JP2012243455A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve output performance in a low charging state.SOLUTION: In a lithium ion secondary battery 100A, an uncoated part 242 of a negative electrode collector 241 is disposed at a side opposite to an uncoated part 222 of a positive electrode collector 221 in a width direction of the positive electrode collector 221. A negative electrode active material layer 243 and a positive electrode active material layer 223 are superposed such that the negative electrode active material layer 243 covers the positive electrode active material layer 223 with separators 262 and 264 interposed between the negative electrode active material layer 243 and the positive electrode active material layer 223. Further the positive electrode collector 221 and the negative electrode collector 241 are wound around a winding axis WL set in a width direction of the positive electrode collector 221. A metal lithium 120 is installed on the uncoated part 242 of the negative electrode collector 241 and in the vicinity thereof.

Description

  The present invention relates to a lithium ion secondary battery.

  In this specification, “secondary battery” refers to a general power storage device that can be repeatedly charged. In the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of electrons accompanying the lithium ions between the positive and negative electrodes.

  For example, in Japanese Patent Laid-Open No. 8-102333 (Patent Document 1), a lithium ion secondary battery having a carbon material as a main constituent material of a negative electrode is electrically connected to the negative electrode and is not in contact with the negative electrode. Alternatively, a lithium alloy is disclosed. This publication discloses a battery in which a positive electrode and a negative electrode stacked with a separator interposed between them are wound into a cylindrical shape and accommodated in a cylindrical container in which metallic lithium is disposed so as to be in contact with the bottom of the can. Japanese Patent Laying-Open No. 2000-82498 (Patent Document 2) discloses a structure in which metallic lithium is provided on a positive electrode current collector.

JP-A-8-102333 JP 2000-82498 A

  By the way, the cylindrical lithium ion secondary battery has, for example, a strip-shaped negative electrode current collector and a strip-shaped positive electrode current collector as disclosed in Patent Document 2. Each of the strip-shaped negative electrode current collector and the strip-shaped positive electrode current collector has a portion where no active material layer is formed at both ends in the length direction. The portion where the active material layer is not formed (uncoated portion) starts winding or ends winding when wound. In Patent Document 2, metallic lithium is attached to an uncoated portion of a current collector that starts or ends winding.

  For example, FIG. 20 is a diagram in which a negative electrode current collector 20 of a cylindrical lithium ion secondary battery is developed based on Patent Document 2. As shown in FIG. 20, the negative electrode current collector 20 is provided with an uncoated portion 24 where the negative electrode active material layer 22 is not formed at the beginning or end of winding. The metallic lithium 26 is attached to an uncoated portion 24 provided at the beginning or end of winding of the negative electrode current collector 20. As described above, when the metal lithium 26 is attached to the uncoated portion 24 provided at the start or end of winding of the negative electrode current collector 20, the portion opposite to the negative electrode active material layer 22 from the portion where the metal lithium 26 is attached. The distance to the side edge is long. The longer the negative electrode current collector 20 is, the more difficult it is that lithium ions supplied from the metal lithium 26 are uniformly diffused throughout the negative electrode active material layer 22. For this reason, it is difficult to obtain the effect of attaching the metal lithium 26.

  Further, when the automobile is driven by the output of the secondary battery, such as so-called hybrid cars, plug-in hybrid cars, and electric cars, it is required to increase the battery capacity. In order to increase the battery capacity, the strip-shaped negative electrode current collector and the strip-shaped positive electrode current collector are each elongated (for example, 1000 mm or more), or a negative electrode active material layer is formed on the negative electrode current collector. It is better to increase the area. In this case, even if metallic lithium is attached at the beginning or end of winding of the current collector, lithium ions supplied from the metallic lithium do not diffuse throughout the negative electrode active material layer.

  The lithium ion secondary battery according to the present invention includes, for example, a strip-shaped positive electrode current collector and a strip-shaped negative electrode current collector. The strip-shaped positive electrode current collector is provided with an uncoated portion along an edge on one side in the width direction. Moreover, the positive electrode active material layer is hold | maintained on both surfaces of the positive electrode electrical power collector except the said uncoated part. The strip-shaped negative electrode current collector is provided with an uncoated portion along an edge on one side in the width direction. Moreover, the negative electrode active material layer is hold | maintained on both surfaces of the negative electrode collector except the said uncoated part. A separator is interposed between the positive electrode active material layer and the negative electrode active material layer.

  The uncoated portion of the negative electrode current collector is disposed on the side opposite to the uncoated portion of the positive electrode current collector in the width direction of the positive electrode current collector. In addition, the negative electrode active material layer and the positive electrode active material layer are stacked so that the negative electrode active material layer covers the positive electrode active material layer with the separator interposed. Furthermore, the positive electrode current collector and the negative electrode current collector are wound around a winding axis set in the width direction of the positive electrode current collector. In this lithium ion secondary battery, metallic lithium is attached to the uncoated portion of the negative electrode current collector and the vicinity thereof.

  According to such a lithium ion secondary battery, since lithium metal is attached to the uncoated portion of the negative electrode current collector and in the vicinity thereof, lithium ions supplied from the metal lithium are likely to diffuse throughout the negative electrode active material layer. . For this reason, the charge / discharge cycle characteristics of the lithium ion secondary battery are improved.

  Further, in the lithium ion secondary battery, the uncoated portion of the negative electrode current collector may be gathered at the intermediate portion in a wound state and the negative electrode terminal may be welded. In this case, metallic lithium may be attached to the uncoated part. Moreover, metallic lithium may be attached to the negative electrode terminal in the vicinity of the uncoated part.

  Moreover, metallic lithium may be attached to the uncoated part of the negative electrode current collector along the length direction of the negative electrode current collector. Furthermore, the metallic lithium is an elongated strip-like foil, and is preferably attached along the edge of the negative electrode active material layer. Moreover, metallic lithium may be intermittently attached along the length direction of the negative electrode current collector. Moreover, metallic lithium may be arrange | positioned at the single side | surface of the negative electrode collector, and may be arrange | positioned at both surfaces of the negative electrode collector.

  In addition, metallic lithium is preferably 10% to 30% of the reversible capacity of the negative electrode. Thereby, the output of a lithium ion secondary battery is maintained high even in a low charge state.

