Patent Publication Number: US-2023135592-A1

Title: Electrode plate for secondary battery, method for producing same, secondary battery, and method for producing same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a secondary battery electrode plate and a method for manufacturing the same, and a secondary battery and a method for manufacturing the same. 
     BACKGROUND 
     A negative or positive electrode plate used for a secondary battery may be manufactured by cutting, to a predetermined size of the electrode, an electrode precursor in which a long piece of active material layer is formed on a long piece of thin-plate-shaped core. 
     Patent Literature 1 discloses preventing a core of a secondary battery electrode plate from protruding more outward than an active material layer at a cut edge when the secondary battery electrode plate is cut with laser. An electrode precursor with an active material layer formed on each side of a long piece of core is cut with laser such that the edge of the core at the edge of the electrode plate is widened into a triangular cross section. The edge of the core is positioned more inward than the edge of the active material layer with respect to the surface plane of the electrode plate, or positioned flush with the edge of the active material layer. 
     Citation List 
     Patent Literature 
     PATENT LITERATURE 1: International Publication No. WO 2018/043444 A 
     SUMMARY 
     When a secondary battery electrode plate is cut from a long piece of electrode precursor, an active material may peel off at a cut edge of the active material layer and fall down. 
     A secondary battery electrode plate according to an embodiment of the present disclosure comprises a core made from a metal foil and having a thin-plate shape, and an active material layer formed on at least one side of the core. A melted portion of the metal foil forming the core disperses at an edge portion of the secondary battery electrode plate such that the melted portion spreads beyond a plate thickness region of the core to adhere to and solidify on an edge of the active material layer. 
     A secondary battery according an embodiment of the present disclosure comprises the secondary battery electrode plate according to an embodiment of the present disclosure. 
     In a secondary battery electrode plate manufacturing method according to an embodiment of the present disclosure, when manufacturing the secondary battery electrode plate or a semi-finished electrode plate to be used as the secondary battery electrode plate by cutting, with laser, an electrode precursor comprising a thin-plate shaped based core made from a metal foil and an active material base layer formed on at least one side of the base core, a melted portion produced by melting the metal foil disperses at an edge portion of the secondary battery electrode plate such that the melted portion spreads beyond a plate thickness region of the core to an edge of the active material layer. 
     The secondary battery electrode plate manufacturing method according to an embodiment of the present disclosure uses the secondary battery electrode plate manufactured by the secondary battery electrode plate manufacturing method according to an embodiment of the present disclosure. 
     A secondary battery electrode plate and a method for manufacturing the same, and a secondary battery and a method for manufacturing the same according to an embodiment of the present disclosure can prevent the active material layer from peeling off at a cut edge without widening an edge portion of the core into a triangular cross section. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross sectional diagram of a secondary battery according to an embodiment of the present disclosure. 
         FIG.  2    is perspective diagram showing an electrode assembly of the secondary battery shown in  FIG.  1    with an unwound winding-end edge. 
         FIG.  3    is an unwound diagram showing a longitudinal portion of a negative electrode precursor used to form a negative electrode plate of the electrode assembly shown in  FIG.  2   . 
         FIG.  4    is a cross sectional diagram cut along line A-A in  FIG.  3   . 
         FIG.  5    is a cross sectional diagram showing a cut edge portion of the negative electrode plate. 
         FIG.  6    is a schematic diagram showing an SEM image of a cut edge of the negative electrode plate according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As a result of thoughtful consideration to address the above problem, the inventors found that, in a structure of a secondary battery electrode plate including a thin-plate-shaped core made from a metal foil and an active material layer formed on at least one side of the core, an active material layer can be prevented from falling down at a cut edge without widening the edge portion of the core into a triangle cross section by using a configuration in which a melted portion of the metal foil forming the core disperses at an edge portion of the secondary battery electrode plate such that the melted portion scatters beyond a plate thickness region of the core to adhere to the edge of the active material layer. This is described in detail below. 
     An embodiment of the present disclosure is described below. In the description below, specific shapes, materials, directions, values, and the like are merely examples used to facilitate understanding of the present disclosure. These specifics may be changed to adapt to usages, purposes, specifications, and so on. In the embodiments described below, the secondary battery is assumed to be a non-aqueous electrolyte secondary battery in which a wound-type electrode assembly is enclosed in a housing which is a rectangular metal case. 
