JP2011034891A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

A means for improving cycle characteristics of a non-aqueous electrolyte secondary battery is provided.
A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of a current collector; a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of a current collector; Is a non-aqueous electrolyte secondary battery having a power generation element including a single battery layer laminated via a separator including an electrolyte, wherein the current collector includes a biodegradable polymer and conductive particles. It is a secondary battery.
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

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

  As a secondary battery for driving a motor, a lithium ion secondary battery having the highest theoretical energy among all the batteries is attracting attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery has a configuration in which a positive electrode and a negative electrode having an active material layer in which an active material or the like is applied to a current collector together with a binder are connected via an electrolyte layer and stored in a battery case. is doing.

  The non-aqueous electrolyte secondary battery used as a motor drive power source for automobiles and the like as described above has extremely high output characteristics compared to consumer non-aqueous electrolyte secondary batteries used in mobile phones, notebook computers, etc. At present, it is required to have such research, and eager research and development is underway to meet such demands.

  The non-aqueous electrolyte secondary battery includes a current collector as a constituent member. For the purpose of reducing the weight of the current collector, a current collector containing a resin (hereinafter also simply referred to as a resin current collector) is used.

  Here, in general, the resin has a property that the surface free energy is very small compared to the metal (see, for example, Non-Patent Document 1).

"Product Knowledge Series: Practical Knowledge of Adhesives" 2nd edition, written by Toshinao Okitsu, published by Toyo Keizai Inc., 43 pages, published on May 23, 1996

  When a resin having a small surface free energy as described in Non-Patent Document 1 is applied to the current collector of a non-aqueous electrolyte secondary battery, the wettability of the current collector surface with the electrode compared to the metal current collector And the adhesive strength is insufficient at the interface between the electrode and the current collector. Therefore, with charging / discharging, there is a problem that the resistance at the interface between the electrode and the current collector increases, and the cycle characteristics of the nonaqueous electrolyte secondary battery deteriorate.

  Then, an object of this invention is to provide the means to improve the cycling characteristics of a nonaqueous electrolyte secondary battery.

  The inventors of the present invention have made extensive studies in view of the above problems. As a result, it has been found that a nonaqueous electrolyte secondary battery provided with a current collector containing a biodegradable polymer and conductive particles solves the above problems, and has completed the present invention.

  Since the biodegradable polymer has a large surface free energy, the wettability with the electrode on the surface of the current collector including the biodegradable polymer and the conductive particles is improved, and the adhesion between the electrode and the current collector is further strengthened. . Therefore, the increase in resistance at the interface between the electrode and the resin current collector accompanying charging / discharging can be suppressed, and the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.

1 is a schematic cross-sectional view showing the structure of a stacked lithium ion secondary battery. 1 is a schematic cross-sectional view showing the structure of a bipolar lithium ion secondary battery. It is a perspective view showing the appearance of a nonaqueous electrolyte secondary battery.

  First, although the nonaqueous electrolyte lithium ion secondary battery which is preferable embodiment is demonstrated, it is not restrict | limited only 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.

  When distinguished by the structure and form of the nonaqueous electrolyte secondary battery, it is not particularly limited, such as a stacked (flat) battery or a wound (cylindrical) battery, and can be applied to any conventionally known structure. .

  Moreover, when it sees in the electrode material of a battery, or the metal ion which moves between electrodes, it does not restrict | limit in particular, It can apply to any well-known electrode material. Examples include lithium ion secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, nickel metal hydride secondary batteries, nickel cadmium secondary batteries, nickel metal hydride batteries, and the like, preferably lithium ion secondary batteries. . This is because in the lithium ion secondary battery, the voltage of the cell (single cell layer) is large, high energy density and high output density can be achieved, and it is excellent as a vehicle driving power source or an auxiliary power source.