FIG. 1 is a diagram illustrating an example of the structure of a lithium ion secondary battery. FIG. 2 is a view showing a wound electrode body of a lithium ion secondary battery. 3 is a cross-sectional view showing a III-III cross section in FIG. 2. FIG. 4 is a cross-sectional view showing the structure of the positive electrode active material layer. FIG. 5 is a cross-sectional view showing the structure of the negative electrode active material layer. FIG. 6 is a side view showing a welding location between an uncoated portion of the wound electrode body and the electrode terminal. FIG. 7 is a diagram schematically illustrating a state of the lithium ion secondary battery during charging. FIG. 8 is a diagram schematically showing a state of the lithium ion secondary battery during discharge. FIG. 9 is a diagram showing a lithium ion secondary battery according to an embodiment of the present invention. FIG. 10 is a development view in which a wound electrode body of a lithium ion secondary battery according to an embodiment of the present invention is developed. FIG. 11 is a diagram illustrating a negative electrode sheet of a lithium ion secondary battery according to an embodiment of the present invention. FIG. 12 is a typical graph showing output characteristics of a lithium ion secondary battery according to an embodiment of the present invention. FIG. 13 is a cross-sectional view showing an intermediate portion of an uncoated portion of the negative electrode current collector of the lithium ion secondary battery according to one embodiment of the present invention. FIG. 14 is a cross-sectional view showing an intermediate portion of an uncoated portion of a negative electrode current collector of a lithium ion secondary battery according to another embodiment. FIG. 15 is a diagram illustrating a negative electrode sheet of a lithium ion secondary battery according to another embodiment. FIG. 16 is a diagram showing a lithium ion secondary battery according to another embodiment. FIG. 17 is a diagram showing a lithium ion secondary battery according to another embodiment. FIG. 18 is a view showing a laminate type battery according to an embodiment of the present invention. FIG. 19 is a diagram illustrating a vehicle equipped with a secondary battery. FIG. 20 is a diagram illustrating a conventional example disclosed in the patent document.

  Here, a structural example of a lithium ion secondary battery will be described first. Thereafter, a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to such structural examples as appropriate. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show | play the same effect | action. Each drawing is schematically drawn and does not necessarily reflect the real thing. Each drawing shows an example only and does not limit the present invention unless otherwise specified.

  FIG. 1 shows a lithium ion secondary battery 100. As shown in FIG. 1, the lithium ion secondary battery 100 includes a wound electrode body 200 and a battery case 300. FIG. 2 is a view showing the wound electrode body 200. FIG. 3 shows a III-III cross section in FIG.

  As shown in FIG. 2, the wound electrode body 200 includes a positive electrode sheet 220, a negative electrode sheet 240, and separators 262 and 264. The positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are respectively strip-shaped sheet materials.

≪Positive electrode sheet 220≫
The positive electrode sheet 220 includes a strip-shaped positive electrode current collector 221 and a positive electrode active material layer 223. For the positive electrode current collector 221, a metal foil suitable for the positive electrode can be suitably used. As the positive electrode current collector 221, for example, a strip-shaped aluminum foil having a predetermined width and a thickness of about 15 μm can be used. An uncoated portion 222 is set along the edge on one side in the width direction of the positive electrode current collector 221. In the illustrated example, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222 set on the positive electrode current collector 221 as shown in FIG. The positive electrode active material layer 223 contains a positive electrode active material. The positive electrode active material layer 223 is formed by applying a positive electrode mixture containing a positive electrode active material to the positive electrode current collector 221.

<< Positive Electrode Active Material Layer 223 and Positive Electrode Active Material Particles 610 >>
Here, FIG. 4 is a cross-sectional view of the positive electrode sheet 220. In FIG. 4, the positive electrode active material particles 610, the conductive material 620, and the binder 630 in the positive electrode active material layer 223 are schematically illustrated so that the structure of the positive electrode active material layer 223 becomes clear. As shown in FIG. 4, the positive electrode active material layer 223 includes positive electrode active material particles 610, a conductive material 620, and a binder 630.

As the positive electrode active material particles 610, a material that can be used as a positive electrode active material of a lithium ion secondary battery can be used. Examples of positive electrode active materials include LiNiCoMnO ₂ (lithium nickel cobalt manganese composite oxide), LiNiO ₂ (lithium nickelate), LiCoO ₂ (lithium cobaltate), LiMn ₂ O ₄ (lithium manganate), LiFePO ₄ ( Lithium transition metal oxides such as lithium iron phosphate). Here, LiMn ₂ O ₄ has, for example, a spinel structure. LiNiO ₂ or LiCoO ₂ has a layered rock salt structure. LiFePO ₄ has, for example, an olivine structure. LiFePO ₄ having an olivine structure includes, for example, nanometer order particles. Moreover, LiFePO _{4 having} an olivine structure can be further covered with a carbon film.

≪Conductive material 620≫
Examples of the conductive material 620 include carbon materials such as carbon powder and carbon fiber. One kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination. As the carbon powder, various carbon blacks (for example, acetylene black, oil furnace black, graphitized carbon black, carbon black, graphite, ketjen black), graphite powder, and the like can be used.

≪Binder 630≫
Further, the binder 630 binds the positive electrode active material particles 610 and the conductive material 620 included in the positive electrode active material layer 223, or binds these particles and the positive electrode current collector 221. As the binder 630, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in a positive electrode mixture composition using an aqueous solvent, a cellulose polymer (carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), etc.), a fluorine resin (eg, polyvinyl alcohol (PVA), polytetrafluoroethylene, etc.) (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP, etc.), rubbers (vinyl acetate copolymer, styrene butadiene copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), etc.) A water-soluble or water-dispersible polymer such as can be preferably used. In the positive electrode mixture composition using a non-aqueous solvent, a polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), etc.) can be preferably employed.

≪Thickener, solvent≫
The positive electrode active material layer 223 is prepared, for example, by preparing a positive electrode mixture in which the above-described positive electrode active material particles 610 and the conductive material 620 are mixed in a paste (slurry) with a solvent, applied to the positive electrode current collector 221, and dried And is formed by rolling. At this time, as the solvent for the positive electrode mixture, either an aqueous solvent or a non-aqueous solvent can be used. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). The polymer material exemplified as the binder 630 may be used for the purpose of exhibiting a function as a thickener or other additive of the positive electrode mixture in addition to the function as a binder.

  The mass ratio of the positive electrode active material in the total positive electrode mixture is preferably about 50 wt% or more (typically 50 to 95 wt%), and usually about 70 to 95 wt% (for example, 75 to 90 wt%). It is more preferable. Moreover, the ratio of the electrically conductive material to the whole positive electrode mixture can be, for example, about 2 to 20 wt%, and is usually preferably about 2 to 15 wt%. The ratio of the binder to the whole positive electrode mixture can be, for example, about 1 to 10 wt%, and is usually preferably about 2 to 5 wt%.

<< Negative Electrode Sheet 240 >>
As illustrated in FIG. 2, the negative electrode sheet 240 includes a strip-shaped negative electrode current collector 241 and a negative electrode active material layer 243. For the negative electrode current collector 241, a metal foil suitable for the negative electrode can be suitably used. The negative electrode current collector 241 is made of a strip-shaped copper foil having a predetermined width and a thickness of about 10 μm. On one side in the width direction of the negative electrode current collector 241, an uncoated part 242 is set along the edge. The negative electrode active material layer 243 is formed on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242 set on the negative electrode current collector 241. The negative electrode active material layer 243 is held by the negative electrode current collector 241 and contains at least a negative electrode active material. In the negative electrode active material layer 243, a negative electrode mixture containing a negative electrode active material is applied to the negative electrode current collector 241.

