JP2011029075A - Negative electrode for lithium ion secondary battery, and lithium ion secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for reducing stress directed toward the surface of a current collector and inhibiting the peeling of an active material layer from the current collector. <P>SOLUTION: A negative electrode for lithium ion secondary battery includes a current collector and an active material layer formed on the current collector. The active material layer includes a first active material layer and a second active material layer having smaller volume variation than the first active material layer due to occlusion and release of lithium. The first active material layer and the second active material layer are alternately disposed towards the surface of the electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same. Specifically, the negative electrode for a lithium ion secondary battery in which two active material layers are alternately arranged in the plane direction and a lithium ion secondary battery using the same.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

Conventionally, carbon / graphite-based materials that are advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, since carbon / graphite-based negative electrode materials are charged / discharged by occlusion / release of lithium ions into / from graphite crystals, the charge / discharge capacity of a theoretical capacity of 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium introduction compound. There is a disadvantage that cannot be obtained. For this reason, it is expected that it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

In contrast, a battery using a material that is alloyed with lithium for the negative electrode (hereinafter also referred to as a lithium alloy negative electrode material) has an improved energy density as compared with a conventional carbon / graphite negative electrode material. It is expected as a negative electrode material. For example, the Si material occludes and releases 4.4 mol of lithium ions per mol as shown in the following reaction formula in charge and discharge, and Li ₂₂ Si ₅ has a theoretical capacity of about 4199 mAh / g.

  However, a lithium ion secondary battery using a lithium alloy-based negative electrode material has a large expansion and contraction of the positive electrode and the negative electrode during charging and discharging. For example, the volume expansion when lithium ions are occluded is about 1.2 times that of graphite, but about 4 times that of Si material.

  As a method for improving the volume expansion of such a Si material, Patent Document 1 discloses the use of a metal foam in which silicon is held as an active material as a negative electrode. With such a configuration, the area where silicon and metal are in contact with each other is increased, and the adhesion between the current collector and the active material is improved.

JP 2004-259636 A

  However, although a large stress occurs in the surface direction of the current collector as the alloy-based active material expands and contracts, the technique of Patent Document 1 does not cope with the stress in the surface direction of the current collector, The solution to the problem of the active material layer peeling off from the current collector has not been sufficient.

  Therefore, an object of the present invention is to provide a negative electrode that reduces stress in the surface direction of the current collector and suppresses the active material layer from peeling from the current collector.

  The inventors of the present invention have made extensive studies in view of the above problems. As a result, the active material layer includes a first active material layer and a second active material layer that has a smaller volume change due to insertion and extraction of lithium than the first active material layer, and the first active material layer and the second active material layer include It has been found that the above object can be achieved by alternately arranging the electrodes in the plane direction.

  According to the present invention, since the second active material layer can absorb the volume change in the surface direction of the first active material layer, the stress in the surface direction of the current collector can be reduced. Therefore, the active material layer can be prevented from peeling from the current collector.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which represented typically the outline | summary of the negative electrode for lithium ion secondary batteries which is one Embodiment (1st Embodiment) of this invention. It is the top view seen from the lamination direction of the electrical power collector used for 1st Embodiment. It is the top view seen from the lamination direction of the electrical power collector which shows the modification of the electrical power collector of FIG. It is the schematic sectional drawing which represented the outline | summary of the negative electrode for lithium ion secondary batteries which is other embodiment (2nd Embodiment) of this invention typically. A is a schematic cross-sectional view schematically showing an outline of a negative electrode for a lithium ion secondary battery according to another embodiment (third embodiment) of the present invention. B is a plan view of the negative electrode A viewed from the stacking direction. C is a plan view seen from the stacking direction showing another arrangement example of the first and second active material layers. FIG. It is the cross-sectional schematic which represented the outline | summary of the negative electrode for lithium ion secondary batteries which is a modification of 3rd Embodiment typically. 1 is a schematic cross-sectional view schematically showing an outline of a stacked flat non-bipolar lithium ion secondary battery which is a typical embodiment of a lithium ion secondary battery of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing an appearance of a stacked flat lithium ion secondary battery that is a typical embodiment of a lithium ion secondary battery according to the present invention. It is the schematic of the lithium ion secondary battery produced in the Example.

  The present invention comprises a current collector and an active material layer formed on the current collector, and the active material layer is formed by a first active material layer and occlusion / release of lithium from the first active material layer. And a second active material layer having a small volume change, wherein the first active material layer and the second active material layer are alternately arranged with respect to the surface direction of the electrode. Since the first and second active material layers are alternately arranged in the plane direction, the second active material layer can absorb the volume change in the plane direction of the first active material layer, and thus in the plane direction of the current collector. The stress of can be reduced. Therefore, the active material layer can be prevented from peeling from the current collector.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery according to one embodiment of the present invention (first embodiment). The negative electrode 50 for a lithium ion secondary battery according to the first embodiment penetrates through a current collector 51, a second active material layer 53 formed on the current collector 51, and an opening of the current collector in the stacking direction. Thus, the first active material layer 52 is present. The second active material layer has a smaller volume change due to insertion and extraction of lithium than the first active material layer. In the present embodiment, the current collector 51 has a grid-like planar shape as shown in FIG. 2, and the openings 51 a are intermittently formed in the surface direction of the current collector 51. Note that the openings 51a are “intermittently formed” means that the openings 51a are formed so as to exist with a certain distance (which may be constant or indefinite). The first active material layer 52 and the second active material layer 53 are alternately arranged in the plane direction because the second active material layer exists on the current collector and the first active material layer exists in the opening. It becomes. In the first embodiment, the first and second active material layers are negative electrode active material layers each including a negative electrode active material.

