Patent Publication Number: US-2023155160-A1

Title: Battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under Japanese Patent Application No.  2021-186979  filed on Nov. 17, 2021, the entire contents whereof are incorporated into the present specification by reference. 
     BACKGROUND OF THE DISCLOSURE 
     1. Technical Field 
     The present disclosure relates to a battery. 
     2. Background 
     A battery such as a lithium ion secondary battery is provided with for instance a power generation element that has a first electrode and a second electrode having a polarity different from that of the first electrode. Japanese Patent Application Publication No. 2018-06138 discloses an electrode made up of a rectangular sheet having a first edge and a second edge. The battery disclosed in Japanese Patent Application Publication No. 2018-06138 is provided with a power generation element in the form of an electrode body in which such rectangular sheet electrodes are laid up on each other across an interposed separator. 
     SUMMARY OF THE INVENTION 
     As a power generation element of this kind of battery, there may be used for instance a so-called wound electrode body in which a strip-shaped first electrode plate and a strip-shaped second electrode plate are wound in the longitudinal direction, across a strip-shaped separator. The inventors aim at reducing further the risk of short-circuits between positive and negative electrodes in a battery having a wound electrode body. 
     The art disclosed herein provides a battery having: a battery case; and a wound electrode body which is accommodated in the battery case, and in which a strip-shaped first electrode plate and a strip-shaped second electrode plate having different polarity from that of the first electrode plate are wound in a longitudinal direction, with a strip-shaped separator interposed therebetween. The first electrode plate has a first long edge, and a second long edge different from the first long edge, extending in the longitudinal direction. The first electrode plate has a first electrode core, and a first electrode active material layer provided on the first electrode core. The first electrode core has a first electrode active material layer existing section at which the first electrode active material layer is provided, and a first electrode active material layer non-existing section at which the first electrode active material layer is not provided. A plurality of first electrode tabs is provided on the first long edge. A first notch is provided at a first corner, on the first long edge side, of a winding initiation end portion of the first electrode plate. At least part of the first notch is provided in the first electrode active material layer non-existing section. 
     It is found that the first corner is one of the portions, of the first electrode plate, that bends particularly readily. In a battery having such a configuration, bending of the first corner that bends readily can be suppressed by providing thus the first notch portion at the first corner. By suppressing bending of the first corner, it becomes possible to prevent damage to separators in the wound electrode body, and by extension, to suppress short-circuits between the positive and negative electrodes. 
     In one implementation of the battery disclosed herein, the first electrode plate is a positive electrode plate, and the second electrode plate is a negative electrode plate. The first corner bends more readily in the positive electrode plate than in the negative electrode plate. Accordingly, the effect of the art disclosed herein can be suitably realized in a battery having the above configuration. 
     In another implementation of the battery disclosed herein, the first electrode active material layer non-existing section is provided with a protective layer; and the first notch is provided at a portion at which the protective layer is provided. Safety can be further improved by virtue of such a configuration. 
     In another implementation of the battery disclosed herein, a thickness of the protective layer is smaller than a thickness of the first electrode active material layer. The effect of the art disclosed herein can be suitably brought out in a battery having such a configuration. 
     In another implementation of the battery disclosed herein, the first notch is a portion formed by laser cutting. In addition to eliciting the above short-circuit suppression effect, such a configuration allows improving battery productivity. 
     In another implementation of the battery disclosed herein, the first notch is formed within the first electrode active material layer non-existing section. Such a configuration allows ensuring battery capacity. 
     In another implementation of the battery disclosed herein, the first notch has a rounded shape. Such a configuration allows suppressing bending in the first notch. 
     In another implementation of the battery disclosed herein, the first electrode plate is a positive electrode plate, and the second electrode plate is a negative electrode plate; the negative electrode plate has a negative electrode core, and a negative electrode active material layer formed on the negative electrode core; and an end of the first notch, on the second long edge side, opposes the negative electrode active material layer across the separator. Safety can be further improved by virtue of such a configuration. 
     In another implementation of the battery disclosed herein, the first electrode plate has a first electrode plate body; and the plurality of first electrode tabs provided on the first long edge. A length of the first electrode plate body, in a direction along a winding axis of the wound electrode body, is 20 cm or larger. The effect of the art disclosed herein can be suitably brought out in a battery having such a configuration. 
     In another implementation of the battery disclosed herein, a second notch is provided at a second corner, on the first long edge side, in a winding termination end portion of the first electrode plate; and a shape of the second notch and a shape of the first notch are dissimilar. In such a configuration, the first notch is a notch of less bendable share, and accordingly the above short-circuit suppression effect can be yet better brought out. 
     In another implementation of the battery disclosed herein, no notch is formed at a third corner, on the second long edge side, of a winding initiation end portion of the first electrode plate. Such a configuration allows ensuring battery capacity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective-view diagram illustrating schematically a battery according to an embodiment; 
         FIG.  2    is a schematic cross-sectional diagram along line II-II of  FIG.  1   ; 
         FIG.  3    is a perspective-view diagram illustrating schematically an electrode body attached to a sealing plate; 
         FIG.  4    is a perspective-view diagram illustrating schematically an electrode body having collectors attached thereto; 
         FIG.  5    is a schematic diagram illustrating the configuration of an electrode body according to an embodiment; 
         FIG.  6    is a plan-view diagram illustrating schematically a positive electrode plate according to an embodiment; 
         FIG.  7    is a plan-view diagram for explaining a production procedure of a positive electrode plate according to an embodiment; 
         FIG.  8    is a plan-view diagram illustrating another example of the shape of a recess depicted in frame A; 
         FIG.  9    is a plan-view diagram illustrating another example of the shape of a recess depicted in frame A; 
         FIG.  10    is a plan-view diagram illustrating another example of the shape of the recess depicted in frame A of  FIG.  7   ; 
         FIG.  11    is a plan-view diagram illustrating an example of a cut portion of the recess depicted in frame D; and 
         FIG.  12    is a plan-view diagram illustrating an example of a cut portion of the recess depicted in frame D. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the art disclosed herein will be explained next with reference to accompanying drawings. Needless to say, the embodiments described herein are not meant to limit the present invention in any particular way. Unless otherwise indicated, the art disclosed herein is not limited to the embodiments explained here. 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 (a secondary battery in the art disclosed herein) 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 techniques 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. In the present specification a secondary battery may also simply be referred to as a “battery”. 