     Secondary Battery Configuration 
     Initially, a configuration of a secondary battery  10  is described with reference to  FIGS.  1  and  2   .  FIG.  1    is a cross sectional diagram of the secondary battery  10 .  FIG.  2    is a perspective diagram showing an unwound winding-end edge of an electrode assembly  20  of the secondary battery  10 . 
     The secondary battery  10  includes a housing  12  used as a case, and the wound-type electrode assembly  20  that is disposed in the housing  12 . Non-aqueous electrolytic solution acting as non-aqueous electrolyte is stored in the housing  12 . The non-aqueous electrolytic solution may be an electrolytic solution that contains, for example, lithium salt, and is lithium-ion conductive. 
     As shown in  FIG.  2   , the electrode assembly  20  has a wound structure with the winding axis O extending in a longitudinal direction of the secondary battery  10 . A positive electrode plate  22  and a negative electrode plate  26  are wound via separators  30 ,  31  into a flat cuboid shape. In the electrode assembly  20 , for example, a long piece of positive electrode plate  22 , a long piece of separator  30 , a long piece of negative electrode plate  26 , and a long piece of separator  31  are stacked and wound such that the separator  31  is disposed at the outermost surface. The positive electrode plate  22  and the negative electrode plate  26  are used as secondary battery electrode plates. 
     As shown in  FIG.  1   , the metal housing  12  has a box shape with an opening at the top. The secondary battery  10  includes a sealing plate  14  which closes the opening. The housing  12  and the sealing plate  14  may be made from aluminum or an aluminum alloy. A positive electrode terminal  15  protrudes at one longitudinal end (around the left end in  FIG.  1   ), whereas a negative electrode terminal  16  protrudes at the other longitudinal end (around the right end in  FIG.  1   ) on the sealing plate  14 . With the positive electrode terminal  15  and the negative electrode terminal  16  being inserted into two through holes made in the sealing plate  14 , these terminals are fastened onto the sealing plate  14  via resin gaskets. The winding axis of the electrode assembly  20  is parallel to the longitudinal direction of the sealing plate  14  (the right-left direction in  FIG.  1   ). An insulation sheet that is folded into a box shape may be provided inside the housing  12  such that the electrode assembly  20  and the housing  12  are insulated from each other. 
     Positive Electrode Plate 
     The positive electrode plate  22  includes a positive electrode core  23 , and a positive electrode active material layer  24  that may be formed on each side of the positive electrode core  23  and contains a positive electrode active material.  FIG.  2    shows the positive electrode active material layer  24  in a hatch pattern of a sand texture. The positive electrode core  23  is a thin-plate-shaped core made from a foil of metal that is stable within a potential range of the positive electrode, such as, aluminum or an aluminum alloy. The positive electrode active material may be a lithium transition metal oxide that allows insertion and release of lithium ions. The positive electrode active material layer  24  may contain a binder and a conductive agent in addition to the positive electrode active material. The positive electrode plate  22  includes a main portion  22   a  in which the positive electrode active material layer  24  is formed on the positive electrode core  23 , and a positive electrode core exposed portion  22   b  in which the positive electrode core  23  is exposed with no positive electrode active layer formed thereon. The positive electrode core exposed portion  22   b  is formed along one of the side edges of the positive electrode plate  22  before being wound. In the positive electrode plate  22 , a porous protective layer thinner than the positive electrode active material layer  24  may be further formed in an area next to the positive electrode active material layer  24  in the positive electrode core exposed portion  22   b . 
     A lithium transition metal oxide containing transition metal elements such as Co, Mn, and Ni may be used as the positive electrode active material. Examples of the lithium transition metal oxide include Li x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co y Ni 1-y O 2 , Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x Mn 2 O 4 , Li x Mn 2-y M y O 4 , LiMPO 4 , and Li 2 MPO 4 F (M: at least one of the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 &lt; x ≤ 1.2, 0 &lt; y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These materials may be used alone or in combination. In order to increase the capacity of the secondary battery  10 , the positive electrode active material may contain a lithium nickel composite oxide, such as Li x NiO 2 , Li x Co y Ni 1-y O 2 , and Li x Ni 1-y M y O z  (M: at least one of the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb. Sb, and B, 0 &lt; x ≤ 1.2, 0 &lt; y ≤ 0.9, 2.0 ≤ z ≤ 2.3). 
