instance the main body 20a) opposing a respective second side wall 12c, on the side closer to the positive electrode current collector member <NUM> (left side in the width direction Y, in <FIG> and <FIG>), will be referred to as "first end surface <NUM>". Similarly, the end surface of each electrode body <NUM> (for instance the main body 20a) opposing a respective second side wall 12c, on the side closer to the negative electrode current collector member <NUM> (right side in the width direction Y, in <FIG> and <FIG>), will be referred to as "second end surface <NUM>".

The positive electrode plate <NUM> has an elongated strip-shaped positive electrode current collector foil 22c (for instance of aluminum foil) and a positive electrode active material layer 22a fixed on at least one surface of the positive electrode current collector foil 22c. Although not particularly limited thereto, a positive electrode protective layer 22p may be provided on one side edge portion of the positive electrode plate <NUM> in the width direction Y, as needed. Materials utilized in this kind of secondary batteries (a lithium ion secondary battery in the present embodiment) can be used, without particular limitations, as the materials that make up the positive electrode active material layer 22a and the positive electrode protective layer 22p; such materials are not a characterizing feature of the art disclosed herein, and accordingly a detailed explanation thereof will be omitted.

A plurality of positive electrode tabs 22t is provided at one end (left end in <FIG>) of the positive electrode current collector foil 22c in the width direction Y. The positive electrode tabs 22t protrude towards one side in the width direction Y (left side in <FIG>). The positive electrode tabs 22t are provided at intervals (intermittently) in the longitudinal direction of the positive electrode plate <NUM>. The positive electrode tabs 22t, which are part of the positive electrode current collector foil 22c, constitute a portion (collector foil exposed portion) of the positive electrode current collector foil 22c at which the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed. In the present embodiment the positive electrode tabs 22t protrude in the width direction Y beyond the separator <NUM>. For instance the positive electrode tabs 22t are stacked at one end (left end in <FIG>) in the width direction Y, to configure the positive electrode tab group <NUM> (see <FIG>). As illustrated in <FIG>, the positive electrode current collector member <NUM> is joined to the positive electrode tab group <NUM>.

The negative electrode plate <NUM> has an elongated strip-shaped negative electrode current collector foil 24c (for instance copper foil) and a negative electrode active material layer 24a fixed on at least one surface of the negative electrode current collector foil 24c. Materials utilized in this kind of secondary batteries (a lithium ion secondary battery in the present embodiment) can be used, without particular limitations, as the materials that make up the negative electrode active material layer 24a; such materials are not a characterizing feature of the art disclosed herein, and accordingly a detailed explanation thereof will be omitted.

A plurality of negative electrode tabs 24t is provided at one end (right end in <FIG>) of the negative electrode current collector foil 24c in the width direction Y. The negative electrode tabs 24t protrude towards one side in the width direction Y (right side in <FIG>). The negative electrode tabs 24t are provided at intervals (intermittently) in the longitudinal direction of the negative electrode plate <NUM>. The negative electrode tabs 24t, which are part of the negative electrode current collector foil 24c, constitute a portion (collector foil exposed portion) of the negative electrode current collector foil 24c at which the negative electrode active material layer 24a is not formed. In the present embodiment the negative electrode tabs 24t protrude in the width direction Y beyond the separator <NUM>. For instance the negative electrode tabs 24t are stacked at one end (right end in <FIG>) in the width direction Y, to configure the negative electrode tab group <NUM> (see <FIG>). As illustrated in <FIG>, the negative electrode current collector member <NUM> is joined to the negative electrode tab group <NUM>.

Each separator <NUM> is a member that insulates the positive electrode active material layer 22a of the positive electrode plate <NUM> and the negative electrode active material layer 24a of the negative electrode plate <NUM>. The separator <NUM> constitutes the outer surface of the electrode body <NUM>. For instance, a porous sheet produced out of a resin made up of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) may be used as the separator <NUM>.

As illustrated in <FIG>, the positive electrode terminal <NUM> and the negative electrode terminal <NUM> are attached to the sealing plate <NUM>. In the present embodiment the positive electrode terminal <NUM> is disposed at one end (left end in <FIG>) of the sealing plate <NUM> in the long-side direction Y. In the present embodiment the negative electrode terminal <NUM> is disposed at the other end (right end in <FIG>) of the sealing plate <NUM> in the long-side direction Y. The positive electrode terminal <NUM> and the negative electrode terminal <NUM> are examples of terminals.

As illustrated in <FIG>, the positive electrode terminal <NUM> is electrically connected to the positive electrode plate <NUM> (see <FIG>) of the electrode body <NUM> via the positive electrode current collector member <NUM>, within the exterior body <NUM>. The positive electrode terminal <NUM> is inserted through a terminal lead-out hole <NUM> and is led out from the interior of the sealing plate <NUM>. The positive electrode terminal <NUM> is insulated from the sealing plate <NUM> by a respective insulator <NUM> and a respective gasket <NUM>. The positive electrode terminal <NUM> is preferably made of a metal, and is more preferably made up of for instance aluminum or an aluminum alloy. An external conductive member <NUM> is fixed on the positive electrode terminal <NUM>. The positive electrode terminal <NUM> is joined to the external conductive member <NUM>.

