JP2015095330A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which enables the suppression of the rise in battery resistance, and the achievement of a high level of safety.SOLUTION: A lithium ion secondary battery comprises a power-generating element including at least one unit cell layer arranged by laminating a positive electrode, an electrolytic layer including an electrolyte and a negative electrode in turn. The positive electrode includes: a collector; and a positive electrode active material layer formed on the surface of the collector and including a positive electrode active material. The negative electrode includes: a collector; and a negative electrode active material layer formed on the surface of the collector and including a negative electrode active material. The positive electrode active material layer, the negative electrode active material layer, or the electrolytic layer includes a lithium hydrogencarbonate (LiHCO). The content of the lithium hydrogencarbonate is 3-14 mass% to the total mass of the electrolyte.

Description

  The present invention relates to a lithium ion secondary battery.

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

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

  A lithium ion secondary battery has a configuration in which a positive electrode and a negative electrode are connected via an electrolyte layer containing an electrolyte and stored in a battery case. The positive electrode or the negative electrode is generally formed by applying an active material slurry in which a positive electrode active material or a negative electrode active material and a binder are dispersed in a solvent to the surface of a current collector.

  Examples of the positive electrode active material of such a lithium ion secondary battery include lithium-transition metals such as lithium-nickel composite oxide, lithium-manganese composite oxide, lithium-cobalt composite oxide, and lithium-iron composite oxide. A composite oxide or the like can be used. Among these, lithium-nickel composite oxides are particularly suitable for motor-driven secondary batteries because of their excellent reactivity and cycle characteristics and low cost, and their practical application is expected.

  By the way, various technologies for ensuring safety at the time of an internal short circuit have been proposed for practical application of lithium ion secondary batteries. For example, Patent Document 1 proposes a technique in which a temperature-decreasing substance or a combustion-suppressing substance enclosed in a polymer resin capsule that melts at a predetermined temperature is mixed into an electrolyte of a lithium ion secondary battery. . According to this technology, the polymer resin capsule melts at a high temperature, and the temperature-decreasing substance or the combustion-suppressing substance enclosed therein diffuses into the electrolyte, thereby reducing the temperature of the battery or suppressing the combustion. It can be done.

Japanese Patent Laid-Open No. 10-340739

  However, the technique described in Patent Document 1 has a problem that the resistance of the battery increases because the polymer resin capsule is mixed in the electrolytic solution.

  Therefore, an object of the present invention is to provide a highly safe lithium ion secondary battery in which an increase in battery resistance is suppressed.

The lithium ion secondary battery of the present invention has a power generation element including at least one unit cell layer in which a positive electrode, an electrolyte layer containing an electrolytic solution, and a negative electrode are sequentially stacked. The positive electrode is formed by forming a positive electrode active material layer containing a positive electrode active material on the surface of the current collector, and the negative electrode is formed by forming a negative electrode active material layer containing a negative electrode active material on the surface of the current collector. And a positive electrode active material layer, a negative electrode active material layer, or an electrolyte layer contains lithium hydrogen carbonate (LiHCO ₃ ), and the content of the lithium hydrogen carbonate is ₃ to 14% by mass with respect to the total mass of the electrolytic solution. It is characterized by a certain point.

According to the present invention, when lithium hydrogen carbonate is contained in the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer, the lithium hydrogen carbonate is thermally decomposed and water (H ₂ ) when the battery becomes high temperature. O) is generated. When the water hydrolyzes the supporting salt in the electrolytic solution, the concentration of the supporting salt in the electrolytic solution is reduced, and an increase in battery temperature can be suppressed. And by making content of the said lithium hydrogen carbonate into 3-14 mass% with respect to the total mass of electrolyte solution, the temperature rise inhibitory effect of a desired battery can be exhibited, suppressing a raise of battery resistance. It is possible to provide a highly safe lithium ion secondary battery.

1 is a cross-sectional view schematically showing an overall structure of a lithium ion secondary battery that is not a flat type (stacked type) bipolar type according to an embodiment of the present invention. It is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios. In the present specification, “X to Y” indicating a range means “X or more and Y or less”, and “weight” and “mass”, “wt%” and “mass%”, “part by weight” and “ “Part by mass” is treated as a synonym.