  In the form shown in FIG. 1, the current collector 51 has openings 51a formed intermittently in the surface direction. Since the formation of the opening 51a is intermittent, the conduction of the part where the opening of the current collector 51 is not formed is ensured throughout, and there is no problem in the function as the current collector (see FIG. 2). ). In addition, there is no restriction | limiting in particular in specific forms, such as a size and the number of the opening parts 51a formed in the electrical power collector 51, As long as the effect of this invention can be exhibited, it can set suitably. As an example, the size (maximum side length) of one opening 51a is about 0.1 to 10 mm. FIG. 3 shows another example of a grid-like current collector.

  Since the first and second active material layers are alternately arranged in the plane direction, the second active material layer can absorb the volume change in the plane direction of the first active material layer, and thus in the plane direction of the current collector. The stress of can be reduced. Therefore, the active material layer can be prevented from peeling from the current collector. Further, the current collector has a lattice shape, and the first active material layer, which is an active material layer having a large volume change, exists through the opening, so that the first active material layer is a plane surface of the current collector. No longer touch. For this reason, the stress of a surface direction is relieved and an active material layer becomes difficult to peel from a collector.

  FIG. 4 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery according to another embodiment of the present invention (second embodiment). In the present embodiment, the current collector 51 is an expanded metal processed into a lattice shape. Similar to the first embodiment, the negative electrode 50a for the lithium ion secondary battery according to the second embodiment includes a second active material layer 53 formed on the current collector 51, and a second active material layer 53 present in the opening of the current collector. The active material layer 52 is formed. The negative electrode of the second embodiment is obtained, for example, by applying a second active material layer in advance on a current collector sheet, expanding the sheet, and then forming the first active material layer in the opening. A grid-like current collector can be easily produced by the expanding process. Thus, the current collector may be formed in a lattice shape by expanding. The current collector has a lattice shape, and the first active material layer, which is an active material layer having a large volume change, exists through the opening, so that the first active material layer is in contact with the planar surface of the current collector. Disappear. For this reason, the stress of a surface direction is relieved and an active material layer becomes difficult to peel from a collector.

  In the first and second embodiments, since the first active material layer is disposed in the penetrating portion of the current collector 51, active material layers having the same polarity are disposed on both sides of the current collector 51. (In other words, it can be used only for a battery that is not a bipolar type described later).

  In the first and second embodiments, the ratio of the opening 51a in the current collector 51 is preferably 10 to 90%, more preferably 20 to 90, with respect to 100% of the surface area of the current collector. %. In the present embodiment, if the presence ratio of the opening 51a is 10% or more, the binding properties of the negative electrode active material layers on both sides that are bonded through the opening 51a can be sufficiently ensured. On the other hand, if the ratio of the opening 51a is 90% or less, the original function of the current collector for taking out the electricity generated in the active material layer to the outside can be sufficiently exhibited. The opening 51a may be provided in at least a part of the current collector 51. However, from the viewpoint of sufficiently exerting the above-described effects, the opening 51a is uniformly formed on the entire surface of the current collector 51. It is preferable to be provided.

  FIG. 5: is a schematic sectional drawing which shows the negative electrode 50b for lithium ion secondary batteries which is other embodiment of this invention (3rd Embodiment). In the present embodiment, the current collector 51 is a metal foil. On the current collector 51, the first active material layers 52 and the second active material layers 53 are alternately arranged in the plane direction. In the present embodiment, the first active material layer and the second active material layer are arranged so as to have a checkered pattern in a plan view as shown in FIG. 5B, but the first active material layer 52 and the second active material layer 53 are Any form may be used as long as it is alternately arranged in the surface direction. For example, as shown in FIG. Since the first and second active material layers are alternately arranged in the plane direction, the second active material layer can absorb the volume change in the plane direction of the first active material layer, and thus in the plane direction of the current collector. The stress of can be reduced. Therefore, the active material layer can be prevented from peeling from the current collector.

  FIG. 6 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery, which is a modification of the third embodiment. In this modification, the first active material layer 52 and the second active material layer 53 are alternately arranged on the current collector 51 in the plane direction, and another active material layer is provided on the side facing the current collector. 54 is laminated. In the present modification, the other active material layer 54 is made of the same material as the second active material layer. The other active material layer 54 is made of the same material as that of the second active material layer, thereby suppressing expansion and contraction in the stacking direction of the first active material layer. However, the material constituting the other active material layer 54 is not particularly limited.

  When a plurality of active material layers are stacked in the stacking direction as in this modification, at least the active material layers in contact with the current collector are alternately arranged in the plane direction with the first and second active material layers. It is preferable. At least in the active material layer in contact with the current collector, the first and second active material layers are alternately arranged in the surface direction, so that the effect of reducing the stress in the surface direction of the current collector is exhibited. It is. As a result of reducing the stress in the surface direction of the current collector, the active material layer can be prevented from peeling from the current collector. When a plurality of active material layers are stacked, from the viewpoint of productivity and thickness, it is preferably 2 to 4 layers, more preferably 2 to 3 layers, and further preferably 2 layers. preferable.

  Hereafter, the member which comprises the negative electrode of each embodiment is demonstrated in detail.