[Battery overall structure]
FIG. 1 is a schematic diagram showing the basic configuration of an embodiment of a flat (stacked) nonaqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”). 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 laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the positive electrode in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11, the electrolyte layer 17, and the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. It has a configuration in which a negative electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10a of the present embodiment 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 13 is arrange | positioned only at one side in the outermost layer positive electrode collector 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 11 and the negative electrode current collector 12 are attached to a positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  FIG. 2 is a schematic cross-sectional view schematically showing the entire structure of the non-aqueous electrolyte bipolar lithium ion secondary battery 10b. The nonaqueous electrolyte bipolar lithium ion secondary battery 10b shown in FIG. 2 has a structure in which a substantially rectangular power generating element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 29 that is a battery exterior material. Have.

  As shown in FIG. 2, the power generation element 21 of the bipolar lithium ion secondary battery 10 b is formed with a positive electrode active material layer 13 that is electrically coupled to one surface of the current collector 11, and is opposite to the current collector 11. It has a plurality of bipolar electrodes 23 formed with a negative electrode active material layer 15 electrically coupled to the side surface. 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 13 of one bipolar electrode 23 and the negative electrode active material layer 15 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 interposed between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. ing.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar lithium ion secondary 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. A positive electrode active material layer 13 is formed only on one side of the positive electrode outermost layer current collector 11 a located in the outermost layer of the power generation element 21. The negative electrode active material layer 15 is formed only on one surface of the outermost current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21. However, the positive electrode active material layer 13 may be formed on both surfaces of the outermost layer current collector 11a on the positive electrode side. Similarly, the negative electrode active material layer 15 may be formed on both surfaces of the outermost layer current collector 11b on the negative electrode side.

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

  In the nonaqueous electrolyte bipolar lithium ion secondary battery 10 b shown in FIG. 2, an insulating part 31 is usually provided around each single cell layer 19. The insulating part 31 prevents the adjacent current collectors 11 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. Is provided. By installing such an insulating portion 31, long-term reliability and safety can be ensured, and a high-quality bipolar lithium ion secondary battery 10b can be provided.

  Note that the number of stacks of the unit cell layers 19 is adjusted according to a desired voltage. In the bipolar lithium ion secondary battery 10b, the number of stacks of the single battery layers 19 may be reduced if a sufficient output can be secured even if the thickness of the battery is reduced as much as possible. Even in the bipolar lithium ion secondary 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 25 and the negative electrode current collector plate 27 are taken out of the laminate film 29.

  The current collector of this embodiment includes a biodegradable polymer. Since the biodegradable polymer has a large surface free energy, when it is applied to a current collector, the wettability of the electrode becomes good, and the adhesive force of the electrode-resin current collector becomes stronger. Therefore, it is possible to suppress an increase in resistance at the interface between the electrode and the resin current collector due to charge / discharge, and the cycle characteristics (durability) of the nonaqueous electrolyte secondary battery can be improved. Furthermore, the biodegradable polymer has a large difference in solubility parameter (SP value) from the electrolyte solution normally used for nonaqueous electrolyte secondary batteries, so that the solvent resistance is good and the cycle characteristics (durability) are improved. Is even more advantageous. In addition, even if a secondary battery equipped with a resin current collector containing a biodegradable polymer is illegally dumped, microorganisms are involved in nature, and the resin current collector eventually passes through a low-molecular compound and then water. It can be decomposed into carbon dioxide and can be an environmentally friendly battery.

  Hereinafter, the current collector of the present embodiment will be described in detail.

(Current collector)
The current collector includes a biodegradable polymer and conductive particles. Hereinafter, the biodegradable polymer and the conductive particles will be described.

<Biodegradable polymer>
The biodegradable polymer used in the present invention is not particularly limited and can be appropriately selected from known ones, and may be derived from natural products or chemically synthesized. Moreover, these may be used independently and may be used in combination of 2 or more type.

  Examples of biodegradable polymers derived from natural products include chitin, chitosan, alginic acid, gluten, collagen, polyamino acids, bacterial cellulose, pullulan, starch and the like.