     The conductive agent used for the positive electrode active material layer  24  may be, for example, carbon particles, such as, carbon black (CB), acetylene black (AB), ketjen black, carbon nanotube (CNT), and graphite. These materials may be used alone or in combination of two or more. Carbon black may be desirably used as the conductive agent for the positive electrode active material layer  24 . 
     The binder used for the positive electrode active material layer  24  may be a resin, for example, a fluorine resin, such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), a polyimide resin, an acrylic resin, and a polyolefin resin. These resins may be used alone or in combination of two or more. Polyvinylidene fluoride may be desirably used as the conductive agent for the positive electrode active material layer  24 . 
     The positive electrode plate  22  may be manufactured by forming the positive electrode active material layer  24  on each side of the positive electrode core  23 . Each positive electrode active material layer  24  may be formed by coating the positive electrode core  23  with a positive electrode active material layer slurry containing the positive electrode active material, the binder, and a dispersion medium, and compressing the coated film after drying the coated film to remove the dispersion medium. The positive electrode plate may also be manufactured by forming the positive electrode active material layer  24  and a protective layer on each side of the positive electrode core  23  by coating the positive electrode core  23  with the positive electrode active material layer slurry and a protective layer slurry, and compressing the coated film after drying the coated film to remove the dispersion medium. 
      Negative Electrode Plate 
     The negative electrode plate  26  includes a negative electrode core  27 , and a negative electrode active material layer  28  that may be formed on each side of the negative electrode core  27  and contains a negative electrode active material.  FIG.  2    shows the negative electrode active material layer  28  in a hatch pattern of a sand texture. The negative electrode core  27  is a thin-plate-shaped core made from a foil of metal that is stable within a potential range of the negative electrode, such as copper or a copper alloy. The negative electrode active material may be a carbon material, a silicon compound, or other material which allows insertion and release of lithium ions. The negative electrode active material layer  28  may contain a binder in addition to the negative electrode active material. The negative electrode plate  26  includes a main portion  26   a  in which the negative electrode active material layer  28  is formed on the negative electrode core  27 , and a negative electrode core exposed portion  26   b  in which the negative electrode core  27  is exposed with no negative electrode active layer formed thereon. The negative electrode core exposed portion  26   b  extends along one of the side edges of the negative electrode plate  26  before being wound. 
     The negative electrode active material is not limited to a particular material as long as, for example, lithium ions can be reversibly absorbed into and released from the material. The negative electrode active material may be, for example, natural graphite, a carbon material, such as artificial graphite, a metal which can form an alloy with lithium, such as silicon (Si) and tin (Sn), an alloy containing a metal element, such as Si or Sn, or an composite oxide. A carbon material may be desirably used as the negative electrode active material. Natural graphite is more desirable. The negative electrode active material may be used alone or in combination of two or more. 
     The negative electrode plate  26  may be manufactured by forming the negative electrode active material layer  28  on each side of the negative electrode core  27 . Each negative electrode active material layer  28  may be formed by coating the negative electrode core  27  with a negative electrode active material layer slurry containing the negative electrode active material, the binder, and a dispersion medium, and compressing the coated film after drying the coated film to remove the dispersion medium. 
     Particularly in this embodiment, as shown in  FIG.  5    described below, in the negative electrode plate  26 , a melted portion of the metal foil forming the negative electrode core  27  disperses beyond a plate thickness region t of the negative electrode core  27  at an edge portion of the negative electrode plate  26  such that the melted portion spreads to adhere to and solidify on the edges of the negative electrode active material layers  28 .  FIG.  5    shows the solidified melted portion of the metal foil of the negative electrode core  27  in a hatch pattern of diagonal lines. As described below, this can prevent each negative electrode active material layer  28  from peeling off at a cut edge  28   a  of the negative electrode active material layer  28  without widening the edge portion of the negative electrode core  27  into a triangular cross section. 
     As shown in  FIG.  1   , in the electrode assembly  20 , the wound positive electrode core exposed portion  22   b  is disposed at one end (the left end in  FIG.  1   ) in the winding axis direction (the right-left direction in  FIG.  1   ). The wound negative electrode core exposed portion  26   b  is positioned at the other end (the right end in  FIG.  1   ) in the winding axis direction of the electrode assembly  20 . 