[Current collector]
The current collector is a member for electrically joining the active material layer and the outside, and is made of a conductive material. There is no restriction | limiting in particular about the specific form of an electrical power collector. As long as it has electroconductivity, the material is not specifically limited, The conventionally well-known form used for the general lithium ion secondary battery can be employ | adopted. For example, a metal or a conductive polymer can be employed. Specifically, iron, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, aluminum, copper, silver, gold, platinum, stainless steel, or carbon can be given. A so-called “resin current collector” having a configuration in which a conductive filler is dispersed in a base material made of a non-conductive polymer can also be adopted as one form of the current collector. Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers. The size of the current collector is determined according to the intended use of the lithium ion secondary battery. If a large electrode used for a large battery is manufactured, a current collector having a large area is used. If a small electrode is produced, a current collector with a small area is used.

[First active material layer and second active material layer]
The second active material layer has a smaller volume change when inserting and extracting lithium than the first active material layer. The volume change of both is calculated by comparing the ratio of the volume change after insertion / extraction of lithium to the volume of the active material layer before insertion / extraction of lithium. The volume change of the active material layer depends on the type of active material contained in each active material layer and the active material content density.

  Preferably, the potential drop when the lithium of the second active material layer is occluded (during charging) is smaller than the potential drop of the first active material layer. At this time, the potential drop is measured by a potential drop (potential drop per unit lithium occlusion) when an equal amount of lithium reacts.

  When storing lithium during charge and discharge, the larger the negative electrode potential drop, the higher the reactivity with lithium. Therefore, lithium is stored relatively preferentially. Lithium once occluded in the active material layer having a large negative electrode potential drop diffuses and moves to the active material layer having a small negative electrode potential drop, so that the expansion and contraction in the plane direction is relatively large. That is, the first active material layer expands and contracts in the plane direction, but the second active material layer can absorb this. Therefore, the expansion and contraction in the surface direction is alleviated.

  The active material contained in the first active material layer (hereinafter also simply referred to as the first active material) is not particularly limited, and examples thereof include an alloy-based material having an element that can be alloyed with lithium. By using an alloy-based material, it is possible to obtain a high-capacity battery having a higher energy density than conventional carbon materials.

  Elements that can be alloyed with lithium are not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl and the like can be mentioned. Among these, from the viewpoint that a battery excellent in capacity and energy density can be configured, the negative electrode active material contains at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. It is preferable to include Si, Sn elements are more preferable, and Si is particularly preferable.

Specific examples of the alloy-based material containing an element that can be alloyed with lithium described above include, for example, metal compounds, metal oxides, lithium metal compounds, lithium metal oxides (including lithium-transition metal composite oxides), and the like. Is mentioned. Examples of the active material in the form of a metal compound include LiAl, Li ₄ Si, Li _4.4 Pb, Li _4.4 Sn, and the like. Moreover, as an active material in the form of a metal oxide, SnO, SnO ₂ , GeO, GeO ₂ , In ₂ O, In ₂ O ₃ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , SiO, ZnO Etc. Of these, Li ₄ Si, Li _4.4 Sn, SnO, SnO ₂ and SiO are preferably used, and SiO is particularly preferably used. These may be used alone or in combination of two or more.

In addition to the alloy material, the first active material layer includes carbon materials such as graphite, soft carbon, and hard carbon, metal materials such as lithium metal, lithium-titanium composite oxide (lithium titanate: Li ₄ Ti Lithium-transition metal composite oxides such as ₅ O ₁₂ ) and other conventionally known negative electrode active materials may be used. In some cases, two or more of these negative electrode active materials may be used in combination.

  However, in order to improve the capacity, it is preferable that a large amount of a negative electrode active material containing an element that can be alloyed with lithium is included in the first active material layer. In a more preferred form, specifically, in the first active material layer, the active material containing an element that can be alloyed with lithium in the negative electrode active material is 60% by mass or more, more preferably 80% by mass or more, and still more preferably 90%. It is contained by mass% or more, particularly preferably 100% by mass.

The active material contained in the second active material layer (hereinafter, also simply referred to as the second active material) is not particularly limited. Specifically, the carbon-based material, lithium-transition metal composite oxide ( Examples thereof include lithium-titanium composite oxides represented by Li _x Ti _y O _z such as Li ₄ Ti ₅ O ₁₂ . A 2nd active material may be used individually by 1 type, and may be used together 2 or more types. Since the expansion of the second active material layer is desirably as small as possible, the second active material preferably has a small expansion when Li is occluded. Examples of such materials include carbon-based materials, lithium-titanium composite oxides, and mixtures thereof, and carbon-based materials are more preferable. Specific examples of the carbon-based material that can be used as the second active material include graphite (natural graphite and artificial graphite), carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. As for these carbon-based materials, only one kind may be used alone, or two or more kinds may be used in combination.

  In addition, the active material of the second active material layer may include an alloy material in addition to the carbon material and the lithium-transition metal composite oxide. However, in order to efficiently exhibit the buffering effect of the second active material layer, it is preferable to include a large amount of carbon-based material in the second active material layer. In a more preferred form, specifically, in the second active material layer, the carbon-based material in the negative electrode active material is 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably. 100% by mass is contained.

  The average particle size of the active material is not particularly limited, but is preferably about 1 to 50 μm from the viewpoint of increasing the output. Moreover, the content of the active material is not particularly limited, but is usually about 50 to 99% by mass in each active material layer. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the particle outline. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

  Of the first and second active material layers, at least the second active material layer preferably has a void portion formed by pre-doping with lithium. Due to the presence of such voids, even if the first active material layer expands and contracts when lithium is occluded / released, it can be buffered by the voids present in the second active material layer. . In particular, it is preferable that only the second active material layer has such a void portion because the expansion and contraction in the surface direction of the first active material layer having a large expansion and contraction can be further relaxed. The porosity of the active material layer is not particularly limited, but is preferably 20 to 60% and more preferably 35 to 50% because the buffering effect can be appropriately exhibited. If only the first active material layer has a void formed by pre-doping with lithium, expansion in the thickness direction may occur during pre-doping.

