JP6573312B2 - Current collector for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a current collector for a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries have been used not only for electronic devices such as mobile phones but also for hybrid cars and electric cars, and their capacity has been increasing. As a result, the amount of chemical energy stored in the battery increases, so ensuring safety is becoming more important.

  As a battery having safety, a bipolar lithium ion secondary battery has been proposed. A bipolar lithium ion secondary battery uses a bipolar electrode in which a positive electrode is formed on one surface of a current collector and a negative electrode is formed on the other surface. A plurality of such bipolar electrodes are laminated so that the positive electrode and the negative electrode face each other through a separator including an electrolyte layer. Therefore, in this bipolar secondary battery, one battery cell (single cell) is constituted by the positive electrode, the negative electrode, and the separator (electrolyte layer) between the current collector and the current collector.

  The current collector used in such a bipolar lithium ion secondary battery is preferably made of a material that is lighter and more conductive in order to ensure a higher output density. Therefore, in recent years, a current collector composed of a polymer material to which a conductive material is added instead of a conventional metal foil has been proposed.

  However, when a polymer material is used for the current collector, lithium ions in the electrolytic solution may be drawn into the current collector from the negative electrode side and trapped. Since the trapped lithium ions are not easily released from the inside of the current collector, the battery capacity may be reduced as a result.

  In order to prevent lithium ions from entering the current collector using a polymer material, for example, Patent Document 1 discloses a current collector for a bipolar secondary battery in which a metal layer is provided on a resin film. Is disclosed.

JP 2013-026192 A

  However, in the technique described in Patent Document 1, if the metal layer is thin, defects are generated and lithium ions are transmitted. However, even if an internal short circuit occurs, it is not appropriate to increase the thickness of the metal layer in view of preventing current concentration at the short circuit site and ensuring safety. Further, it has been found that lithium ions may pass through the metal layer, resulting in a decrease in battery capacity.

  Then, an object of this invention is to provide the means which can suppress the fall of battery capacity in a lithium ion secondary battery.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the surface of a conductive layer such as a resin layer having conductivity is formed by plating, and there is no crystal grain boundary, or at least one end of the crystal grain boundary is in the lithium ion barrier metal layer. It has been found that the above problem can be solved by providing an existing lithium ion barrier metal layer, and the present invention has been completed.

  That is, the present invention has a conductive layer and a lithium ion barrier metal layer disposed on the surface of the conductive layer, and the lithium ion barrier metal layer is formed by plating and has no crystal grain boundary, or A current collector for a lithium ion secondary battery, wherein at least one end of a crystal grain boundary is present in the lithium ion barrier metal layer.

  The current collector for a lithium ion secondary battery of the present invention is formed by plating and has no crystal grain boundary, or at least one end of the crystal grain boundary exists in the lithium ion barrier metal layer. It has a metal layer. Thereby, it can suppress that the lithium ion in electrolyte solution reaches | attains a conductive layer through a crystal grain boundary. Therefore, lithium ions are not easily taken into the conductive layer. As a result, it is possible to suppress a decrease in battery capacity due to occlusion of lithium ions into the conductive layer.

1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat type (stacked type) bipolar type, which is an embodiment of a lithium ion secondary battery. It is the cross-sectional schematic which shows the basic composition of the bipolar lithium ion secondary battery which is other embodiment of a lithium ion secondary battery. It is the schematic which showed the cross section of the electrical power collector of this embodiment typically. It is the schematic which showed the cross section of the electrical power collector of this embodiment typically. It is the schematic which showed the cross section of the electrical power collector of this embodiment typically. It is the schematic which showed the cross section of the electrical power collector of this embodiment typically. It is the photograph which observed the cross section of the electrical power collector produced in the Example and the comparative example with SEM. Dotted lines indicate the upper surface, lower surface, and grain boundaries of the lithium ion barrier metal layer.

  First, a lithium ion secondary battery in which an electrode according to an embodiment is preferably used will be described, but is not limited to the following embodiment. 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.

  The lithium ion secondary battery that is the subject of the present embodiment is not particularly limited as long as it uses a current collector that will be described below.

  For example, when the lithium ion secondary battery is distinguished by form / structure, it can be applied to any conventionally known form / structure such as a stacked (flat) battery or a wound (cylindrical) battery. 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.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

  When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a liquid electrolyte type battery using a liquid electrolyte such as a non-aqueous electrolyte in the electrolyte layer, a polymer battery using a polymer electrolyte in the electrolyte layer, etc. It can be applied to any conventionally known electrolyte layer type. The polymer battery is further classified into a gel electrolyte type battery using a gel polymer 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). .

  FIG. 1 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type. As shown in FIG. 1, the stacked battery 10 a of this 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 battery exterior material 29 that is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, an electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 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 stacked battery 10a shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the positive electrode active material layer 15 is arrange | positioned only in the single side | surface in all the outermost layer positive electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. In addition, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 1, so that the outermost layer negative electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost layer negative electrode current collector is disposed on one or both surfaces. A negative electrode active material layer may be disposed.

  The positive electrode current collector 12 and the negative electrode current collector 11 have a positive electrode current collector plate 27 and a negative electrode current collector plate 25 connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the battery exterior material 29. Thus, it has a structure led out of the battery exterior material 29. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  FIG. 2 is a schematic cross-sectional view schematically showing the basic configuration of a bipolar nonaqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “bipolar battery”) 10b. The bipolar battery 10b shown in FIG. 2 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 film 29 that is a battery exterior material.

  As shown in FIG. 2, in the power generation element 21 of the bipolar battery 10b, a positive electrode active material layer 15 electrically coupled to one surface of the current collector 11c is formed, and on the surface opposite to the current collector 11c. It has a plurality of bipolar electrodes 23 in which a negative electrode active material layer 13 that is electrically coupled is formed. Each bipolar electrode 23 is laminated via the electrolyte layer 17 to form the power generation element 21. The electrolyte layer 17 has a configuration in which an electrolyte is held at the center in the surface direction of a separator as a base material. At this time, the positive electrode active material layer 15 of one bipolar electrode 23 and the negative electrode active material layer 13 of another bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other through the electrolyte layer 17. The bipolar electrodes 23 and the electrolyte layers 17 are alternately stacked. That is, the electrolyte layer 17 is disposed between the positive electrode active material layer 15 of one bipolar electrode 23 and the negative electrode active material layer 13 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. ing.

  The adjacent positive electrode active material layer 15, electrolyte layer 17, and negative electrode active material layer 13 constitute one unit cell layer 19. Therefore, it can be said that the bipolar battery 10b has a configuration in which the single battery layers 19 are stacked. Further, for the purpose of preventing liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17, a seal portion (insulating layer) 31 is disposed on the outer peripheral portion of the unit cell layer 19. The positive electrode active material layer 15 is formed only on one side of the positive electrode outermost layer current collector 11 b located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 13 is formed on only one side of the negative electrode side outermost current collector 11 a located in the outermost layer of the power generation element 21. However, the positive electrode active material layer 15 may be formed on both surfaces of the outermost layer current collector 11b on the positive electrode side. Similarly, the negative electrode active material layer 13 may be formed on both surfaces of the outermost layer current collector 11a on the negative electrode side.

  Further, in the bipolar battery 10b shown in FIG. 2, a positive electrode current collector plate 27 is disposed adjacent to the outermost layer current collector 11b on the positive electrode side, and this is extended and led out from a laminate film 29 which is a battery exterior material. ing. On the other hand, the negative electrode current collector plate 25 is disposed so as to be adjacent to the outermost layer current collector 11a on the negative electrode side, and is similarly extended to be led out from the laminate film 29 which is an exterior of the battery.

  In the bipolar battery 10 b shown in FIG. 2, a seal portion 31 is usually provided around each single cell layer 19. The purpose of this seal portion 31 is to prevent the adjacent current collectors 11c in the battery from coming into contact with each other and a short circuit caused by a slight irregularity at the end of the unit cell layer 19 in the power generation element 21. Provided. By installing such a seal portion 31, long-term reliability and safety can be ensured, and a high-quality bipolar battery 10b can be provided.