<< Negative Electrode Active Material Layer 243 >>
FIG. 5 is a cross-sectional view of the negative electrode sheet 240 of the lithium ion secondary battery 100. As shown in FIG. 5, the negative electrode active material layer 243 includes a negative electrode active material 710, a thickener (not shown), a binder 730, and the like. In FIG. 5, the negative electrode active material 710 and the binder 730 in the negative electrode active material layer 243 are schematically illustrated so that the structure of the negative electrode active material layer 243 becomes clear.

≪Negative electrode active material≫
As the negative electrode active material 710, one kind or two or more kinds of materials conventionally used for lithium ion secondary batteries can be used without any particular limitation. For example, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least in part. More specifically, the negative electrode active material is, for example, natural graphite, natural graphite coated with an amorphous carbon material, graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon ( Soft carbon) or a carbon material combining these may be used. Note that here, the negative electrode active material 710 is illustrated using so-called flake graphite, but the negative electrode active material 710 is not limited to the illustrated example.

≪Thickener, solvent≫
The negative electrode active material layer 243 is prepared, for example, by preparing a negative electrode mixture in which the negative electrode active material 710 and the binder 730 described above are mixed in a paste (slurry) with a solvent, applied to the negative electrode current collector 241, and dried. It is formed by rolling. At this time, any of an aqueous solvent and a non-aqueous solvent can be used as the solvent for the negative electrode mixture. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). For the binder 730, the polymer material exemplified as the binder 630 of the positive electrode active material layer 223 (see FIG. 4) can be used. Further, the polymer material exemplified as the binder 630 of the positive electrode active material layer 223 may be used for the purpose of exhibiting a function as a thickener or other additive of the positive electrode mixture in addition to the function as a binder. possible.

<< Separators 262, 264 >>
The separators 262 and 264 are members that separate the positive electrode sheet 220 and the negative electrode sheet 240 as shown in FIG. 1 or FIG. In this example, the separators 262 and 264 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 262 and 264, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. In this example, as shown in FIGS. 2 and 3, the width b1 of the negative electrode active material layer 243 is slightly wider than the width a1 of the positive electrode active material layer 223. Furthermore, the widths c1 and c2 of the separators 262 and 264 are slightly wider than the width b1 of the negative electrode active material layer 243 (c1, c2>b1> a1).

  In the example shown in FIGS. 1 and 2, the separators 262 and 264 are made of sheet-like members. The separators 262 and 264 may be members that insulate the positive electrode active material layer 223 and the negative electrode active material layer 243 and allow the electrolyte to move. Therefore, it is not limited to a sheet-like member. The separators 262 and 264 may be formed of a layer of insulating particles formed on the surface of the positive electrode active material layer 223 or the negative electrode active material layer 243, for example, instead of the sheet-like member. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ).

≪Battery case 300≫
In this example, as shown in FIG. 1, the battery case 300 is a so-called square battery case, and includes a container body 320 and a lid 340. The container main body 320 has a bottomed rectangular tube shape and is a flat box-shaped container having one side surface (upper surface) opened. The lid 340 is a member that is attached to the opening (opening on the upper surface) of the container body 320 and closes the opening.

  In an in-vehicle secondary battery, it is desired to improve the weight energy efficiency (battery capacity per unit weight) in order to improve the fuel efficiency of the vehicle. For this reason, in this embodiment, lightweight metals, such as aluminum and an aluminum alloy, are employ | adopted for the container main body 320 and the cover body 340 which comprise the battery case 300. FIG. Thereby, the weight energy efficiency can be improved.

  The battery case 300 has a flat rectangular internal space as a space for accommodating the wound electrode body 200. Further, as shown in FIG. 1, the flat internal space of the battery case 300 is slightly wider than the wound electrode body 200. In this embodiment, the battery case 300 includes a bottomed rectangular tubular container body 320 and a lid 340 that closes the opening of the container body 320. Electrode terminals 420 and 440 are attached to the lid 340 of the battery case 300. The electrode terminals 420 and 440 pass through the battery case 300 (lid 340) and come out of the battery case 300. The lid 340 is provided with a liquid injection hole 350 and a safety valve 360.

  As shown in FIG. 2, the wound electrode body 200 is flatly pushed and bent in one direction orthogonal to the winding axis WL. In the example shown in FIG. 2, the uncoated part 222 of the positive electrode current collector 221 and the uncoated part 242 of the negative electrode current collector 241 are spirally exposed on both sides of the separators 262 and 264, respectively. As shown in FIG. 6, in this embodiment, the intermediate portions 224 and 244 of the uncoated portions 222 and 242 are gathered together and welded to the tip portions 420 a and 440 a of the electrode terminals 420 and 440. At this time, for example, ultrasonic welding is used for welding the electrode terminal 420 and the positive electrode current collector 221 due to the difference in materials. Further, for example, resistance welding is used for welding the electrode terminal 440 and the negative electrode current collector 241. Here, FIG. 6 is a side view showing a welded portion between the intermediate portion 224 (244) of the uncoated portion 222 (242) of the wound electrode body 200 and the electrode terminal 420 (440), and VI in FIG. It is -VI sectional drawing.

  The wound electrode body 200 is attached to the electrode terminals 420 and 440 fixed to the lid body 340 in a state where the wound electrode body 200 is pressed and bent flat. The wound electrode body 200 is accommodated in a flat internal space of the container body 320 as shown in FIG. The container body 320 is closed by the lid 340 after the wound electrode body 200 is accommodated. The joint 322 (see FIG. 1) between the lid 340 and the container main body 320 is welded and sealed, for example, by laser welding. Thus, in this example, the wound electrode body 200 is positioned in the battery case 300 by the electrode terminals 420 and 440 fixed to the lid 340 (battery case 300).

≪Electrolytic solution≫
Thereafter, an electrolytic solution is injected into the battery case 300 from a liquid injection hole 350 provided in the lid 340. As the electrolytic solution, a so-called non-aqueous electrolytic solution that does not use water as a solvent is used. In this example, an electrolytic solution in which LiPF ₆ is contained at a concentration of about 1 mol / liter in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mixed solvent having a volume ratio of about 1: 1) is used. Yes. Thereafter, a metal sealing cap 352 is attached (for example, welded) to the liquid injection hole 350 to seal the battery case 300. The electrolytic solution is not limited to the electrolytic solution exemplified here. For example, non-aqueous electrolytes conventionally used for lithium ion secondary batteries can be used as appropriate.