  The gap formed by lithium pre-doping is not particularly limited, but as described in detail below, the active material layer contains lithium powder at the time of manufacture, and after the battery is assembled, the initial charge is performed. It is formed by doing. This is because lithium in the lithium powder is doped, and the portion where the lithium powder is located becomes a void.

  In the negative electrode, the content ratio of the first active material layer and the second active material layer is not particularly limited, but since the effect of the present invention is more exerted, the first active material layer by volume ratio: The second active material layer is preferably 1: 0.5 to 3, and more preferably 1: 1 to 2.

  Each active material layer includes a material that occludes and releases lithium as described above, and a conductive aid, binder, electrolyte (polymer matrix, ion-conductive polymer, electrolytic solution, etc.) for enhancing electrical conductivity as necessary. ), An electrolyte supporting salt (lithium salt) for increasing ion conductivity, and the like.

  The compounding ratio of the components contained in each active material layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a lithium ion secondary battery can be referred suitably. For example, the thickness of the active material layer is about 2 to 150 μm.

  A conductive assistant means the additive mix | blended in order to improve electroconductivity. The conductive auxiliary agent that can be used in the present embodiment is not particularly limited, and conventionally known forms can be appropriately referred to. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  Although it does not specifically limit as a binder, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FE) ), Tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) , Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluoro rubber (VDF-PFP-TFE fluoro rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber Examples thereof include vinylidene fluoride-based fluororubber such as (VDF-CTFE-based fluororubber), an epoxy resin, and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window and are stable at the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

  The amount of the binder is not particularly limited as long as it is an amount capable of binding the alloy-based material and the conductive material, but is preferably 0.5 to 25% by mass with respect to the active material layer, More preferably, it is 1-20 mass%.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The negative electrode for lithium ion secondary batteries which concerns on embodiment mentioned above can be used for a lithium ion secondary battery. That is, one embodiment of the present invention is a lithium ion secondary battery including the negative electrode for a lithium ion secondary battery according to the above-described embodiment. The negative electrode of the above embodiment can be suitably used for a drive power source of a vehicle and the like because the active material layer is difficult to peel from the current collector, and thus the cycle characteristics are improved and the long-term reliability is excellent. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable / mobile devices such as mobile phones and notebook computers that are strongly required to be small and have high capacity.

  Lithium ion secondary batteries can be applied to any conventionally known forms / structures such as stacked (flat) batteries and wound (cylindrical) batteries, for example, when distinguished by form / structure. Is. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  When distinguished by the type of electrolyte in the lithium ion secondary battery, a conventionally known battery such as a solution electrolyte type battery using a solution electrolyte such as a non-aqueous electrolyte as the electrolyte, a polymer battery using a polymer electrolyte as the electrolyte, etc. It can be applied to any electrolyte type. It is preferably applied to a polymer battery using a polymer electrolyte as the electrolyte. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). It is done. Among them, polymer batteries, especially solid polymer (all solid) batteries, do not cause liquid leakage, so there is no problem of liquid junction, high reliability, and a simple configuration with excellent output characteristics. This is advantageous in that it can be done.

  In the following description, a lithium ion secondary battery that is not a bipolar type (internal parallel connection type) lithium ion secondary battery will be described with reference to the drawings. However, the present invention should not be limited to these.

  Hereinafter, the structure of the lithium ion secondary battery will be described.

  FIG. 7 is a schematic cross-sectional view schematically showing the overall structure of a stacked lithium ion secondary battery (stacked battery) that is not bipolar. In this type of battery, the negative electrode in any of the above-described FIGS. 1 and 3 to 6 (modified examples of the first to third embodiments and the third embodiment) can be used.

  As shown in FIG. 7, the lithium ion secondary battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior. Have. Specifically, the power generation element 21 is housed and sealed by using a polymer-metal composite laminate sheet as the battery exterior and joining all of its peripheral parts by thermal fusion.

  The power generation element 21 includes a positive electrode in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11, an electrolyte layer 17, and a negative electrode in which the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. It has a stacked configuration. Specifically, the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the lithium ion battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode active material layer 12 is disposed only on one side of the outermost positive electrode current collector located in both outermost layers of the power generation element 21. 7, the arrangement of the positive electrode and the negative electrode is reversed so that the outermost negative electrode current collector is positioned in both outermost layers of the power generation element 21, and the negative electrode is formed only on one side of the outermost negative electrode current collector. An active material layer may be arranged.

  A positive electrode current collector plate (positive electrode tab) 25 and a negative electrode current collector plate (negative electrode tab) 27, which are electrically connected to the respective electrodes (positive electrode and negative electrode), are attached to the positive electrode current collector 11 and the negative electrode current collector 12, respectively. . These current collector plates (25, 27) are led out of the laminate sheet 29 so as to be sandwiched between the end portions of the laminate sheet 29, respectively. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like. In addition, it is preferable to use a normal current collector as the positive electrode current collector, and specifically, a current collector plate described in the column of a positive electrode current collector plate and a negative electrode current collector plate described later can be used.

  Hereinafter, components other than the negative electrode constituting the battery described above will be briefly described, but are not limited to the following modes.