<FIG> is a partial enlarged-view diagram of an enlargement of the vicinity of the positive electrode terminal <NUM> in <FIG>. <FIG> is a partial enlarged-view diagram of an enlargement of part of <FIG>. As illustrated in <FIG>, the positive electrode terminal <NUM> has an insertion portion 30a, a flange portion 30b, and a projecting portion 30c.

The external shape of the insertion portion 30a is smaller than that of the terminal lead-out hole <NUM> of the sealing plate <NUM>. In the present embodiment the insertion portion 30a runs through the sealing plate <NUM> of the battery case <NUM>. As illustrated in <FIG>, the insertion portion 30a is sequentially inserted, from the sealing plate <NUM> side, through the interior of a tubular portion <NUM> of the gasket <NUM>, the terminal lead-out hole <NUM> of the sealing plate <NUM>, a hole <NUM> of the respective insulator <NUM>, and a hole <NUM> of the first collector portion <NUM>. The lower end of the insertion portion 30a is joined to the first collector portion <NUM> for instance by welding or mechanical joining (crimping or the like).

The flange portion 30b is for instance a portion (large-diameter portion) having a larger external shape than that of the terminal lead-out hole <NUM> of the sealing plate <NUM>. In the present embodiment the flange portion 30b is disposed at the upper end of the insertion portion 30a. As illustrated in <FIG>, the flange portion 30b protrudes from the terminal lead-out hole <NUM>, and is disposed outside the battery case <NUM>. The flange portion 30b is disposed on the upper surface of the sealing plate <NUM> (on the farther surface from the exterior body <NUM>). The flange portion 30b is formed to for instance a substantially circular shape, or a polygonal shape such as a quadrangular shape, in a plan view. For instance an external conductive member <NUM> is disposed over the flange portion 30b. The flange portion 30b is in direct contact with the external conductive member <NUM>.

The projecting portion 30c is for instance a portion that protrudes upward (away from to the insertion portion 30a), from the upper end of the flange portion 30b. As illustrated in <FIG>, the projecting portion 30c is disposed in (inserted into) a through-hole <NUM> of the external conductive member <NUM>. In the present embodiment the projecting portion 30c is joined to the external conductive member <NUM>. A joint portion 31w with the external conductive member <NUM> is formed on the projecting portion 30c. The projecting portion 30c is formed in a substantially annular shape (preferably a circular ring shape), in a plan view. The projecting portion 30c may however be formed in a columnar shape (solid shape).

The external conductive member <NUM> is for instance a member joined to the positive electrode terminal <NUM> outside the battery case <NUM>. The external conductive member <NUM> has a substantially rectangular shape that is elongated in the long-side direction Y, as illustrated in <FIG>. The external conductive member <NUM> is preferably plate-shaped. The external conductive member <NUM> is for instance made up of a metal. The external conductive member <NUM> is preferably made up of aluminum or an aluminum alloy. For instance the external conductive member <NUM> is attached to the sealing plate <NUM>, on the positive electrode side of the secondary battery <NUM>, in a state of being insulated from the sealing plate <NUM> by a respective external insulating member <NUM>. In the present embodiment a lower surface 35d of the external conductive member <NUM> is disposed on the sealing plate <NUM> side. A respective bus bar is joined to the external conductive member <NUM>, for instance during construction of an assembled battery. In the present embodiment a bus bar is joined to an upper surface 35u, on the reverse side from that of the lower surface 35d. The upper surface 35u and the lower surface 35d will be further described further on.

In the present embodiment the external conductive member <NUM> is joined to the positive electrode terminal <NUM> at the joint portion 31w.

The terminal and the external conductive member are joined for instance by irradiation with energy rays, for example by laser welding. For instance when energy rays are projected onto the site envisaged for joining, spatter may fly off and adhere to the external conductive member. The inventors endeavored to suppress adhesion of scattered spatter to the external conductive member at the time of joining of the terminal and the external conductive member, and to achieve yet more stable joining between the external conductive member and the bus bar. To that end, the inventors diligently studied the shape of the external conductive member and methods for joining the terminal and the external conductive member.

As illustrated in <FIG>, the external conductive member <NUM> has the through-hole <NUM>. The through-hole <NUM> is for instance substantially circular in a plan view. In the present embodiment the through-hole <NUM> is provided closer to one end in the long-side direction (for instance the left end in the width direction Y in <FIG>) than the center of the external conductive member <NUM> in the long-side direction. In the present embodiment part of the positive electrode terminal <NUM> (for instance the projecting portion 30c) is disposed within the through-hole <NUM>. The joint portion 31w at which the external conductive member <NUM> and the positive electrode terminal <NUM> (in the figure, the projecting portion 30c) are joined to each other is provided around the through-hole <NUM>. In the present embodiment the joint portion 31w is a weld joint provided through welding resulting from projection of energy rays.

The joint portion 31w is provided for instance as a substantially annular shape (for instance a circular ring shape), in a plan view. For instance the formation width (for example the ring width) of the joint portion 31w in the radial direction of the through-hole <NUM> is preferably set to be <NUM> to <NUM>, in order to stabilize the joint between the external conductive member <NUM> and the positive electrode terminal <NUM>. The joint portion 31w is preferably provided continuously. Alternatively, the joint portion 31w may be provided intermittently or in the form of a dashed line. For instance, the joint portion 31w may be provided to be axially symmetrical with respect to the axis of the positive electrode terminal <NUM>.

