JP4867210B2 - Winding type power storage device - Google Patents

Description

  The present invention relates to a power storage device (battery, capacitor, etc.) provided with a wound electrode unit obtained by winding positive and negative electrode sheets. Specifically, the electrode sheets are bundled together at both ends in the winding axis direction of the electrode unit. The present invention relates to a wound power storage device in a form in which electrical terminals are connected.

  2. Description of the Related Art A battery having a configuration in which an electrode unit obtained by superposing and winding a positive electrode sheet and a negative electrode sheet is accommodated in a container is known. In one typical configuration of such a wound battery, the relative position between the positive electrode sheet and the negative electrode sheet is shifted in the winding axis direction of the electrode unit (the width direction of the sheet) from one end and the other end of the shaft. The positive electrode sheet and the negative electrode sheet are respectively protruded, and the protruding positive electrode sheet and negative electrode sheet are bundled and connected to the positive electrode terminal and the negative electrode terminal, respectively. Such a configuration is generally more productive than a configuration in which lead wires (sometimes referred to as current collecting tabs) drawn from the positive and negative electrode sheets are collected and connected to the terminals, and the battery is downsized. This is also advantageous. For example, in Patent Document 1, positive and negative metal foils protruding from both ends of an electrode unit wound in a long cylindrical shape are bundled separately on the left and right sides of the winding shaft, and the bundle of metal foils is used as a current collector connector. A welded battery is described.

  By the way, the battery may generate gas inside the battery container depending on its use condition and the like. For this reason, generally, a container of a sealed battery is provided with an internal pressure releasing means (such as a safety valve) that allows the inside and outside of the container to communicate with each other to release the gas in the container to the outside when the internal pressure of the container increases. The gas generated inside the electrode unit is discharged from the inside of the unit to the outside of the battery through the internal space of the container outside the unit by the internal pressure releasing means. Patent document 2 is mentioned as a prior art document regarding this kind of battery, for example.

JP 2003-346769 A Japanese Patent Laid-Open No. 2004-030946

  Here, the gas generated inside the wound electrode unit as described above is prevented from flowing out in the radial direction by the electrode sheet on the wound outer peripheral side. To the direction of the winding axis of the unit. However, in a battery in which the electrode sheets protruding from both ends of the winding shaft are bundled and connected to the terminal (typically welding), the electrode sheets that are wound in the radial direction are adjacent to each other (on the outer peripheral side and the inner peripheral side). ) Since it is fixed by the connection with the electrode sheet, the axial escape of gas is hindered.

  Accordingly, the present invention provides a power storage device having a configuration in which a current collecting terminal is connected to an end portion in the axial direction of a wound electrode unit, and gas generated inside the unit easily escapes to the outside of the unit (gas It is an object of the present invention to provide a power storage device that is easily disconnected.

A wound power storage device provided by the present invention includes a wound electrode unit in which positive and negative electrode sheets are wound flatly, and a current collecting terminal connected to an end of the electrode unit in the winding axis direction. Is provided. In the electrode unit, the electrode sheet is bundled and connected to the current collecting terminal at both ends in the longitudinal direction when the unit is viewed from the end surface side, and the central part in the longitudinal direction is connected to the inside of the unit. The gas generated in is released so as to be able to escape in the winding axis direction.
In the power storage device having such a configuration, the central portion in the longitudinal direction of the end surface shape of the wound electrode unit is opened, so that even when gas is generated inside the electrode unit, the gas is discharged from the end surface of the electrode unit. It is possible to efficiently escape (that is, the gas escape of the electrode unit is good). Therefore, the gas generated in the container (exterior body) of the power storage device can be appropriately released to the outside of the container. Further, in the power storage device having a configuration in which the container is provided with an internal pressure release mechanism such as a safety valve, the internal pressure release mechanism can be more appropriately operated.

In one preferred embodiment of the invention disclosed herein, the current collector terminal, each at least one pair of pinching from both sides in the width direction of each end surface shape longitudinal both ends of the end face shape of the electrode unit It is provided with a sandwiching part. The electrode sheets are bundled between the sandwiching portions and connected to the sandwiching portion.
According to the current collector terminal having such a sandwiching portion, the electrode sheets constituting the end portion are easily gathered from the outer side in the width direction in the end face shape to the inner side at the end portion in the axial direction of the electrode unit. (Bundled). For this reason, the operation of attaching (connecting) the current collecting terminal to the electrode unit can be performed efficiently. Therefore, the power storage device having an aspect including the current collecting terminal having such a configuration can have good manufacturing efficiency.