  FIG. 1 is a cross-sectional view schematically showing the overall structure of a lithium ion secondary battery that is not a flat type (stacked type) bipolar type according to an embodiment of the present invention. The lithium ion secondary battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 22 that is a battery exterior material. Specifically, the power generation element 17 is housed and sealed by using a polymer-metal composite laminate film as a battery exterior material and joining all of its peripheral parts by thermal fusion.

  The power generation element 17 includes a negative electrode in which the negative electrode active material layer 12 is disposed on both sides of the negative electrode current collector 11 (only one side for the lowermost layer and the uppermost layer of the power generation element), an electrolyte layer 13, and a positive electrode current collector 14. And a positive electrode in which the positive electrode active material layer 15 is disposed on both sides. Specifically, the negative electrode, the electrolyte layer 13 and the positive electrode are laminated in this order so that one negative electrode active material layer 12 and the positive electrode active material layer 15 adjacent to the negative electrode active material layer 15 face each other with the electrolyte layer 13 therebetween. Yes.

  Thus, the adjacent negative electrode, electrolyte layer 13 and positive electrode constitute one single cell layer 16. Therefore, it can be said that the lithium ion secondary battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Further, a seal portion (insulating layer) (not shown) for insulating between the adjacent negative electrode current collector 11 and the positive electrode current collector 14 may be provided on the outer periphery of the unit cell layer 16. . The negative electrode active material layer 12 is disposed only on one side of the outermost layer negative electrode current collector 11 a located in both outermost layers of the power generation element 17. By reversing the arrangement of the negative electrode and the positive electrode, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 17, and the positive electrode active material layer is provided only on one side of the outermost layer positive electrode current collector. It may be arranged.

  The negative electrode current collector 11 and the positive electrode current collector 14 are respectively attached with a negative electrode current collector plate (negative electrode tab) 18 and a positive electrode current collector plate (positive electrode tab) 19 that are electrically connected to the respective electrodes (negative electrode and positive electrode). It has a structure led out of the laminate film 22 so as to be sandwiched between the end portions of the film 22. The negative electrode current collector plate (negative electrode tab) 18 and the positive electrode current collector plate (positive electrode tab) 19 are connected to the negative electrode current collector 11 and the positive electrode current collector of each electrode via a negative electrode terminal lead 20 and a positive electrode terminal lead 21 as necessary. The body 14 may be attached by ultrasonic welding or resistance welding. However, the negative electrode current collector 11 may be extended to form a negative electrode current collector plate (negative electrode tab) 18 and may be led out from the laminate film 22. Similarly, the positive electrode current collector 14 may be extended to form a positive electrode current collector plate (positive electrode tab) 19, and may be similarly derived from the battery exterior material 22.

  Here, the embodiment of the present invention has been described by taking as an example a lithium ion secondary battery that is not a flat (stacked) bipolar type, but the types of lithium ion secondary batteries to which the present invention can be applied are particularly Not limited. For example, in a power generation element, a bipolar electrode having a positive electrode active material layer formed on one surface of a current collector and a negative electrode active material layer formed on the other surface is laminated via an electrolyte layer (single cell layer). It is also applicable to a so-called bipolar lithium ion secondary battery of a type in which are connected in series. Hereinafter, each component of the lithium ion secondary battery of this embodiment will be described.

[Current collector]
The current collector is made of a conductive material, and an active material layer is disposed on the surface of the current collector to form a battery electrode. Although there is no restriction | limiting in particular in the material which comprises a collector, For example, a metal and resin which has electroconductivity can be employ | adopted.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. 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, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material by sputtering to the current collector.

  Examples of the latter resin having conductivity include a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material as necessary. Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin.

  The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

  The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  Note that the current collector of this embodiment may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include a conductive resin layer made of at least a conductive resin. Further, from the viewpoint of blocking the movement of lithium ions between the unit cell layers, a metal layer may be provided on a part of the current collector.

[Electrode active material layer]
The lithium ion secondary battery of this embodiment essentially includes an active material, and may further include additives such as a conductive additive and a binder as necessary.

(Active material)
The active material occludes and releases ions during charge and 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 electrode active material layer of this embodiment functions as a positive electrode active material layer when a positive electrode active material is used as the active material, and conversely 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. Among these, from the viewpoint of battery capacity, it is preferable to include at least one lithium-nickel composite oxide containing lithium and nickel and having a layered structure as the positive electrode active material. More preferably, Li (Ni—Mn—Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter also simply referred to as “NMC composite oxide”) are used.