In the present embodiment, a substantially annular first recess 35a that is sunk from the upper surface 35u of the external conductive member <NUM> is provided around the through-hole <NUM>. In the present specification the "upper surface 35u of the external conductive member <NUM>" denotes one end surface of the external conductive member <NUM>, in the direction of penetration into the through-hole <NUM> (for instance direction Z in <FIG>), on the reverse side from that of the sealing plate <NUM>. As illustrated in <FIG>, the diameter of the first recess 35a is larger than the diameter of the through-hole <NUM>. The first recess 35a is provided so as to surround the periphery of the joint portion 31w. As illustrated in <FIG>, an inner wall surface 35a2 of the first recess 35a extends, substantially vertically, from a bottom surface 35a1 towards the upper surface 35u. The angle formed by the inner wall surface 35a2 and the bottom surface 35a1 is for instance from <NUM> degrees to <NUM> degrees. The first recess 35a is an example of the "recess".

In the present embodiment a shortest distance W1 from the peripheral edge of the through-hole <NUM> to the outer peripheral edge of the first recess 35a in a plan view, as seen from the direction of arrow A in <FIG> (hereafter also simply referred to as "distance W1"), is <NUM> or larger (for instance <NUM> or larger). When the distance W1 lies within the above range, adhesion of spatter to the upper surface 35u can be suppressed in the production process of the secondary battery <NUM>, and the external conductive member <NUM> and the bus bar can be more stably joined to each other as a result. From the above standpoint, the distance W1 is preferably <NUM> or larger. The distance W1 is for instance <NUM> or smaller, and in terms of joining to the bus bar, is preferably <NUM> or smaller, and more preferably <NUM> or smaller.

As illustrated in <FIG>, a protrusion 35b is provided within the first recess 35a, on the peripheral edge of the through-hole <NUM>. The protrusion 35b has for instance a substantially annular shape (for instance a circular ring shape) in a plan view. In the present embodiment the protrusion 35b protrudes from the bottom surface 35a1 of the first recess 35a towards the upper surface 35u. As illustrated in <FIG>, a tip portion 35b1 of the protrusion 35b in the protrusion direction stands closer to the bottom surface 35a1 than to the upper surface 35u. In the present embodiment the joint portion 31w is provided at the boundary of the tip portion 35b1 and the projecting portion 30c. By providing thus the protrusion 35b, for instance joining through projection of energy rays to the boundary of the external conductive member <NUM> and the positive electrode terminal <NUM> can be rendered more efficient, and as a result the output of energy rays is curtailed, whereby spatter can be suppressed, and the effect of suppressing adhesion of spatter can be made yet more pronounced. Formation of the protrusion 35b is however not essential herein, and can be omitted in other embodiments.

A first depth D1 of the first recess 35a is for instance from <NUM> to <NUM>. In the present specification the "first depth D1 of the first recess 35a" denotes for instance a maximum depth from the upper surface 35u of the external conductive member <NUM> to the bottom surface 35a1 of the first recess 35a. A second depth D2 of the first recess 35a is for instance <NUM> or larger, preferably <NUM> or larger, and more preferably <NUM> or larger. The second depth D2 is for instance <NUM> or smaller, or <NUM> or smaller. In the present specification the "second depth D2 of the first recess 35a" denotes for instance the maximum depth from the upper surface 35u of the external conductive member <NUM> to the tip portion 35b1 of the protrusion 35b. In the present embodiment the second depth D2 may also be defined by the maximum depth from the upper surface 35u to the joint portion 31w.

In the embodiment illustrated in <FIG>, a substantially annular second recess 35c sunk from the lower surface 35d of the external conductive member <NUM> is provided around the through-hole <NUM>. In the present specification the "lower surface 35d of the external conductive member <NUM>" denotes one end surface of the external conductive member <NUM>, in the direction of penetration into the through-hole <NUM> (for instance direction Z in <FIG>), on the side of the sealing plate <NUM>. In the present embodiment the second recess 35c opposes the flange portion 30b of the positive electrode terminal <NUM>. The diameter of the second recess 35c is for instance larger than the diameter of the through-hole <NUM>. A space <NUM> is secured around the through-hole <NUM> by providing thus the second recess 35c. The external conductive member <NUM> can be prevented, by the space <NUM>, from interfering with the boundary of the flange portion 30b and the projecting portion 30c. Thereby, the external conductive member <NUM> can be stably disposed on the flange portion 30b, and the occurrence of spatter during welding can be suppressed as a result.

A thin portion 35t becomes formed when providing the second recess 35c. The thickness of the thin portion 35t is smaller than the thickness of other portions, of the external conductive member <NUM>, at which neither the first recess 35a nor the second recess 35c is provided. The thin portion 35t may be configured to melt when for instance a current of <NUM> A or larger (for instance a short-circuit current) flows in the secondary battery <NUM>. Formation of the second recess 35c is however not essential herein, and may be omitted in other embodiments.