In another preferred aspect of the invention disclosed herein, the shape of the current collecting terminal viewed from the end surface side of the electrode unit is such that the outer surface of the unit is from one end in the longitudinal direction of the end surface shape of the unit. A U-shape extending in the longitudinal direction along both outer sides in the width direction of the end face shape.
According to such a current collector terminal, the end of the electrode unit can be appropriately held between the two arms having the U-shape. For this reason, the operation of assembling (connecting) the current collecting terminal to the electrode unit can be performed efficiently. Typically, the pair of sandwiching portions are formed by corresponding portions of the one arm portion and the other arm portion in the U-shape. Thus, since a pair of clamping part is formed of one member, position alignment of the clamping parts which comprise these pairs is easy. Further, for example, by arranging the current collecting terminal so that the U-shaped folded portion (corresponding to the bottom of the U-shape) abuts on one end portion in the longitudinal direction of the end surface shape of the electrode unit, Positioning of the current collecting terminal with respect to the electrode unit (particularly, positioning in the longitudinal direction in the end face shape of the electrode unit) can be performed easily and appropriately.

In another preferable aspect of the invention disclosed herein, the current collecting terminal includes at least a pair of sandwiching portions provided on the U-shaped back side (folded portion side), and the U-shaped And at least a pair of sandwiching portions provided on the inlet side. One end portion in the longitudinal direction of the end face shape of the electrode unit is connected to the back-side sandwiching portion, and the other end portion is connected to the entrance-side sandwiching portion.
According to this aspect, the one end part and the other end part in the longitudinal direction in the end face shape of the electrode unit can be bundled and connected to the current collecting terminal by one current collecting terminal. Since these two pairs of sandwiching portions are connected by the arms in the U-shape, the positional relationship between the two pairs of sandwiching portions can be appropriately maintained. Therefore, by connecting the current collecting terminal to the end portion of the electrode unit, the shape maintaining property of the axial end portion of the electrode unit can be improved. Thereby, for example, the handleability of the electrode unit to which the current collecting terminal is connected (operability when inserted into the container, etc.) is improved.

In another preferable aspect of the invention disclosed herein, the current collecting terminal is positioned on the inner side in the winding axis direction than the sandwiching portion along one end portion in the longitudinal direction of the end surface shape of the electrode unit ( It has a positioning part extending to the center side.
In the power storage device including the current collecting terminal having such a shape, by arranging the current collecting terminal so that the positioning portion abuts on one end portion in the longitudinal direction of the end face shape of the electrode unit, the electrode The current collecting terminal can be positioned with respect to the unit more easily and appropriately.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that the technical matters other than those specifically mentioned in the present specification, which are necessary for the implementation of the present invention (for example, the composition of the electrode active material layer, the type of the electrolyte, the method for producing the current collector terminal, the electrode A specific operation method (for example, welding conditions) at the time of connecting the sheet and the current collecting terminal can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.

  A wound power storage device disclosed herein includes a wound electrode unit in which positive and negative electrode sheets are wound flatly, and a current collecting terminal connected to an end of the electrode unit in the winding axis direction. There are no particular limitations on the manufacturing process, the type of power storage device, and the like. Here, the “power storage device” refers to a device capable of exhibiting a power storage function (also referred to as a power generation function) for storing and releasing predetermined power, and is a concept including both a so-called battery and a capacitor. Typical power storage devices include various types of primary batteries (eg, lithium primary batteries, manganese batteries), secondary batteries (eg, lithium secondary batteries, nickel metal hydride batteries), or capacitors (eg, electric double layer capacitors). be able to.

  The present invention is applicable to any type of power storage device of a sealed type and an open type (non-sealed type). For any type of power storage device, the gas generated in the electrode unit first escapes from the unit and then is released to the outside of the device (outside the container housing the electrode unit). Therefore, the effect of application of the present invention for improving the outgassing of the electrode unit can be appropriately exhibited in any type of power storage device. In general, a sealed power storage device is provided with an internal pressure releasing means such as a safety valve. When the gas generated in the electrode unit is accumulated outside the unit (that is, if the electrode unit has insufficient gas release properties). There is a risk that the unit will swell, thereby preventing proper operation of the internal pressure release means (for example, the opening formed by the operation of the safety valve is blocked). From this point of view, the present invention is preferably applied to a sealed power storage device. In addition, a power storage device using a non-aqueous electrolyte is more likely to generate gas in the container than a power storage device using a water-based electrolyte. Therefore, the present invention is directed to a power storage device including a non-aqueous electrolyte. Preferably applied. A particularly preferable application target of the present invention is a lithium secondary battery (typically, a lithium ion secondary battery).