  Examples of chemically synthesized biodegradable polymers include, for example, polyhydroxybutyrate, polyε-caprolactone, polyethylene succinate, polybutylene succinate, polyethylene adipate, polybutylene succinate adipate, polyhydroxyvalylate, polydioxanone. , Polyglycolic acid, polylactic acid, polymalic acid, polyglactin, polyglyconate, polygrecapron and other aliphatic polyesters; polybutylene adipate terephthalate, polybutylene succinate terephthalate and other aromatic polyesters; polyvinyl alcohol; polyurethane; Examples thereof include aliphatic polycarbonates such as trimethylene carbonate.

  Of these biodegradable polymers, aliphatic polyesters are preferred. Since aliphatic polyester has a large surface free energy, the adhesive force between the electrode and the resin current collector is strengthened, and the resistance at the interface between the electrode and the resin current collector due to charge / discharge is more easily reduced. More preferred are polybutylene succinate and polylactic acid.

<Conductive particles>
In addition, the current collector of this embodiment includes conductive particles. The conductive particles used are selected from materials having conductivity. Preferably, from the viewpoint of suppressing ion permeation in the conductive resin layer, it is desirable to use a material that does not have conductivity with respect to ions used as the charge transfer medium. The said electroconductive particle may be used independently and may be used in combination of 2 or more type.

  Specific examples include, but are not limited to, aluminum materials, stainless steel (SUS) materials, carbon materials such as graphite and carbon black, silver materials, gold materials, copper materials, and titanium materials. These conductive fillers may be used alone or in combination of two or more. Moreover, these alloy materials may be used. An aluminum material, a stainless steel material, a carbon material, a silver material, and a gold material are preferable, and a gold material and a carbon material are more preferable. These conductive particles may be those obtained by coating a conductive material around a particle ceramic material or resin material with plating or the like.

  In addition, the shape (form) of the conductive particles may be used in the form of particles, but is not limited to the form of particles, and in a form other than the form of particles practically used as a so-called filler-based conductive resin composition such as carbon nanotube. There may be.

  Examples of the carbon material include, for example, acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, single wall carbon nanotube, double wall carbon nanotube, multi-wall carbon nanotube carbon nanohorn, carbon nanoballoon, or fullerene. Is mentioned. The carbon material has a very wide potential window, is stable in a wide range with respect to both the positive electrode potential and the negative electrode potential, and is excellent in conductivity. Also, since the carbon material is very lightweight, the increase in mass is minimized. Furthermore, 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 particles, it is possible to reduce the compatibility of the electrolyte by applying a hydrophobic treatment to the surface of the carbon, making it difficult for the electrolyte to penetrate into the current collector holes. is there.

  The average particle diameter of the conductive particles is not particularly limited, but is preferably about 0.01 to 10 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. Particle diameters and average particle diameters of active material particles to be described later can be defined similarly.

  Although content of the electroconductive particle in a collector is not specifically limited, Preferably, 1-30 mass% electroconductive particle exists with respect to the total mass of a collector. By allowing a sufficient amount of conductive particles to be present, sufficient conductivity in the resin layer can be secured.

  In addition to the biodegradable polymer, the current collector may include other polymers such as a conductive polymer and a non-conductive polymer.

  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. Specifically, polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole, or a mixture thereof is preferable. Polyaniline, polypyrrole, polythiophene, and polyacetylene are more preferable from the viewpoint of electronic conductivity and stable use in the battery.

  Examples of non-conductive polymers include low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polybutylene and other olefin resins, ethylene-acetic acid Vinyl copolymer (EVA), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), styrene-butadiene block copolymer, polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polycarbonate Boneto (PC), epoxy resin, or a mixture thereof, and the like. These materials have a very wide potential window and are stable to both positive and negative electrode potentials. Moreover, since it is lightweight, the output density of a battery can be increased.

  When the current collector contains another polymer, the content of the other polymer is preferably 0.1 to 10% by mass with respect to the total mass of the current collector. The other polymer may be mixed with the biodegradable polymer to form one layer, or may form another layer from the biodegradable polymer.