       FIG.  1    is a perspective-view diagram illustrating schematically a battery according to an embodiment.  FIG.  2    is a schematic cross-sectional diagram along line II-II of  FIG.  1   . 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 battery  1  is installed. 
     As illustrated in  FIG.  1    and  FIG.  2   , the battery  1  includes a battery case  10 , an electrode body  20 , a positive electrode terminal  30 , a negative electrode terminal  40 , a positive electrode collector  50 , a negative electrode collector  60 , insulators  70  and gaskets  90 . Although not illustrated in the figures, the battery  1  further includes an electrolyte solution. The battery  1  is a lithium ion secondary battery. 
     The battery case  10  is a housing for accommodating the electrode body  20 . The battery case  10  has herein a flat and bottomed cuboid (square) outer shape. The material of the battery case  10  is not particularly limited, and may be identical to conventionally used materials. The battery case  10  is preferably made of a metal, and is more preferably made up of for instance aluminum, an aluminum alloy, iron, or an iron alloy. Besides the electrode body  20 , also an electrolyte solution (not shown) is accommodated within the battery case  10 . Electrolyte solutions used in 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. 
     The battery case  10  includes an exterior body  12  having an opening  12   h , and a sealing plate (lid)  14  that plugs the opening  12   h . As illustrated in  FIG.  1   , the exterior body  12  includes a flat rectangular bottom wall  12   a , a pair of mutually opposing first side walls  12   b  extending in the height direction Z from a pair of opposing sides of the bottom wall  12   a , and a pair of mutually opposing second side walls  12   c  extending in the height direction Z from another pair of opposing sides of the bottom wall  12   a . In the present embodiment the first side walls  12   b  are long side walls extending from a pair of mutually opposing long sides of the bottom wall  12   a . The second side walls  12   c  are short side walls extending from a pair of mutually opposing short sides of the bottom wall  12   a . In the present embodiment the surface area of the second side walls  12   c  is smaller than the surface area of the first side walls  12   b . As illustrated in  FIG.  2   , the bottom wall  12   a  opposes the opening  12   h . The sealing plate  14  seals the opening  12   h  of the exterior body  12 . The sealing plate  14  opposes the bottom wall  12   a  of the exterior body  12 . The sealing plate  14  has a substantially rectangular shape in a plan view. The battery case  10  is integrated through joining of the sealing plate  14  to the peripheral edge of the opening  12   h  of the exterior body  12 . The battery case  10  is airtight sealed. 
     The sealing plate  14  is provided with a liquid injection hole  15 , a gas discharge valve  17 , and two terminal lead-out holes  18 ,  19 . The purpose of the liquid injection hole  15  is to inject an electrolyte solution after assembly of the sealing plate  14  to the exterior body  12 . The liquid injection hole  15  is sealed by a sealing member  16 . The gas discharge valve  17  is a thin-walled portion configured to break, and release gas to the exterior of the battery case  10 , when the pressure within the battery case  10  exceeds a predetermined value. The terminal lead-out holes  18 ,  19  are formed at either respective end of the sealing plate  14  in the width direction Y. The terminal lead-out holes  18 ,  19  run through the sealing plate  14  in the height direction Z. The terminal lead-out holes  18 ,  19  each have an inner diameter that is large enough as to enable insertion of the positive electrode terminal  30  and the negative electrode terminal  40  before attachment to the sealing plate  14  (before crimping). 
     The positive electrode terminal  30  and the negative electrode terminal  40  are attached to the sealing plate  14 . The positive electrode terminal  30  is disposed on one side (left side in  FIG.  1    and  FIG.  2   ) of the sealing plate  14  in the width direction Y. The negative electrode terminal  40  is disposed on the other side (right side in  FIG.  1    and  FIG.  2   ) of the sealing plate  14  in the width direction Y. For instance, aluminum is used in the positive electrode terminal  30 . For instance, copper is used in the negative electrode terminal  40 . 
     The positive electrode terminal  30  has a flat plate-shaped base portion  31  disposed on the outer surface of the sealing plate  14 , and a shaft portion  32  extending from the base portion  31  downwards in the height direction Z (towards the bottom wall  12   a ). The base portion  31  of the positive electrode terminal  30  is exposed on the outer surface of the sealing plate  14 . The shaft portion  32  of the positive electrode terminal  30  extends from the exterior to the interior of the sealing plate  14 , through the terminal lead-out hole  18 . The shaft portion  32  is fixed to a below-described first collector portion  51  of the positive electrode collector  50  via a through-hole of the first collector portion  51 , in the interior of the battery case  10 . Herein, the positive electrode terminal  30  is fixed, by crimping, to the peripheral edge portion of the sealing plate  14  surrounding the terminal lead-out hole  18 . Also, the negative electrode terminal  40  in the battery  1  has a structure substantially similar to that of the positive electrode terminal  30 . Accordingly, a detailed depiction and explanation of the structure of the negative electrode terminal  40  will be omitted herein. The reference numeral  41  in  FIG.  2    denotes the base portion, and the reference numeral  42  denotes the shaft portion, of the negative electrode terminal  40 . 