The lithium-nickel composite oxide includes not only a composite oxide containing only lithium and nickel as metal elements, but also a composite oxide in which a part of Ni is substituted with an element such as Co, Mn, and Al. Specific examples of such a lithium-nickel composite oxide include LiNiO ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.9 Al _{0. 1} O _{2 and the} like are exemplified.

  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 contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that 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, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

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 Co, d represents the atomic ratio of Mn, 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.

In a more preferred embodiment, in the general formula (1), b, c and d are 0.49 ≦ b ≦ 0.51, 0.29 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.21. 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 to the above, the capacity per unit weight is large, and the energy density can be improved, so that a battery having a compact and high capacity can be produced, which is preferable from the 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.

(Conductive aid)
A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive auxiliary agent include carbon materials such as carbon black such as ketjen black and acetylene black, graphite, and carbon fiber. 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.

(Binder)
The binder has a function of holding the structure of the electrode 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 electrode active material layer containing a negative electrode active material, it is preferable that a water-system 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 type resins (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, 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 weight ratio between 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 weight, preferably 90 to 100% by weight, and preferably 100% by weight 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 is preferably 0.5 to 15% by mass with respect to the active material, and more preferably 1 -10 mass%.

[Electrolyte layer]
Although there is no restriction | limiting in particular in the electrolyte used for the electrolyte layer of this form, From a viewpoint of ensuring the ionic conductivity of an electrode active material layer, a liquid electrolyte, a gel polymer electrolyte, and an ionic liquid electrolyte are used.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte that constitutes the electrolyte layer has a form in which a lithium salt that is a supporting salt is dissolved in an organic solvent that is 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 6, LiCF 3 SO 3, LiBF ₃ (C ₂ F ₅ ) and other compounds may be 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 amount of the liquid electrolyte contained in the lithium ion secondary battery of this embodiment is not particularly limited and can be appropriately set by those skilled in the art. In general, the amount of the liquid electrolyte is 1.0 to 2.5 times, preferably 1.5 to 2.0 times the capacity of all the holes in the battery. Further, the content of the supporting salt in the liquid electrolyte is not particularly limited, but is usually 0.5 to 2.0M, preferably 0.7 to 1.8M, more preferably 0.8 to 1. .2M.

  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 ⁻ ), trifluoromethane sulfonate 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.

  In the lithium ion secondary battery of this embodiment, 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 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 separator is preferably a separator (heat-resistant insulating layer-attached separator) in which a heat-resistant insulating layer is laminated on a porous substrate. The heat resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a highly heat-resistant separator having a melting point or a heat softening point of 150 ° C. or higher, preferably 200 ° C. or higher is used. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the battery manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

The inorganic particles in the heat resistant insulating layer contribute to the mechanical strength and heat shrinkage suppressing effect of the heat resistant insulating layer. The material used as the inorganic particles is not particularly limited. Examples thereof include silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. Moreover, only 1 type may be used individually for these inorganic particles, and 2 or more types may be used together. Of these, silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) is preferably used, and alumina (Al ₂ O ₃ ) is more preferably used from the viewpoint of cost.

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . If it is this range, sufficient ion conductivity will be acquired and it is preferable at the point which maintains heat resistant strength.

  The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles or the inorganic particles and the resin porous substrate layer. By the binder, the heat resistant insulating layer is stably formed, and peeling between the porous substrate layer and the heat resistant insulating layer is prevented.

  The binder used for the heat-resistant insulating layer is not particularly limited. For example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber A compound such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or methyl acrylate can be used as the binder. Of these, carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. As for these compounds, only 1 type may be used independently and 2 or more types may be used together.

  The binder content in the heat resistant insulating layer is preferably 2 to 20% by weight with respect to 100% by weight of the heat resistant insulating layer. When the binder content is 2% by weight or more, the peel strength between the heat-resistant insulating layer and the porous substrate layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by weight or less, the gap between the inorganic particles is appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The thermal contraction rate of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour at 150 ° C. and ² gf / cm ² . By using such a material having high heat resistance, it is possible to effectively prevent the separator from contracting even if the positive electrode heat generation amount increases and the battery internal temperature reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise.