As illustrated in <FIG>, the negative electrode terminal <NUM> is electrically connected to the negative electrode plate <NUM> (see <FIG>) of the electrode body <NUM> via the negative electrode current collector member <NUM>, inside the exterior body <NUM>. The negative electrode terminal <NUM> is inserted through the terminal lead-out hole <NUM> and is led out from the interior of the sealing plate <NUM>. The negative electrode terminal <NUM> is insulated from the sealing plate <NUM> by a respective insulator <NUM> and a respective gasket <NUM>. The negative electrode terminal <NUM> is preferably made of a metal, and is more preferably made up of for instance copper or a copper alloy. The negative electrode terminal <NUM> may be configured through joining and integration of two conductive members. For instance, the negative electrode terminal <NUM> may be made up of copper or a copper alloy at a portion connected to the negative electrode current collector member <NUM>, and may be made up of aluminum or an aluminum alloy at a portion exposed outside the sealing plate <NUM>. The negative electrode terminal <NUM> may be configured out of a cladding material of an aluminum-based metal and a copper-based metal. The concrete configuration of the negative electrode terminal <NUM> may be identical to that of the positive electrode terminal <NUM>. An external conductive member <NUM> is fixed on the negative electrode terminal <NUM>. The negative electrode terminal <NUM> is joined to the external conductive member <NUM>.

The external conductive member <NUM> is for instance a member joined to the negative electrode terminal <NUM> outside the battery case <NUM>. For instance the external conductive member <NUM> is attached to the sealing plate <NUM>, on the negative electrode side of the secondary battery <NUM>, in a state of being insulated from the sealing plate <NUM> by a respective external insulating member <NUM>. The shape, structure, and constituent materials of the external conductive member <NUM> may be identical to those of the external conductive member <NUM> on the positive electrode side.

The positive electrode current collector member <NUM> is for instance a member that electrically connects the positive electrode plate <NUM> of the electrode body <NUM> and the positive electrode terminal <NUM>, inside the exterior body <NUM>. As illustrated in <FIG>, the positive electrode current collector member <NUM> has the first collector portion <NUM> and the second collector portions <NUM>. The first collector portion <NUM> is formed to have an L-shaped cross section. The first collector portion <NUM> has for instance a base portion 51a and a lead portion 51b. As illustrated in <FIG>, the base portion 51a is disposed along the inner surface of the sealing plate <NUM>. The hole <NUM> is formed in the base portion 51a at a position corresponding to the terminal lead-out hole <NUM> of the sealing plate <NUM>, as illustrated in <FIG>. For instance the insertion portion 30a of the positive electrode terminal <NUM> is inserted through the hole <NUM>. The lead portion 51b extends for instance from one end of the base portion 51a, in the width direction Y towards the bottom portion 12a. For instance the second collector portions <NUM> are connected to the lead portion 51b.

As illustrated in <FIG>, the second collector portions <NUM> extend towards the bottom portion 12a of the exterior body <NUM>. In the present embodiment each second collector portion <NUM> has a first connecting portion 52a and a second connecting portion 52b. The first connecting portion 52a is for instance a portion electrically connected to the first collector portion <NUM>. In the present embodiment the first connecting portion 52a is connected to the first collector portion <NUM> via a connection portion <NUM>. The connection portion <NUM> is for instance a thin portion. For instance, the first connecting portion 52a extends in the vertical direction Z. In the present embodiment the first connecting portion 52a is disposed substantially perpendicularly to the winding axis WL of the respective electrode body <NUM>.

As illustrated in <FIG>, a respective fuse portion 52f is formed in each first connecting portion 52a. The first connecting portion 52a is configured so that the fuse portion 52f fuses when a current of <NUM> A or more (for instance a short-circuit current) flows through the secondary battery <NUM>. The fuse portion 52f is for instance a portion of the first connecting portion 52a having a smaller cross-sectional area than that of other portions excluding the fuse portion 52f and the connection portion <NUM>. The fuse portion 52f is for instance an opening or a thin portion. The fuse portion 52f is formed in the first connecting portion 52a, and hence the first connecting portion 52a is configured to fuse upon flow of a current such as the above. Safety is improved as a result.

Each second connecting portion 52b is for instance a portion that is joined to the positive electrode tab group <NUM>. In the present embodiment the second connecting portion extends along the vertical direction Z. The second connecting portion 52b is disposed substantially perpendicular to the winding axis WL of the respective electrode body <NUM>. The surface of the second connecting portion 52b that is connected to the positive electrode tabs 22t is disposed substantially parallelly to the second side walls 12c of the exterior body <NUM>.

The negative electrode current collector member <NUM> is a member that electrically connects the negative electrode plate <NUM> of the electrode body <NUM> and the negative electrode terminal <NUM>, inside the exterior body <NUM>. As illustrated in <FIG>, the negative electrode current collector member <NUM> has a first collector portion <NUM> and second collector portions <NUM>. The first collector portion <NUM> has a base portion 61a and a lead portion 61b. Each second collector portion <NUM> has a first connecting portion 62a and a second connecting portion 62b. The configuration of the negative electrode current collector member <NUM> is identical to the configuration of the positive electrode current collector member <NUM> described above, and hence a detailed description thereof will be omitted herein. In the negative electrode current collector member <NUM>, the reference numeral "<NUM>" in <FIG> denotes a connecting portion, the reference numeral "62a" denotes a first connecting portion, the reference numeral "62b" denotes a second connecting portion, and the reference numeral "62f" denotes a fuse portion.