  Note that the number of stacks of the unit cell layers 19 is adjusted according to a desired voltage. Further, in the bipolar battery 10b, the number of stacks of the single battery layers 19 may be reduced if a sufficient output can be ensured even if the battery is made as thin as possible. Even in the bipolar battery 10b, it is necessary to prevent external impact and environmental degradation during use. Therefore, the power generation element 21 is preferably sealed in a laminate film 29 that is a battery exterior material, and the positive electrode current collector plate 27 and the negative electrode current collector plate 25 are taken out of the laminate film 29.

[Current collector]
The current collector of this embodiment has a conductive layer and a lithium ion barrier metal layer disposed on the surface of the conductive layer. The conductive layer has conductivity and contributes to the function of mediating the movement of electrons from one surface of the current collector to the other surface. The lithium ion barrier metal layer has a function of preventing lithium ions from entering and occluded into the conductive layer.

(Lithium ion barrier metal layer)
FIG. 3A is a schematic cross-sectional view showing an embodiment of the current collector of the present invention. A current collector 1 shown in FIG. 3A has a lithium ion barrier metal layer 3 formed by plating on the surface of the conductive layer 2, preferably at least on the negative electrode active material layer side. Here, the lithium ion barrier metal layer 3 has no crystal grain boundary, or at least one end 5 of the crystal grain boundary 4 exists in the lithium ion barrier metal layer 3. That is, there is no crystal grain boundary connected in the thickness direction from the surface (upper surface) of the lithium ion barrier metal layer 3 on the negative electrode active material layer side to the interface (lower surface) with the conductive layer 2.

  For the purpose of improving the power density per weight of a lithium ion secondary battery, a technique using a current collector containing a polymer material instead of a metal foil is known. At this time, in order to prevent lithium ions from entering the polymer material film, a metal layer can be provided on the film containing the polymer material.

  However, it has been found that the durability of a lithium ion secondary battery using such a current collector, particularly the charge / discharge cycle durability of the electrode, is insufficient. Therefore, when the present inventors examined this problem in detail, lithium ions permeate through the metal layer, reach the film containing the polymer material as the conductive layer, and are occluded in the polymer material. I found that is one of the causes. As a result, lithium ions in the electrolytic solution are reduced, which is thought to lead to a decrease in capacity. Therefore, the present inventors examined a path through which lithium ions permeate through the metal layer.

  Since the metal layer obtained by a method such as vapor deposition or sputtering is a layer in which metal fine particles of about 10 to 200 nm are deposited, it is easy to create a flow path for the electrolyte to enter between the metal fine particles. For this reason, it has been found that lithium ions pass between the metal fine particles and enter the conductive layer, and the lithium ions are occluded, so that the capacity of the battery tends to decrease.

  A metal layer formed by a plating method such as electrolytic plating can be manufactured at a lower cost than methods such as vapor deposition and sputtering. In addition, a dense crystal grain grows on the conductive layer to form a metal layer. Therefore, compared with a metal layer obtained by a method such as vapor deposition or sputtering, the electrolytic solution is less permeable.

  However, the present inventors have found that even when a metal layer produced by a plating method is used, the effect of suppressing deterioration of the cycle characteristics of the battery is not sufficient.

  In the plating method, crystal grains grow in a columnar shape in the thickness direction starting from the nucleus. The metal layer obtained by plating is an aggregate of crystal grains. When the phases of adjacent crystal grains are the same, these interfaces are called crystal grain boundaries (or grain boundaries, crystal boundaries). The metal layer obtained by a normal plating method has crystal grain boundaries in the thickness direction. For example, as shown in FIG. 3B, in the current collector 1b, the crystal grain boundaries 4 are connected in the thickness direction from the upper surface to the lower surface of the lithium ion barrier metal layer 3, and both ends 5 of the crystal grain boundaries 4 are on the surface. It will come out. In this case, the lithium ions in the electrolytic solution pass through the crystal grain boundary 4, pass through the lithium ion barrier metal layer 3, and enter the conductive layer 2. As a result, lithium ions are trapped in the conductive layer 2. For this reason, the amount of lithium ions when viewed in the entire battery system is reduced, leading to a reduction in battery capacity. In particular, when a polymer material is used for the conductive layer, lithium ions invade, so that deterioration of the polymer material due to repeated charge / discharge increases, and battery durability cannot be obtained.

  On the other hand, the current collector 1 of this embodiment shown in FIG. 3A has no crystal grain boundary, or at least one end of the crystal grain boundary exists inside the lithium ion barrier metal layer. . In this way, even if lithium ions in the electrolyte enter the lithium ion barrier metal layer 3 through the crystal grain boundaries 4, the end portions 5 of the crystal grain boundaries 4 are in the lithium ion barrier metal layer 3. The presence of the lithium ion breaks the lithium ion intrusion path and does not easily reach the conductive layer 2. As a result, a decrease in battery capacity can be suppressed.

  The crystal grain boundary in the lithium ion barrier metal layer can be confirmed by observing the cross section of the current collector with a scanning electron microscope (SEM).

  When electrons enter a crystalline sample, the penetration depth changes depending on the angle between the crystal lattice plane and the incident electrons, and changes greatly before and after the Bragg angle (electron channeling). As a result, the penetration depth of incident electrons varies depending on the crystal orientation. The amount of reflected electrons decreases in the portion where the electrons penetrate deeply, and the amount of reflected electrons increases in the portion where the depth of penetration of the electrons is shallow. Therefore, in the reflected electron image measured by SEM, contrast between light and dark is observed due to the difference in crystal orientation of crystal grains. Therefore, the position and shape of the crystal grain boundary can be confirmed from the SEM image.

  In this specification, the presence / absence, the number of crystal grain boundaries in the lithium ion barrier metal layer, and the positions of the end portions are observed in a region having the same width as the thickness d0 of the lithium ion barrier metal layer when the cross section is observed by SEM. It means the presence / absence and number of crystal grain boundaries to be observed, and the positions of the ends.

  The lithium ion barrier metal layer 3 is preferably formed on the surface of the conductive layer 2 at least on the negative electrode active material layer side. Lithium ions in the electrolyte enter into the conductive layer 2 mainly from the joint surface between the negative electrode active material layer and the conductive layer 2. Therefore, if the lithium ion barrier metal layer 3 is formed on the negative electrode active material layer side, the effect of preventing intrusion of lithium ions in the electrolytic solution becomes higher, and the capacity retention rate of the battery is improved. Furthermore, if it is a bipolar type electrode, it is more preferable that it is formed on both surfaces of the positive electrode active material layer side and the negative electrode active material layer side. If the electrode is not a bipolar type, it is more preferable that the lithium ion barrier metal layer 3 is formed on both surfaces of the conductive layer 2 in the negative electrode current collector. Here, “arranged on the surface of the conductive layer” includes both the case where it is disposed in contact with the surface of the conductive layer and the case where it is disposed via another material. For example, as will be described later, when a base layer is provided between the conductive layer 2 and the lithium ion barrier metal layer 3, the adhesion between the conductive layer 2 and the lithium ion barrier metal layer 3 can be further improved. Moreover, when the conductive layer 2 is a resin layer, the conductivity can be improved.

  Moreover, as shown in FIG. 4, it is preferable that the lithium ion barrier metal layer 3 has a crystal grain boundary shifted in the in-plane direction. This is a case where the crystal grain boundaries 4a and 4b generated in the thickness direction are shifted in the in-plane direction, so that lithium ions in the electrolyte enter the lithium ion barrier metal layer 3 from the surface on the negative electrode active material layer side. However, the crystal grain boundary is interrupted at the portion having the deviation in the in-plane direction, so that it does not reach the conductive layer 2.

  Preferably, the lithium ion barrier metal layer is composed of two or more metal layers 3 a and 3 b as shown in FIG. 4, and is in contact with the crystal grain boundary 4 a of the outermost metal layer 3 a and the conductive layer 2. It is preferable that the crystal grain boundary 4b of the layer 3b is shifted in the in-plane direction. By doing in this way, the capacity | capacitance fall of a battery can be suppressed more effectively. For example, the metal layer may be used by laminating 2 to 5 layers, preferably 2 to 3 layers. The metals constituting each metal layer may be the same or different from each other, but are preferably composed of the same metal as described later.