     Separator 
     When wound, the separator  30  is disposed between the positive electrode plate  22  and the negative electrode plate  26  to electrically separate the positive electrode plate  22  and the negative electrode plate  26 . The outermost separator  31  prevents short circuits between the negative electrode plate  26 , which is the outermost electrode, and external elements. 
     Ion-permeable and insulative porous sheets are used for the separators  30 ,  31 . The porous sheets may be, for example, microporous thin films, woven fabrics, or non-woven fabrics. A suitable material for the separators  30 ,  31  includes an olefin resin, such as polyethylene and polypropylene, and cellulose. Each separator  30 ,  31  may be a laminate including thermoplastic resin fiber layers, such as cellulose fiber layers and olefin resin layers. Each separator  30 ,  31  may be a multi-layered separator including a polyethylene layer and a polypropylene layer. The separator  30 ,  31  may be coated with a material such as an aramid resin or ceramic. For example, each separator  30 ,  31  may be a three-layered separator constructed from polyethylene layers with a polypropylene layer sandwiched therebetween. 
     In the electrode assembly  20 , a piece of insulation tape  60  ( FIG.  1   ) is adhered on the front or back surface of the electrode assembly  20  to fix the winding-end edge of the outermost separator  31  on the outer circumference of the electrode assembly  20 . 
     A positive electrode current collector  47  is electrically connected to the wound positive electrode core exposed portion  22   b . This electrically connects the positive electrode current collector  47  to the positive electrode plate  22 . The positive electrode current collector  47  and a positive electrode receiving element  48  disposed on one side (the front side of the sheet of paper on which  FIG.  1    is drawn) of the electrode assembly  20  opposite from the positive electrode current collector  47  are unitedly and electrically connected to the positive electrode plate  22  with the positive electrode core exposed portion  22   b  sandwiched therebetween. The positive electrode current collector  47  is electrically connected to the bottom of the positive electrode terminal  15  which extends vertically through a first insulating member  61  disposed on the inner surface of the sealing plate  14 . 
      A negative electrode current collector  50  is electrically connected to the wound negative electrode core exposed portion  26   b . This electrically connects the negative electrode current collector  50  to the negative electrode plate  26 . The negative electrode current collector  50  and a negative electrode receiving element  58  disposed on one side (the front side of the sheet of paper on which  FIG.  1    is drawn) of the electrode assembly  20  opposite from the negative electrode current collector  50  are unitedly and electrically connected to the negative electrode plate  26  with the negative electrode core exposed portion  26   b  sandwiched therebetween. The negative electrode current collector  50  is electrically connected to the bottom of the negative electrode terminal  16  which extends vertically through a second insulating member  62  disposed on the inner surface of the sealing plate  14 . 
     The opening of the housing  12  is closed with the sealing plate  14  welded along the opening edge. 
     Manufacturing Method of Negative Electrode Plate and Secondary Battery 
     With reference to  FIGS.  3  to  6   , a manufacturing method of the secondary battery  10 , in particular, the negative electrode plate  26  ( FIGS.  2  and  5   ), is described below.  FIG.  3    is an unwound diagram showing a longitudinal portion of a negative electrode precursor  32  used to form the negative electrode plate  26 .  FIG.  4    is a cross-sectional view cut along line A-A in  FIG.  3   . In a manufacturing method of the negative electrode plate  26  according to the present embodiment of the present disclosure, two or more negative electrode plates  26  are manufactured at the same time. First, a precursor manufacturing process is performed to manufacture the negative electrode precursor  32  ( FIGS.  3  and  4   ) having a width W ( FIG.  3   ) which equals to the total of widths d ( FIGS.  2  and  3   ) of the two negative electrode plates  26 . The negative electrode precursor  32  is a longitudinal plate including a longitudinal negative electrode base core  33 , on each side of which a negative electrode active material base layer  34  is formed. The negative electrode precursor  32   corresponds to an electrode precursor.  FIGS. ,  3  and  4    show the negative electrode active material base layer  34  in a hatch pattern of a sand texture. The negative electrode active material base layer  34  may be formed by preparing a negative electrode active material layer slurry containing a negative electrode active material, a binder, and a dispersion medium, coating each surface of the negative electrode base core  33  with the slurry, and drying the coated film to remove the dispersion medium. A core exposed portion  35  extends along the longitudinal direction (the right-left direction in  FIG.  3   , and the front-rear direction of the sheet of paper on which  FIG.  4    is drawn) at each lateral (the vertical direction in  FIG.  3   , and the right-left direction in  FIG.  4   ) end of the negative electrode precursor  32 . The core exposed portions  35  are where no active material layer is formed and the negative electrode base core  33  is exposed. The core exposed portions  35  may be formed by not applying the negative active material layer slurry. Alternatively, the core exposed portions  35  may be formed by first forming the negative active material layers on the entire areas on both sides, and then partially removing the negative electrode active material layers. The negative electrode base core  33  corresponds to a base core, and the negative electrode active material base layer  34  corresponds to an active material base layer. 