The insulator <NUM> is an insulating member disposed between the positive electrode current collector member <NUM> and the inner surface of the sealing plate <NUM>. The hole <NUM> is formed in the insulator <NUM>. The gasket <NUM> is an insulating member disposed between the positive electrode terminal <NUM> and the outer surface of the sealing plate <NUM>. The gasket <NUM> has a hollow cylindrical tubular portion <NUM> that is inserted into the terminal lead-out hole <NUM> of the sealing plate <NUM>. The tubular portion <NUM> of the gasket <NUM> is disposed along the inner circumference of the hole <NUM> of the insulator <NUM>. A structure similar to the insulating structure relying on an insulator <NUM> and a gasket <NUM> is also provided on the negative electrode terminal <NUM> side, but a detailed description thereof will be omitted herein.

The constituent materials of the insulators <NUM> and the gaskets <NUM> are not particularly limited, and include resin materials such as polyolefin resins (for example polypropylene (PP) and polyethylene (PE)), and fluororesins (for example perfluoroalkoxyalkanes (PFAs) and polytetrafluoroethylene (PTFE)). Such resin materials can also be used as the constituent material of the external insulating members <NUM>.

The secondary battery <NUM> described above has: the electrode body <NUM> including the positive electrode plate <NUM> and the negative electrode plate <NUM>; the battery case <NUM> that accommodates the electrode body <NUM>; the positive electrode terminal <NUM> electrically connected to the positive electrode plate <NUM> and attached to the battery case <NUM>; and the external conductive member <NUM> joined to the positive electrode terminal <NUM> outside the battery case <NUM>. The external conductive member <NUM> has the through-hole <NUM>. Part of the positive electrode terminal <NUM> is disposed in the through-hole <NUM>. The joint portion 31w of the external conductive member <NUM> and the positive electrode terminal <NUM> is provided around the through-hole <NUM>; the substantially annular first recess 35a sunk from the upper surface 35u of the external conductive member <NUM> is likewise provided around the through-hole <NUM>. The distance W1 from the peripheral edge of the through-hole <NUM> to the outer peripheral edge of the first recess 35a in a plan view is <NUM> or larger.

In the secondary battery <NUM>, in other words, the external conductive member <NUM> and the positive electrode terminal <NUM> disposed within the through-hole <NUM>, which is in turn provided within the first recess 35a sunk from the upper surface 35u of the external conductive member <NUM>, are joined in the periphery of the through-hole <NUM>. The positive electrode terminal <NUM> and the external conductive member <NUM> can be joined at a portion recessed from the upper surface 35u of the external conductive member <NUM>. There is a distance of <NUM> or more from the peripheral edge of the through-hole <NUM> to the outer peripheral edge of the first recess 35a, in a plan view. The upper surface 35u can be kept removed from the joint site of the positive electrode terminal <NUM> and the external conductive member <NUM>, and adhesion of spatter to the upper surface 35u can be suppressed at the time of joining. The external conductive member <NUM> and the bus bar can be joined more stably as a result.

The secondary battery <NUM> can be used in various applications, and for instance the battery can be suitably used as a power source (drive power source) for a motor, mounted on a vehicle such as a passenger car or a truck. The kind of vehicle is not particularly limited, and examples thereof include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs) and electric vehicles (BEVs).

The above-described battery case <NUM>, electrode body <NUM>, positive electrode terminal <NUM>, negative electrode terminal <NUM>, external conductive members <NUM>, <NUM>, positive electrode current collector member <NUM>, negative electrode current collector member <NUM>, insulators <NUM>, gaskets <NUM> and external insulating members <NUM> are prepared, and the secondary battery <NUM> is produced in accordance with a production method that includes for instance an attachment step, an arrangement step, a covering step and a joining step. The production method may include further steps at any stage. The explanation below will refer to <FIG> as appropriate.

In the attachment step, for instance, the positive electrode terminal <NUM> is attached to the battery case <NUM>. In the present embodiment, firstly the positive electrode terminal <NUM>, a respective gasket <NUM>, the first collector portion <NUM>, and a respective insulator <NUM> are attached to the sealing plate <NUM>.

The positive electrode terminal <NUM>, the first collector portion <NUM>, and the insulator <NUM> are fixed to the sealing plate <NUM> for instance by crimping (riveting). In the crimping process, as illustrated in <FIG>, the gasket <NUM> is clamped between the outer surface of the sealing plate <NUM> and the positive electrode terminal <NUM>, and the insulator <NUM> is clamped between the inner surface of the sealing plate <NUM> and the first collector portion <NUM>. For instance, the insertion portion 30a of the positive electrode terminal <NUM> prior to crimping is sequentially inserted, from above the sealing plate <NUM>, into the tubular portion <NUM> of the gasket <NUM>, the terminal lead-out hole <NUM> of the sealing plate <NUM>, the hole <NUM> of the insulator <NUM>, and the hole <NUM> of the first collector portion <NUM>, so as to protrude downward of the sealing plate <NUM>. The section of the insertion portion 30a that protrudes downward of the sealing plate <NUM> is crimped so that a compressive force is exerted in the vertical direction Z. The negative electrode terminal <NUM>, a respective gasket <NUM>, the first collector portion <NUM> and a respective insulator <NUM> are fixed to the sealing plate <NUM> in accordance with a similar procedure.