  In the lithium ion barrier metal layer in the form of FIG. 4, the average size of crystal grains constituting the lithium ion barrier metal layer 3 is not particularly limited, but is, for example, 0.01 to 4 μm, and preferably 0.1. ˜1 μm. The size of the crystal grain means a maximum distance L among distances between arbitrary two points on the contour line of the crystal grain by observing a cross section of the lithium ion barrier metal layer by SEM. As an average value of crystal grain size, a value calculated as an average value of crystal grain size observed in several to several tens of fields is adopted.

  As another preferred embodiment of the current collector of the present invention, as shown in FIG. 5, the lithium ion barrier metal layer has a crystal grain boundary including both ends. By including both ends 5 of the crystal grain boundary 4 inside the lithium ion barrier metal layer 3, the effect of blocking lithium ions is enhanced, and a reduction in battery capacity can be effectively suppressed.

  Specifically, in the cross section of the lithium ion barrier metal layer 3, when a region having a width equivalent to the thickness d0 is observed, at least one crystal grain boundary 4 including both end portions 5 is included. preferable.

  As another preferred embodiment of the current collector of the present invention, as shown in FIG. 6, the number of crystal grain boundaries observed in a region having a width equivalent to the thickness in the cross section of the lithium ion barrier metal layer is 5 or less. As the crystal grain boundary contained in the lithium ion barrier metal layer 3 is smaller, the lithium ions that permeate from the lithium ion barrier metal layer to the conductive layer are reduced, so that the capacity reduction of the battery can be effectively suppressed. The number of crystal grain boundaries observed in the range of the width d0 equivalent to the thickness is preferably 3 or less, more preferably 1 or less, and still more preferably no crystal grain boundary is observed.

  In the current collector of the present embodiment, the lithium ion barrier metal layer may have a form in which the structures of the lithium ion barrier metal layers shown in FIGS.

  The lithium ion barrier metal layer is preferably composed of a single material. When the lithium ion barrier metal layer is composed of two or more metal layers, it is preferable that all the metal layers are composed of the same single material. By using a single material for the lithium ion barrier metal layer, the process can be simplified. Moreover, it can prevent that each metal layer peels in a lithium ion barrier metal layer, and can produce a lithium ion barrier metal layer with high intensity | strength.

  In addition, the lithium ion barrier metal layer is mainly composed of copper (Cu), nickel (Ni), cobalt (Co), oxides and nitrides of these metals, and these metals which are not alloyed with lithium. Preferably, it is composed of at least one selected from the group consisting of alloys. Since these materials are not alloyed with lithium, they can be used stably without being alloyed even in a negative electrode potential atmosphere. Among these, copper is preferable in consideration of the lithium ion barrier property. The “main component” means that the ratio of the total mass of the specific metal component to the total mass of the alloy is 50% by mass or more. The proportion is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 95% by mass or more.

  Although the thickness of a lithium ion barrier metal layer is not specifically limited, Preferably it is 0.01-3 micrometers, More preferably, it is 0.1-1 micrometer. If it is 0.01 micrometer or more, it is excellent in the interruption | blocking property of lithium ion. Moreover, if it is 3 micrometers or less, the crystal grain boundary connected to the thickness direction will not arise easily in a lithium ion barrier metal layer. Moreover, if it is such a range, it is possible to fully reduce the internal resistance of the battery while suppressing the battery weight. Furthermore, if it is 3 μm or less, even if an internal short circuit occurs, it is possible to prevent current from concentrating on the short circuit region along the surface direction of the current collector. In addition, when a lithium ion barrier metal layer is comprised from 2 or more metal layers, it is preferable that total thickness is the said range.

(Conductive layer)
The conductive layer may be a conductive resin layer or another conductive layer using a metal material or the like. A specific form of the conductive layer will be described below.

(Conductive resin layer)
The current collector preferably includes a resin layer having conductivity from the viewpoint of reducing the weight of the battery. Examples of the material constituting the conductive resin layer include a resin in which a conductive filler is added to a conductive polymer or a non-conductive polymer as necessary.

  The conductive polymer is selected from materials that are conductive and have no conductivity with respect to ions used as charge transfer media. These conductive polymers are considered to be conductive because the conjugated polyene system forms an energy band. As a typical example, a polyene-based conductive polymer that has been put into practical use in an electrolytic capacitor or the like can be used. Specific examples include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole, and mixtures thereof. Polyaniline, polypyrrole, polythiophene, and polyacetylene are more preferable from the viewpoint of conductivity and stable use in the battery.

  Examples of the polymer material having no electrical conductivity include, for example, polyethylene (PE) (high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET). ), Polyether nitrile (PEN), polyimide (PI), polyamide (PA), polyamide imide (PAI), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVDC), or mixtures thereof. These materials have a very wide potential window, are stable with respect to both the positive electrode potential and the negative electrode potential, and are lightweight, so that the output density of the battery can be increased. Of these, various polyolefins such as polypropylene and polyethylene, copolymers thereof and mixtures thereof are preferable from the viewpoint of durability against the electrolytic solution used. Further, from the viewpoint of positive electrode potential resistance, polyimide can be preferably used. Polyimide is easy to occlude lithium ions, and is liable to deteriorate due to ring opening of an imide ring when in contact with lithium ions. Therefore, the battery capacity and the battery durability are greatly reduced due to deterioration of the polymer material, and the effects of the invention can be obtained more remarkably.

  The conductive filler is selected from materials having conductivity. Preferably, from the viewpoint of suppressing ion permeation in the resin layer having conductivity, it is preferable to use a material that does not have conductivity with respect to ions.

  Specifically, carbon materials, aluminum (Al), gold (Au), silver (Ag), copper (Cu), iron (Fe), platinum (Pt), chromium (Cr), tin (Sn), indium ( In), antimony (Sb), titanium (Ti), nickel (Ni), and the like, but are not limited thereto. These conductive fillers may be used alone or in combination of two or more. Moreover, these alloy materials, such as stainless steel (SUS), may be used. From the viewpoint of corrosion resistance, Al, SUS, carbon material, and Ni are preferable, and carbon material and Ni are more preferable. In addition, these conductive fillers may be obtained by coating the metal shown above with a plating or the like around a particulate ceramic material or a polymer material.

  Examples of the carbon material include at least selected from the group consisting of acetylene black, carbon black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, hard carbon, and fullerene. One type is mentioned. These carbon materials have a very wide potential window, are stable in a wide range with respect to both the positive electrode potential and the negative electrode potential, and are excellent in conductivity. Also, since the carbon material is very light, the increase in mass is minimized. Further, since carbon materials are often used as conductive aids for electrodes, even if they come into contact with these conductive aids, the contact resistance is very low because of the same material. When carbon materials are used as conductive fillers, it is possible to reduce the compatibility of the electrolyte by applying a hydrophobic treatment to the surface of the carbon material, making it possible for the electrolyte to hardly penetrate into the current collector holes. It is.

  When the charge / discharge potential of the negative electrode active material is close to the deposition potential of Li, the conductive filler such as a carbon material hurts the current collector because Li ions are inserted and expanded by charge / discharge (current collection). There is a risk of injury to the body). Therefore, the conductive filler of the current collector that faces the negative electrode is preferably a material such as Ni, Cu, Fe, or SUS that does not cause Li formation. In addition, a conductive filler whose surface is coated with a carbon material or the like can be preferably used.

  The shape of the conductive filler is not particularly limited, and a known shape such as a particle shape, a powder shape, a fiber shape, a plate shape, a lump shape, a cloth shape, or a mesh shape can be appropriately selected. For example, when it is desired to impart conductivity over a wide range, it is preferable to use a particulate conductive filler. On the other hand, when it is desired to further improve the conductivity in a specific direction, it is preferable to use a conductive filler having a certain direction in the shape, such as a fibrous shape.