  The wound electrode unit constituting the power storage device of the present invention is wound flat. Therefore, when the unit is viewed from the end surface side (that is, the winding axis direction), the length in one direction (longitudinal direction) is longer than the length in the other direction (width direction). Typically, the shape of the electrode unit as viewed from the end face side (hereinafter sometimes referred to as “end face shape”) is oval or elliptical. Here, the “flatly wound electrode unit” included in the power storage device refers to a wound electrode unit that exhibits a flat outer shape at least in a state in which the power storage device is configured. It is not limited to what was rolled up flatly. Therefore, for example, a wound electrode unit obtained by winding a long electrode sheet into a cylindrical shape and then crushing it to form a flat shape is one of the “flatly wound electrode units” constituting the power storage device of the present invention. It can be included in the concept.

  A current collecting terminal is connected to at least one end (positive end or negative end) of the electrode unit in the winding axis direction. A power storage device having a configuration in which a positive current collecting terminal and a negative current collecting terminal are respectively connected to both ends (positive electrode side end and negative electrode side end) of the electrode unit in the winding axis direction is preferable. The current collecting terminal is connected to at least one end in the longitudinal direction of the end face shape of the electrode unit. A current collecting terminal is preferably connected to one end and the other end in the longitudinal direction of the end face shape. In this case, for example, a part of one positive current collector terminal is connected to one end in the longitudinal direction of the end face shape of the positive electrode side end of the electrode unit, and the other part of the positive current collector terminal is It can be set as the form connected to the other edge part of the longitudinal direction. Alternatively, the first positive electrode current collector terminal is connected to one end portion in the longitudinal direction in the end face shape of the positive electrode side end portion of the electrode unit, and the second positive electrode current collector terminal is connected to the other end portion in the longitudinal direction. (It is good also as a form to which the (current collector terminal for 1st positive electrodes) was connected. From the standpoint of improving the shape maintaining property of the electrode unit end, a part of one positive electrode current collector terminal and the other part may be connected to one end and the other end in the longitudinal direction. preferable. The same applies to the connection form between the negative electrode side end and the negative electrode current collector terminal.

  In a typical aspect of the power storage device disclosed herein, the electrode sheets constituting the end portions in the longitudinal direction in the end face shape are bundled (that is, the wound electrode sheets are gathered together in the radial direction), The electrode sheet is connected to the current collecting terminal in the bundled state. The method for connecting the electrode sheet and the current collecting terminal is not particularly limited, and an appropriate one may be selected from various conventionally known methods. For example, the electrode sheet and the current collecting terminal can be connected (joined) by a method including welding (for example, spot welding) such as resistance welding or ultrasonic welding.

  In a preferred embodiment, the current collecting terminal includes a pair of sandwiching portions, and the electrode sheets are bundled between the pair of sandwiching portions. The pair of sandwiching portions may be constituted by one current collecting terminal or may be constituted by a plurality of current collecting terminals. Since the positioning of the paired sandwiching portions is easy, a sandwiching portion constituted by a part of one current collecting terminal and other portions is preferable. For example, when ultrasonic spot welding is employed as a method of connecting the electrode sheet and the current collecting terminal, the end portion in the longitudinal direction in the end face shape is sandwiched between the pair of sandwiching portions, and the end portion is The electrode sheets to be configured are bundled, and ultrasonic energy is applied from the outside of the pair of sandwiching portions. Thereby, while bundling electrode sheets can be joined, this electrode sheet and the clamping part of a current collection terminal can be joined.

  On the other hand, the central portion in the longitudinal direction of the end face shape of the electrode unit is open so that the gas generated in the unit can escape in the winding axis direction. Here, the gas can be released means that the wound electrode sheets are not fixed to each other (for example, joined by welding), and the gas generated between the wound electrode sheets is adjacent in the radial direction. It can be discharged to the outside from the end face of the electrode unit through the gap between the electrode sheets. Therefore, in a normal state (a state where no gas is generated), even if a part of the wound electrode sheet is in contact with a radially adjacent (outer or inner) electrode sheet, those electrodes It is only necessary that the sheets are not fixed to each other and the gas can escape through the gap between the adjacent electrode sheets when the gas is generated. For example, the width of the central portion in the longitudinal direction in the end face shape of the electrode unit is compared with the central portion in the winding axis direction of the electrode unit (corresponding to the thickness between the flat surfaces of the electrode unit wound flatly). Even if the end portion of the electrode unit in the winding axis direction is narrower (see FIG. 4), if the gas can escape through the narrowed portion of the electrode sheet, the central portion of the electrode unit It can be said that it is open so that it can escape.