[Positive electrode (positive electrode active material layer)]
The positive electrode active material layer 13 includes a positive electrode active material, and further includes other additives as necessary.

i The positive electrode active material layer 13 contains a positive electrode active material. Examples of positive electrode active materials include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium- Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , lithium-transition metal sulfate compounds, and the like. In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoints of capacity and output characteristics, a lithium-transition metal composite oxide and a lithium-transition metal phosphate compound are used as the positive electrode active material. Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in the positive electrode active material layer 13 is not particularly limited, but is preferably 1 to 20 μm from the viewpoint of increasing the output.

  The positive electrode active material layer 13 includes a binder. These binders are as described in the negative electrode column. Further, like the negative electrode, other additives can be included. Examples of other additives that can be included in the positive electrode active material layer include a conductive additive, an electrolyte, and an electrolyte supporting salt. Details are as described in the column of the negative electrode.

  The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. The thickness of each active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. For example, the thickness of the active material layer is about 2 to 100 μm.

[Electrolyte layer]
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

  The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). Further, as the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiBETI, can be similarly employed.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials.

[Lead]
The positive terminal lead and the negative terminal lead are also used as necessary. As the material of the positive terminal lead and the negative terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. It should be noted that the part taken out from the battery outer packaging material 29 has a heat insulating property so as not to affect the product (for example, automobile parts, particularly electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube.

[Battery exterior materials]
As the battery exterior material 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover a power generation element (battery element) can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. In the present invention, a laminate film that is excellent in high output and cooling performance and that can be suitably used for a battery for large equipment for EV and HEV is desirable.

  The laminated battery 10 of this embodiment uses the negative electrode of the above-described embodiment. In the negative electrode of the above embodiment, since the active material layer is difficult to peel from the current collector, the cycle characteristics of the battery are improved when applied to a lithium ion secondary battery.

  Although the non-bipolar (internal parallel connection type) stacked battery has been described in the above embodiment, a bipolar (internal series connection type) stacked battery may be used. For the bipolar battery, the negative electrode shown in FIGS. 5 and 6 (third embodiment and its modification) can be used. In the bipolar battery, a positive electrode active material layer electrically connected to one surface of the current collector is formed, and a plurality of negative electrode active material layers electrically connected to the opposite surface of the current collector are formed. Bipolar electrode. Bipolar electrodes are stacked via an electrolyte layer to form a power generation element. The adjacent positive electrode active material layer, electrolyte layer, and negative electrode active material layer constitute one unit cell layer. Further, for the purpose of preventing liquid junction due to leakage of the electrolyte from the electrolyte layer, a seal portion may be disposed on the outer peripheral portion of the single cell layer. The constituent elements and the manufacturing method of the non-bipolar battery and the bipolar battery are basically the same except that the electrical connection form (electrode structure) in both batteries is different.

<Appearance structure of lithium ion secondary battery>
FIG. 8 is a perspective view showing the appearance of a laminated flat non-bipolar lithium ion secondary battery according to a typical embodiment.

  As shown in FIG. 8, the laminated flat lithium ion secondary battery 150 has a rectangular flat shape, and a positive electrode tab 158 and a negative electrode tab 159 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 157 is wrapped by the battery exterior material 152 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element (battery element) 157 includes the positive electrode tab 158 and the negative electrode tab 159. It is sealed in a state where it is pulled out to the outside. Here, the power generation element (battery element) 157 corresponds to the power generation element (battery element) 21 of the non-bipolar lithium ion secondary battery 10 shown in FIG. Layer) 13, electrolyte layer 17, and negative electrode (negative electrode active material layer) 15, a plurality of single battery layers (single cells) 19 are stacked.

  Note that the lithium ion secondary battery is not limited to a stacked flat shape, and a wound lithium ion secondary battery may have a cylindrical shape. It is not particularly limited, for example, a cylindrical shape may be deformed into a rectangular flat shape. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit. Preferably, the power generation element (battery element) is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Also, the tabs 158 and 159 shown in FIG. 8 are not particularly limited, and the positive electrode tab 158 and the negative electrode tab 159 may be pulled out from the same side, or the positive electrode tab 158 and the negative electrode tab 159 may be drawn out. However, the present invention is not limited to the one shown in FIG. 8, for example. Further, in the wound type lithium ion secondary battery, instead of the tab, for example, a terminal may be formed using a cylindrical can (metal can).

<Battery assembly>
You may produce the assembled battery comprised by connecting two or more lithium ion secondary batteries of the said embodiment. The assembled battery is formed by connecting a plurality of the batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

  The assembled battery is formed by connecting a plurality of non-bipolar batteries in series or in parallel to form a small assembled battery that can be attached / detached, and further connecting a plurality of these removable batteries in series or in parallel. Thus, an assembled battery having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require a high volume energy density and a high volume output density can be formed. The small assembled batteries that can be attached and detached are connected to each other using an electrical connecting means such as a bus bar, and the assembled batteries are stacked in a plurality of stages using a connecting jig. Depending on the battery capacity and output of the mounted vehicle (electric vehicle), how many batteries are connected to make an assembled battery and how many stages of assembled batteries are stacked to make an assembled battery Just decide.

<Vehicle>
The lithium ion secondary battery of the above embodiment or a combination battery formed by combining a plurality of them can be mounted on a vehicle as a motor driving power source.