  The average particle size of the conductive filler (average particle size of primary particles) is not particularly limited, but is preferably about 0.01 to 10 μm, more preferably about 0.01 to 1 μm. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the conductive filler. 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.

  When the conductive filler is fibrous, the average fiber length is not particularly limited, but is preferably 0.1 to 100 μm. In addition, in this specification, average fiber length is the fiber length of the fiber observed in several to several dozen visual fields using observation means, such as a scanning electron microscope (SEM) and a transmission electron microscope (TEM). A value calculated as an average value shall be adopted. Moreover, the average diameter in case a conductive filler is fibrous is not specifically limited, However, It is preferable that it is 0.01-1 micrometer.

  The content of the polymer material in the conductive resin layer is not particularly limited, but preferably 10 to 95, with the total amount of the polymer material and the conductive filler in the conductive resin layer being 100 parts by mass. It is a mass part, More preferably, it is 12-90 mass parts.

  Further, the content of the conductive filler in the resin layer having conductivity is not particularly limited. However, the content of the conductive filler is preferably 5 to 90 parts by mass, more preferably 10 to 88 parts by mass, with the total amount of the polymer material and the conductive filler in the conductive resin layer being 100 parts by mass. Part. By adding such an amount of the conductive filler to the polymer material, it is possible to impart sufficient conductivity to the current collector while suppressing an increase in the mass of the current collector.

  The resin layer having conductivity may contain other additives other than the polymer material and the conductive filler. Examples of other additives include carboxylic acid-modified polypropylene such as maleic anhydride-modified polypropylene. Although it does not restrict | limit especially as addition amount of another additive, 1-25 mass parts is preferable with respect to a total of 100 mass parts of a polymeric material and a conductive filler.

  The thickness of the resin layer having conductivity is preferably 1 to 200 μm, more preferably 3 to 150 μm, and still more preferably 5 to 100 μm. Note that the conductive resin layer may have a single layer structure or a laminated structure in which layers made of these materials are appropriately combined.

  The method for producing the resin layer having conductivity is not particularly limited. For example, after melt-kneading the polymer material and, if necessary, each component of the conductive filler and additive with an extruder, etc., the melt-kneaded The method of rolling a material with a hot press machine is mentioned.

(Other conductive layers)
In the current collector of the present embodiment, the material of the conductive layer is not particularly limited, and a conventionally known material may be used. For example, metal materials, such as aluminum, iron, stainless steel, titanium, copper, are mentioned. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity and battery operating potential. In particular, when a metal that is easily alloyed with lithium, such as aluminum, is used for the conductive layer, lithium ions in the electrolytic solution are taken in by alloying with lithium, which may reduce battery capacity. However, by using the lithium ion barrier metal layer of the present embodiment, lithium ions can be efficiently suppressed from being taken into the conductive layer.

  The thickness of the conductive layer using a metal material is not particularly limited, but is usually about 1 to 500 μm, preferably 2 to 100 μm.

  Further, the current collector of the present embodiment may have other layers in addition to the above-described conductive resin layer and lithium ion barrier metal layer.

(Underlayer)
In order to further improve the adhesion between the conductive layer such as a resin layer having conductivity and the lithium ion barrier metal layer, an underlayer can be further formed between the conductive layer and the lithium ion barrier metal layer. By forming the base layer, when the conductive layer is a resin layer, it is possible to prevent the metal species constituting the lithium ion barrier metal layer from migrating to the resin layer. Further, the conductivity can be further increased in the resin layer having conductivity.

  The material constituting the underlayer is not particularly limited as long as it is a material that is not alloyed with lithium. Preferably, a metal material different from the lithium ion barrier metal layer is used, and examples thereof include copper, nickel, cobalt, gold, silver, tin, palladium, platinum, rhodium, and ruthenium. Among these, since plating techniques are generally established, at least one selected from the group consisting of gold, silver, copper, nickel and cobalt is preferable, and nickel is particularly preferable.

  Although it does not restrict | limit especially as thickness of a base layer, For example, it is 0.01-1 micrometer, Preferably it is 0.05-0.2 micrometer.

  The underlayer can be formed on the conductive layer by a plating method such as an electroless plating method or an electrolytic plating method.

[Current collector manufacturing method]
There is no restriction | limiting in particular about the manufacturing method of the electrical power collector of this embodiment, A conventionally well-known knowledge can be referred suitably. For example, in order to form a lithium ion barrier metal layer having no crystal grain boundary or having at least one end of the crystal grain boundary inside, it is preferable to increase the crystal grain size. That is, the number of crystals in the lithium ion barrier metal layer produced by plating can be reduced by reducing the number of base points on which crystals grow. As a result, the number of grain boundaries is reduced, and a lithium ion barrier metal layer having the above configuration can be obtained. As an example of a manufacturing method for making the lithium ion barrier metal layer include a crystal grain boundary having a specific structure as described above, there is the following method.

(Lithium ion barrier metal layer with grain boundaries shifted in the in-plane direction)
As shown in FIG. 4 above, in order to form a lithium ion barrier metal layer having a grain boundary shifted in the in-plane direction, the plating process is divided into two or more steps to form a laminated structure of two or more layers. The method of doing is mentioned. The metal layer constituting the lithium ion barrier layer may be 2 to 5 layers, for example.

  For example, a metal layer (3b in FIG. 4) is formed on the conductive layer by electroplating the metal constituting the lithium ion barrier metal layer to, for example, half the desired thickness. Thereafter, the sample is taken out from the plating solution and washed. Thereafter, electroplating is performed again to form an outermost metal layer (3a in FIG. 4) having a thickness that is ½ of a desired thickness, for example.

  In electrolytic plating, crystals usually grow in the thickness direction from the starting grains. Therefore, a crystal grain boundary is formed in the thickness direction in the obtained metal layer. In the electroplating process, even if the current is stopped halfway, if the current is subsequently applied and the plating is restarted, crystals will grow along the grain boundaries created before the current was stopped, resulting in the thickness direction. In addition, a crystal grain boundary connected from the upper surface to the lower surface of the metal layer is formed. However, once the sample is taken out of the plating solution, the crystal grows from a starting point different from the position of the lower grain boundary, and the crystal grain boundary is cut off between the two metal layers.

  In particular, it is preferable to form a lower metal layer, remove it from the plating solution, wash it, and dry it by applying heat. Furthermore, if time is passed thereafter, a lithium ion barrier metal layer in which crystal grain boundaries are broken can be obtained more efficiently. This is presumably because the metal oxide film is formed by applying heat, the surface is stabilized, and the strength is increased.

  As a specific method for producing a metal layer by a plating method, conventionally known knowledge can be appropriately employed.

  In general, first, pretreatment such as cleaning (degreasing) and washing is performed on a conductive layer on which a plating layer is to be formed. As the cleaner (degreasing), for example, cleaning is performed using a cleaning liquid obtained by adding a surfactant to sodium hydroxide, sodium silicate, sodium phosphate or the like. In the case of a conductive layer made of a metal material, the surface oxide film may be removed by acid cleaning.

  Thereafter, washing with water is performed to remove the treatment liquid on the surface of the conductive layer. Although the specific form of the water washing is not particularly limited, for example, it is washed with water at 25 to 45 ° C. for 1 to 5 minutes. This washing operation may be repeated a plurality of times, for example, 2 to 5 times.

  When forming an underlayer between the conductive layer and the lithium ion barrier metal layer, the underlayer is formed by, for example, electroless plating or electrolytic plating.

  In electroless plating, a plating solution containing metal ions of a metal species constituting a base layer and a reducing agent is brought into contact with a conductive layer to reduce metal ions. Although it does not restrict | limit especially as a reducing agent, For example, formaldehyde, a phosphinate, a tetrahydroborate, a hypophosphite etc. can be used.