     Plate-shaped external conductive members  35 ,  45  are attached to the outer surface of the sealing plate  14 . The external conductive member  35  on the positive electrode side is electrically connected to the positive electrode terminal  30 . The external conductive member  45  on the negative electrode side is electrically connected to the negative electrode terminal  40 . The external conductive members  35 ,  45  are members to which respective bus bars are attached when multiple batteries  1  are electrically connected to each other. The external conductive members  35 ,  45  are made of for instance aluminum or an aluminum alloy. The external conductive members  35 ,  45  are insulated from the sealing plate  14  by respective external insulating members  92 . The external conductive members  35 ,  45  are however not essential, and may be omitted in other embodiments. The resin materials illustrated as constituent materials of the below-described insulators  70  and gaskets  90  can be used herein as the constituent material of the external insulating members  92 . 
     A respective insulator  70  is disposed between the positive electrode collector  50  (for instance the terminal connection portion  51   a  of the first collector portion  51 ) and the inner surface of the sealing plate  14 . A through-hole is formed in the insulator  70 . A respective gasket  90  is disposed between the positive electrode terminal  30  (specifically, the base portion  31 ) and the outer surface of the sealing plate  14 . The gasket  90  has a cylindrical protrusion that is inserted into the terminal lead-out hole  18  of the sealing plate  14 . The protrusion of the gasket  90  is disposed along the inner periphery of the through-hole of the insulator  70 . By providing the insulator  70  and the gasket  90  thus configured it becomes possible to prevent contact between the positive electrode collector  50  and the sealing plate  14 , and contact between the positive electrode terminal  30  and the sealing plate  14 . Although a detailed explanation thereof will be omitted herein, the same insulating structure relying on an insulator and a gasket is provided on the negative electrode terminal  40  side. The constituent materials of the insulators  70  and the gaskets  90  are not particularly limited, and may be for example a polyolefin resin (for instance polypropylene (PP) or polyethylene (PE)), a fluororesin (for instance a perfluoroalkoxy alkane (PFA) or polytetrafluoroethylene) (PTFE)). 
       FIG.  3    is a perspective-view diagram illustrating schematically an electrode body attached to a sealing plate.  FIG.  4    is a perspective-view diagram illustrating schematically an electrode body having collectors attached thereto. As illustrated in  FIG.  3   , the battery  1  includes one or multiple electrode bodies  20 . In the present embodiment the battery  1  includes three electrode bodies  20 . As illustrated in  FIG.  2   , each electrode body  20  is disposed inside the exterior body  12  in a state of being covered with an electrode body holder  29  made up of a resin sheet of polyethylene (PE). 
       FIG.  5    is a schematic diagram illustrating the configuration of an electrode body according to an embodiment. As illustrated in  FIG.  5   , the electrode body  20  is a wound electrode body in which a strip-shaped positive electrode plate  22  and a strip-shaped negative electrode plate  24  are laid up on each other via a respective strip-shaped separator  26 , with the resulting stack wound in the longitudinal direction. In the present specification the electrode body  20  may also be referred to as “wound electrode body 20”. The positive electrode plate  22  is an example of the “first electrode plate” of the battery disclosed herein. The negative electrode plate  24  is an example of the “second electrode plate” of the battery disclosed herein. The wound electrode body  20  includes a main body  20   a , a positive electrode tab group  23 , and a negative electrode tab group  25  (see  FIG.  2    to  FIG.  4   ). The main body  20   a  is a portion in which the positive electrode plate  22 , the negative electrode plate  24 , and the separators  26  are laid up on each other, and has for instance a flat shape. 
     As illustrated in  FIG.  1   ,  FIG.  2    and  FIG.  5   , the wound electrode body  20  is disposed inside the exterior body  12  so that a winding axis WL is parallel to the width direction Y. In the present embodiment the wound electrode body  20  is disposed inside the exterior body  12  in an orientation such that the winding axis WL is parallel to the bottom wall  12   a  and perpendicular to the second side walls  12   c . The end faces of the wound electrode body  20  in the direction along the winding axis WL oppose the second side walls  12   c  of the exterior body  12 . In the present specification, for convenience of explanation, the end face of each wound electrode body  20  (for instance the main body  20   a ) opposing one second side wall  12   c , on the side closer to the positive electrode collector  50  (left side in the width direction Y, in  FIG.  2   ), will be referred to as “first end face  201 ”. Similarly, the end face of each wound electrode body  20  (for instance the main body  20   a ) opposing one second side wall  12   c , on the side closer to the negative electrode collector  60  (right side in the width direction Y, in  FIG.  2   ), will be referred to as “second end face  202 ”. 
     Each electrode plate that makes up the wound electrode body has for instance a strip-shaped electrode core and an electrode active material layer formed on the electrode core. The electrode core has for instance an electrode active material layer existing section in which the electrode active material layer is formed, and an electrode active material layer non-existing section in which the electrode active material layer is not formed. By virtue of not having the electrode active material layer formed thereon, the electrode active material layer non-existing section is softer and more readily bendable than the electrode active material layer existing section. 
     For instance in the process of producing the wound electrode body, the corners of the electrode plates at the end portions in the longitudinal direction (winding direction) are interfered with, by equipment, to a greater degree (for instance in terms of contact with a jig) than other portions. The corners may be brought to a state of being more readily bendable, therefore, when the corners are made up of by the electrode active material layer non-existing section. In an endeavor to reduce the risk of short-circuits between the positive and negative electrodes due to separator damage derived from bent corners, in the interior of the wound electrode body, the inventors studied configurations that allowed suppressing bending of corners at the winding initiation end portion of the electrode plates. 