  In a preferred embodiment, the current collecting terminal is disposed so as not to cover the central portion in the longitudinal direction when viewed from the end face side of the electrode unit. In another preferred embodiment, a part of the current collecting terminal protrudes outward in the winding axis direction from the end face of the electrode unit. As a result, a gap is secured between the inner wall surface of the container and the electrode unit, and the gas that has escaped from the electrode unit can be efficiently introduced into the inner space of the container. For example, the internal pressure releasing mechanism can be appropriately operated by increasing the internal pressure of the container with the gas. Further, the gas that has escaped from the electrode unit can smoothly reach the through hole for releasing the internal pressure and be discharged out of the container.

  As described above, the electrode sheet is bundled at the end in the longitudinal direction of the end face shape of the electrode unit and connected to the current collector terminal, while the central portion in the longitudinal direction is opened, thereby allowing the electrode unit to escape gas. A highly efficient wound type power storage device can be realized. The “end portion” in the longitudinal direction in the end face shape of the electrode unit may be a portion that is biased to any end with respect to the center in the longitudinal direction, and the degree of the bias and the length of the end portion are not particularly limited. For example, in a form in which the current collector terminal is connected to both one end and the other end in the longitudinal direction in the end face shape of the electrode unit, the length of each end is defined as the total length in the longitudinal direction being 100%. Is preferably within 30% (more preferably within 25%) of the edge. Moreover, in the form in which the current collecting terminal is connected to only one end portion in the longitudinal direction, the length of the end portion is preferably within 40% from the end, and within 30%. Is more preferable. The length of the “central portion” in the longitudinal direction in the end face shape of the electrode unit is 30% or more (more preferably 40% or more, more preferably 50%) including the center in the longitudinal direction, where the total length in the longitudinal direction is 100%. % Or more).

  Specific examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

An embodiment in which the present invention is applied to a lithium secondary battery will be described with reference to the drawings.
As shown in FIGS. 1 and 2, a lithium secondary battery 1 according to the present embodiment includes a container 2 having a flat rectangular parallelepiped outer shape, and an electrode housed in the container 2 and wound in a flat shape A positive current collecting terminal 40 and a negative current collecting terminal 50 connected to the unit 10, the positive electrode sheet 12 and the negative electrode sheet 14, respectively, constituting both end portions in the axial direction of the electrode unit 10 (left and right end portions in FIG. 1). A positive external terminal 4 and a negative external terminal 5 which are connected to the current collecting terminals 40 and 50 and project through the container 2 to the outside thereof are provided.

The container 2 is made of a conductive metal such as aluminum, and has two terminal mounting holes (not shown) through which the positive and negative external terminals 4 and 5 penetrate, respectively, on one upper end surface thereof. At the center of the upper end surface, there is provided a safety valve 3 that allows the inside and outside of the container to communicate with each other and the gas in the container 2 to escape to the outside when the internal pressure of the container 2 becomes higher than a predetermined value. The container 2 contains a liquid electrolyte (electrolytic solution) (not shown) and is impregnated in the electrode unit 10. The composition of the electrolytic solution is not particularly limited. For example, a lithium salt (LiPF ₆ or the like) as a supporting salt is mixed in a mixed solvent containing diethyl carbonate (DEC) and ethylene carbonate (EC) in a mass ratio of about 7: 3. A nonaqueous electrolytic solution dissolved at a concentration of about 1 mol / L can be suitably used.

  As the electrode unit 10, the same electrode unit as that provided in a conventional flat wound battery can be used. For example, the positive electrode sheet 12 having a layer containing a positive electrode active material (positive electrode active material layer) on the surface of the positive electrode current collector 122 and the negative electrode sheet 14 having a negative electrode active material layer on the surface of the negative electrode current collector 342 are separated into separators. It is possible to use the electrode unit 10 having a structure in which the sheets are stacked via sheets (not shown) and the sheets are wound flatly. The shape of the electrode unit 10 viewed from the end surface side (hereinafter, also referred to as “end surface shape”) is substantially oval (see FIG. 3). At one end in the width direction of the positive electrode current collector 122, a band-like region (current collector terminal connection portion) where the positive electrode active material layer is not formed is provided. Similarly, at one end in the width direction of the negative electrode current collector 142, a band-like region (current collector terminal connection portion) where the negative electrode active material layer is not formed is provided. The width of the separator sheet is slightly narrower than that of the positive electrode sheet 12 and the negative electrode sheet 14, and the positive electrode sheet 12, the negative electrode sheet 14, and the separator sheet are overlapped so that the current collector terminal connection portion protrudes from both sides in the width direction of the separator sheet. Has been. By winding the overlapped sheets in this way, one end portion 10a in the winding axis direction of the electrode unit 10 is substantially from the current collector terminal connection portion (that is, the positive electrode current collector 122) of the positive electrode sheet 12. The other end portion 10b is substantially composed of a current collector terminal connection portion of the negative electrode sheet 14 (that is, the negative electrode current collector 142).