≪Hole≫
Here, the positive electrode active material layer 223 has minute gaps 225 that should also be referred to as cavities, for example, between the positive electrode active material particles 610 and the conductive material 620 (see FIG. 4). An electrolytic solution (not shown) can penetrate into the minute gaps of the positive electrode active material layer 223. In addition, the negative electrode active material layer 243 has minute gaps 245 that should also be referred to as cavities, for example, between the particles of the negative electrode active material 710 (see FIG. 5). Here, the gaps 225 and 245 (cavities) are appropriately referred to as “holes”. As shown in FIG. 2, the wound electrode body 200 has uncoated portions 222 and 242 spirally wound on both sides along the winding axis WL. On both sides 252 and 254 along the winding axis WL, the electrolytic solution can permeate from the gaps between the uncoated portions 222 and 242. For this reason, in the lithium ion secondary battery 100, the electrolytic solution is immersed in the positive electrode active material layer 223 and the negative electrode active material layer 243.

≪Gas escape route≫
In this example, the flat internal space of the battery case 300 is slightly wider than the wound electrode body 200 deformed flat. On both sides of the wound electrode body 200, gaps 310 and 312 are provided between the wound electrode body 200 and the battery case 300. The gaps 310 and 312 serve as a gas escape path. For example, in the case where overcharge occurs, when the temperature of the lithium ion secondary battery 100 exceeds a predetermined value, the internal pressure of the battery case 300 may increase due to gas generated due to decomposition of the electrolytic solution or the like. In this embodiment, the generated gas moves toward the safety valve 360 through the gaps 310 and 312 between the wound electrode body 200 and the battery case 300 on both sides of the wound electrode body 200, and from the safety valve 360 to the outside of the battery case 300. Exhausted.

  In the lithium ion secondary battery 100, the positive electrode current collector 221 and the negative electrode current collector 241 are electrically connected to an external device through electrode terminals 420 and 440 that penetrate the battery case 300. Hereinafter, the operation of the lithium ion secondary battery 100 during charging and discharging will be described.

≪Operation when charging≫
FIG. 7 schematically shows the state of the lithium ion secondary battery 100 during charging. At the time of charging, as shown in FIG. 7, electrode terminals 420 and 440 (see FIG. 1) of lithium ion secondary battery 100 are connected to charger 290. Due to the action of the charger 290, lithium ions (Li) are released from the positive electrode active material in the positive electrode active material layer 223 to the electrolytic solution 280 during charging. In addition, charges are released from the positive electrode active material layer 223. The discharged electric charge is sent to the positive electrode current collector 221 through a conductive material (not shown), and further sent to the negative electrode sheet 240 through the charger 290. In the negative electrode sheet 240, electric charges are stored, and lithium ions (Li) in the electrolytic solution 280 are absorbed and stored in the negative electrode active material in the negative electrode active material layer 243.

<< Operation during discharge >>
FIG. 8 schematically shows a state of the lithium ion secondary battery 100 during discharging. At the time of discharging, as shown in FIG. 8, charges are sent from the negative electrode sheet 240 to the positive electrode sheet 220, and lithium ions stored in the negative electrode active material layer 243 are released to the electrolyte solution 280. In the positive electrode, lithium ions in the electrolytic solution 280 are taken into the positive electrode active material in the positive electrode active material layer 223.

  Thus, in charging / discharging of the lithium ion secondary battery 100, lithium ions travel between the positive electrode active material layer 223 and the negative electrode active material layer 243 through the electrolytic solution 280. At the time of charging, electric charge is sent from the positive electrode active material to the positive electrode current collector 221 through the conductive material. On the other hand, at the time of discharging, the charge is returned from the positive electrode current collector 221 to the positive electrode active material through the conductive material.

  During charging, the smoother the movement of lithium ions and the movement of electrons, the more efficient and rapid charging is considered possible. At the time of discharging, it is considered that the smoother the movement of lithium ions and the movement of electrons, the lower the resistance of the battery, the amount of discharge, and the output of the battery.

≪Other battery types≫
The above shows an example of a lithium ion secondary battery. The lithium ion secondary battery is not limited to the above form. Similarly, an electrode sheet in which an electrode mixture is applied to a metal foil is used in various other battery forms. For example, as another battery type, a cylindrical battery or a laminate battery is known. A cylindrical battery is a battery in which a wound electrode body is accommodated in a cylindrical battery case. A laminate type battery is a battery in which a positive electrode sheet and a negative electrode sheet are stacked with a separator interposed therebetween.

  Hereinafter, a lithium ion secondary battery according to an embodiment of the present invention will be described.

≪Lithium ion secondary battery 100A≫
FIG. 9 shows a lithium ion secondary battery 100A according to an embodiment of the present invention. FIG. 10 is a development view in which the wound electrode body 200A of the lithium ion secondary battery 100A is developed. FIG. 11 is a diagram showing a negative electrode sheet 240A of the lithium ion secondary battery 100A. The basic structure of the lithium ion secondary battery 100A is the same as that of the lithium ion secondary battery 100 shown in FIGS. 1 to 8, and a duplicate description is omitted here. Further, description will be made with reference to the drawings of the lithium ion secondary battery 100 described above as appropriate.

≪Metal lithium 120≫
In the lithium ion secondary battery 100A shown in FIG. In this embodiment, as shown in FIGS. 10 and 11, the metallic lithium 120 is attached along the length direction of the negative electrode current collector 241. More specifically, as shown in FIG. 11, the metallic lithium 120 is an elongated strip-like foil (in this embodiment, a strip-like foil having a width of about 2 mm) and extends along the edge 243 a of the negative electrode active material layer 243. It is attached. At this time, the method for attaching the metallic lithium 120 to the uncoated portion 242 of the negative electrode current collector 241 is not particularly limited. For example, the foil-like metallic lithium 120 and the uncoated portion 242 of the negative electrode current collector 241 may be pressure-bonded by an embossing process. Thereby, the foil-like metallic lithium 120 can be attached to the uncoated part 242 of the negative electrode current collector 241 without using an adhesive or a screw.

  In this embodiment, a carbon material is used as the negative electrode active material. In this test battery, the wound electrode body 200A is accommodated in a battery case 300, and an electrolytic solution is placed therein. At this time, in the initial stage, the potential of the carbon material as the negative electrode active material is about 3V, and the potential of the metallic lithium 120 is 0V. Therefore, when the lithium ion secondary battery 100A is left in the initial stage, the metal lithium 120 is eluted by the potential difference between the negative electrode active material layer 243 and the metal lithium 120, and further, the lithium ions eluted from the metal lithium 120 are the negative electrode active material. It penetrates into the layer 243. For this reason, the lithium ions supplied from the metal lithium 120 are easily diffused throughout the negative electrode active material layer 243, and the charge / discharge cycle characteristics of the lithium ion secondary battery 100A are improved.

  In this case, the lithium ion supplied from the metal lithium 120 can be sufficiently infiltrated into the negative electrode active material layer 243 by leaving the electrolyte solution for about 10 hours. Furthermore, when the lithium ions supplied from the metallic lithium 120 are sufficiently infiltrated into the negative electrode active material layer 243, the battery voltage is approximately 2.0 V or higher. For this reason, when the wound electrode body 200 is accommodated in the battery case 300 and the electrolyte is put, for example, the wound electrode body 200 is left for about 10 hours and the initial charging is performed after the battery voltage becomes 2.0 V or higher. Good.