       FIG.  6    is a plan-view diagram illustrating schematically a positive electrode plate according to the embodiment. The positive electrode plate  22  has an elongated strip shape, as illustrated in  FIG.  5    and  FIG.  6   . In the present embodiment the positive electrode plate  22  includes a positive electrode plate body  22   x  and a plurality of positive electrode tabs  22   t . As illustrated in  FIG.  5    and  FIG.  6   , the positive electrode plate body  22   x  is a portion of the positive electrode plate  22  flanked by a first long edge  221  and a second long edge  222 . The first long edge  221  is for instance a side extending in a longitudinal direction P of the positive electrode plate  22 . The second long edge  222  is for instance a side, different from the first long edge  221 , extending in the longitudinal direction P of the positive electrode plate  22 . The multiple positive electrode tabs  22   t  are provided on for instance the first long edge  221 . In the present embodiment the positive electrode tabs  22   t  are part of a positive electrode core  22   c . In the present embodiment the positive electrode tabs  22   t  are provided (intermittently) at intervals along the longitudinal direction P of the positive electrode plate  22 . The positive electrode tabs  22   t  project from the first long edge  221  along a transverse direction Q of the positive electrode plate  22 . As illustrated in  FIG.  5   , the positive electrode tabs  22   t  in the wound electrode body  20  project beyond the separator  26  in the width direction Y. 
     The length of the positive electrode plate body  22   x  in the transverse direction Q of the positive electrode plate  22  is for instance from 10 cm to 60 cm. Such a length is 20 cm or larger (for instance 25 cm or larger, or 30 cm or larger) in the present embodiment. The greater the length of the positive electrode plate body  22   x , the more difficult it becomes to wind stably the positive electrode plate body  22   x , for instance in the production process of the wound electrode body  20 . In the positive electrode plate  22  having the positive electrode plate body  22   x  such as that described above, the corners at the ends of the positive electrode plate  22  in the longitudinal direction P are readily bent. Accordingly, the effect of the art disclosed herein can be suitably brought out in a case where such a positive electrode plate  22  is used. 
     The positive electrode plate  22  has the positive electrode core  22   c  and a positive electrode active material layer  22   a  formed on at least one surface of the positive electrode core  22   c . 
     The positive electrode core  22   c  is for instance strip-shaped. The positive electrode core  22   c  is a metal foil made of for instance aluminum, an aluminum alloy, nickel or stainless steel. As illustrated in  FIG.  6   , the positive electrode core  22   c  has a positive electrode active material layer existing section  22   c   1  and a positive electrode active material layer non-existing section  22   c   2 . The positive electrode active material layer existing section  22   c   1  is for instance a portion at which the positive electrode active material layer  22   a  is formed. In the present embodiment the positive electrode active material layer existing section  22   c   1  is a portion provided in the form of a strip, on the second long edge  222  side, of the positive electrode plate  22 , along the longitudinal direction P. The positive electrode active material layer non-existing section  22   c   2  is for instance a portion at which the positive electrode active material layer  22   a  is not formed. In the present embodiment the positive electrode active material layer non-existing section  22   c   2  is provided on a strip-shaped portion of the positive electrode plate  22  along the first long edge  221  and on the positive electrode tabs  22   t . As illustrated in  FIG.  6   , the positive electrode active material layer non-existing section  22   c   2  has a protective layer  22   p . As illustrated in  FIG.  5    and  FIG.  6   , the protective layer  22   p  is provided at a strip-shaped portion along a side edge of the positive electrode active material layer  22   a , on the first long edge  221  side, and at part of the base end side of the positive electrode tabs  22   t . 
     The positive electrode active material layer  22   a  contains a positive electrode active material (for instance a lithium-transition metal complex oxide such as a lithium-nickel-cobalt-manganese complex oxide) capable of reversibly storing and releasing a charge carrier. The positive electrode active material layer  22   a  contains for instance 80 mass% or more (preferably 90 mass% or more, more preferably 95 mass% or more) of the positive electrode active material, relative to 100 mass% as the total solids of the positive electrode active material layer  22   a . The positive electrode active material layer  22   a  may contain optional components, for instance a conductive material, a binder and various additional components, besides the positive electrode active material. Examples of the conductive material include carbon materials such as acetylene black (AB). Examples of the binder include polyvinylidene fluoride (PVdF). 
     The protective layer  22   p  is for instance a layer of higher resistance than that of the positive electrode active material layer  22   a . The protective layer  22   p  contains for instance inorganic particles and a resin (binder). Examples of the inorganic particles include inorganic oxides such as alumina, boehmite, magnesia, silica and titania. Examples of the resin (binder) include polyvinylidene fluoride (PVdF). Alternatively, the protective layer  22   p  may be a layer made up of a resin. The protective layer  22   p  may contain a conductive material such as a carbon material, as needed. The effect of suppressing short-circuits between the positive electrode plate  22  and the negative electrode plate  24  in the wound electrode body  20  can be enhanced by providing the protective layer  22   p . 
     For instance the thickness of the protective layer  22   p  is smaller than the thickness of the positive electrode active material layer  22   a . The corners at the ends of the positive electrode plate  22  in the longitudinal direction P are more readily bendable when the thickness of the protective layer  22   p  is smaller than the thickness of the positive electrode active material layer  22   a . Accordingly, the effect of the art disclosed herein can be suitably realized in a case where the thickness of the protective layer  22   p  is smaller than the thickness of the positive electrode active material layer  22   a . The smaller the thickness of the protective layer  22   p , the more readily bendable are the corners at the ends of the positive electrode plate  22  in the longitudinal direction P. The effect of the art disclosed herein is preferably brought out in a case where the thickness of the protective layer  22   p  is 0.7 or less, and more preferably in a case where the above thickness is 0.5 or less, relative to  1  as the thickness of the positive electrode active material layer  22   a . Formation of the protective layer  22   p  is not essential, and may be omitted in other embodiments. 