As the positive electrode current collector 122, a metal foil such as an aluminum foil is preferably used. As the positive electrode active material contained in the positive electrode active material layer, one or two or more materials conventionally used as the positive electrode active material of the lithium secondary battery can be used without any particular limitation. Preferable examples include lithium transition metal oxides such as LiMn ₂ O ₄ , LiCoO ₂ , and LiNiO ₂ . As the negative electrode current collector 142, a metal foil such as a copper foil is preferably used. As the negative electrode active material contained in the negative electrode active material layer, one or more kinds of materials conventionally used as the negative electrode active material of the lithium secondary battery can be used without particular limitation. Preferable examples include carbon materials such as graphite carbon and amorphous carbon, lithium transition metal oxides, transition metal nitrides, and the like. As the separator sheet disposed between the positive and negative electrode sheets, for example, a porous sheet made of an olefin resin (polypropylene resin or the like) can be used.

  The positive current collecting terminal 40 is connected to one end (positive side end) 10a of the electrode unit 10 configured as described above, and the negative current collecting terminal 50 is connected to the other end 10b (negative side end). Has been. As the material of the positive current collecting terminal 40, a metal such as aluminum can be preferably used. As the material of the negative current collecting terminal 50, a metal such as copper can be preferably used. In the present embodiment, the shapes of the positive current collecting terminal 40 and the negative current collecting terminal 50 are substantially the same. Therefore, in the following description, the positive current collecting terminal 40 will be described as an example.

As shown in FIGS. 2 and 3, the positive current collecting terminal 40 is substantially U-shaped when viewed from the end face side of the electrode unit 10 in a state of being attached to the positive electrode side end portion 10 a. By aligning the position of one end portion 102 (upper end in FIG. 2) 102 in the longitudinal direction of the end face shape of the electrode unit 10 and the folded portion 42 (corresponding to the bottom of the U shape) 42 of the current collecting terminal 40, The current collector terminal 40 can be easily positioned with respect to 10 (particularly, the current collector terminal 40 can be positioned in the longitudinal direction (vertical direction in FIG. 2)). The folded portion 42 is provided with a positioning portion 422 that extends inward in the axial direction (left side in FIG. 2) along the upper end 102 of the electrode unit 10. As a result, the current collecting terminal 40 can be positioned more stably.
The current collecting terminal 40 has two arm portions 44 and 46 following the folded portion 42. These arm portions 44 and 46 extend substantially parallel to each other in the longitudinal direction of the end surface shape along both sides in the width direction (left and right ends in FIG. 3) in the end surface shape of the electrode unit 10. The distal end portions 44a and 46a of the arm portions 44 and 46 reach the other end portion 104 (the lower end in FIG. 2) in the longitudinal direction.

  The tip portions 44a, 46a of the arm portions 44, 46 are thicker toward the inside of the U-shape of the current collecting terminal 40 than the central portions 44c, 46c in the longitudinal direction of the arm portions 44, 46. Is formed. Therefore, the distance between the opposing surfaces of the tip portions 44a and 46a is smaller than the distance between the opposing surfaces in the central portions 44c and 46c. The positive electrode sheet 12 constituting the positive electrode side end portion 10 a of the electrode unit 10 is sandwiched between the tip portions 44 a and 46 a at the lower end 104 of the unit 10. That is, the tip portions 44a and 46a constitute a pair of sandwiching portions (entrance side sandwiching portions) 404 that bundle the other end (lower end) 104 in the longitudinal direction in the end face shape of the electrode unit 10. The positive electrode sheet 12 and the sandwiching portion 404 sandwiched between the entrance side sandwiching portions 404 are welded by ultrasonic spot welding or the like. This ultrasonic welding can be performed, for example, by applying ultrasonic energy between the outer sides of the tip portions 44a and 46a. Typically, the wound positive electrode sheets 12 are joined together by the ultrasonic welding, and the positive electrode sheet 12 and the sandwiching portion 404 are joined.

  The base portions 44b and 46b of the arm portions 44 and 46 are also formed to be thicker toward the inside of the U-shape of the current collecting terminal 40 than the central portions 44c and 46c. Thereby, the distance between the opposing surfaces of the root portions 44b and 46b is smaller than the distance between the opposing surfaces in the central portions 44c and 46c. The positive electrode sheet 12 constituting the positive electrode side end portion 10 a of the electrode unit 10 is sandwiched between the root portions 44 b and 46 b at the upper end 102 of the unit 10. The root portion 44b and the root portion 46b constitute a pair of sandwiching portions (back-side sandwiching portions) 402 that bundle one end (upper end) 102 in the longitudinal direction in the end face shape of the electrode unit 10. The positive electrode sheet 12 and the sandwiching portion 402 sandwiched between the back side sandwiching portions 402 are welded by ultrasonic spot welding or the like. In the same manner as described above, this ultrasonic welding can be performed by applying ultrasonic energy between the outer sides of the base portions 44b and 46b. Typically, the wound positive electrode sheets 12 are joined together by the ultrasonic welding, and the positive electrode sheet 12 and the sandwiching portion 402 are joined.