In the arrangement step, for instance, a portion of the positive electrode terminal <NUM> attached to the battery case <NUM> is disposed within the through-hole <NUM> of the external conductive member <NUM>. In the present embodiment, the attachment step is followed by arrangement of the respective external insulating member <NUM> from above the sealing plate <NUM>, so that the flange portion 30b of the positive electrode terminal <NUM> and the gasket <NUM> are accommodated within a hole <NUM> of the external insulating member <NUM>. The external conductive member <NUM> is superimposed next on the positive electrode terminal <NUM>, from above the sealing plate <NUM> in such a manner that the lower surface 35d and the flange portion 30b face each other, and the projecting portion 30c is inserted into the through-hole <NUM>. On the negative electrode side as well, for instance a portion of the negative electrode terminal <NUM> (for instance the projecting portion of the negative electrode terminal <NUM>) attached to the battery case <NUM> is arranged (not shown) into a through-hole of the external conductive member <NUM>, in accordance with a similar procedure.

In the covering step, for instance at least part of the upper surface of the external conductive member <NUM> is covered with a cover member, after the arrangement step. <FIG> are diagrams for explaining a step in the production method according to an embodiment. <FIG> is a diagram illustrating a state in which the upper surface 35u of the external conductive member <NUM> is covered with a cover member <NUM>, after the arrangement step, as viewed from the upper surface 35u. <FIG> is a partial cross-sectional diagram viewed from the direction of arrow IX in <FIG>. The cover member <NUM> is not particularly limited, but is for instance a component of an apparatus used for producing the secondary battery <NUM>. Although not particularly limited thereto, the cover member <NUM> is preferably made of a resin or a metal. The constituent material of the cover member <NUM> is preferably a material that is not prone to melting or deforming during the joining step described below.

In the present embodiment an opening <NUM> is formed in the cover member <NUM>. As illustrated in <FIG>, the opening <NUM> has an annular shape in a plan view. Preferably, an inner diameter Dc of the opening <NUM> is smaller than an outer diameter Da of the first recess 35a. By using the cover member <NUM> having formed therein an opening high a smaller inner diameter than the outer diameter Da of the first recess 35a it becomes possible to yet better prevent adhesion, to the upper surface 35u, of spatter generated in the joining step. In the present specification the "outer diameter Da of the first recess 35a" denotes the diameter (labeled with reference symbol K in <FIG>) of the first recess 35a in the upper surface 35u of the external conductive member <NUM>, as illustrated in <FIG>. In the present embodiment, the inner diameter Dc of the opening <NUM> is larger than an inner diameter Db of the through-hole <NUM>.

In the covering step, as illustrated in <FIG>, the upper surface 35u is covered by the cover member <NUM> in such a manner that an inner edge of the opening <NUM> of the cover member <NUM> is disposed between a planned joint portion 31w of the external conductive member <NUM> and the positive electrode terminal <NUM>, and the outer peripheral edge (labeled with reference symbol K in <FIG>) of the first recess 35a, in a cross-sectional view along the direction of penetration of the through-hole <NUM> (direction Z in <FIG>). The planned joint portion 31w is for instance a site that yields the joint portion 31w (see <FIG>) after the below-described joining step has been carried out. For instance, the planned joint portion 31w lies at the boundary of the peripheral edge of the through-hole <NUM> and the outer edge of the projecting portion 30c.

In the embodiment illustrated in <FIG> the cover member <NUM> covers all the portions of the upper surface 35u of the external conductive member <NUM>, except for the first recess 35a.

In the joining step, for instance, the external conductive member <NUM> and the positive electrode terminal <NUM> are joined by being irradiated with energy rays, after the covering step. For instance the joint portion 31w (see <FIG>) is formed thus as a result of the joining step. In the covering step, the external conductive member <NUM> and the positive electrode terminal <NUM> are joined in a state where the edge portion of the opening <NUM> of the cover member <NUM> is disposed between the planned joint portion 31w of the external conductive member <NUM> and the positive electrode terminal <NUM>, and the outer peripheral edge of the first recess 35a, in a cross-sectional view along the direction of penetration of the through-hole <NUM> (direction Z in <FIG>). The external conductive member <NUM> and the positive electrode terminal <NUM> are joined in a state where the upper surface 35u around the through-hole <NUM> is covered with the cover member <NUM>; this allows suppressing, as a result, adhesion of spatter to the upper surface 35u.

The energy used for energy ray irradiation herein is for instance light energy, electron energy or thermal energy. In the joining step, the joint portion 31w is formed for instance by relying on a welding means such as laser welding, electron beam welding, ultrasonic welding, resistance welding or TIG (Tungsten Inert Gas) welding. Laser welding can be preferably resorted to among the foregoing.