≪Arrangement of metallic lithium 120≫
In this embodiment, as shown in FIG. 9, in the lithium ion secondary battery 100 </ b> A, an uncoated portion 242 is provided along an edge on one side in the width direction of the strip-shaped negative electrode current collector 241. Furthermore, as shown in FIG. 11, the metallic lithium 120 is attached to the uncoated portion 242 of the negative electrode current collector 241 along the length direction of the negative electrode current collector 241.

  In this case, in order for the lithium ions supplied from the metal lithium 120 to diffuse throughout the negative electrode active material layer 243, for example, the negative electrode active material layer 243 may be crossed in the width direction. At this time, the movement distance of lithium ions required for lithium ions supplied from metallic lithium to diffuse throughout the negative electrode active material layer 243 is generally short. Thus, in the lithium ion secondary battery 100A, lithium ions are easily diffused throughout the negative electrode active material layer 243, and the effect of attaching the metal lithium 120 as the entire negative electrode active material layer 243 is easily obtained.

  The output of the lithium ion secondary battery 100A is improved particularly when the state of charge (SOC) is low. FIG. 12 is a typical graph comparing the output characteristics of the lithium ion secondary battery 100 </ b> A according to the embodiment of the present invention with the case where the metallic lithium 120 is not attached. In FIG. 12, A shows the output characteristic (charge state-voltage) of the lithium ion secondary battery 100A according to one embodiment of the present invention, and B shows the output characteristic (charge) when the metallic lithium 120 is not attached. State-voltage). That is, the lithium ion secondary battery indicated by B has the same configuration as the lithium ion secondary battery 100A according to an embodiment of the present invention indicated by A except that the metal lithium 120 is not attached. is there.

  As indicated by B in FIG. 12, when the metallic lithium 120 is not attached, the output (voltage) rapidly decreases when the SOC decreases (in the example shown, the SOC decreases to about 10%). . On the other hand, in the lithium ion secondary battery 100A to which the metallic lithium 120 is attached, the output (voltage) rapidly decreases from about 5% SOC. Thus, by attaching the metal lithium 120, the lithium ion secondary battery 100A can maintain a high output in a low charged state.

  Furthermore, in this embodiment, the metal lithium 120 is a strip-like foil (in this embodiment, a strip-like foil having a width of about 3 mm) as shown in FIG. 11, and extends along the edge 243a of the negative electrode active material layer 243. Attached. The edge 243a of the negative electrode active material layer 243 is an entrance through which lithium ions enter the negative electrode active material layer 243 through the electrolytic solution. In this embodiment, since the strip-shaped metal lithium 120 is attached along the edge 243a of the negative electrode active material layer 243, lithium ions supplied from the metal lithium 120 efficiently penetrate into the negative electrode active material layer 243. . For this reason, it can prevent more effectively that the metal lithium 120 runs short in the negative electrode active material layer 243.

  Further, in this embodiment, the uncoated portion 242 of the negative electrode current collector 241 is welded to the negative electrode terminal 440 with the intermediate portion 244 gathered in a wound state as shown in FIGS. 9 and 13. ing. FIG. 13 is a cross-sectional view (XIII-XIII cross section in FIG. 9) showing an intermediate portion 244 of the uncoated portion 242 of the negative electrode current collector 241 gathered and welded. For convenience of illustration, FIG. 13 is particularly simplified. In this embodiment, as shown in FIG. 13, the metal lithium 120 is a strip-like foil, and is attached along the edge 243 a of the negative electrode active material layer 243.

  In this lithium ion secondary battery 100 </ b> A, an uncoated portion 242 is provided along an edge on one side in the width direction of the strip-shaped negative electrode current collector 241. The negative electrode active material layer 243 is held on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242. As shown in FIG. 9, the negative electrode current collector 241 is welded with the intermediate portion 244 gathered in a wound state. In this case, as shown in FIG. 13, there is a slight gap near the edge 243a of the negative electrode active material layer 243. In this embodiment, foil-like metallic lithium 120 is accommodated in the gap.

  Thus, in the lithium ion secondary battery 100A, the intermediate part 244 of the uncoated part 242 is gathered and welded in a state where the negative electrode current collector 241 is wound. In this case, as shown in FIG. 13, the region where the negative electrode active material layer 243 is disposed is partitioned by a wound negative electrode current collector 241 as shown in FIG. In this embodiment, in each space partitioned by the negative electrode current collector 241, an elongated foil-like metal lithium 120 is attached to the edge 243 a of the negative electrode active material layer 243. For this reason, lithium ions supplied from the metal lithium 120 enter the negative electrode active material layer 243 more efficiently.

  In this embodiment, as shown in FIG. 13, the metal lithium 120 is disposed on one side of the negative electrode current collector 241. Here, in consideration of the thickness of the metal lithium 120 and the workability of the winding process with respect to the negative electrode current collector 241 and the negative electrode active material layer 243, the foil-shaped metal lithium 120 is disposed on one surface of the negative electrode current collector 241. doing. In this case, the metal lithium 120 may be disposed only on one surface of the negative electrode current collector 241, so that the metal lithium 120 can be easily attached.

  Further, as shown in FIG. 14, the metal lithium 120 may be disposed on both surfaces of the negative electrode current collector 241. Even in this case, in the configuration in which the intermediate portion 244 of the uncoated portion 242 of the negative electrode current collector 241 is gathered and welded, the metal lithium 120 can be disposed in each space partitioned by the negative electrode current collector 241. . In this embodiment, the negative electrode active material layer 243 is provided on both surfaces of the negative electrode current collector 241, and the metal lithium 120 can be supplied uniformly by the negative electrode active material layers 243 on both surfaces of the negative electrode current collector 241.

  In this embodiment, the lithium metal 120 is attached along the length direction of the negative electrode current collector 241, but the negative electrode current collector 241 is wound and further bent flat. As shown in FIG. 15, the metallic lithium 120 may be intermittently attached along the length direction of the negative electrode current collector 241. In such a form, for example, foil-shaped metallic lithium 120 having a length of about 2 mm to 15 mm may be attached to the negative electrode current collector 241 with a gap therebetween. Thereby, the flexibility of the negative electrode current collector 241 in a state where the metallic lithium 120 is attached in the length direction can be ensured.

  As described above, the arrangement example of the metal lithium 120 that is particularly suitable for diffusing the lithium ions supplied from the metal lithium 120 into the negative electrode active material layer 243 has been described. The arrangement of the metal lithium 120 is not limited to the above.

  For example, the metallic lithium 120 may be attached to the negative terminal 440 as shown in FIG. In addition, as shown in FIG. 17, the metallic lithium 120 may be attached to the uncoated portion 242 on the outermost periphery of the wound negative electrode current collector 241. In the form shown in FIG. 17, the structure of the negative electrode terminal 440 is different from that in FIGS. 9 and 16. Even in such a case, in the lithium metal 120, lithium ions eluted from the metal lithium 120 enter the negative electrode active material layer 243 due to a potential difference between the carbon material as the negative electrode active material in the initial stage and the metal lithium 120. For this reason, the lithium ions supplied from the metal lithium 120 are easily diffused throughout the negative electrode active material layer 243, and the charge / discharge cycle characteristics of the lithium ion secondary battery 100A are improved.