  The vehicle according to the present embodiment is characterized in that the lithium ion secondary battery according to the above-described embodiment or an assembled battery formed by combining a plurality of these is mounted. Since a long-life battery excellent in reliability and output characteristics can be configured for a long time, when such a battery is installed, a plug-in hybrid electric vehicle having a long EV travel distance or an electric vehicle having a long charge travel distance can be configured. In other words, a lithium ion secondary battery or an assembled battery formed by combining a plurality of these can be used as a power source for driving a vehicle. Lithium ion secondary batteries or battery packs made by combining a plurality of these are used, for example, in the case of automobiles, such as hybrid cars, fuel cell cars, electric cars (all four-wheeled vehicles (passenger cars, trucks, buses and other commercial vehicles, light vehicles) Etc.), and motorcycles (including motorcycles) and tricycles), the vehicle has a long life and high reliability. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  In order to mount the assembled battery on a vehicle such as an electric vehicle, it can be mounted under the seat in the center of the body of the electric vehicle. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery is mounted is not limited to the position under the seat, but may be the lower part of the rear trunk room or the engine room in front of the vehicle. An electric vehicle using the assembled battery as described above has high durability and can provide a sufficient output even when used for a long time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and driving performance.

<Method for producing negative electrode for lithium ion secondary battery>
Although the manufacturing method in particular of the negative electrode for lithium ion secondary batteries of the above-mentioned embodiment is not restrict | limited, The manufacturing method of a typical negative electrode is described below.

(Current collector preparation process)
As in the first embodiment and the second embodiment, there is no particular limitation on a specific method for processing the current collector into a lattice shape, and conventionally known knowledge can be appropriately referred to. As an example, a lattice-shaped expanded metal can be obtained by subjecting a metal foil to an expanding process. In some cases, a grid-like current collector may be obtained by performing a process such as punching on the metal foil. Moreover, what is necessary is just to prepare suitable foil, when using collector foil like 3rd Embodiment and its modification.

(Negative electrode active material layer forming step)
Next, the first active material layer and the second active material layer are alternately arranged on the current collector in the surface direction. Here, as the current collector, the above-described grid-shaped current collector may be used, or a general current collector foil may be used. The method for forming the active material layer on the current collector surface is not particularly limited, and a known method can be used. Specifically, the following methods are mentioned.

  First, a substance (active material) that occludes / releases lithium and, if necessary, a conductive aid, an electrolyte salt for enhancing ion conductivity, a binder, and the like (hereinafter also referred to as other materials) are appropriately used. An active material layer slurry is prepared by dispersing and dissolving in a solvent. This is applied on the current collector. In this case, the solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane and the like can be used.

  In the case where the negative electrode active material layer is pre-doped with lithium, the slurry for the active material layer may contain lithium powder. The lithium powder has a function of compensating for the irreversible capacity of the electrode that occurs during the first charge / discharge. The shape of the lithium powder is not particularly limited, and may take any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape.

  Moreover, there is no restriction | limiting in particular also about the average particle diameter of lithium powder. However, the average particle diameter of the lithium powder is preferably 1 to 100 μm and more preferably 1 to 50 μm from the viewpoint of the pre-doping speed. The content of the lithium powder in the slurry for active material is appropriately set in consideration of the amount of lithium to be doped by the aging treatment described later, the active material species to be selected, and the like. Lithium particles are doped with lithium by an aging process in an aging process described later. Therefore, the lithium powder disappears in the aging process, and voids are formed in the active material layer. The volume expansion / contraction of the active material layer can be mitigated by the voids formed as described above. It is preferable that at least the second active material slurry contains lithium powder, and preferably only the second active material slurry is contained.

  The means for applying the slurry for the active material layer is not particularly limited, and conventionally known methods can be appropriately employed in the battery manufacturing field. For example, methods such as a doctor blade method, an ink jet method, a screen printing method, and a die coater method are exemplified.

  Subsequently, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the slurry and the volatilization rate of the slurry viscosity adjusting solvent. The density, porosity, and thickness of the electrode are adjusted by pressing the obtained dried product. This press treatment may be performed before drying. Thereby, a negative electrode active material layer is formed on the surface of the current collector. In addition, when manufacturing the negative electrode in which the negative electrode active material layer is formed on both sides of the current collector, the above treatment is performed on the both sides of the grid-shaped current collector obtained above or the prepared current collector. Can be applied. On the other hand, when producing a bipolar electrode used in a bipolar battery, a positive electrode active material layer is formed by the same method on the other surface of the current collector on which the negative electrode active material layer is formed by the above method. That's fine.

  When an expanded metal is used as the current collector as in the second embodiment, the negative electrode can be obtained by the following manufacturing method.

  First, the slurry for 2nd active material layers is apply | coated to the collector (collector foil) before an expand process, and a coating film is dried. Thereafter, the current collector foil is expanded, and the first active material layer slurry is applied to the opening and dried. Thereafter, pressing is performed as necessary.

(4) Electric power generation element production process Subsequently, an electric power generation element is produced using the negative electrode or bipolar electrode produced above. Specifically, the electrode and the separator are laminated so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator interposed therebetween. At this time, in order to fabricate a stacked battery, lamination of negative electrode / separator / positive electrode / separator is repeated using a separately prepared positive electrode in which a positive electrode active material layer is formed on both sides of a current collector. On the other hand, to manufacture a bipolar battery, bipolar electrodes and separators are alternately stacked. Thereby, a power generation element is produced. At this time, the stacking of the separator and the electrode is repeated until the number of single battery layers reaches a desired number.

  Then, current collecting plates and / or leads are connected to both ends of the obtained power generating element as necessary, and the power generating elements are accommodated in a bag made of an aluminum laminate sheet so that the current collecting plates or leads are led out. Then, the battery is completed by injecting the electrolytic solution with a liquid injector and sealing the end under reduced pressure.