After the joining step, for instance the electrode body <NUM> is attached to the construct obtained in the joining step. A conventionally known method may be resorted to, without particular limitations, as the method for producing the electrode body <NUM>. In the present embodiment the second collector portion <NUM> of the positive electrode current collector member <NUM> is attached to the positive electrode tab group <NUM> of the electrode body <NUM>, and the second collector portion <NUM> of the negative electrode current collector member <NUM> is attached to the negative electrode tab group <NUM>. Next, the second collector portions <NUM>, <NUM> attached to the electrode body <NUM> are in turn respectively attached to the first collector portions <NUM>, <NUM> of identical polarity in the construct obtained in the joining step. The electrode body <NUM> is accommodated next in the electrode body holder <NUM>. The electrode body <NUM> covered with the electrode body holder <NUM> is inserted next into the exterior body <NUM>. In this state, the sealing plate <NUM> is laid on the opening <NUM> of the exterior body <NUM>, and the foregoing are welded, to thereby seal the exterior body <NUM>.

Once the exterior body <NUM> has been sealed, an electrolyte solution is injected thereafter into the battery case <NUM> through the liquid injection hole <NUM>, in accordance with a conventionally known method. After injection of the electrolyte solution, the liquid injection hole <NUM> is sealed using the sealing member <NUM>. The liquid injection hole <NUM> is plugged for instance by a metal-made sealing plug that is used herein as the sealing member <NUM>. The liquid injection hole <NUM> is sealed next for instance by laser welding in a state where the liquid injection hole <NUM> has been closed with the sealing member <NUM>. The above sealing is for instance followed by an initial charging treatment and an aging treatment performed under predetermined conditions; a secondary battery <NUM> in a usable state can be obtained.

The secondary battery <NUM> can be suitably used for instance as a unit cell that makes up an assembled battery. <FIG> is a perspective view of an assembled battery according to an embodiment. In an assembled battery <NUM>, as illustrated in <FIG>, multiple secondary batteries <NUM> are electrically connected to each other via respective bus bars <NUM>. In the present embodiment a respective bus bar <NUM> is disposed between the upper surface 35u of the external conductive member <NUM> on the positive electrode side of one of two adjacent secondary batteries <NUM> and an upper surface 45u of the external conductive member <NUM> on the negative electrode side of the other secondary battery <NUM>. The secondary batteries <NUM> are connected to each other via these bus bars <NUM>. As described above, adhesion of spatter to the upper surface 35u of the external conductive member <NUM> (herein the surface to which the bus bar <NUM> is joined) is suppressed in the secondary battery <NUM>. As a result, the bus bar <NUM> can be more stably joined to the external conductive member <NUM>.

The bus bar <NUM> is for instance a plate-like (rod-like) member. The bus bar <NUM> has a substantially rectangular shape elongated in direction X. The external conductive members <NUM>, <NUM> and the bus bar <NUM> are electrically connected for instance by welding such as laser welding. The bus bar <NUM> is made up of a conductive metal such as aluminum, an aluminum alloy, nickel or stainless steel.

In the embodiment illustrated in <FIG>, each bus bar <NUM> respectively covers the through-hole <NUM> and the first recess 35a on the positive side, and covers a through-hole <NUM> and a first recess 45a on the negative side. In consequence, energization paths in the assembled battery <NUM> can be made shorter, and energization-derived generation of heat can be suppressed as a result. For instance <NUM>% or more (preferably <NUM>% or more, and more preferably <NUM>% or more) of the surface area of the first recess, in a plan view, may be covered with the bus bar <NUM>.

A method for producing the assembled battery <NUM> includes for instance producing secondary batteries <NUM> as unit cells, and arranging respective bus bars <NUM> on the upper surfaces 35u, 45u of the external conductive members <NUM>, <NUM>, to thereby connect the external conductive members. For instance, multiple secondary batteries <NUM> are disposed such that respective first side walls 12b oppose each other. Herein two adjacent secondary batteries <NUM> are disposed in an array direction of the secondary battery <NUM> (direction X in <FIG>) in such a manner that the external conductive member <NUM> and the external conductive member <NUM> are adjacent to each other in the array direction. Next, the adjacent external conductive member <NUM> and external conductive member <NUM> are connected to each other by being bridged over by a respective bus bar <NUM>. The assembled battery <NUM> can then be produced for instance by being clamped, from both ends in the arrangement direction, by a pair of end plates, with a predetermined restraining pressure being imparted by bind bars that bridge the end plates. In the secondary battery <NUM>, adhesion of spatter to upper surface 35u of the external conductive member <NUM> (herein the surface to which the bus bar <NUM> is joined) is suppressed, as described above. As a result, the bus bar <NUM> can be joined more stably to the external conductive member <NUM>.