≪Amount of metallic lithium 120≫
Moreover, the metallic lithium 120 to be attached is preferably 10% to 30% of the reversible capacity of the negative electrode. Here, the “reversible capacity of the negative electrode” corresponds to an amount of electricity that can reversibly charge and discharge the lithium ion secondary battery 100. That is, when a carbon material is used as the negative electrode active material, a part of lithium inserted into the negative electrode by the initial charge is substantially fixed to the negative electrode and is not released from the negative electrode. For this reason, when charge (initial charge) is performed for the first time, an event may occur in which the amount corresponding to the charge amount cannot be discharged. The “reversible capacity of the negative electrode” is an amount of electricity that can substantially charge and discharge the lithium ion secondary battery 100. “Reversible capacity of the negative electrode” means, for example, measuring the discharge capacity when the negative electrode is charged to the potential of metal lithium (0V) and discharged to about 1.5V (Li / Li ⁺ ) with the metal lithium as the counter electrode It is good to decide by.

  For example, when the reversible capacity of the negative electrode is 6 Ah, 20% of the reversible capacity of the negative electrode is 1.2 Ah, and the metallic lithium 120 corresponding to 1.2 Ah is applied to the uncoated portion 242 of the negative electrode current collector 241. It is good to attach to. Here, the metallic lithium 120 corresponding to 1.2 Ah is theoretically about 311 mg.

  Here, a test battery was prepared, and the characteristics of the lithium ion secondary battery 100A were examined by changing the amount of the metallic lithium 120.

≪Test battery≫
The basic configuration of the test battery is the form shown in FIG. 16, and here, metallic lithium 120 is attached to negative electrode terminal 440.

Here, in the test battery, the positive electrode active material layers 223 are formed on both surfaces of the positive electrode current collector 221 made of an aluminum foil having a thickness of about 15 μm, a width of 114.0 mm, and a length of 3000 mm. The positive electrode active material contained in the positive electrode active material layer 223 is a LiNiCoAlO ₂ composite oxide, the conductive material is acetylene black (AB), and the binder is polyvinylidene fluoride (PVDF). The weight ratio of the positive electrode active material, the conductive material, and the binder was positive electrode active material: conductive material: binder = 100: 5: 5. In the positive electrode sheet 220, the thickness of the portion where the positive electrode active material layer 223 is coated on the positive electrode current collector 221 is approximately 100 μm after rolling, and the thickness of the positive electrode current collector 221 is approximately 42 to 43 μm on both sides. A positive electrode active material layer 223 is formed. The width of the positive electrode current collector 221 coated with the positive electrode active material layer 223 is 98.0 mm.

  In the test battery, negative electrode active material layers 243 are formed on both surfaces of a negative electrode current collector 241 made of a copper foil having a thickness of about 20 μm, a width of 119.0 mm, and a length of 3300 mm. The negative electrode active material contained in the negative electrode active material layer 243 is graphite, and the binder is polyvinylidene fluoride (PVDF). The negative electrode active material and the binder were in a weight ratio of negative electrode active material: binder = 100: 7. In the negative electrode sheet 240, the thickness of the portion where the negative electrode active material layer 243 is coated on the negative electrode current collector 241 is approximately 120 μm after rolling, and the negative electrode active material having a thickness of approximately 50 μm on both surfaces of the negative electrode current collector 241. A material layer 243 is formed. The width of the negative electrode active material layer 243 applied to the negative electrode current collector 241 is 103.0 mm.

Further, as the separators 262 and 264, a separator having a three-layer structure (PP / PE / PP) in which both sides of polyethylene (PE) are sandwiched by polypropylene (PP) is used. The separators 262 and 264 have a thickness of 20 μm. In addition, in the electrolyte solution, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mixed solvent in a volume ratio of EC: DMC: EMC = 3: 4: 3. An electrolytic solution containing LiPF ₆ at a concentration of about 1 mol / liter was used. The electrolytic solution is injected in a state where the metal lithium 120 is attached to the negative electrode terminal 440.

≪Sample≫
Here, with respect to the test battery described above, a plurality of samples in which the amount of the metallic lithium 120 attached to the negative electrode terminal 440 was changed were prepared, and the amount of the metallic lithium 120 suitable for attaching in the vicinity of the negative electrode was examined.

  Here, the predetermined conditioning process was performed with respect to each sample, and the output characteristics in the SOC 20% charge state were measured.

<< conditioning >>
Next, the test battery constructed as described above was poured for about 10 hours after injecting the electrolytic solution, and was initially charged after the battery voltage became 2.0 V or higher. The conditioning process is performed by the following procedures 1 and 2.
Procedure 1: After reaching 4.1 V with a constant current charge of 1 C, pause for 5 minutes.
Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

≪Measurement of rated capacity≫
Next, the rated capacity is measured by the following procedures 1 to 3 at a temperature of 25 ° C. and a voltage range of 3.0 V to 4.1 V for the test battery after the conditioning step.
Procedure 1: After reaching 3.0V by constant current discharge of 1C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
Procedure 2: After reaching 4.1 V by constant current charging at 1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.
Procedure 3: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 is defined as the rated capacity. In this test battery, the rated capacity is about 4.6 Ah.

≪SOC adjustment≫
The SOC adjustment is performed by the following procedures 1 and 2. Here, the SOC adjustment may be performed after the conditioning process and the measurement of the rated capacity. Here, in order to make the influence of temperature constant, SOC adjustment is performed in a temperature environment of 25 ° C.
Procedure 1: Charging at a constant current of 3V to 1C to obtain a charged state (SOC 20%) of about 20% of the rated capacity.
Procedure 2: After procedure 1, charge at constant voltage for 2.5 hours.
Thereby, the test battery can be adjusted to a predetermined state of charge.

≪Output characteristics at 20% SOC≫
Here, the test battery was evaluated by the output characteristics at SOC 20%. The output characteristics at 20% SOC were measured as follows.

  The test battery adjusted to SOC 20% is discharged at a predetermined pulse current with respect to the test battery adjusted to SOC 20%. At this time, the pulse current is increased stepwise in order of 0.3C, 1C, 3C, 5C, and 10C, and the voltage (terminal voltage) between the terminals of the positive electrode terminal 420 and the negative electrode terminal 440 10 seconds after the start of discharge, respectively. It was measured. Then, based on the terminal voltage measured when the pulse current is 0.3C, 1C, 3C, 5C, 10C, the current value CA extrapolated to 3.0V, which is the discharge end voltage of the test battery, is minimized. It was obtained by linear approximation by the square method. Here, the output CW1 of the test battery is obtained by CW1 = CA (A) × 3.0 (V). The output CW1 was set as an output characteristic at SOC 20%.