     As illustrated in  FIG.  6   , a first notch N 1  is provided at a first corner C 1 , on the first long edge  221  side, of the winding initiation end portion  22   s  of the positive electrode plate  22 . In the present specification the “winding initiation end portion  22   s  of the positive electrode plate  22 ” denotes an end portion of the positive electrode plate  22 , in the longitudinal direction P, and disposed on the innermost circumference of the wound electrode body  20 . In  FIG.  6   , the first short edge on the left side flanked between the first long edge  221  and the second long edge  222  serves as the winding initiation end portion  22   s . In the present specification, the “first corner C 1 ” denotes a corner formed by a straight line L 1  along the first long edge  221 , and by a straight line L 2  along the first short edge. 
     In the present embodiment at least part of the first notch N 1  is provided in the positive electrode active material layer non-existing section  22   c   2 . It is considered that the first corner C 1  is one of the portions, of the positive electrode plate  22 , that bends particularly readily. Bending of the first corner C 1  can be suppressed by providing thus the first notch N 1  at the first corner C 1  that bends readily. By curtailing bending of the first corner C 1  an effect can thus be elicited of suppressing damage to the separators  26  in the wound electrode body  20 , which in turn allows eliciting the effect of suppressing short-circuits between the positive and negative electrodes. 
     In the present embodiment the first notch N 1  is formed within the positive electrode active material layer non-existing section  22   c   2 . For instance, a first end portion N 1   a , on the second long edge  222  side, of the first notch N 1  and a second end portion N 1   b  on the first long edge  221  side are provided within the positive electrode active material layer non-existing section  22   c   2 . As illustrated in  FIG.  6   , the first notch N 1  is kept within the positive electrode active material layer non-existing section  22   c   2 , without reaching the positive electrode active material layer existing section  22   c   1 ; this allows preventing loss of the positive electrode active material layer  22   a . Battery capacity can be secured as a result. 
     In the present embodiment the first notch N 1  is provided at each portion at which the protective layer  22   p  is provided. For instance, the first end portion N 1   a  and the second end portion N 1   b  are provided at portions where the protective layer  22   p  is provided. As illustrated in  FIG.  6   , the first notch N 1  is provided at a portion where the protective layer  22   p  is provided (in other words, a portion where the positive electrode core  22   c  is not exposed), thanks to which safety can be further improved. 
     In the present embodiment, moreover, the first notch N 1  has a rounded shape. In the present specification the feature wherein “the first notch N 1  has a rounded shape” signifies for instance that the first notch N 1  is made up of a curve (for instance not a straight portion) between the first end portion N 1   a  and the second end portion N 1   b . Accumulation of stress at the first notch N 1  (for instance stress derived from contact with a jig during the production process of the wound electrode body  20 ) can be suppressed by imparting the first notch N 1   with a rounded shape. As a result, it becomes possible to suppress bending in the first notch N 1 . 
     In the present embodiment, moreover, the first notch N 1  exhibits an angle α, formed by the first notch N 1  and the winding initiation end portion  22   s  (first short edge), in the range from 90 degrees to 160 degrees. Such an angle is preferably 95 degrees or larger, more preferably 100 degrees or larger, and yet more preferably 120 degrees or larger. In a case where the first notch N 1  has a rounded shape, the angle α can be defined by for instance the angle formed by a tangent line T 1  passing through the first end portion N 1   a  and the winding initiation end portion  22   s  (first short edge). 
     As illustrated in  FIG.  6   , a second notch N 2  is provided in a second corner C 2 , on the first long edge  221  side, of a winding termination end portion  22   e  of the positive electrode plate  22 . In the present specification the “winding termination end portion  22   e  of the positive electrode plate  22 ” denotes the end portion, of the positive electrode plate  22 , disposed on the outermost circumference of the wound electrode body  20 . In  FIG.  6    the second short edge on the right side flanked between the first long edge  221  and the second long edge  222  serves as the winding termination end portion  22   e . In the present specification the “second corner C 2 ” signifies a corner formed by the straight line L 1  along the first long edge  221  and a straight line L 3  along the second short edge. 
     In the present embodiment the shape of the second notch N 2  and the shape of the first notch N 1  are different from each other. For instance, the first notch N 1  is formed so that the angle α is 90 degrees or larger, while an angle β formed by the second notch N 2  and the winding termination end portion  22   e  is set to be smaller than 90 degrees. In a case where the second notch N 2  has a rounded shape, the angle β can be defined for instance by the angle formed by a tangent line T 2  passing through a third end portion N 2   a  on the second long edge  222  side of the second notch N 2 , and the winding termination end portion  22   e  (second short edge). Alternatively, the surface area of the cutout for forming the first notch N 1  can be set to be smaller than the surface area of the cutout for forming the second notch N 2 . 
     In the production of the positive electrode plate  22  for instance the second notch N 2  can also be formed upon formation of the first notch N 1  in accordance with the procedure described below. Formation of such notches may involve forming two notches of mutually dissimilar shapes, in the positive electrode plate  22 . In the production process of the wound electrode body  20 , the positive electrode active material layer non-existing section  22   c   2  at the winding initiation end portion  22   s  of the positive electrode plate  22  is unlikelier to be interfered with, by equipment, than the winding termination end portion  22   e , for instance due to interference with a winding core of a winding machine or with an electrode plate draw-out chuck. Therefore, the first corner C 1  bends more readily than the second corner C 2 . By configuring the first notch N 1  in the form of a notch having a less bendable shape it becomes therefore possible to elicit yet better the effect of suppressing damage to the separators  26 , and by extension the effect of suppressing short-circuits. Moreover, the productivity of the positive electrode plate  22  can be improved. The method of forming the notches will be further described below. 