[Lithium hydrogen carbonate]
The lithium ion secondary battery of this embodiment is characterized in that the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer contains lithium hydrogen carbonate. By including the lithium hydrogen carbonate in the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer, even when the temperature of the lithium ion secondary battery is increased, the heat generation of the electrolyte is suppressed, Safety can be ensured.

It has been confirmed that lithium hydrogen carbonate thermally decomposes into carbon dioxide (CO ₂ ), water (H ₂ O), and lithium oxide (Li ₂ O) at a temperature of 170 ° C. or higher. The thermal decomposition temperature of lithium hydrogen carbonate (about 170 ° C.) is lower than the decomposition temperature of the electrolyte (about 230 ° C.). Therefore, when the battery temperature rises due to an internal short circuit or the like, first, thermal decomposition of lithium hydrogen carbonate occurs at around 170 ° C., and water is generated. The supporting salt is hydrolyzed by the water. The hydrolysis reaction when the supporting salt is LiPF ₆ is as follows.

  Due to the hydrolysis reaction as described above, the concentration of the supporting salt in the electrolytic solution is reduced, so that the progress of the chemical reaction in the battery is suppressed. As a result, since heat generation of the electrolyte can be suppressed, a highly safe lithium ion secondary battery can be obtained.

  In this embodiment, the lithium hydrogen carbonate may be present in at least part of the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer. For example, any one of the positive electrode active material layer, the negative electrode active material layer, and the electrolyte solution It may exist only in a part or may exist throughout them. Further, when the battery has a plurality of unit cell layers, lithium hydrogen carbonate may be present in at least one unit cell layer, may be present only in some unit cell layers, or all unit cell layers. However, in order to suppress more effective heat generation, it is preferable that lithium hydrogen carbonate exists in all unit cell layers.

  A preferable form includes a form in which lithium hydrogen carbonate is present on at least a part of the surface of the positive electrode active material. In other words, the lithium hydrogen carbonate preferably covers at least a part of the surface of the positive electrode active material. When a lithium-transition metal composite oxide such as a lithium-nickel composite oxide, which is a positive electrode active material, is exposed to air, the surface reacts with water and carbon dioxide in the air as shown in the following formula, and lithium hydrogen carbonate is formed on the surface. A coating containing can be formed.

  By manufacturing a battery using such a positive electrode active material on which a coating containing lithium hydrogen carbonate is formed, it is not necessary to separately perform a process for incorporating a mechanism for suppressing the temperature rise of the battery. As a result, it is possible to provide a highly safe lithium ion secondary battery while suppressing a decrease in production efficiency and an increase in cost.

  In this embodiment, the content of lithium hydrogen carbonate is 3 to 14% by mass, preferably 4 to 13% by mass, and more preferably 6 to 11% by mass with respect to the total mass of the electrolytic solution. When the lithium hydrogen carbonate content is 3% by mass or more, an increase in battery temperature can be effectively suppressed, and when the content is 14% by mass or less, an increase in battery resistance can be suppressed (battery). The rate of increase in resistance can be suppressed to about 10% or less).

  Moreover, the content of the lithium hydrogen carbonate is preferably 1.3 to 4.3% by mass, and more preferably 2.0 to 3.7% by mass with respect to the total amount of the active material. When the content of the lithium hydrogen carbonate is 1% by mass or more, an increase in battery temperature can be effectively suppressed, and when it is 5% by mass or less, an increase in battery resistance can be suppressed.

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

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and leaking electricity. It is preferable to coat with a tube or the like.

[Battery exterior]
As the battery outer case 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation 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. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily and it is easy to adjust to the desired electrolyte layer thickness, the exterior body is more preferably an aluminate laminate.

[Cell size]
FIG. 3 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery.

  As shown in FIG. 3, the 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 are drawn out from both sides thereof. Yes. The power generation element 57 is wrapped by a battery exterior material (laminate film 52) of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. Sealed. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 illustrated in FIG. 2 described above. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

  The lithium ion secondary battery is not limited to a stacked flat shape. 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.

  Also, the removal of the tabs 58 and 59 shown in FIG. 3 is not particularly limited. The negative electrode tab 58 and the positive electrode tab 59 may be drawn out from the same side, or the negative electrode tab 58 and the positive 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).