Table 1 shows the output characteristics at SOC 20% for Samples 1-5. Here, it is considered that the output of the test battery is maintained even in a low state of charge as the output characteristic at SOC 20% is larger.

  In this case, in Sample 1, the amount of metal lithium 120 attached to the negative electrode terminal 440 was set to an amount corresponding to 20% of the reversible capacity of the negative electrode. In sample 1, the output characteristics at 20% SOC were 550 W.

  In Sample 2, the amount of metal lithium 120 attached to the negative electrode terminal 440 was set to an amount corresponding to 10% of the reversible capacity of the negative electrode. In sample 2, the output characteristic at 20% SOC was 500 W.

  In Sample 3, the amount of metal lithium 120 attached to the negative electrode terminal 440 was 30% of the negative electrode's reversible capacity. In sample 3, the output characteristics at 20% SOC were 520 W.

  In Sample 4, the amount of metal lithium 120 attached to the negative electrode terminal 440 was equivalent to 40% of the reversible capacity of the negative electrode. In sample 4, the output characteristics at SOC 20% were 350 W.

  In Sample 5, the amount of metallic lithium 120 attached to the negative electrode terminal 440 was equivalent to 5% of the reversible capacity of the negative electrode. In sample 5, the output characteristic at 20% SOC was 300 W.

  Here, if the amount of metallic lithium 120 attached to the negative electrode terminal 440 is about 5% of the reversible capacity of the negative electrode, the amount of metallic lithium 120 may be insufficient. Further, when the metal lithium 120 attached to the negative electrode terminal 440 is about 40% of the reversible capacity of the negative electrode, a part of the metal lithium 120 attached to the negative electrode terminal 440 does not enter the negative electrode active material layer 243. It is possible that it remains. If a part of the metal lithium 120 remains without entering the negative electrode active material layer 243, for example, the remaining metal lithium 120 causes a side reaction with the electrolyte, and the internal resistance of the test battery increases. The output characteristics at SOC 20% deteriorate.

  Thus, if the amount of metallic lithium 120 attached in the vicinity of the negative electrode is about 10% or more and 30% or less with respect to the reversible capacity of the negative electrode, the output characteristics of the test battery at 20% SOC are approximately 500 W or more. It is considered that the effect of attaching the metallic lithium 120 can be obtained more appropriately. For this reason, in the above-described lithium ion secondary battery 100A, the uncoated portion 242 of the negative electrode current collector 241 and metallic lithium attached in the vicinity thereof are in an amount of about 10% to 30% with respect to the reversible capacity of the negative electrode. Is desirable. Thereby, the output of the lithium ion secondary battery 100A is maintained high even in a low charged state. Note that the metal lithium 120 is more preferably 12% or more, more preferably 15% or more of the reversible capacity of the negative electrode. Further, the metallic lithium 120 is more preferably 28% or less, and further preferably 25% or less of the reversible capacity of the negative electrode.

  As described above, a lithium ion secondary battery 100A according to an embodiment of the present invention includes, for example, a strip-shaped positive electrode current collector 221 and a strip-shaped negative electrode current collector 241 as shown in FIG. I have. The strip-shaped positive electrode current collector 221 is provided with an uncoated portion 222 along an edge on one side in the width direction. Further, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222. The strip-shaped negative electrode current collector 241 is provided with an uncoated portion 242 along an edge on one side in the width direction. Further, the negative electrode active material layer 243 is held on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242. Separators 262 and 264 are interposed between the positive electrode active material layer 223 and the negative electrode active material layer 243.

  The uncoated portion 242 of the negative electrode current collector 241 is disposed on the side opposite to the uncoated portion 222 of the positive electrode current collector 221 in the width direction of the positive electrode current collector 221. In addition, the negative electrode active material layer 243 and the positive electrode active material layer 223 are stacked so that the negative electrode active material layer 243 covers the positive electrode active material layer 223 with the separators 262 and 264 interposed therebetween. Further, the positive electrode current collector 221 and the negative electrode current collector 241 are wound around a winding axis WL set in the width direction of the positive electrode current collector 221. In the lithium ion secondary battery 100A, the metallic lithium 120 is attached to the uncoated portion 242 of the negative electrode current collector 241 and the vicinity thereof.

  According to the lithium ion secondary battery 100A, since the metal lithium 120 is attached to the uncoated portion 242 of the negative electrode current collector 241 and the vicinity thereof, the lithium ions supplied from the metal lithium 120 are negative electrode active material layers. It is easy to diffuse throughout the entire H.243. For this reason, the charge / discharge cycle characteristics of the lithium ion secondary battery 100A are improved.

  In addition, as shown in FIG. 9, in the lithium ion secondary battery 100A, the uncoated portion 242 of the negative electrode current collector 241 is gathered together with the intermediate portion 244 in a wound state, and the negative electrode terminal 440 is welded. It may be. In this case, the metallic lithium 120 may be attached to the uncoated part 242 as shown in FIG. Further, as shown in FIG. 16, the metallic lithium 120 may be attached to the negative electrode terminal 440 in the vicinity of the uncoated portion 242. When the metal lithium 120 is attached to the negative electrode terminal 440, it is natural that the metal lithium 120 is attached to the negative electrode terminal 440 in the battery case 300.

  Further, as shown in FIGS. 9 to 11, the metallic lithium 120 may be attached to the uncoated portion 242 of the negative electrode current collector 241 along the length direction of the negative electrode current collector 241. In this case, for example, lithium ions supplied from the metal lithium 120 may cross the negative electrode active material layer 243 in the width direction in order to diffuse throughout the negative electrode active material layer 243. For this reason, in the lithium ion secondary battery 100A, lithium ions are easily diffused throughout the negative electrode active material layer 243, and the effect of attaching the metal lithium 120 as the entire negative electrode active material layer 243 is easily obtained.

  Furthermore, as shown in FIG. 11, the metal lithium 120 is an elongated strip-like foil, and is preferably attached along the edge 243 a of the negative electrode active material layer 243. The edge 243a of the negative electrode active material layer 243 is an entrance through which lithium ions enter the negative electrode active material layer 243 through the electrolytic solution. In this embodiment, since the strip-shaped metal lithium 120 is attached along the edge 243a of the negative electrode active material layer 243, lithium ions supplied from the metal lithium 120 efficiently penetrate into the negative electrode active material layer 243. . For this reason, it can prevent more effectively that the metal lithium 120 runs short in the negative electrode active material layer 243.

  Moreover, the metal lithium 120 may be intermittently attached along the length direction of the negative electrode current collector 241 as shown in FIG. Thereby, the flexibility of the negative electrode current collector 241 in a state where the metallic lithium 120 is attached in the length direction can be ensured.

  Further, the metallic lithium 120 may be disposed on one side of the negative electrode current collector 241 or may be disposed on both sides of the negative electrode current collector 241.