     In the present embodiment the second notch N 2  is formed within the positive electrode active material layer non-existing section  22   c   2 . For instance, a third end portion N 2   a , and a fourth end portion N 2   b , on the first long edge  221  side, of the second notch N 2  are provided in the positive electrode active material layer non-existing section  22   c   2 . The second notch N 2  is provided at a portion at which the protective layer  22   p  is provided. For instance, the third end portion N 2   a  and the fourth end portion N 2   b  are provided at a portion at which the protective layer  22   p  is provided. 
     In the present embodiment no notch is formed in a third corner C 3 , on the second long edge  222  side, of the winding initiation end portion  22   s  of the positive electrode plate  22 . Also, no notch is formed in a fourth corner C 4 , on the second long edge  222  side, of the winding termination end portion  22   e  of the positive electrode plate  22 . In the present specification, the “third corner C 3 ” denotes a corner formed by the second long edge  222  and the first short edge (winding initiation end portion  22   s ). In the present specification, the “fourth corner C 4 ” denotes a corner formed by the second long edge  222  and the second short edge (winding termination end portion  22   e ). Loss of the positive electrode active material layer  22   a  can be prevented, since no notch is formed in the third corner C 3  or the fourth corner C 4 . Battery capacity can be secured as a result. 
       FIG.  7    is a plan-view diagram for explaining a production procedure of a positive electrode plate according to an embodiment. Production of the positive electrode plate  22  includes for instance preparing a positive electrode precursor  21  and cutting the positive electrode precursor  21  (see  FIG.  7   ). 
     To prepare the positive electrode precursor  21 , for instance, firstly a paste for positive electrode active material layer formation containing a constituent material of the positive electrode active material layer  22   a  is applied, on a region denoted the reference numeral  22   a  in  FIG.  7   , along the longitudinal direction P of the positive electrode core  22   c . Next, a paste for protective layer formation containing a constituent material of the protective layer  22   p  is applied in the region denoted the reference numeral  22   p  in  FIG.  7   , along the longitudinal direction P of the positive electrode core  22   c . In the positive electrode precursor  21  illustrated in  FIG.  7   , a coating region of the paste for protective layer formation, flanks a coating region of the paste for positive electrode active material layer formation, from the transverse direction Q of the positive electrode core  22   c . The positive electrode precursor  21  can be prepared through drying of the pastes. 
     The positive electrode precursor  21  is cut next. Cutting of the positive electrode precursor  21  involves for instance cutting the positive electrode precursor  21  along a dotted line L p1 , a two-dot chain line L p2 , and a two-dot chain line L p3  in  FIG.  7   . Through cutting along the dotted line L p1  it becomes possible to cut part of the positive electrode precursor  21  out in bulging shapes, to form the positive electrode tabs  22   t  (see  FIG.  5    and  FIG.  6   ). In the present embodiment, the recess depicted in frame A is formed through cutting along the dotted line L p1 . By forming such a recess, it becomes possible to form a notch through cutting along the below-described two-dot chain line L p3 . Cutting along the dotted line L p1  may involve conventional cutting using laser, a cutting blade, a die or a cutter. Laser cutting is preferably resorted to for cutting along the dotted line L p1 . The notch can be produced with higher quality, and with higher speed, by laser cutting. In a case where the first notch N 1  is a portion formed by laser cutting, the positive electrode core  22   c  melted by the laser solidifies at the edge portion of the first notch N 1 . Accordingly, the thickness of such an edge portion is larger than the thickness of the positive electrode core  22   c . 
     Cutting along the two-dot chain line L p2 , involves cutting the central portion of the positive electrode precursor  21  in the transverse direction Q, along the longitudinal direction P. Through cutting along the two-dot chain line L p2  it becomes possible to produce the positive electrode plate  22  having the protective layer  22   p  and positive electrode tabs  22   t  formed only on one long edge (first long edge  221  in  FIG.  6   ). Cutting along the two-dot chain line L p2  is not particularly limited, and may be involve conventional cutting using a laser, a cutting blade, a die, a cutter or the like. 
     Cutting along the two-dot chain line L p3  involves cutting the recess depicted in frame A in the transverse direction Q. By cutting along the two-dot chain line L p3 , respective notches can be formed on the left side and the on right side of the two-dot chain line L p3 . either the left side or the right side of the two-dot chain line L p3  is set as the winding initiation end portion  22   s , and the other is set as the winding termination end portion  22   e , for instance on the basis of the shape of the formed notch. The positive electrode plate  22  having the first notch N 1  formed at the first corner C 1  and the second notch N 2  formed at the second corner C 2  can be produced in this way. 
     As illustrated in  FIG.  5   , the negative electrode plate  24  has an elongated strip shape. In the present embodiment the negative electrode plate  24  includes a negative electrode plate body (not shown) and a plurality of negative electrode tabs  24   t . The negative electrode plate body is for instance a portion of the negative electrode plate  24  flanked between a first long edge  241  and a second long edge  242 . The first long edge  241  is for instance a side, of the negative electrode plate  24 , extending in the longitudinal direction. The second long edge  242  is for instance a side, of the negative electrode plate  24 , different from the first long edge  241 , extending in the longitudinal direction. The multiple electrode tabs  24   t  are provided on for instance the first long edge  241 . In the present embodiment the negative electrode tabs  24   t  are part of the negative electrode core  24   c . In the present embodiment the negative electrode tabs  24   t  are provided (intermittently) at intervals along the longitudinal direction of the negative electrode plate  24 . The negative electrode tabs  24   t  project from the first long edge  241  in the transverse direction of the negative electrode plate  24 . As illustrated in  FIG.  5   , the negative electrode tabs  24   t  in the wound electrode body  20  project from the separator  26  in the width direction Y. 