     Next in the manufacturing method of the negative electrode plate  26 , the negative electrode precursor  32  is compressed using a compression roller or other means to compress the negative electrode active material base layer  34  in a compression process. In the manufacturing method of the negative electrode plate, the negative electrode precursor  32  is then cut along the lateral center (broken line C in  FIGS.  3  and  4   ), and further cut to a predetermined longitudinal length in a cut process. In order to cut the negative electrode precursor  32  at the lateral center, a laser device can be used to emit a laser beam  70  ( FIG.  4   ) to the lateral center of the negative electrode precursor  32  while changing a relative position between a processing head of the laser device and the negative electrode precursor  32  along the longitudinal direction (the front-rear direction of the sheet of paper on which  FIG.  4    is drawn) of the negative electrode precursor  32 . For example, the negative electrode precursor  32  may be fed by a conveyor in the front-rear direction of the sheet of paper on which  FIG.  4    is drawn. The position of the processing head of the laser device may be fixed, or moved in the direction opposite to the movement of the negative electrode precursor  32 . 
     The laser device includes, for example, a laser oscillator, and a processing head with a built-in galvano scanner. The laser oscillator emits laser light in a continuous wave mode in which the laser oscillator can continuously produce oscillations. For example, a fiber laser, a YAG laser, a Co 2  laser, or an Ar laser may be used as the laser oscillator. In the laser device, a collimator that convers laser light outputted from the laser oscillator to parallel light is disposed between the laser oscillator and the galvano scanner. The galvano scanner guides the laser light which has passed through the collimator to a reflective mirror, an optical element such as a diffractive optical element, an x-axis mirror, and a y-axis mirror in this order. The x axis extends along the longitudinal direction of the negative electrode precursor  32 . The y-axis extends along the lateral direction of the negative electrode precursor  32 . The laser light reflected by the x-axis mirror and the y-axis mirror passes through an Fθ lens and a protective glass, and then to the negative electrode precursor  32 . The laser light scanning can be performed while moving the x-axis mirror and the y-axis mirror, and the radiation spots can be changed in plane. 
     For the laser radiation using the laser device, a continuous wave laser (CW laser) may be used to produce laser output (laser light output) of 1,200 W to 1,550 W at the scan speed (cut speed) of the laser beam of 3,000 mm/sec to 8,000 mm/sec with respect to the negative electrode precursor  32 . More preferably, using the continuous wave laser for the laser radiation, with the scan speed of the laser beam of 5,000 mm/sec to 8,000 mm/sec with respect to the negative electrode precursor  32 , the laser output may be from 1,200 W to 1,400 W, whereas with the scan speed of the laser beam of 3,000 mm/sec to less than 5,000 mm/sec with respect to the negative electrode precursor  32 , the laser output may be from 1,300 W to 1,550 W. This allows a melted portion produced by melting the metal foil when cutting the negative electrode plate  26  from the negative electrode precursor  32  with laser to disperse at a cut edge portion of the negative electrode plate  26  such that the melted portion spreads on the cut edge  28   a  of the negative electrode active material layer  28  beyond the thickness region of the negative electrode core  27  in the manufacturing method of the negative electrode plate  26 . 
     In the present embodiment, as described above, the width W ( FIG.  3   ) of the negative electrode precursor  32  equals to the total ( FIGS.  2  and  3   ) of widths d of the two negative electrode plates  26 . Two longitudinal semi-finished negative electrodes cut to have a width d corresponding to the width of the negative electrode plate  26  can be obtained by cutting the negative electrode precursor  32  along the longitudinal direction by radiating the laser beam to the negative electrode precursor  32  along the lateral center as described above. 