  In particular, when a conductive resin layer is used as the conductive layer, the electroless plating layer can be efficiently formed by using a catalyst for the oxidation reaction of the reducing agent. Examples of the catalyst include palladium, silver, copper and the like. For example, before performing electroless plating, the conductive layer is immersed in a colloidal solution containing palladium chloride and tin chloride to give a catalyst to the surface of the resin layer. Thereafter, preferably, the catalyst palladium is activated by immersing it in an accelerator solution such as a sulfuric acid solution (10 to 20 mL / L, 30 to 40 ° C.) and dissolving chlorine and tin on the surface. After performing such catalyst application and activation, it is preferable to perform electroless plating by immersing in an electroless plating solution.

  The lithium ion barrier metal layer is preferably formed by electrolytic plating. The specific form of electroplating is not specifically limited.

  As a composition of the plating solution, a general plating solution can be used. For example, conventionally known various additives may be added to an aqueous solution containing an acid component in addition to metal ions. As additives, chloride ions, surfactants, nitrogen-containing compounds, nitrogen-containing compounds, organic additives as alteration inhibitors, and the like are appropriately added.

  For example, copper ion reduction used in the plating solution for electrolytic copper plating includes copper sulfate, copper oxide, copper chloride, copper carbonate, copper pyrophosphate, copper alkane sulfonate, copper alkanol sulfonate, and organic acid copper. Can be used. Although the copper ion concentration in a plating solution is not specifically limited, For example, it is a density | concentration of 10-80 g / L.

  There is no restriction | limiting in particular as an acid component, Organic acids, such as alkanesulfonic acid, such as methanesulfonic acid, alkanolsulfonic acid, and inorganic acids, such as a sulfuric acid, can be used 1 type or 2 types or more.

  The chloride ion is supplied from hydrochloric acid, sodium chloride or the like and used at a concentration of about 2 to 100 [mg / L].

  The surfactant is not particularly limited, and polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol, or copolymers thereof can be used. These concentrations are used at about 0.01 to 10 [g / L].

  The sulfur-containing compound is a plating accelerator usually called brightener, and 3-mercaptopropanesulfonic acid and its sodium salt, bis (3-sulfopropyl) disulfide, and its sodium salt are used. The concentration is about 0.01 to 200 [mg / L].

  As the nitrogen-containing organic compound (leveler), a phenazine compound, a safranin compound, a polyalkylene, a thiourea derivative, polyacrylamide, or the like is used at a concentration of 0.1 to 200 [mg / L]. An organic additive is used as the alteration preventing agent.

  As organic additives, alkyne compounds include propargyl alcohol, alkyne compounds such as N, N-dimethyl-3-aminopropyne-3-aminobutyn-3-ol, sodium avinylsulfonate, buten-3-ol Alkene compounds such as buten-4-ol and 1-propen-3ol are used.

Electrolytic plating conditions are not particularly limited. For example, the temperature of the plating solution is controlled to 20 to 60 ° C., the pH is controlled to 1 or less, the current density is 0.5 to 5.0 A / dm ² , and the plating time is 0.5 to 6 minutes. preferable.

  After obtaining a lithium ion barrier metal layer by electrolytic plating, it is preferable to wash with water and dry.

  Although the specific form of the water washing is not particularly limited, for example, it is washed with water at 25 to 45 ° C. for 1 to 5 minutes. This washing operation may be repeated a plurality of times, for example, 2 to 5 times. Drying can be performed, for example, at 50 to 200 ° C. for 1 to 10 minutes.

(Lithium ion barrier metal layer having grain boundaries with both ends inside)
As shown in FIG. 5 above, as a method of forming a lithium ion barrier metal layer having a crystal grain boundary having both ends inside, an underlayer is provided. At that time, the above-described catalyst application and catalyst activation are performed. It is preferable to repeat the process three times or more. And after that, it is preferable to form a lithium ion barrier metal layer on the underlayer by electroless plating. By doing so, the density of the catalyst adsorbed on the surface of the conductive layer is increased, and the number of grain boundaries having edges at the interface with the conductive layer is reduced. As a result, the lithium ion barrier metal layer has an internal structure. It is considered that the ratio of crystal grain boundaries having both end faces increases.

  Conventionally known plating methods can be employed except that the catalyst application and catalyst activation steps are repeated three or more times.

(Lithium ion barrier metal layer having 5 or less grain boundaries)
As shown in FIG. 6 above, the number of grain boundaries observed in a region having a width equivalent to the thickness in the cross section of the lithium ion barrier metal layer is 5 or less, more preferably 3 or less, and particularly preferably 1 or less. In order to form the lithium ion barrier metal layer, it is preferable to provide a base layer and control the thickness of the base layer to, for example, 150 to 200 nm. By doing so, the density of the catalyst adsorbed on the surface of the conductive layer is increased, and a denser underlayer can be formed. Therefore, it is considered that the number of crystal grain boundaries in the lithium ion barrier metal layer is reduced.

  A conventionally known plating method can be employed except that the thickness of the underlayer is controlled within the above range.

[Active material layer]
The active material layer includes an active material. Here, the active material occludes / releases ions during charge / discharge to generate electrical energy. The active material includes a positive electrode active material having a composition that occludes ions during discharging and releases ions during charging, and a negative electrode active material having a composition that can release ions during discharging and occlude ions during charging. The active material layer of this embodiment functions as a positive electrode active material layer when a positive electrode active material is used as an active material, and functions as a negative electrode active material layer when a negative electrode active material is used. In this specification, the matters common to the positive electrode active material and the negative electrode active material are simply described as “active materials”.

Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter, Simply referred to as “NMC composite oxide”). The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is included. Therefore, the amount of Li that can be taken out is twice that of the spinel-type lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn and the like. Preferred is Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, and more preferred is Ti, Zr, P, Al, Mg, Cr. More preferably, Ti, Zr, Al, Mg, and Cr are used.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc. that have been proven in general consumer batteries. Compared with, the capacity per unit mass is large. Moreover, it has the advantage that a compact and high capacity | capacitance battery can be produced by enabling improvement of an energy density, and it is preferable also from a viewpoint of cruising distance. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in terms of a larger capacity, but there are difficulties in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has life characteristics as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

On the other hand, preferable negative electrode active materials include metals such as Si and Sn, or metal oxides such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, SnO ₂ , and Li _4/3 Ti _5/3 O. ₄ or Li ₇ MnN and other complex oxides of lithium and transition metals, Li—Pb alloys, Li—Al alloys, Li, or graphite (natural graphite, artificial graphite), carbon black, activated carbon, carbon fiber, coke , Carbon materials such as soft carbon and hard carbon. Moreover, it is preferable that a negative electrode active material contains the element alloyed with lithium. By using an element that forms an alloy with lithium, it is possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a carbon material. These negative electrode active materials may be used alone or in combination of two or more.

  When an active material other than the carbon material (hereinafter also referred to as “non-carbon active material”) is used, a material obtained by coating the surface of the non-carbon active material with a carbon material may be used as the active material. preferable. According to such a configuration, a conductive network is established between the active materials or between the active material and the conductive auxiliary agent described later, and even when an active material having a large expansion / contraction is used, the conductivity in the electrode A pass can be secured. As a result, it is possible to suppress an increase in resistance even when charging and discharging are repeated. More preferably, from the viewpoint of improving the energy density of the electrode, a material that is alloyed with high-capacity lithium and coated with a carbon material is used as the active material. In this case, the coating amount of the carbon material is such that the electrical contact between the active materials or between the active material and the conductive additive is good depending on the particle size of the non-carbon active material (particle). do it. Preferably, it is about 2 to 20% by mass with respect to the total mass of the coated active material. In the present invention, the term “coating” includes not only the form in which the entire surface of the active material is covered with the carbon material but also the form in which the carbon material is present (attached) on a part of the surface of the active material. Shall be.