  In a general electric vehicle, the battery storage space is about 170L. Since auxiliary devices such as cells and charge / discharge control devices are stored in this space, the storage efficiency of a normal cell is about 50%. The efficiency of loading cells into this space is a factor that governs the cruising range of electric vehicles. If the size of the single cell is reduced, the loading efficiency is impaired, so that the cruising distance cannot be secured.

  Therefore, in the present invention, the battery structure in which the power generation element is covered with the exterior body is preferably large. Specifically, the length of the short side of the laminated cell battery is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the laminated cell battery refers to the side having the shortest length. The upper limit of the short side length is not particularly limited, but is usually 400 mm or less.

[Volume energy density and rated discharge capacity]
In a general electric vehicle, a travel distance (cruising range) by a single charge is 100 km. Considering such a cruising distance, the volume energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Wh or more.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, the ratio of the battery area (projected area of the battery including the battery outer package) to the rated capacity is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. In some batteries, the battery area per unit capacity is large. Therefore, the problem of deterioration of battery characteristics (cycle characteristics) caused by the collapse of the crystal structure accompanying expansion and contraction of the active material is more likely to become apparent. Therefore, it is preferable that the lithium ion secondary battery according to the present embodiment is a battery having a large size as described above, from the viewpoint that the merit due to the manifestation of the effects of the present invention is greater. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both required vehicle performance and mounting space can be achieved.

[Battery]
The assembled battery is configured by connecting a plurality of 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.

  A plurality of batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The lithium ion secondary battery of the present invention maintains the discharge capacity even when used for a long time, and has good cycle characteristics. Furthermore, the volume energy density and the volume output density are high, and Dr. Ann is excellent. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the lithium ion secondary battery can be suitably used as a vehicle power source, for example, as a vehicle driving power source or an auxiliary power source.

  Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a battery having a long life with excellent safety, long-term reliability and output characteristics can be configured, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV mileage or a long charge mileage is charged. An electric vehicle can be configured. For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. 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.

The invention is explained in more detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples.

[Example 1]
LiNiO ₂ and a conductive additive were mixed at a mass ratio of 95: 5 to form a test electrode (φ13), and a coin cell was produced using Li foil (φ14) as a counter electrode. An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (3: 7) was used. After the charged coin cell was disassembled in an Ar atmosphere, the test electrode (LiNiO ₂ electrode) was taken out, and the electrode powder was subjected to differential scanning calorimetry (DSC) in the presence of an electrolytic solution. A pressure-resistant sealed measuring vessel was used for the measurement. The electrode powder was 1 mg and the electrolyte solution was 0.5 mg. The DSC measurement was performed from room temperature to 400 ° C. When the total calorific value (room temperature to 400 ° C.) when using an electrolytic solution to which no lithium hydrogen carbonate is added is 1 (blank), and an electrolytic solution in which 10% by mass of lithium hydrogen carbonate is added to the amount of the electrolytic solution is used. The change rate of the total calorific value (room temperature to 400 ° C.) was determined. Moreover, the electrolyte solution which added lithium hydrogencarbonate 10 mass% with respect to IR (cell voltage 4.2V, electric current value 2mA) (blank) of the coin cell produced using the electrolyte solution which does not add lithium hydrogen carbonate with respect to the amount of electrolyte solution The rate of increase in IR (cell voltage 4.2 V, current value 2 mA) was determined as a percentage [%]. IR was calculated from ΔV when a current was passed for 1 second.

[Comparative Example 1]
LiNiO ₂ and a conductive additive were mixed at a mass ratio of 95: 5 to form a test electrode (φ13), and a coin cell was produced using Li foil (φ14) as a counter electrode. An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (3: 7) was used. After the charged coin cell was disassembled in an Ar atmosphere, the test electrode (LiNiO ₂ electrode) was taken out, and the electrode powder was subjected to differential scanning calorimetry (DSC) in the presence of an electrolytic solution. A pressure-resistant sealed measuring vessel was used for the measurement. The electrode powder was 1 mg and the electrolyte solution was 0.5 mg. The DSC measurement was performed from room temperature (25 ° C.) to 400 ° C. When the total calorific value (room temperature to 400 ° C.) when using an electrolytic solution to which no lithium hydrogen carbonate is added is 1 (blank), and an electrolytic solution in which 2% by mass of lithium hydrogen carbonate is added to the amount of the electrolytic solution is used. The change rate of the total calorific value (room temperature to 400 ° C.) was determined.