In this way, as shown well in FIG. 3, both ends (upper end 102 and lower end 104) in the longitudinal direction of the positive electrode side end portion 10a are bundled and connected to the positive current collecting terminal 40. On the other hand, the positive electrode sheets 12 are opened without being fixed at the central portion 103 in the longitudinal direction of the positive electrode side end portion 10a. In FIG. 3, only a part of the positive electrode sheet 10 is schematically shown in order to make the drawing easy to see.
In this embodiment, as schematically shown in FIG. 4, the distance between the outer surfaces of the central portions 44 c and 46 c of the arm portions 44 and 46 is substantially equal to the distance between the flat surfaces in the central portion in the axial direction of the electrode unit 10. It is. Further, the distance between the inner surfaces (between the opposing surfaces) of the central portions 44c and 46c is smaller than the distance between the flat surfaces by the thickness of the central portions 44c and 46c. According to such a configuration, since the width of the electrode unit 10 (that is, the distance between the flat surfaces) and the width of the current collecting terminal 40 are substantially equal when viewed from the end face side of the electrode unit 10, the space in the container 2 is effectively used. Can be used. Unlike the central portion in the axial direction of the electrode unit 10, the negative electrode sheet 14, the separator sheet, and the positive electrode active material layer do not exist at the axial end portion 10 a of the electrode unit 10. For this reason, even if the width of the central portion 103 of the end portion 10a is reduced by the thickness of the central portions 44c and 46c, it is possible to sufficiently ensure the gas detachability of the electrode unit 10. Alternatively, as a modification of the present embodiment, the distance between the opposing surfaces of the central portions 44c and 46c may be substantially equal to the distance between the flat surfaces in the central portion of the electrode unit 10 in the axial direction. According to such a configuration, better outgassing properties can be realized. In FIG. 4, the positive electrode active material layer, the negative electrode active material layer, and the separator sheet are not shown in order to make the drawing easier to see.
In any of these examples, the substantially entire length in the longitudinal direction of the end face shape of the electrode unit 10 is held between the arm portions 44 and 46 of the current collecting terminal 40 (see FIG. 3), whereby the electrode unit 10 and the current collector are collected. The workability at the time of accommodating the composite body with the electric body 40 in the container 2 is good.

  As shown well in FIG. 2, when viewed from the flat surface side (front side of FIG. 2) of the electrode unit 10, the central portions 44 c and 46 c of the arm portions 44 and 46 are axially inward from the end surface of the electrode unit 10 (see FIG. 2). 2 on the left). On the other hand, the tip portions 44 a and 46 a and the base portions 44 b and 46 b of the arm portions 44 and 46 protrude outward in the axial direction (right side in FIG. 2) from the end surface of the electrode unit 10. These projecting portions abut against the inner wall surface of the container 2, so that the end surface of the electrode unit 10 is prevented from coming into close contact with the inner wall surface of the container 2, and the gas escape properties from this end surface are maintained well. That is, the protruding portion can function as a spacer that secures a gas passage by separating the end surface of the electrode unit 10 and the inner wall surface of the container 2.

  The connection between the positive electrode side end portion 10a of the electrode unit 10 and the positive current collecting terminal 40 can be performed, for example, by the following procedure. First, the electrode unit 10 and the current collecting terminal 40 are arranged so that the U-shaped entrance (between the arm portions 44 and 46) of the current collecting terminal 40 is located outside the upper end 102 of the positive electrode side end portion 10a of the electrode unit 10. Deploy. At this time, it is preferable that the extending direction of the arm portions 44 and 46 of the current collecting terminal 40 and the longitudinal direction of the end face shape of the electrode unit 10 are substantially matched. Then, the current collecting terminal 40 is moved in the longitudinal direction in the end face shape until the folded portion 42 contacts the upper end 102 of the electrode unit 10. As a result, the positive electrode side end portion 10a of the electrode unit 10 is inserted into the arm portions 44 and 46 from the direction perpendicular to the winding axis. Thus, by setting the current collecting terminal 40 from the direction perpendicular to the winding axis, the current collecting terminal 40 is smoothly arranged without unnecessarily disturbing the shape of the positive electrode sheet 12 constituting the positive electrode side end portion 10a. be able to. In addition, you may insert the electrode unit 10 in the state which bent the arm parts 44 and 46 in the direction in which the front-end | tip parts 44a and 46a space apart from each other (U-shaped opening direction).