  The average particle size of the active material is not particularly limited, but is preferably 1 to 100 μm, and more preferably 1 to 20 μm, from the viewpoints of high battery capacity, reactivity, and cycle durability. Within such a range, the secondary battery can suppress an increase in the internal resistance of the battery during charging and discharging under high output conditions, and can extract a sufficient current. In addition, when the active material is secondary particles, it can be said that the average particle diameter of primary particles constituting the secondary particles is desirably in the range of 10 nm to 1 μm. It is not limited. However, it goes without saying that, depending on the production method, the active material may not be a secondary particle formed by aggregation, lump or the like. As the particle diameter of the active material and the particle diameter of the primary particles, the median diameter obtained using a laser diffraction method can be used. In addition, the shape of the active material varies depending on the type and manufacturing method, and examples thereof include a spherical shape (powder shape), a plate shape, a needle shape, a column shape, and a square shape, but are not limited thereto. Rather, any shape can be used without problems. Preferably, an optimal shape that can improve battery characteristics such as charge / discharge characteristics is appropriately selected.

  The active material layer of this embodiment contains other additives such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and a lithium salt for enhancing ion conductivity as necessary. In addition. However, the content of a material that can function as an active material in the active material layer is preferably 85 to 99.5% by mass.

  A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive aid include carbon materials such as carbon black such as ketjen black and acetylene black, and carbon fibers. When the active material layer contains a conductive additive, a conductive network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery. Here, the content of the conductive auxiliary agent is not particularly limited as long as the conductivity of the active material layer can be improved to a desired level, but is 0.5 to 15% by mass with respect to the total amount of the active material layer (in terms of solid content). And more preferably 1 to 10% by mass.

  The binder has a function of holding the structure of the active material layer and the conductive network by binding the active material, the conductive auxiliary agent, and the like. Although the material used as a binder is not specifically limited, When using for the active material layer containing a negative electrode active material, it is preferable that an aqueous binder is included. A water-based binder has high binding power, and it is easy to procure water as a raw material. In addition, water vapor is generated during drying, which greatly reduces capital investment on the production line and reduces environmental impact. There is an advantage that it is possible to reduce the above.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder containing water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meta ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl methacrylate Rate), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer , Polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80. Mol% or more, more preferably 90 mol% or more) and a modified product thereof (saponified product of 1 to 80 mol% of vinyl acetate units of a copolymer of ethylene / vinyl acetate = 2/98 to 30/70 mol ratio) , Polyvi 1 to 50 mol% partially acetalized alcohol, etc.), starch and modified products thereof (oxidized starch, phosphated starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, And their salts), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, alkyl (meth) acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich Denatured body, Lumarin condensation resins (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamines or dialkylamine-epichlorohydrin copolymers, polyethyleneimine, casein, soy protein, synthetic proteins, and water-soluble polymers such as mannangalactan derivatives Is mentioned. These aqueous binders may be used alone or in combination of two or more.

  The aqueous binder contains at least one rubber binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  When styrene-butadiene rubber is used as the aqueous binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving the coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Especially, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose (salt) as a binder. The content mass ratio of the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.1-10, 0 More preferably, it is 5-2.

  The content of the aqueous binder is preferably 80 to 100% by mass, preferably 90 to 100% by mass, and preferably 100% by mass with respect to the total amount of the binder.

  The binder material other than the water-based binder is not particularly limited. For example, polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethylcellulose. (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 Copolymers and hydrogenated products thereof, thermoplastic polymers such as styrene / isoprene / styrene block copolymers and hydrogenated products thereof, polyvinylidene fluoride (PVdF), Lafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychloro Fluoropolymers such as trifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF) PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene-based fluororubber (VDF-PFMVE) -TFE-based fluororubber), vinylidene fluoride-chlorofluoroethylene-based fluororubber (VDF-CTFE-based fluororubber) and other vinylidene fluoride-based fluororubbers, epoxy resins and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and 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 content of the binder is not particularly limited as long as it is an amount capable of binding the active material, but preferably 0.5 to 15% by mass with respect to the total amount of the active material layer (in terms of solid content). More preferably, it is 1-10 mass%.

(Electrolyte layer)
The electrolyte used in the electrolyte layer of the present embodiment is not particularly limited, but from the viewpoint of ensuring the ionic conductivity of the active material layer for the nonaqueous electrolyte secondary battery described above, a liquid electrolyte, a gel polymer electrolyte, or an ionic liquid An electrolyte is used.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte constituting the electrolytic solution layer 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 used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and the ion conductivity between the layers is easily cut off. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA), and copolymers thereof.

  The matrix polymer of the gel 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.

  The ionic liquid electrolyte is obtained by dissolving a lithium salt in an ionic liquid. In addition, an ionic liquid is a salt comprised only from a cation and an anion, and means a series of compounds which are liquid at normal temperature.

  The cation component constituting the ionic liquid is substituted or unsubstituted imidazolium ion, substituted or unsubstituted pyridinium ion, substituted or unsubstituted pyrrolium ion, substituted or unsubstituted Pyrazolium ion, substituted or unsubstituted pyrrolinium ion, substituted or unsubstituted pyrrolidinium ion, substituted or unsubstituted piperidinium ion, substituted or unsubstituted tria It is preferably at least one selected from the group consisting of dinium ions and substituted or unsubstituted ammonium ions.

Specific examples of the anion component constituting the ionic liquid include halide ions such as fluoride ion, chloride ion, bromide ion, iodide ion, nitrate ion (NO ₃ ⁻ ), tetrafluoroborate ion (BF ₄ ⁻ ), Hexafluorophosphate ion (PF ₆ ⁻ ), (FSO ₂ ) ₂ N ⁻ , AlCl ₃ ⁻ , lactate ion, acetate ion (CH ₃ COO ⁻ ), trifluoroacetate ion (CF ₃ COO ⁻ ), methanesulfone Acid ion (CH ₃ SO ₃ ⁻ ), trifluoromethanesulfonic acid ion (CF ₃ SO ₃ ⁻ ), bis (trifluoromethanesulfonyl) imide ion ((CF ₃ SO ₂ ) ₂ N ⁻ ), bis (pentafluoroethylsulfonyl) imide ion ((C ₂ F ₅ SO ₂ ) ₂ N ⁻ ), BF ₃ C ₂ F ₅ ⁻ , Tris (trifluoromethanesulfonyl) carbonic acid ion ((CF ₃ SO ₂ ) ₃ C ⁻ ), perchlorate ion (ClO ₄ ⁻ ), dicyanamide ion ((CN) ₂ N ⁻ ), organic sulfate ion, organic sulfone acid ^{ion, R 1 COO -, HOOCR 1} COO -, - OOCR 1 COO -, NH 2 CHR 1 COO - ( Here, ^{R 1} is a substituent, an aliphatic hydrocarbon group, alicyclic hydrocarbon group, An aromatic hydrocarbon group, an ether group, an ester group, or an acyl group, and the substituent may include a fluorine atom).

  Examples of preferred ionic liquids include 1-methyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide and N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide. As for these ionic liquids, only 1 type may be used independently and 2 or more types may be used together.

  The lithium salt used for the ionic liquid electrolyte is the same as the lithium salt used for the liquid electrolyte described above. In addition, it is preferable that the density | concentration of the said lithium salt is 0.1-2.0M, and it is more preferable that it is 0.8-1.2M.

  Moreover, you may add the following additives to an ionic liquid. By including an additive, charge / discharge characteristics and cycle characteristics at a high rate can be further improved. Specific examples of the additive include, for example, vinylene carbonate, ethylene carbonate, propylene carbonate, γ-butyllactone, γ-valerolactone, methyl diglyme, sulfolane, trimethyl phosphate, triethyl phosphate, methoxymethyl ethyl carbonate, Examples thereof include fluorinated ethylene carbonate. These may be used alone or in combination of two or more. The amount of the additive used is preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass with respect to the ionic liquid.

  A separator may be used for the electrolyte layer. The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode. In particular, when a liquid electrolyte or an ionic liquid electrolyte is used as the electrolyte, it is preferable to use a separator.

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

  As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  The current collector of the present invention produced as described above is suitably used for a lithium ion secondary battery. The lithium ion secondary battery is not limited to a stacked flat shape, and may be a wound lithium ion secondary battery. The wound lithium ion secondary battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. There is no particular limitation. 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 is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  In the lithium ion secondary battery, conventionally known knowledge is appropriately adopted for main constituent members other than the electrodes (active material layer, electrolyte layer, current collector plate, lead, exterior material, etc.). Moreover, said lithium ion secondary battery can be manufactured with a conventionally well-known manufacturing method.