  The current collector may contain other additives in addition to the biodegradable polymer, the conductive particles, and other polymers included as necessary.

  As described above, the current collector of this embodiment includes a biodegradable polymer. Since the biodegradable polymer has a large surface free energy, when it is applied to a current collector, the wettability with the electrode is improved, and the adhesion between the electrode and the resin current collector is further strengthened. Therefore, it is possible to suppress an increase in resistance at the interface between the electrode and the resin current collector due to charge / discharge, and the cycle characteristics (durability) of the nonaqueous electrolyte secondary battery can be improved. Furthermore, since the biodegradable polymer has a large difference in solubility parameter (SP value) from the electrolyte solution normally used in non-aqueous electrolyte secondary batteries, the solvent resistance is good and the durability is further improved. It becomes. In addition, even if a secondary battery including a resin current collector using a biodegradable polymer is illegally dumped, microorganisms are involved in nature, and the resin current collector eventually passes through a low-molecular compound and then water. It can be decomposed into carbon dioxide and can be an environmentally friendly battery.

  The non-aqueous electrolyte secondary battery described above is characterized by the configuration of the current collector. Hereinafter, other main components will be described.

(Active material layer)
[Positive electrode (positive electrode active material layer) and negative electrode (negative electrode active material layer)]
The active material layer 13 or 15 contains an active material, and further contains other additives as necessary.

The positive electrode active material layer 13 includes a positive electrode active material. As the positive electrode active material, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium-such as those in which a part of these transition metals are substituted 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. Of course, positive electrode active materials other than those described above may be used.

The negative electrode active material layer 15 includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. . In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in each active material layer 13, 15 is not particularly limited, but is preferably 1 to 20 μm from the viewpoint of increasing the output.

  The positive electrode active material layer 13 and the negative electrode active material layer 15 include a binder.

  Although it does not specifically limit as a binder used for an active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FE) ), Tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) , Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluoro rubber (VDF-PFP-TFE fluoro rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber Examples thereof include vinylidene fluoride-based fluororubber such as (VDF-CTFE-based fluororubber), an epoxy resin, and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, 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 amount of the binder contained in the active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. Yes, more preferably 1 to 10% by mass.

  Examples of other additives that can be included in the active material layer include a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

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

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

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

(Electrolyte layer)
As the electrolyte constituting the electrolyte layer 13, a liquid electrolyte or a polymer electrolyte can be used.

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

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

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

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

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

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

(Outermost layer current collector)
As the material of the outermost layer current collector, for example, a metal or a conductive polymer can be adopted. From the viewpoint of ease of taking out electricity, a metal material is preferably used. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum and copper are preferable from the viewpoints of electron conductivity and battery operating potential.

(Tabs and leads)
A tab may be used for the purpose of taking out the current outside the battery. The tab is electrically connected to the outermost layer current collector or current collector plate, and is taken out of the laminate sheet which is a battery exterior material.

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

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

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

(Insulation part)
The insulating part 31 prevents a liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17. In addition, the insulating part 31 prevents the adjacent current collectors in the battery from coming into contact with each other or the occurrence of a short circuit due to a slight irregularity at the end of the unit cell layer 19 in the power generation element 21. Is provided.

  The material constituting the insulating portion 31 may have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance at the battery operating temperature, and the like. That's fine. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Among these, polyethylene resin and polypropylene resin are preferably used as the constituent material of the insulating portion 31 from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming property), economy, and the like.

  In addition, said non-aqueous electrolyte secondary battery can be manufactured with a conventionally well-known manufacturing method.

<External configuration of nonaqueous electrolyte secondary battery>
FIG. 3 is a perspective view showing the appearance of a stacked flat lithium ion secondary battery which is a typical embodiment of a nonaqueous electrolyte secondary battery.