  In the above description, the battery in the case where the electrolyte is a liquid electrolyte has been described as an example. However, the production of a battery using a gel electrolyte or an intrinsic polymer electrolyte can also be performed with reference to a known technique, but detailed description thereof is omitted here.

(5) Aging process When the negative electrode active material layer is pre-doped with lithium, an aging process is performed. In the aging step, the battery produced in the above (4) is aged for a predetermined time. Thereby, lithium existing in the lithium layer formed on the surface of the grid-like current collector is ionized and doped into the active material existing in the negative electrode active material layer and / or the positive electrode active material layer. By performing the aging step, the lithium doping amount per unit area in the active material layer can be made uniform, and a battery with improved reliability can be obtained.

  The aging temperature is preferably 20 to 80 ° C., more preferably 40 to 60 ° C. from the viewpoint of completing lithium doping in a short time. Further, the aging time may be appropriately determined so that the voltage of the battery after aging becomes a desired level, but is usually about 24 to 120 hours.

  The voltage of the battery after the aging process is preferably 1.0 V or more, and more preferably 1.0 to 4.0 V. If the voltage of the battery after the aging step is a value within such a range, lithium is sufficiently doped into the active material layer.

  The aging may be performed after battery assembly or preliminary charging. The conditions for the preliminary charging are not particularly limited. For example, a method of charging at a constant current method (current: 0.5 C) at 20 to 60 ° C. for 10 minutes may be used.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

Example 1
1. Production of negative electrode SiO (average particle diameter 5 μm) as a negative electrode active material (first active material), acetylene black as a conductive auxiliary agent and polyimide (PI) as a binder were mixed in a mass ratio of 80:10:10, A slurry for an active material layer was obtained.

  Graphite (average particle size 10 μm) as a negative electrode active material (second active material), lithium powder (average particle size 35 μm), acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder 73.3: The mixture was mixed at a mass ratio of 6.7: 10: 10 to obtain a slurry for the second active material layer.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for 2nd active material layers was apply | coated to both surfaces (only one surface is only the outermost layer negative electrode) of the expanded material collector prepared above, and it dried with hot air at 80 degreeC, and obtained the laminated body. The laminate was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 1st active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 150 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

2. Production of Positive Electrode LiNiPO ₄ as a positive electrode active material, acetylene black as a conductive auxiliary agent, and PVDF as a binder were mixed in a mass ratio of 86: 6: 8 to obtain a positive electrode slurry. Next, the slurry was applied to both surfaces of an aluminum current collector, dried with hot air at 130 ° C., and then roll-rolled to form a sheet. The thickness of the positive electrode active material layer was 100 μm. An aluminum current extraction tab was joined to the obtained positive electrode by ultrasonic welding, and punched out so that the electrode size was 34 mm × 24 mm.

3. Production of Battery A polyethylene microporous membrane (thickness = 25 μm) was prepared as a separator. Further, as the _{electrolyte, 1M LiPF 6 / (EC:} DEC) (EC: DEC = 1: 1 volume ratio) was used.

  As shown in FIG. 9, the negative electrode 63 including the negative electrode active material layer prepared / prepared as described above, three separators 62, four positive electrodes 61, and the negative electrode laminate is disposed on both sides. A battery was manufactured by stacking in the order of / separator / positive electrode / separator... In FIG. 9, 64 is an Al positive electrode lead plate, and 65 is a Ni negative electrode lead plate.

  The obtained power generation element was placed in a bag made of an aluminum laminate sheet as an exterior, and the electrolytic solution prepared above was injected. Under vacuum conditions, the opening of the aluminum laminate sheet bag was sealed so that the current extraction tabs connected to both electrodes were led out to complete the test cell.

(5) Aging process The test cell produced above was subjected to aging treatment at 55 ° C. for 72 hours. The cell voltage after aging was 3.9V.

(Example 2)
As the negative electrode active material (first active material), SiO (average particle size of 5 μm), lithium powder (average particle size of 35 μm), acetylene black as the conductive additive, and polyimide (PI) as the binder are 74.7: 5.3. Was mixed at a mass ratio of 10:10 to obtain a slurry for the first active material layer.

  Graphite (average particle diameter 10 μm) as a negative electrode active material (second active material), lithium powder (average particle diameter 35 μm), acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder 76.7: The mixture was mixed at a mass ratio of 3.3: 10: 10 to obtain a slurry for the second active material layer.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for 2nd active material layers was apply | coated to both surfaces (only one surface is only the outermost layer negative electrode) of the expanded material collector prepared above, and it dried with hot air at 80 degreeC. The sheet was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 1st active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

(Example 3)
SiO (average particle diameter of 5 μm) as a negative electrode active material (first active material), acetylene black as a conductive auxiliary agent, and polyimide (PI) as a binder are mixed in a mass ratio of 80:10:10 to obtain a first active material. A layer slurry was obtained.

  Graphite (average particle diameter 10 μm) as a negative electrode active material (second active material), acetylene black as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 80:10:10, A slurry for the two active material layers was obtained.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for 2nd active material layers was apply | coated to both surfaces (only one surface is only the outermost layer negative electrode) of the expanded material collector prepared above, and it dried with hot air at 80 degreeC. The sheet was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 1st active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

Example 4
As the negative electrode active material (first active material), SiO (average particle size of 5 μm), lithium powder (average particle size of 35 μm), acetylene black as the conductive additive, and polyimide (PI) as the binder are 69.3: 10.7. Was mixed at a mass ratio of 10:10 to obtain a slurry for the first active material layer.