     As illustrated in  FIG.  5   , the negative electrode plate  24  has a negative electrode core  24   c  and a negative electrode active material layer  24   a  formed on at least one surface of the negative electrode core  24   c . 
     The negative electrode core  24   c  is for instance strip-shaped. The negative electrode core  24   c  is a metal foil made of for instance copper or a copper alloy. The negative electrode core  24   c  has for instance a negative electrode active material layer existing section and a negative electrode active material layer non-existing section. The negative electrode active material layer existing section is for instance a section at which the negative electrode active material layer  24   a  is formed. In the present embodiment the negative electrode active material layer existing section is provided at a portion (for instance the negative electrode plate body) in the form of a strip between the first long edge  241  and the second long edge  242  of the negative electrode plate  24 , along the longitudinal direction, and at part of the base end side (for instance the first long edge  241  side) of the negative electrode tabs  24   t . The negative electrode active material layer non-existing section is for instance a section at which the negative electrode active material layer  24   a  is not formed. In the present embodiment the negative electrode active material layer non-existing section is part of a projecting end side of the negative electrode tabs  24   t . 
     The negative electrode active material layer  24   a  has a negative electrode active material (for instance a carbon material such as graphite, hard carbon, soft carbon or amorphous carbon; or a silicon-based material such as silicon or silicon oxide (silica)) capable of reversibly storing and releasing a charge carrier. The negative electrode active material layer  24   a  contains for instance  80  mass% or more (preferably  90  mass% or more, more preferably  95  mass% or more) of the negative electrode active material, relative to  100  mass% as the total solids of the negative electrode active material layer  24   a . The negative electrode active material layer  24   a  may contain optional components, for instance a binder, a thickener and various additional components, besides the negative electrode active material. Examples of the binder include styrene-butadiene rubber (SBR). Examples of the thickener include carboxymethyl cellulose (CMC). 
     Each separator  26  is a member that insulates the positive electrode active material layer  22   a  of the positive electrode plate  22  and the negative electrode active material layer  24   a  of the negative electrode plate  24 . The separator  26  constitutes the outer surface of the wound electrode body  20 . For instance, a porous sheet made up of a resin made up of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) may be used as the separator  26 . The separator  26  has for instance a base material portion made up of a resin-made porous sheet and a heat resistance layer formed on at least one surface of the base material portion. The heat-resistant layer is for instance a layer containing an inorganic filler and a binder. Examples of the inorganic filler include alumina, boehmite, aluminum hydroxide and titania. Examples of the binder include polyvinylidene fluoride (PVdF). 
     The wound electrode body  20  is produced by laying up the positive electrode plate  22  and the negative electrode plate  24  across two separators  26 , and winding then the resulting stack in the longitudinal direction. During such winding, preferably, the first end portion N 1   a  of the first notch N 1  does not face the negative electrode active material layer  24   a , even across the separator  26 . However, the first end portion N 1   a  of the first notch N 1  may oppose the negative electrode active material layer  24   a  across the separator  26 . Bending of the first corner C 1  is suppressed at the winding initiation end portion  22   s  of the positive electrode plate  22 , as described above. In consequence, damage to the separators  26  is suppressed, even in a case where the first end portion N 1   a  opposes the negative electrode active material layer  24   a  across the separator  26 , and in consequence short-circuits between the positive and negative electrodes are suppressed. Also, even when the first end portion N 1   a  is bent, direct contact with the negative electrode core  24   c  is suppressed, at a time where the bent portion of the first end portion N 1   a  reaches the negative electrode plate  24 . The safety of the battery  1  is further enhanced as a result. 
     Multiple positive electrode tabs  22   t  protruding from the first end face  201  of the main body  20   a  become stacked at the time of the above winding; a positive electrode tab group  23  is formed as a result that includes the plurality of positive electrode tabs  22   t . As illustrated in  FIG.  1    to  FIG.  4   , the tips of the positive electrode tabs  22   t  that make up the positive electrode tab group  23  are bent so as to be disposed along a respective second side wall  12   c . Parts of the bent positive electrode tabs  22   t  are joined to a respective tab joint portion  52   b  of the positive electrode collector  50 . Examples of such joining means include ultrasonic welding, resistance welding and laser welding (the same applies to the negative electrode). 
     Also, multiple negative electrode tabs  24   t  protruding from the second end face  202  of the main body  20   a  become stacked at the time of the above winding; a negative electrode tab group  25  is formed as a result that includes the plurality of negative electrode tabs  24   t . As illustrated in  FIG.  1    to  FIG.  4    the tips of the negative electrode tabs  24   t  that make up the negative electrode tab group  25  are bent so as to be disposed along a respective second side wall  12   c . Parts of the bent negative electrode tabs  24   t  are joined to a respective tab joint portion  62   b  of the negative electrode collector  60 . 
     The positive electrode collector  50  is a member that electrically connects the positive electrode plate  22  of the wound electrode body  20  and the positive electrode terminal  30 , inside the exterior body  12 . As illustrated in  FIG.  2   , the positive electrode collector  50  includes the first collector portion  51  and second collector portions  52 . The first collector portion  51  is formed to have an L-shaped cross section. The first collector portion  51  has a terminal connection portion  51   a  disposed along the inner surface of the sealing plate  14 , and a lead portion  51   b  extending from one end of the terminal connection portion  51   a  in the width direction Y toward the bottom wall  12   a . A through-hole is formed in the terminal connection portion  51   a , at a position corresponding to the terminal lead-out hole  18  of the sealing plate  14 . The shaft portion  32  of the positive electrode terminal  30  is inserted into the through-hole. 