  As shown in FIG. 3, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element (battery element) 57 includes a positive electrode tab 58 and a negative electrode tab 59. It is sealed in a state where it is pulled out to the outside. Here, the power generation element (battery element) 57 corresponds to the power generation element (battery element) 21 of the nonaqueous electrolyte secondary battery 10 shown in FIGS. 1 and 2 described above. The power generation element (battery element) 57 is formed by laminating a plurality of single battery layers (single cells) 19 including a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15. .

  The lithium ion battery is not limited to a stacked flat shape. In the wound type lithium ion battery, it may have a cylindrical shape, or it may be such that the cylindrical shape is transformed into a rectangular flat shape, etc. 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 (battery element) is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Also, the removal of the tabs 58 and 59 shown in FIG. 3 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  The lithium ion battery is suitable as a power source for driving a vehicle or an auxiliary power source that requires a high volume energy density and a high volume output density as a large capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, etc. Can be used.

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

  The assembled battery forms a small assembled battery in which a plurality of nonaqueous electrolyte secondary batteries are connected in series or in parallel to be detachable. A large number of small, detachable assembled batteries can be connected in series or in parallel to provide a large capacity and high output suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery can also be formed. The small assembled batteries that can be attached and detached are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries are stacked in a plurality of stages using a connection jig. How many non-aqueous electrolyte secondary batteries are connected to produce an assembled battery, and how many assembled batteries are laminated to produce an assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) Depending on the output.

<Vehicle>
A vehicle is equipped with the non-aqueous electrolyte secondary battery or an assembled battery formed by combining a plurality of these. Since a long-life battery excellent in long-term reliability and output characteristics can be configured, it is possible to configure a plug-in hybrid electric vehicle having a long EV mileage and an electric vehicle having a long charge mileage when such a battery is mounted. In other words, the non-aqueous electrolyte secondary battery or an assembled battery formed by combining a plurality of these can be used as a power source for driving the vehicle. A non-aqueous electrolyte secondary battery or a combination battery formed by combining a plurality of these batteries, for example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (a passenger car that is a four-wheeled vehicle, a commercial vehicle such as a truck or a bus, a light vehicle) Etc.). It can also be used for motorcycles and tricycles. This is because the vehicle has a long life and high reliability. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

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

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

Example 1
1. Preparation of Current Collector Polylactic acid (95% by mass) and ketjen black (5% by mass, average particle size: 30 nm) as conductive particles were mixed, and a slurry was prepared using dichloromethane as a solvent. The slurry was cast on a PET film and dried at 60 ° C. for 8 hours to prepare a resin current collector.

2. Step of forming positive electrode layer As a positive electrode active material, a solid content of 85% by mass of LiMn ₂ O ₄ (average particle size: 10 μm), 5% by mass of acetylene black as a conductive additive, and 10% by mass of PVdF as a binder was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a positive electrode slurry.

  The positive electrode slurry is mixed with the 1. The positive electrode layer was formed by applying and drying on one side of the current collector prepared in (1). Pressing was performed so that the thickness of the positive electrode layer was 36 μm.

3. Formation of negative electrode layer and completion process of bipolar electrode NMP, which is a slurry viscosity adjusting solvent, is used as a negative electrode active material with respect to a solid content of 90% by mass of hard carbon (average particle size: 10 μm) and 10% by mass of PVdF as a binder. An appropriate amount was added to prepare a negative electrode slurry.

  The negative electrode slurry was applied to the surface of the current collector on which one side of the positive electrode layer was formed, on which the positive electrode layer was not formed, and dried to form a negative electrode layer. The negative electrode layer was pressed so that the thickness was 30 μm. This formed a bipolar electrode in which a positive electrode layer was formed on one side of the current collector and a negative electrode layer was formed on the other side.

  The obtained bipolar electrode was cut into 140 mm × 90 mm, and a peripheral portion of the electrode 10 mm was prepared with a portion to which no electrode layer (both positive electrode layer and negative electrode layer) was previously applied. As a result, a bipolar electrode having a 120 mm × 70 mm electrode portion and a 10 mm seal margin in the peripheral portion was produced.