  The lithium ion secondary battery having the above electrode is suitable as a power source for driving a vehicle or an auxiliary power source that requires a high mass energy density, a high mass output density, etc., such as an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, and a hybrid fuel cell vehicle. Can be used.

  The current collector for a lithium ion secondary battery of the present invention will be described in more detail using the following examples, but the present invention is not limited to only the following examples. Unless otherwise specified, the following operations were performed at room temperature (25 ° C.).

<Comparative Example 1>
[Conductive resin layer]
First, a polyimide foil as a resin layer was prepared. Specifically, a film-like resin layer having a thickness of 25 μm was prepared by dispersing 15% by mass of carbon particles (particle diameter: 10 nm) as a conductive filler with respect to 100% by mass of polyimide as a polymer material. . Specifically, a polyimide containing polyamic acid is dissolved in N-methylpyrrolidone (NMP) as a solvent, carbon particles are dispersed therein, and a film is produced by a melt casting method to obtain a conductive resin layer. It was.

[Electroless Ni plating process]
On one surface of the resin layer prepared above, 0.1 μm of an electroless Ni plating layer was deposited as a base layer. The electroless Ni plating step was performed in the order of cleaner, water washing, Pd catalyst application, water washing, Pd catalyst activation, water washing, electroless Ni plating deposition (0.1 μm), water washing, and drying step. The procedure of each process is as follows.

(cleaner)
The surface of the sample was cleaned by washing with an alkaline aqueous solution at 50 ° C. for 2 minutes.

(Washing)
Washed with water at 25 ° C. for 1 minute.

(Pd catalyst provided)
The sample was immersed in a Pd catalyst imparting agent at 50 ° C. for 1 minute to impart a Pd catalyst to the surface.

(Washing)
Washing with water was performed in the same procedure as above.

(Pd catalyst activation)
The sample provided with the Pd catalyst was immersed in an activating agent at 40 ° C. for 2 minutes to metallize Pd ions (activation treatment).

(Washing)
Washing with water was performed in the same procedure as above.

(Electroless Ni plating deposition)
A hypophosphorous acid aqueous solution was used as a plating solution.

  The sample was immersed in the plating solution at a temperature of 40 ° C. for 5 minutes to deposit an electroless Ni plating layer having a thickness of 0.1 μm.

(Washing)
Washing with water was performed in the same procedure as above.

(Dry)
The sample was dried at 180 ° C. for 5 minutes.

[Electrolytic Cu plating process]
Next, 0.5 μm of an electrolytic Cu plating layer was deposited as a lithium ion barrier metal layer on the electroless Ni plating layer to complete a current collector. The electrolytic Cu plating step includes degreasing, water washing, sulfuric acid washing, copper sulfate plating precipitation (0.5 μm), water washing and drying.

  The procedure of each process is as follows.

(Washing)
The washing process is the same as above.

(Washing with sulfuric acid)
The sample was washed with 0.5 mol / L sulfuric acid at 25 ° C. for 0.5 minutes.

(Copper sulfate plating deposition)
The composition of the plating solution is as follows.

Copper sulfate (0.2 mol / L),
Sulfuric acid (2 mol / L),
Using the above plating solution, electrolytic copper plating was performed at a current density of 1 A / dm ² and a temperature of 25 ° C. for 3 minutes to deposit an electrolytic Cu plating layer having a thickness of 0.5 μm on the surface of the electroless Ni plating layer. .

(Washing)
The washing process is the same as above.

(Dry)
The drying process is the same as described above.

<Example 1>
[Conductive resin layer]
The resin layer having conductivity was the same as in Comparative Example 1 above.

[Electroless Ni plating process]
The electroless Ni plating step was performed in the same procedure as in Comparative Example 1 above.

[Electrolytic Cu plating process]
On the electroless Ni plating layer produced above, the electrolytic Cu plating layer was divided into 0.3 μm and 0.2 μm twice, and a total of 0.5 μm was deposited to complete the Cu metal layer on the surface of the polyimide foil. .

  Specifically, in the electrolytic Cu plating step, degreasing, water washing, sulfuric acid washing, copper sulfate plating precipitation 0.3 μm, water washing, copper sulfate plating 0.2 μm, water washing, and drying were sequentially performed.

  That is, as a process of copper sulfate plating precipitation 0.3 μm, using the same plating solution as in Comparative Example 1 and performing electrolytic copper plating at the same current density and temperature, the sample was taken out from the plating solution and washed with water. Then, it returned to the plating solution, and electrolytic copper plating was performed again at the current density and temperature of Comparative Example 1 as a 0.2 μm copper sulfate plating step. The specific operation of each process other than the above is the same as that in Comparative Example 1.

<Example 2>
[Conductive resin layer]
The resin layer having conductivity was the same as in Comparative Example 1 above.

[Electroless Ni plating process]
An electroless Ni plating layer was deposited as a base layer on the surface of the resin layer by 0.1 μm. The electroless Ni plating process includes: cleaning, water washing, Pd catalyst application, water washing, Pd catalyst activation, water washing, Pd catalyst application, water washing, Pd catalyst activation, water washing, Pd catalyst application, water washing, Pd catalyst activation, water washing, Electroless Ni plating deposition (0.1 μm), washing with water, and drying were performed in this order. That is, the steps of applying the Pd catalyst to activating the Pd catalyst were repeated three times.

  The specific operation of each process is the same as that of the comparative example 1.

[Electrolytic Cu plating process]
The same procedure as in Comparative Example 1 was performed.

<Example 3>
[Conductive resin layer]
The resin layer having conductivity was the same as in Comparative Example 1 above.

[Electroless Ni plating process]
The electroless Ni plating step was performed in the same procedure as in Comparative Example 1 except that the thickness of the electroless plating layer was changed from 0.1 μm to 0.15 μm.

[Electrolytic Cu plating process]
The same procedure as in Comparative Example 1 was performed.

<Observation of current collector cross section>
The cross section of the current collector produced in each example and comparative example was observed with SEM.

  FIG. 7 shows SEM photographs of cross sections of the current collectors produced in (a) Comparative Example 1, (b) Example 1, (c) Example 2, and (d) Example 3.

  As shown to Fig.7 (a), in the electrical power collector produced by the comparative example 1, the electroplating Cu layer which is a metal layer is laminated | stacked on the polyimide foil, The inside of a metal layer is the time of formation. There are many crystal grain boundaries between crystal grains. This is connected from the upper surface to the lower surface of the metal layer.

  As shown in FIG. 7B, it can be seen that in the current collector manufactured in Example 1, the crystal grain boundary is shifted at the interface between the two metal layers. In the electrolytic Cu plating process of Comparative Example 1, a 0.5 μm film was deposited by one copper sulfate plating, whereas in Example 1, after washing with 0.3 μm copper sulfate, it was washed once with water. Then, 0.2 μm copper sulfate plating is performed again. Thus, in Example 1, it is considered that the grain boundary was formed at a shifted position without scratching the first grain boundary in the second plating step.

  As shown in FIG. 7C, in the current collector manufactured in Example 2, the crystal grain boundary connected in the thickness direction from the plating upper surface to the plating lower surface is not observed. Further, the ratio of crystal grain boundaries having both end faces was large in the lithium ion barrier metal layer. This is because, by repeating the Pd catalyst application to Pd catalyst activation process three times in the electrolytic Cu plating process, the density of catalyst adsorption increases and the number of crystal grain boundaries having ends at the interface with the polyimide foil decreases. It is thought that. As a result, it is considered that the ratio of crystal grain boundaries having both end faces increased in the lithium ion barrier metal layer.

  As shown in FIG. 7D, the current collector manufactured in Example 3 does not include a crystal grain boundary inside the lithium ion barrier metal layer. This is because by increasing the thickness of the base layer 0.1 μm of Comparative Example 1 to 0.15 μm, the number of crystal grain boundaries having ends at the polyimide interface is further suppressed, and a metal layer that does not contain crystal grain boundaries is obtained. It is thought that it was possible.