  Graphite (average particle diameter 10 μm) as a negative electrode active material (second active material), acetylene black as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 80:10:10, and second An active material layer slurry was obtained.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for 2nd active material layers was apply | coated to both surfaces (only one surface is only the outermost layer negative electrode) of the expanded material collector prepared above, and it dried with hot air at 80 degreeC. The sheet was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 1st active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

(Example 5)
SiO (average particle diameter of 5 μm) as a negative electrode active material (first active material), acetylene black as a conductive auxiliary agent, and polyimide (PI) as a binder are mixed in a mass ratio of 80:10:10 to obtain a first active material. A layer slurry was obtained.

  Graphite (average particle diameter 10 μm) as a negative electrode active material (second active material), acetylene black as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 80:10:10, and second An active material layer slurry was obtained.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for the first active material layer was applied to both surfaces (only one surface of the outermost layer negative electrode) of the expanded material current collector prepared above, and dried with hot air at 80 ° C. The sheet was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 2nd active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

(Example 6)
SiO (average particle diameter of 5 μm) as a negative electrode active material (first active material), acetylene black as a conductive auxiliary agent and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 80:10:10, An active material layer slurry was obtained.

  As the negative electrode active material (second active material), graphite (average particle size 10 μm), lithium powder (average particle size 35 μm), acetylene black as a conductive additive, and polyimide (PI) as a binder 62.9: 17.1. Was mixed at a mass ratio of 10:10 to obtain a slurry for the second active material layer.

  Next, an unexpanded copper expanded current collector (thickness: 70 μm) was prepared. The slurry for the first active material layer was applied to both surfaces (only one surface of the outermost layer negative electrode) of the expanded material current collector prepared above, and dried with hot air at 80 ° C. The sheet was expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. Furthermore, the slurry for 2nd active material layers was apply | coated to the opening part, it dried with hot air at 80 degreeC, and was pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm. Moreover, the ratio of the first active material layer and the second active material layer was 1: 1 by volume ratio.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

(Comparative Example 1)
1. Production of Negative Electrode As the negative electrode active material, SiO (average particle diameter 5 μm), graphite (average particle diameter 10 μm), lithium powder (average particle diameter 35 μm), acetylene black as a conductive additive and polyimide (PI) as a binder 36. The mixture was mixed at a mass ratio of 7: 36.7: 6.7: 10: 10 to obtain an active material layer slurry.

  Next, an unexpanded copper expanded current collector (thickness 70 μm) was prepared and expanded. At this time, the ratio (opening ratio) of the openings formed by the expanding process was 25%. The slurry for active material layer was applied to both surfaces (only one surface of the outermost layer negative electrode) of the expanded material current collector prepared above, dried in hot air at 80 ° C., and pressed. A nickel current extraction tab was joined to the obtained negative electrode by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. The thickness of the active material layer was 40 μm.

  A test cell was produced in the same manner as in Example 1 except that the negative electrode was produced. The cell voltage after aging was 3.9V.

(Evaluation of test cell)
Each test cell was charged for 13 hours in the atmosphere at 25 ° C. by a constant current constant voltage method (CCCV, current: 0.1 C, voltage: 4.2 V). Next, after a 10-minute pause, discharge treatment was performed to 2.5 V by a constant current method (CC, current: 0.1 C).

  Subsequently, after a further 10 minutes of rest, the battery was charged for 3 hours by a constant current constant voltage method (CCCV, current: 1 C, voltage: 4.2 V), and the charge capacity was measured. Then, it discharged to 2.5V with constant current (CC, electric current: 1C), and measured the discharge capacity. These cycles were repeated (cycle test), and the value of the discharge capacity at the 1st, 100th, and 500th cycles relative to the initial charge capacity was calculated as the capacity retention rate. The results are shown in Table 1 below.

  From the results shown in Table 1, it can be seen that in all of the examples, the capacity retention rate is higher than that of the comparative example. This is because the decrease in adhesion between the current collector and the negative electrode active material layer is suppressed by the second active material layer relaxing the expansion and contraction in the plane direction of the first active material layer. it is conceivable that.

4 Al positive electrode lead plate,
5 Ni negative electrode lead plate,
10 stacked battery,
11 Current collector (positive electrode current collector),
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
25 positive current collector,
27 negative current collector,
29,152 Laminate sheet,
50, 50a, 50b, 50c Lithium ion secondary battery electrode,
51 current collector,
51a opening,
52 first active material layer,
53 second active material layer,
54 Other active material layers,
61 positive electrode,
62 separator,
63 negative electrode,
64 positive lead plate,
65 negative electrode lead plate,
150 lithium ion secondary battery,
158 positive electrode tab,
159 Negative electrode tab.

Claims (7)

A current collector,
An active material layer formed on the current collector,
The active material layer includes a first active material layer, and a second active material layer having a smaller volume change due to insertion and extraction of lithium than the first active material layer,
A negative electrode for a lithium ion secondary battery, wherein the first active material layer and the second active material layer are alternately arranged with respect to the surface direction of the electrode.   The negative electrode for a lithium ion secondary battery according to claim 1, wherein a potential drop when lithium in the second active material layer is occluded is smaller than a potential drop when lithium in the first active material layer is occluded.   The negative electrode for a lithium ion secondary battery according to claim 1, wherein the current collector has a lattice shape, and the first active material layer penetrates through an opening of the current collector.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the first active material layer includes an alloy material having at least an element that can be alloyed with lithium as an active material.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the second active material layer includes at least a carbon-based material as an active material.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein at least the second active material layer has a void formed by pre-doping lithium.   The lithium ion secondary battery using the negative electrode of any one of Claims 1-6.