  Next, the following materials were mixed at a predetermined ratio to prepare an electrolyte material (pregel solution).

As an electrolytic solution, 90% by mass of propylene carbonate (PC) -ethylene carbonate (EC) (1: 1 (volume ratio)) containing 1.0 M LiPF ₆ was used. As the host polymer, 10% by mass of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) containing 10% by mass of the HFP component was used. An appropriate amount of DMC was used as a viscosity adjusting solvent. An electrolyte material (pregel solution) was prepared by mixing an electrolyte solution, a host polymer, and a viscosity adjusting solvent.

  The electrolyte material (pregel solution) was applied to the entire surface of the positive electrode layer and the negative electrode layer on both sides of the bipolar electrode formed in advance, and the DMC was removed by drying at room temperature, so that the gel electrolyte was infiltrated. A bipolar electrode was completed. Note that the thickness of the positive electrode layer remained 36 μm, and the thickness of the negative electrode layer remained 30 μm.

4). Gel Polymer Electrolyte Layer Production Process Gel polymer infiltrated with gel electrolyte by applying the electrolyte material (pregel solution) on both sides of a polypropylene porous film separator (thickness 20 μm) and drying DMC at room temperature. An electrolyte layer (thickness 20 μm) was obtained.

5). Lamination Step A gel electrolyte layer was placed on the positive electrode layer of the bipolar electrode obtained above, and a PE (polyethylene) film having a width of 12 mm and a thickness of 100 μm was placed around it as a sealing material. After laminating 6 layers of such bipolar electrodes, the sealing material is pressed (heat and pressure) from the top and bottom, and each layer is sealed (press conditions: 0.2 MPa, 80 ° C., 5 s) to seal Part was formed.

  A part (electrode tab: electrode tab: part of a 130 μm × 80 mm 100 μm thick Al plate (electrode current collector plate) that can cover the entire projection surface of the obtained battery element. An electrode current collector (high voltage terminal) having a width of 20 mm was produced. The battery element was sandwiched between and covered with the current collector plate, and was vacuum-sealed with a laminate film containing aluminum as a battery exterior material, whereby both sides of the battery element were pressed and pressurized at atmospheric pressure. Then, a bipolar secondary battery structure having a five-line structure (a structure in which five cells are connected in series) in which the contact between the electrode current collector plate and the battery element was enhanced was produced.

The bipolar secondary battery structure was hot pressed with a hot press at a surface pressure of 1 kg / cm ² for 1 hour to cure the uncured seal portion. Thus, a bipolar secondary battery was completed.

(Example 2)
Bipolar type in the same manner as in Example 1 except that single-walled carbon nanotubes (hereinafter also simply referred to as SWCNT, average diameter: 10 nm, average length: 300 nm) were used instead of ketjen black. A secondary battery was produced.

(Example 3)
A bipolar secondary battery was fabricated in the same manner as in Example 1 except that gold fine particles (average particle size: 15 nm) were used instead of ketjen black.

Example 4
Polybutylene succinate (95% by mass) and ketjen black (5% by mass) as conductive particles were mixed, and a slurry was prepared using dichloromethane as a solvent. The slurry was cast on a PET film and dried at 60 ° C. for 8 hours to prepare a resin current collector.

  A bipolar secondary battery was fabricated in the same manner as in Example 1 except that this resin current collector was used.

(Example 5)
A bipolar secondary battery was fabricated in the same manner as in Example 4 except that gold fine particles (average particle size: 15 nm) were used instead of ketjen black.

(Example 6)
Polybutylene succinate (47.5% by mass), polylactic acid (47.5% by mass), and ketjen black (5% by mass, average particle size: 30 nm) as conductive particles are mixed, and dichloromethane is used as a solvent. A slurry was prepared. The slurry was cast on a PET film and dried at 60 ° C. for 8 hours to prepare a resin current collector.