  With this operation, the positive electrode side end portion 10 a of the electrode unit 10 is disposed inside the arm portions 44 and 46 of the current collecting terminal 40. Thereby, the positive electrode sheet 12 constituting the upper end 102 of the positive electrode side end portion 10a is bundled between the root portions 44b and 46b, and the positive electrode sheet 12 constituting the lower end 104 is bundled between the tip portions 44a and 46a. In this state, ultrasonic energy is applied between the tip portions 44a and 46a and between the root portions 44b and 46b. As a result, the positive electrode sheet 12 and the current collector terminal 40 sandwiched between the sandwiching portions 402 and 404 are joined together, and the sandwiched positive electrode sheets 12 are joined together. In this way, the positive electrode side end portion 10a and the positive current collecting terminal 40 can be connected. Connection between the negative electrode side end portion 10b of the electrode unit 10 and the negative current collecting terminal 50 can be performed in the same procedure.

  As described above, in the lithium secondary battery 1 of the present embodiment, the positive electrode terminal 12 constituting the upper end 102 and the lower end 104 in the longitudinal direction is bundled at the positive end 10a of the electrode unit 10, and the positive collector terminal 40. On the other hand, the positive electrode sheet 12 which comprises the center part 103 of the longitudinal direction of the positive electrode side edge part 10a is open | released, without mutually adhering. The same applies to the negative electrode side end portion 10b. Thereby, according to the lithium secondary battery 1 of the present embodiment, even when gas is generated inside the electrode unit 10, the gas can be smoothly discharged from the end portions 10 a and 10 b of the electrode unit 10. Therefore, when the internal pressure of the container 2 becomes higher than a predetermined value and the safety valve 3 is activated, the gas in the container 2 including the gas generated in the electrode unit 10 is appropriately released from the safety valve 3 to the outside. Can do. Further, since the gas escape of the electrode unit 10 is good, the electrode unit 10 is deformed (for example, swells) by the gas retained in the electrode unit 10 to block the safety valve 3, or the gas retained in the electrode unit 10 An event in which the electrode unit 10 is damaged when it comes out of the device and the damaged portion blocks the safety valve 3 to prevent proper operation is prevented.

The effect of improving the outgassing property by adopting the configuration of the above example was confirmed by the following experiment.
A paste was prepared by mixing LiNiO ₂ as a positive electrode active material, carbon powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder with N-methylpyrrolidone (NMP), and the paste was collected as a positive electrode current collector. A positive electrode sheet was prepared by applying to the surface of an aluminum foil as a foil. Moreover, the paste which mixed the carbon powder as a negative electrode active material, and PVdF as a binder with NMP was prepared, and this paste was provided to the surface of the copper foil as negative electrode current collection foil, and the negative electrode sheet was produced. These positive electrode sheet, negative electrode sheet and polypropylene porous sheet (separator sheet) were rolled flat to obtain an electrode unit. An aluminum positive current collector terminal having the shape shown in FIGS. 2 to 4 and a copper negative current collector terminal having the same shape as shown in FIGS. 2 to 4 were joined to both ends in the winding axis direction of the electrode unit thus obtained by spot welding. This was housed in a container having a safety valve together with a liquid electrolyte (electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent containing DEC: EC at a mass ratio of 7: 3). Thereafter, the container was sealed to produce a lithium secondary battery having the structure shown in the above example. Hereinafter, this lithium secondary battery is referred to as a battery A.
In this battery A, as well shown in FIG. 4, the positive electrode sheets 12 constituting the central portion in the longitudinal direction of the positive electrode side end portion 10a are opened without being fixed to each other. The same applies to the negative electrode side end.

As a comparative example, an aluminum positive current collecting terminal 740 having the shape shown in FIG. 5 and a copper negative current collecting terminal having the same shape are provided at both ends in the axial direction of the same electrode unit as that used for the manufacture of the battery A. A connected lithium secondary battery was produced. That is, as shown in FIGS. 6 and 7, the plate-like portion 744 of the positive current collecting terminal 740 is inserted into the winding center portion of the positive electrode side end portion 10a of the electrode unit 10 to form the positive electrode side end portion 10a. The sheet was bundled on both sides of the plate-like portion 744 and spot welded. Similarly, a copper negative collector terminal having the same shape as the positive collector terminal 740 was spot welded to the negative electrode side end of the electrode unit 10. In other respects, a lithium secondary battery was produced in the same manner as battery A. Hereinafter, this lithium secondary battery is referred to as a battery B.
In this battery B, as well shown in FIG. 7, the positive electrode sheet 12 constituting the central portion in the longitudinal direction of the positive electrode side end portion 10 a is gathered on the plate-like portion 744 of the positive current collecting terminal 740 and welded. ing. The same applies to the negative electrode side end.