     As the negative electrode precursor  32  is linearly cut at the lateral center with the laser beam, the laser device may be configured to radiate the laser beam in a single dimension. For example, in the laser device, the y-axis mirror may be omitted or immovably disposed. 
     In the cutting process, the two semi-finished negative electrodes obtained above may be cut at certain longitudinal positions to obtain multiple negative electrode plates  26  of a predetermined length. While the continuous wave laser may be used to cut at predetermined longitudinal positions, another conventionally-known general means, such as a cutter, may be used. The negative electrode precursor  32  may have the length in the longitudinal direction equal to that of the negative electrode plate  26 . In this case, in the cutting process, the two negative electrode plates  26  may be obtained by cutting the negative electrode precursor  32  at the lateral center without further cutting the negative electrode precursor  32  at the predetermined longitudinal positions. 
       FIG.  5    is a cross sectional view of an edge portion of the negative electrode plate  26  on the cut edge  28   a  side.  FIG.  5    shows the negative electrode active material layer  28  in a hatch pattern of a sand texture, and the solidified portion of the metal foil that is used as the negative electrode core  27  and melted with the laser in a hatch pattern of diagonal lines. As shown in  FIG.  5   , in the negative electrode plate  26 , the melted portion of the metal foil forming the negative electrode core  27  disperses such that the melted portion scatters to adhere to and solidify on the edges of the negative electrode active material layers  28  beyond the plate thickness region t of the negative electrode core  27  at the edge portion of the negative electrode plate  26  on the cut edge  28   a  side cut with the laser. The cross section such as the one shown in  FIG.  5    can be obtained by, for example, using the continuous wave laser at the laser output of 1,200 W to 1,550 W and at the scan speed (cut speed) of the laser beam of 3,000 mm/sec to 8,000 mm/sec with respect to the negative electrode precursor  32  and by adjusting the combination of the laser output and the scan speed. Such a cross section like the one shown in  FIG.  5    can also be obtained by using the continuous wave laser at the laser output of 1,200 W to 1,400 W with the scan speed of the laser beam of 5,000 mm/sec to 8,000 mm/sec, or at the laser output of 1,300 W to 1,550 W with the scan speed of the laser beam of 3,000 mm/sec to less than 5,000 mm/sec with respect to the negative electrode precursor  32 . 
     As shown in  FIG.  5   , at least a longitudinal (the front-rear direction of the sheet of paper on which  FIG.  5    is drawn) portion of the solidified portion of the melted portion at the edge portion of negative electrode core  27  on the cut edge  28   a  side extends outwards in the plate thickness direction to be joined to the cut edges  28   a  of the negative electrode active material layers  28 . Although the cross section of the negative electrode plate  26  at a single longitudinal point is shown in  FIG.  5   , the cross section of the negative electrode plate  26  is likely to be similar to the one in  FIG.  5    at other longitudinal points. 
       FIG.  6    depicts an SEM image of the cut edge of the negative electrode plate  26  according to an embodiment of the present disclosure. In  FIG.  6   , the black areas indicate the dispersed and deposited portions of the metal foil, such as a copper foil, dispersed and welded by the heat of the laser in the cutting process. Such a cut edge can be obtained by using, for example, the continuous wave laser with the laser output at 1,200 W to 1,550 W at the scan speed of the laser beam of 3,000 mm/sec to 8,000 mm/sec with respect to the negative electrode precursor  32 , and adjusting the combination of the laser output and the scan speed. As shown in  FIG.  6   , at the cut edge of the negative electrode plate  26 , the melted portion of the metal foil disperses such that the melted portion is welded to and solidified on the cut edges  28   a  of the lower and upper negative electrode active material layers  28  beyond the plate thickness region t of the negative electrode core  27 . These solidified portions form a metal coating  29  that extends beyond the plate thickness region of the negative electrode core  27 . The metal coating  29  is joined to the cut edges  28   a  of the two negative electrode active material layers  28  disposed on both sides in the plate thickness direction. 