  A bipolar secondary battery was fabricated in the same manner as in Example 1 except that this resin current collector was used.

(Example 7)
A bipolar secondary battery was fabricated in the same manner as in Example 6 except that gold fine particles (average particle size: 15 nm) were used instead of ketjen black.

(Example 8)
Polylactic acid (95% by mass), ketjen black (2.5% by mass, average particle size: 30 nm) and SWCNT (2.5% by mass) as conductive particles are mixed, and a slurry is prepared using dichloromethane as a solvent. did. The slurry was cast on a PET film and dried at 60 ° C. for 8 hours to prepare a resin current collector.

  A bipolar secondary battery was fabricated in the same manner as in Example 1 except that this resin current collector was used.

(Comparative example)
Polyethylene (95% by mass) and ketjen black (5% by mass, average particle size: 30 nm) were mixed to prepare a slurry using dichloromethane as a solvent. The slurry was cast on a PET film and dried at 60 ° C. for 8 hours to prepare a resin current collector.

  A bipolar secondary battery was fabricated in the same manner as in Example 1 except that this resin current collector was used.

(Evaluation 1: charge / discharge test)
A charge / discharge test was performed on each of the bipolar secondary batteries obtained in Examples and Comparative Examples. The test is a constant current charge (CC) up to 21.0 V with a current of 0.5 mA, then a constant voltage (CV), and a total of 10 hours, and then a 25-cycle endurance test with a discharge capacity of 1 C. Capacitance measurement was performed. The capacity after 25 cycles with respect to the capacity at the time of initial charge at that time was defined as the capacity retention rate.

(Evaluation 2: Calculation of surface free energy)
The contact angles of three probe liquids (water, diiodomethane, 1 bromonaphthalene) with known surface free energy and the resin current collector were measured. From the results, the interface interaction energies W ₁ , W ₂ , and W ₃ between the probe liquid and the resin current collector were obtained using the Young-Dupre equation (see Equation 1 below).

Here, γn represents the surface free energy of each probe liquid, and θn represents the contact angle. Further, by solving the ternary simultaneous equation obtained from the extended Fowkes equation (see the following equation 2), the surface energy dispersion force (van der Waals force) component γ ^d , dipole force component γ ^p , The hydrogen bonding force component γ ^h was determined.

Finally, the surface free energy of the resin current collector was obtained by the sum of three components, that is, γ = γ ^d + γ ^p + γ ^h .

  The evaluation results are shown in Table 1 below.

  In the bipolar secondary battery of the example, by using a resin current collector containing a biodegradable polymer, the surface free energy of the resin current collector is increased, and an electrode (electrolyte enters during charging / discharging). ) And the resin current collector became stronger. Therefore, the increase in resistance at the interface between the resin current collector and the electrode due to charge / discharge can be suppressed, and the capacity retention rate is improved.

  In the bipolar secondary battery of the comparative example, since the surface free energy of the resin current collector is small, the adhesive force between the electrode and the resin current collector is weakened, and the interface between the electrode and the resin current collector due to charge / discharge is reduced. Resistance increase was observed, and the capacity retention rate was reduced.

10a, 10b, 50 non-aqueous electrolyte secondary battery,
11 Current collector,
11a The outermost layer current collector on the positive electrode side,
11b The outermost layer current collector on the negative electrode side,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 power generation element,
23 Bipolar electrode,
25 positive current collector,
27 negative current collector,
29 Laminated film,
31 seal part,
52 Battery exterior material,
58 positive electrode tab,
59 Negative electrode tab.

Claims (4)

A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of the current collector, and a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the current collector include an electrolyte. A non-aqueous electrolyte secondary battery having a power generation element including a single battery layer laminated via a separator,
A non-aqueous electrolyte secondary battery, wherein the current collector includes a biodegradable polymer and conductive particles.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the biodegradable polymer is an aliphatic polyester.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the conductive particles are carbon particles or metal particles.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, which is a bipolar type.

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