With respect to the battery A and the battery B, with a design capacity of the electrode unit as a reference, a constant voltage / constant voltage of up to 4.1 V at a current that is 1/5 of the capacity (that is, a current value that fully charges the battery in 5 hours) The battery was charged with current and kept in a non-energized state for 5 minutes, then discharged to 3 V at the same current as that during charging, and kept in a non-energized state for 5 minutes. This charge / discharge cycle was repeated 5 times to perform initial activation (conditioning) of the battery.
Ten batteries A and B, each of which has completed the initial activation, were prepared. These batteries A and B were subjected to an overcharge test in which they were charged until they could not be energized with a current that was twice the design capacity, and the state of the batteries at that time was observed. As a result, in each battery A in which the central portion in the longitudinal direction in the shape of the electrode unit viewed from the end face side was opened, the safety valve operated normally, and the internal pressure of the battery could be properly released. On the other hand, in the battery B in which the center part in the longitudinal direction in the end face shape was closed by welding, in some batteries, deformation of the container due to excessive increase of the internal pressure was observed. When these containers were examined in detail, it was found that the safety valve was clogged with fragments of the electrode unit (negative electrode current collector foil).

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, in the above embodiment, a battery including a metallic outer container has been described, but the material of the outer container is not limited thereto. The present invention is also applicable to, for example, a power storage device (such as a lithium secondary battery) provided with a film outer package.
In addition, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Moreover, the technique illustrated in this specification or the drawings achieves a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

It is a front view which shows the lithium secondary battery which concerns on one Example. It is a front view which shows the electrode unit and current collection terminal of the lithium secondary battery which concern on one Example. FIG. 3 is a view in the direction of arrow III in FIG. 2. It is the IV-IV sectional view taken on the line of FIG. It is a perspective view which shows the current collection terminal of the lithium secondary battery which concerns on a comparative example. It is a front view which shows the electrode unit and current collection terminal of the lithium secondary battery which concern on a comparative example. It is the VII-VII sectional view taken on the line of FIG.

Explanation of symbols

1: Lithium secondary battery 3: Safety valve (internal pressure release mechanism)
10: Electrode unit 10a: One end (positive electrode side end)
10b: the other end (negative electrode side end)
102: One end (upper end)
103: Central portion 104: The other end (lower end)
12: Positive electrode sheet 14: Negative electrode sheet 40: Positive current collecting terminal 402: Back side pinching part 404: Entrance side pinching part 42: Folding part 422: Positioning part 44, 46: Arm part 44a, 46a: Tip part 44b, 46b: Root portion 50: Negative current collecting terminal

Claims (5)

A wound power storage device comprising a wound electrode unit in which positive and negative electrode sheets are wound flatly and a current collecting terminal connected to an end of the electrode unit in the winding axis direction,
In the electrode unit, the electrode sheet is bundled and connected to the current collecting terminal at both ends in the longitudinal direction when the unit is viewed from the end surface side, and the central part in the longitudinal direction is connected to the inside of the unit. A wound type power storage device in which the gas generated in step 1 is opened so as to be able to escape in the winding axis direction. The current collector terminal is provided with a nip portion of each at least one pair pinching from both outer longitudinal both ends of each of the edge shapes in the width direction of the end face shape of the electrode unit, between 該挟 write unit The power storage device according to claim 1, wherein the electrode sheets are bundled and connected to the sandwiching portion.   The shape of the current collector terminal viewed from the end face side of the electrode unit is such that the outer surface of the unit extends from one end portion in the longitudinal direction of the end face shape of the unit along both outer sides in the width direction of the end face shape. The power storage device according to claim 2, wherein the power storage device has a U shape extending in a straight line. The current collecting terminal includes at least a pair of sandwiching portions provided on the back side of the U-shape, and at least a pair of sandwiching portions provided on the U-shaped entrance side,
The one end part of the longitudinal direction in the end surface shape of the said electrode unit is connected to the said clamping part by the side of the back, The other edge part is connected to the clamping part by the side of the said entrance. Power storage device.   The said current collection terminal has a positioning part extended in the winding-axis direction inner side rather than the said clamping part along one edge part of the longitudinal direction in the end surface shape of the said electrode unit, Any one of Claim 2 to 4 The power storage device according to item.

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