     In a manufacturing method of the secondary battery  10 , the positive electrode plate  22  is also manufactured. Similarly to the negative electrode plate  26 , two semi-finished positive electrode plates or two positive electrode plates  22  can be manufactured by cutting, with laser, a positive electrode precursor at the lateral center after the compression process in which the positive electrode active material base layer is compressed. The positive electrode precursor includes a thin-plate-shaped positive electrode base core formed from a metal foil and a positive electrode active material base layer formed on each side of the positive electrode base core. Multiple positive electrode plates  22  of a predetermined length may be obtained from the two semi-finished positive electrode plates by cutting the two semi-finished positive electrode plates  22  at predetermined positions. 
     The method for manufacturing the secondary battery  10  includes, after manufacturing the positive electrode plate  22 , the negative electrode plate  26 , and the separators  30 ,  31 , stacking the positive electrode plate  22 , the negative electrode plate  26 , and the separators  30 ,  31 , and winding the stack to manufacture the electrode assembly  20 . The secondary battery  10  can be manufactured by disposing the electrode assembly  20  and non-aqueous electrolytic solution in the housing  12  after the electrode assembly  20  is manufactured, and welding the sealing plate  14  around the opening edge of the housing  12 . In this manner, the secondary battery  10  is manufactured using the negative electrode plate  26  manufactured by the above described method. 
     Advantages 
     In the negative electrode plate  26  and the method for manufacturing the same, and the secondary battery  10  and the method for manufacturing the same, the solidified portion of the melted portion of the metal foil of the negative electrode core  27  at least partially extends outward in the plate thickness direction at the cut edge portion of the negative electrode core  27 , and forms the metal coating  29  joined to the cut edges of the negative electrode active material layers  28 . This can prevent the negative electrode active material layers  28  from peeling off at the cut edges  28   a . According to embodiments of the present disclosure, the edge of the negative electrode core  27  does not need to be widened into a triangular cross section as required in the structure disclosed in Patent Literature 1. 
     When cutting the positive electrode precursor with the laser at the lateral center, similarly as the manufacturing method of the negative electrode plate  26 , the melted portion produced by melting of the metal foil of the positive electrode core  23  may disperse to extend beyond the plate thickness region of the positive electrode core  23  at the cut edge portion of the positive electrode plate  22  and spread at the edges of the positive electrode active material layers  24 . Using such a manufacturing method of the positive electrode plate  22 , the positive electrode plate  22  may be configured such that the melted portion of the metal foil at the edge portion of the positive electrode plate  22  disperses beyond the plate thickness region of the positive electrode core  23  to adhere to and solidify on the edges of the positive electrode active material layers  24 . In this case, because the solidified portion of the melted portion of the metal foil of the positive electrode core  23  at least partially extends outwardly in the plate thickness direction at the cut edge portion of the positive electrode core  23 , and forms a metal coating joined to the cut edges of the positive electrode active material layers  24 , the positive electrode active material layers  24  can be prevented from peeling off at the cut edges. 
     Although, in the above embodiments, the negative electrode active material layer  28  is formed on each side of the negative electrode core  27  and the positive electrode active material layer  24  is formed on each side of the positive electrode core  23 , the negative electrode plate and the positive electrode plate manufactured using the methods of the present disclosure are not limited to these configurations. The negative electrode active material layer may be formed only on a single side of the negative electrode core, and the positive electrode active material layer may be formed only on a single side of the positive electrode core. 
     Reference Signs List 
     
         
           10  secondary battery 
           12  housing 
           14  sealing plate 
           15  positive electrode terminal 
           16  negative electrode terminal 
           20  electrode assembly 
           22  positive electrode plate 
           22   a  main portion 
           22   b  positive electrode core exposed portion 
           23  positive electrode core 
           24  positive electrode active material layer 
           26  negative electrode plate 
           26   a  main portion 
           26   b  negative electrode core exposed portion 
           27  negative electrode core 
           28  negative electrode active material layer 
           28   a  cut edge 
           29  metal coating 
           30 ,  31  separators 
           32  negative electrode precursor 
           33  negative electrode base core 
           34  negative electrode active material base layer 
           35  core exposed portion 
           47  positive electrode current collector 
           48  positive electrode receiving element 
           50  negative electrode current collector 
           58  negative electrode receiving element 
           60  insulation tape 
           61  first insulating member 
           62  second insulating member