In the first embodiment the inner wall surface 35a2 of the first recess 35a is substantially perpendicular to the bottom surface 35a1. However, the invention is not limited thereto. <FIG> is a partial enlarged-view diagram of an enlargement of the vicinity of a positive electrode terminal in another embodiment. <FIG> illustrates a cross-sectional view along the direction of penetration (direction Z in the figure) of the through-hole <NUM>. In the embodiment illustrated in <FIG>, an inner wall surface 35a3 of the first recess 35a is a tapered surface that becomes wider from the bottom surface 35a1 of the first recess 35a towards the upper surface 35u of the external conductive member <NUM>. The amount of metal in the outer peripheral edge of the first recess 35a can be reduced by forming thus the inner wall surface 35a3 as a tapered surface. During formation of the first recess 35a, the metal on the outer peripheral edge of the first recess 35a escapes in the radial direction of the first recess 35a, and thus the outer peripheral edge may bulge up as a result. Such bulging can be curtailed, and deformation of the external conductive member can be suppressed, by forming the inner wall surface 35a3 as a tapered surface. Moreover, stress can be prevented from concentrating at the thin portion 35t on account of external forces. In addition, the heat capacity of the external conductive member <NUM> can be increased, which allows reducing generation of heat during energization. In the explanation that follows the inner wall surface 35a3 is also referred to as "tapered surface 35a3".

In the present embodiment an inclination angle θ of the inner wall surface 35a3 is smaller than <NUM> degrees, and is preferably <NUM> degrees or less. The inclination angle θ is more preferably from <NUM> degrees to <NUM> degrees, and yet more preferably from <NUM> degrees to <NUM> degrees, in terms of better bringing out the above-described effects. In the present specification the "inclination angle θ of the inner wall surface 35a3" denotes for instance the angle formed by the inner wall surface 35a3 and a straight line L1 along the bottom surface 35a1, in the cross-sectional view illustrated in <FIG>.

In the present embodiment a ratio (W2/W1) of the above-described distance W1 and a shortest distance W2 from a boundary B of the tapered surface 35a3 and the bottom surface 35a1 up to the outer peripheral edge of the first recess 35a (hereafter also referred to as "distance W2"), in a plan view from the direction of arrow A in <FIG>, is <NUM> or higher. The ratio (W2/W1) is preferably <NUM> or higher, in terms of better bringing out the above-described effects.

In the production method of the secondary battery of the second embodiment there is used the external conductive member <NUM> having the inner wall surface 35a3 exhibiting the above-described tapered surface. In the covering step, for instance, the upper surface 35u of the external conductive member <NUM> may be covered with the cover member <NUM> so that the inner edge of the opening <NUM> of the cover member <NUM> overlaps the tapered surface 35a3 (see <FIG> and <FIG>). The present embodiment allows suppressing adhesion of spatter, generated in the joining step, to peripheral members, and curtailing deformation of the outer peripheral edge of the first recess 35a, as described above. The reliability of joint portions between members that make up the secondary battery <NUM> or the assembled battery <NUM> can be improved accordingly.

The shape of the first recess 35a is not particularly limited, provided that the shape allows bringing out the effects of the art disclosed herein. Except for the above-described features, the explanation of the first embodiment applies likewise to the second embodiment, and hence a redundant explanation will be omitted.

In the first embodiment above the cover member <NUM> covers the entire upper surface 35u of the external conductive member <NUM>, as illustrated in <FIG>. However, the surface area covered by the cover member <NUM> is not particularly limited, so long as it allows bringing out the effects of the art disclosed herein. From this standpoint, the surface area covered by the cover member <NUM> is preferably <NUM>% or more, more preferably <NUM>% or more, and yet more preferably <NUM>% or more, of the surface area of the upper surface 35u.

Claim 1:
A method for producing a secondary battery (<NUM>) that comprises:
an electrode body (<NUM>) comprising a positive electrode (<NUM>) and a negative electrode (<NUM>);
a battery case (<NUM>) that accommodates the electrode body (<NUM>);
a terminal (<NUM>, <NUM>) electrically connected to the positive electrode (<NUM>) or the negative electrode (<NUM>), and attached to the battery case (<NUM>); and
an external conductive member (<NUM>) having a through-hole (<NUM>), and joined to the terminal (<NUM>, <NUM>) outside the battery case (<NUM>);
the method comprising:
an attachment step of attaching the terminal (<NUM>, <NUM>) to the battery case (<NUM>);
an arrangement step of arranging part of the terminal (<NUM>) which is attached to the battery case (<NUM>), within the through-hole (<NUM>) of the external conductive member (<NUM>);
a covering step of, after the arrangement step, covering at least part of an upper surface (35u) of the external conductive member (<NUM>) with a cover member (<NUM>); and
a joining step of, after the covering step, joining the external conductive member (<NUM>) and the terminal (<NUM>) through irradiation with energy rays,
wherein
the external conductive member (<NUM>) comprises a substantially annular recess (35a), sunk from the upper surface (35u) of the external conductive member (<NUM>), around the through-hole (<NUM>);
in a plan view, a shortest distance W1 from a peripheral edge of the through-hole (<NUM>) up to the outer peripheral edge of the recess (35a) is <NUM> or larger; and
in the joining step, in a cross-sectional view along a direction of penetration into the through-hole (<NUM>), the external conductive member (<NUM>) and the terminal (<NUM>) are joined in a state where an edge portion of the cover member (<NUM>) is disposed between a planned joint portion (31w) of the external conductive member (<NUM>) and the terminal (<NUM>), and an outer peripheral edge of the recess (35a).