     As illustrated in  FIG.  2    to  FIG.  4   , each second collector portion  52  extends toward the bottom wall  12   a  of the exterior body  12 . Each second collector portion  52  has a first collector portion connection portion  52   a  and a tab joint portion  52   b . The first collector portion connection portion  52   a  is a portion that is electrically connected to the first collector portion  51 . The first collector portion connection portion  52   a  extends along the vertical direction Z. The first collector portion connection portion  52   a  is disposed substantially perpendicularly to the winding axis WL of the respective wound electrode body  20 . The tab joint portion  52   b  is a portion joined to the positive electrode tab group  23 . The tab joint portion  52   b  extends along the vertical direction Z. The tab joint portion  52   b  is disposed substantially perpendicularly to the winding axis WL of the respective wound electrode body  20 . The surfaces of the tab joint portions  52   b  connected to respective positive electrode tabs  22   t  are disposed substantially parallelly to the second side walls  12   c  of the exterior body  12 . 
     The negative electrode collector  60  is a member that electrically connects the negative electrode plate  24  of each wound electrode body  20  and the negative electrode terminal  40 , in the interior of the exterior body  12 . As illustrated in  FIG.  2    to  FIG.  4   , the negative electrode collector  60  includes a first collector portion  61  and second collector portions  62 . The first collector portion  61  has a terminal connecting portion  61   a  and a lead portion  61   b . Each second collector portion  62  has a first collector portion connection portion  62   a  and a tab joint portion  62   b . The configuration of the negative electrode collector  60  is identical to the configuration of the positive electrode collector  50  described above, and hence a detailed description of the negative electrode collector  60  will be omitted herein. 
     The battery  1  can be used in various purposes, 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). 
     Concrete examples of the art disclosed herein have been explained in detail above, but these are merely illustrative in nature, and are not meant to limit the scope of the claims. The features set forth in the claims encompass various modifications and alterations of the concrete examples illustrated above. 
     In the above embodiments, for instance, the first notch N 1  is produced through cutting of the recess depicted in frame A of the positive electrode precursor  21  illustrated in  FIG.  7   , along the two-dot chain line L p3 . However, the shape of the recess depicted in frame A is not particularly limited, provided that a first notch N 1  can be formed having a shape that allows bringing out the effect of the art disclosed herein.  FIG.  8    to  FIG.  10    are plan-view diagrams illustrating other examples of the shape of the recess depicted within the frame A of  FIG.  7   . The recess depicted in frame A in  FIG.  7    may have a recess in the shape illustrated in frame B in  FIG.  8   . For instance, the recess depicted in frame B of  FIG.  8    has a straight portion  b   1  parallel to the first long edge  221  at the bottom of the recess (see  FIG.  6   ). For instance, cutting along the two-dot chain line L p3  may be performed within the straight portion  b   1 . The angle α and the angle β formed by a cut line along the two-dot chain line L p3 , and the straight portion  b   1  after cutting, are both 90 degrees. The first notch N 1  having a suitable shape can therefore be provided by relying on a recess having the shape illustrated in frame B of  FIG.  8   . 
     For instance the recess depicted in frame C of  FIG.  9    has a straight portion CA, exhibiting an inclination angle γ (where γ is larger than 0 degrees, and smaller than 90 degrees) relative to the first long edge  221 , at the bottom of the recess (see  FIG.  6   ). For instance, cutting along the two-dot chain line L p3  may be performed within the straight portion CA. The angle exhibiting an angle of 90 degrees or larger (angle α in  FIG.  9   ), from among the angle α and the angle β formed by the cut line along the two-dot chain line L p3 , and the straight portion CA after cutting, can be set as the winding initiation end portion 22 s of the positive electrode plate  22 . 
     For instance, the recess depicted in frame D of  FIG.  10    has a rounded bottom  d   1  and a straight portion  d   2  that connects the first long edge  221  and the bottom  d   1  (see  FIG.  6   ).  FIG.  11    and  FIG.  12    are plan-view diagrams illustrating examples of a cut portion of the recess depicted in frame D. As illustrated in  FIG.  11   , cutting along the two-dot chain line L p3  may be performed at an arbitrary point K 1  within the straight portion  d   2  (see  FIG.  7    and  FIG.  10   ). The angle (angle α in  FIG.  11   ) of 90 degrees or larger from among the angle α and angle β, formed by the cut line along the two-dot chain line L p3  and the straight portion  d   2  after cutting, may be set as the winding initiation end portion  22   s  of the positive electrode plate  22 . As illustrated in  FIG.  12   , cutting along the two-dot chain line L p3  may alternatively be performed at an arbitrary point K 2  on the bottom  d   1  (see  FIG.  7    and  FIG.  10   ). The angle (angle α in  FIG.  12   ) of 90 degrees or larger, from among the angles α and β formed by the cut line along the two-dot chain line L p3  and the bottom  d   1  after cutting, may be set as the winding initiation end portion  22   s  of the positive electrode plate  22 . In  FIG.  12   , the angle α is for instance the angle formed by a side  21   a  formed by the above cutting, and a tangent line T 2  passing through point K 2 . The angle β is for instance the angle formed by a side  21   b  formed by the above cutting, and a tangent line T 3  passing through point K 2 . 
     Alternatively, there need not be formed a recess for notch formation, in the cutting along the dotted line L p1  in  FIG.  7   . For instance, the interior of frame A in  FIG.  7    may be set to be a flat portion. The first notch N 1  having a desired shape may be formed after cutting of the flat portion in frame A along the two-dot chain line L p3 . 
     In the above embodiment, the first electrode plate was the positive electrode plate  22 , and the second electrode plate was the negative electrode plate  24 . However, the invention is not limited thereto. The first electrode plate may be the negative electrode plate  24 , and the second electrode plate may be the positive electrode plate  22 . In the above embodiment, a battery case  10  was used that included the exterior body  12  and the lid  14 . However, the invention is not limited thereto. The battery case of the battery  1  may be a laminate exterior body.