[Comparative Example 2]
LiNiO ₂ and a conductive additive were mixed at a mass ratio of 95: 5 to form a test electrode (φ13), and a coin cell was produced using Li foil (φ14) as a counter electrode. An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (3: 7) was used. After the charged coin cell was disassembled in an Ar atmosphere, the test electrode (LiNiO ₂ electrode) was taken out, and the electrode powder was subjected to differential scanning calorimetry (DSC) in the presence of an electrolytic solution. A pressure-resistant sealed measuring vessel was used for the measurement. The electrode powder was 1 mg and the electrolyte solution was 0.5 mg. The DSC measurement was performed from room temperature to 400 ° C. For the coin cell IR (cell voltage 4.2 V, current value 2 mA) (blank) when using an electrolytic solution to which no lithium hydrogen carbonate is added, an electrolytic solution in which 20% by mass of lithium hydrogen carbonate is added to the amount of the electrolytic solution is used. The increase rate of IR (cell voltage 4.2 V, current value 2 mA) was calculated as a percentage [%]. IR was calculated from ΔV when a current was passed for 1 second.

[Comparative Example 3]
A mixture of LiNiO ₂ and a conductive additive at a mass ratio of 95: 5 mixed with 4% by mass of a capsule (0.1 μm) with respect to the mass of the positive electrode is used as the test electrode (φ13), and the Li electrode (φ14) is used as the counter electrode. The coin cell was produced using. An electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (3: 7) was used. IR (cell voltage 4.2V, current value 2 mA) when 4% by mass of capsule is added to the positive electrode mass relative to IR (cell voltage 4.2V, current value 2 mA) (blank) of the coin cell when the capsule is not mixed The rate of increase was calculated as a percentage [%].

  The results are shown in the table below.

As can be seen from the above table, Example 1 in which 10% by mass of lithium hydrogen carbonate was added to the electrolytic solution was able to exhibit a sufficient calorific value suppression effect while suppressing the IR increase rate to 8%. Indicated. As the temperature rises, lithium hydrogen carbonate is thermally decomposed to generate water (H ₂ O), and the supporting salt concentration in the electrolytic solution is reduced by hydrolyzing the supporting salt in the electrolytic solution, This was considered to be because the temperature rise of the battery was suppressed.

  On the other hand, Comparative Example 1 in which 2% by mass of lithium hydrogen carbonate was added to the electrolytic solution was not sufficient in suppressing the calorific value. In Comparative Example 2 in which 20% by mass of lithium hydrogen carbonate was added, the IR increase rate was 21%, and a significant increase in battery resistance was observed. Furthermore, Example 3 in which capsules were mixed in the electrolyte also had an IR increase rate of 15%, indicating that sufficient battery performance could not be maintained.

  From the above results, it was shown that the present invention provides a highly safe lithium ion secondary battery that can exert the effect of suppressing the temperature rise of a desired battery while suppressing an increase in battery resistance. .

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
11a outermost layer negative electrode current collector,
12 negative electrode active material layer,
13 electrolyte layer,
14 positive electrode current collector,
15 positive electrode active material layer,
16 cell layer,
17, 57 Power generation element,
18, 58 Negative electrode current collector (negative electrode tab),
19, 59 positive current collector (positive electrode tab),
20 Negative terminal lead,
21 positive terminal lead,
22, 52 Laminated film.

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;
An electrolyte layer containing an electrolyte solution;
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;
In a lithium ion secondary battery having a power generation element including at least one single battery layer that is sequentially stacked,
The positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer contains lithium hydrogen carbonate,
Content of the said lithium hydrogen carbonate is a lithium ion secondary battery which is 3-14 mass% with respect to the total mass of the said electrolyte solution.   2. The lithium ion secondary battery according to claim 1, wherein a content of the lithium hydrogen carbonate is 4 to 13 mass% with respect to a total mass of the electrolytic solution.   The lithium ion secondary battery according to claim 1 or 2, wherein the lithium hydrogen carbonate is present on at least a part of a surface of the positive electrode active material.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material includes a lithium-nickel composite oxide.