<Production and evaluation of battery>
A bipolar lithium ion secondary battery was prepared and evaluated according to the following procedure.

(Production of bipolar electrode)
An appropriate amount of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent with respect to the solid content of graphite (90% by mass) as the negative electrode active material and polyvinylidene fluoride (PVdF) (10% by mass) as the binder Were mixed to prepare a negative electrode active material slurry.

On the other hand, a slurry viscosity adjusting solvent with respect to a solid content of LiNiO ₂ (85% by mass) as a positive electrode active material, acetylene black (5% by mass) as a conductive additive, and PVdF (10% by mass) as a binder. A proper amount of NMP was mixed to prepare a positive electrode active material slurry.

  The negative electrode active material slurry prepared above was applied to the surface of the Cu metal layer of the current collector prepared in each Example and Comparative Example and dried to form a negative electrode active material layer (thickness: 100 μm). Similarly, the positive electrode active material slurry prepared above was applied to the other surface of the current collector prepared in each Example and Comparative Example and dried to form a positive electrode active material layer (thickness: 100 μm). . At this time, the area of the negative electrode active material layer and the area of the positive electrode active material layer are the same (40 mm × 25 mm), and the projections of the negative electrode active material layer and the positive electrode active material layer on the current collector are matched. It adjusted and the negative electrode active material layer and the positive electrode active material layer were formed. Moreover, it was set as the state which left the margin of each side width 10mm as a seal part on both surfaces of the electrical power collector.

(Production of bipolar lithium-ion secondary battery)
First, an electrolyte solution prepared by dissolving LiPF ₆ as a lithium salt at a concentration of 1 mol / L in an equal volume mixture of propylene carbonate and ethylene carbonate was prepared. Next, a sealing material (thermoplastic) having a width of 10 mm is disposed on the surface exposed portion (blank portion) on the Cu metal layer side of the bipolar electrode produced above, and this electrode and separator (size that covers the active material layer) Were stacked alternately to form a laminate of two layers (two positive / negative electrode combinations).

  The obtained laminate was subjected to hot press treatment (0.2 MPa, 80 ° C., 5 seconds) in the laminating direction, and the seal portion was fused to seal between adjacent bipolar electrodes, and the prepared electrolysis Liquid was injected and sealed to complete the power generation element. Furthermore, a bipolar lithium ion secondary battery is obtained by sandwiching the power generation element using a high-power terminal in which a part of the aluminum plate that can cover the entire projection surface of the obtained power generation element extends to the outside of the projection surface of the power generation element. Completed.

(Production of electrodes that are not bipolar)
The positive electrode active material slurry and the negative electrode active material slurry were subjected to the same procedure as in the production of the bipolar electrode.

  The prepared negative electrode active material slurry was prepared as negative electrode current collectors of Examples and Comparative Examples (electroless Ni plating layer and electrolytic Cu plating layer formed on both surfaces of a conductive resin layer by the procedures of Examples and Comparative Examples) ) And dried to form a negative electrode active material layer (thickness: 100 μm). Similarly, the prepared positive electrode active material slurry was applied on both sides of a positive electrode current collector (film similar to the negative electrode current collector, but without plating) and dried to form a positive electrode active material layer (thickness: 100 μm). . At this time, the area of the negative electrode active material layer and the area of the positive electrode active material layer are made the same, and the negative electrode active material layer and the positive electrode active material layer are adjusted so that the projected views on the current collector match, An active material layer and a positive electrode active material layer were formed. Each current collector was provided with a tab having a length of 50 mm and a width of 10 mm.

<Production of non-bipolar lithium ion secondary battery>
The electrolytic solution was prepared by the same procedure as that for the bipolar lithium ion secondary battery. Next, the non-bipolar electrode produced above was stacked in the order of negative electrode → separator → positive electrode → separator → negative electrode to form a laminate of two layers (two combinations of positive electrode / negative electrode). The obtained laminate was put in an aluminum laminate bag and sealed on three sides so that the tabs were exposed to the outside. Since there are two sets of negative electrodes in this configuration, the tabs of these negative electrode current collectors are combined to form a negative electrode tab. Next, the electrolytic solution prepared above was poured into an aluminum laminate bag and sealed to complete the power generation element. Finally, a high voltage terminal was connected to each of the negative electrode tab and the positive electrode tab to complete a non-bipolar lithium ion secondary battery.

<Cycle test>
Bipolar lithium ion secondary batteries and non-bipolar lithium ion secondary batteries produced using the current collectors of the examples and comparative examples were fully charged at a rate of 1 C in an atmosphere of 45 ° C. Until constant current (CC) charging. Thereafter, the battery was charged at a constant voltage (CV) and charged for a total of 3 hours. Thereafter, constant current discharge was performed, and this was regarded as one cycle, and 300 charge / discharge cycle tests were conducted. The discharge capacity retention ratio after the cycle (discharge capacity after 300 cycles / initial discharge capacity × 100 [%]) was determined. The results are shown in Table 1.

From the results of the discharge capacity retention rate in Table 1 above, the battery using the current collectors of Examples 1 to 3 having no crystal grain boundaries or no crystal grain boundaries connected from the upper surface to the lower surface in the thickness direction of the metal layer is as follows. Compared to the battery using the current collector of Comparative Example 1, it was shown that the capacity was reduced and the performance could be maintained.

  This is because in the current collector of Comparative Example 1, the crystal grain boundary between crystal grains is connected to the inside of the metal layer from the upper surface to the lower surface of the metal layer. This is thought to be trapped. In this case, the amount of lithium ions in the entire battery is reduced, and polyimide is also deteriorated, which is considered to lead to a reduction in battery capacity.

  On the other hand, in the current collectors of Examples 1 to 3, the crystal grain boundaries generated at the time of plating production are broken in the plating layer, or there are no crystal grain boundaries themselves, so lithium ions do not reach the polyimide foil. This is probably because lithium ions are not consumed.

1, 1b current collector,
2 conductive layer,
3, 3a, 3b lithium ion barrier metal layer,
4, 4a, 4b grain boundaries,
5 Edges of grain boundaries,
10a, 10b lithium ion secondary battery,
11 negative electrode current collector,
11a The outermost layer current collector on the negative electrode side,
11b The outermost layer current collector on the positive electrode side,
11c Bipolar electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 Battery exterior materials,
31 Seal part.

Claims (7)

A conductive layer, and a lithium ion barrier metal layer disposed on the surface of the conductive layer,
The lithium ion barrier metal layer is formed by plating and has no crystal grain boundary, or at least one end of the crystal grain boundary exists in the lithium ion barrier metal layer ,
A current collector for a lithium ion secondary battery , wherein the number of crystal grain boundaries observed in a region having a width equivalent to the thickness in the cross section of the lithium ion barrier metal layer is 5 or less .   2. The current collector for a lithium ion secondary battery according to claim 1, wherein the lithium ion barrier metal layer has a grain boundary shifted in an in-plane direction.   The lithium ion barrier metal layer is composed of two or more metal layers, and the crystal grain boundary of the outermost metal layer and the crystal grain boundary of the metal layer in contact with the conductive layer are shifted in the in-plane direction. The current collector for a lithium ion secondary battery according to claim 2.   The current collector for a lithium ion secondary battery according to claim 1, wherein the current collector has a crystal grain boundary having both ends inside the lithium ion barrier metal layer. The said lithium ion barrier metal layer is a collector for lithium ion secondary batteries of any one of Claims 1-4 comprised from a single material. The lithium ion barrier metal layer is selected from the group consisting of copper (Cu), nickel (Ni), cobalt (Co), oxides and nitrides of these metals, and alloys based on these metals. The current collector for a lithium ion secondary battery according to any one of claims 1 to 5 , comprising at least one kind. A lithium ion secondary battery comprising the current collector for a lithium ion secondary battery according to any one of claims 1 to 6 ,
The lithium ion secondary battery by which a negative electrode active material layer is arrange | positioned at the surface by the side of the said lithium ion barrier metal layer in the said collector for lithium ion secondary batteries.