  Further, the metallic lithium 120 is preferably 10% or more and 30% or less of the reversible capacity of the negative electrode. Thereby, the output of the lithium ion secondary battery 100A is maintained high even in a low charged state.

  In the above, the lithium ion secondary battery which concerns on one Embodiment of this invention was demonstrated. Note that the present invention is not limited to any of the above-described embodiments unless otherwise specified.

  For example, in the above-described embodiment, the lithium ion secondary battery 100A in which the wound electrode body 200 pushed and bent flat is accommodated in the rectangular battery case 300 is exemplified. A so-called laminate-type battery in which the wound electrode body 200 pushed and bent flat is accommodated in a soft container may be configured.

  FIG. 18 shows a laminate-type lithium ion secondary battery 100B. Laminated battery container 300B (exterior material) is indicated by a two-dot chain line, and for example, an aluminum laminate film may be used. The wound electrode body 200B has substantially the same structure as the wound electrode body 200A of the lithium ion secondary battery 100A shown in FIG. 9, and the same reference numerals are given to members and parts that have the same action.

  In this embodiment, along the winding axis WL of the wound electrode body 200B, the uncoated part 222B of the positive electrode current collector 221 is disposed on one side, and the uncoated part 242B of the negative electrode current collector 241 is disposed on the other side of the separator 262. H.264. And in the said protrusion part, the intermediate part 224B of the uncoated part 222B of the positive electrode collector 221 is gathered together, and the positive electrode terminal 420B is attached to the said intermediate part 224B. Similarly, the intermediate portion 244B of the uncoated portion 242B of the negative electrode current collector 241 is gathered together, and the negative electrode terminal 440B is attached to the intermediate portion 244B.

  As described above, the present invention may be configured as a laminate-type battery. In this case as well, the metal lithium 120 may be attached to the uncoated portion 242B of the negative electrode current collector 241 and the vicinity thereof. As a result, lithium ions supplied from the metal lithium 120 diffuse throughout the negative electrode active material layer 243, and the charge / discharge cycle characteristics of the lithium ion secondary battery 100B, particularly the output characteristics of the lithium ion secondary battery 100B in a low charge state. improves.

  Further, as described above, the present invention contributes to the improvement of the output characteristics of the lithium ion secondary battery in a particularly low charge state. For this reason, the lithium ion secondary battery according to the present invention is a vehicle drive power source such as a hybrid vehicle (particularly, a plug-in hybrid vehicle) or a drive battery for an electric vehicle, which requires a high level of output characteristics particularly in a low charge state. It is suitable for a secondary battery.

  In this case, the lithium ion secondary battery according to an embodiment of the present invention is, for example, in the form of an assembled battery in which a plurality of secondary batteries are connected and combined as shown in FIG. It can be suitably used as a vehicle drive battery 1000 for driving the motor (electric motor). In particular, the lithium ion secondary battery according to the present invention can stably exhibit a high output even at a low charge amount, and can withstand use at a lower charge amount. Therefore, the battery can be used efficiently, and even when the required level of capacity is high, the number of batteries to be used can be reduced and the cost can be reduced. A lithium ion secondary battery according to an embodiment of the present invention is, for example, a lithium ion secondary battery having a rated capacity of 3.0 Ah or more as a driving battery for a hybrid vehicle (particularly, a plug-in hybrid vehicle) or an electric vehicle. Suitable for batteries.

1 Vehicle 100, 100A, 100B Lithium ion secondary battery 120 Metallic lithium 200, 200A, 200B Winding electrode body 220 Positive electrode sheet 221 Positive electrode current collector 222, 222B Uncoated part 223 Positive electrode active material layer 224, 224B Intermediate part 225 Gap 240, 240A Negative electrode sheet 241 Negative electrode current collector 242, 242B Uncoated portion 243 Negative electrode active material layer 243a Edge 244, 244B of negative electrode active material layer Intermediate portion 245 Gap 252, 254 Along the winding axis of wound electrode body Both sides 262, 264 Separator 280 Electrolyte 290 Battery charger 300 Battery case 300B Container (exterior material, laminate film)
310, 312 Gap 320 Container body 322 Lid and container body joint 340 Lid 350 Injection hole 352 Sealing cap 360 Safety valve 420, 420B Positive terminal (electrode terminal)
420a Tip portion 440, 440B of positive terminal (electrode terminal) Negative terminal (electrode terminal)
440a Tip part 610 of negative electrode terminal (electrode terminal) Positive electrode active material particle 620 Conductive material 630 Binder 710 Negative electrode active material 730 Binder 1000 Vehicle drive battery WL Winding shaft

Claims (9)

A belt-like positive electrode current collector;
A positive electrode active material layer containing a positive electrode active material, which is held on both surfaces of the positive electrode current collector except for an uncoated portion provided along an edge on one side in the width direction of the positive electrode current collector;
A strip-shaped negative electrode current collector;
A negative electrode active material layer containing a negative electrode active material, which is held on both surfaces of the negative electrode current collector except for an uncoated portion provided along an edge on one side in the width direction of the negative electrode current collector;
A separator interposed between the positive electrode active material layer and the negative electrode active material layer;
With
The uncoated portion of the negative electrode current collector is disposed on the side opposite to the uncoated portion of the positive electrode current collector in the width direction of the positive electrode current collector, and the separator is interposed in the state where the separator is interposed. The negative electrode active material layer and the positive electrode active material layer are overlapped so that the negative electrode active material layer covers the positive electrode active material layer, and the positive electrode current collector and the negative electrode current collector further include the positive electrode current collector. It is wound around the winding axis set in the width direction of the body,
A lithium ion secondary battery in which metallic lithium is attached to an uncoated portion of the negative electrode current collector and the vicinity thereof. In the wound state, the uncoated portion of the negative electrode current collector is gathered in the middle portion and the negative electrode terminal is welded,
The lithium ion secondary battery according to claim 1, wherein the metallic lithium is attached to the uncoated portion or the negative electrode terminal.   3. The lithium ion secondary battery according to claim 2, wherein the metallic lithium is attached to the uncoated portion of the negative electrode current collector along a length direction of the negative electrode current collector.   4. The lithium ion secondary battery according to claim 3, wherein the metallic lithium is an elongated strip-like foil, and is attached along an edge of the negative electrode active material layer. 5.   5. The lithium ion secondary battery according to claim 3, wherein the metallic lithium is intermittently attached along a length direction of the negative electrode current collector.   The lithium metal secondary battery according to any one of claims 3 to 5, wherein the metallic lithium is disposed on one surface of the negative electrode current collector.   The lithium metal secondary battery according to any one of claims 3 to 5, wherein the metallic lithium is disposed on both surfaces of the negative electrode current collector.   The lithium ion secondary battery according to any one of claims 1 to 7, wherein the metallic lithium is 10% or more and 30% or less of a reversible capacity of the negative electrode.   The lithium ion secondary battery according to any one of claims 1 to 8, wherein the rated capacity is 3.0 Ah or more.

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