JP6506499B2 - Lithium ion secondary battery - Google Patents

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 is strongly desired. In the automobile industry, there are high hopes for reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and development of motor drive secondary batteries that hold the key to their practical use is thriving It has been done.

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

  The 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, on the surface of a current collector.

  As a positive electrode active material of such a lithium ion secondary battery, for example, a lithium-transition metal such as lithium-nickel complex oxide, lithium-manganese complex oxide, lithium-cobalt complex oxide, lithium-iron complex oxide, etc. Complex oxides and the like can be used. Among these, lithium-nickel composite oxide is particularly suitable for a motor drive secondary battery because of its excellent reactivity and cycle characteristics and low cost, and its practical application is expected.

  By the way, various technologies for securing safety at the time of an internal short circuit are proposed towards practical use of a lithium ion secondary battery. For example, Patent Document 1 proposes a technique in which a substance in which a temperature decreasing substance or a combustion suppressing substance is sealed in a polymer resin capsule which is melted at a predetermined temperature is mixed in an electrolyte solution of a lithium ion secondary battery . According to the related art, the polymer resin capsule is melted at high temperature, and the temperature-lowering substance or the combustion suppressing substance encapsulated therein diffuses into the electrolyte, thereby lowering the temperature of the battery or suppressing the combustion. Can be

JP 10-340739 A

  However, in the technology described in Patent Document 1, there is 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 laminated. The positive electrode has a positive electrode active material layer containing a positive electrode active material formed on the surface of a current collector, and the negative electrode has a negative electrode active material layer containing a negative electrode active material formed on the surface of a current collector. The positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer contains lithium hydrogen carbonate (LiHCO ₃ ), and the content of lithium hydrogen carbonate is ₃ to 14% by mass with respect to the total mass of the electrolytic solution. It has a feature at a certain point.

According to the present invention, lithium hydrogencarbonate is thermally decomposed to contain water (H ₂ ) when the temperature of the battery becomes high by containing lithium hydrogencarbonate in the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer. O) Generate. When the water hydrolyzes the support salt in the electrolytic solution, the concentration of the support salt in the electrolytic solution decreases, and the temperature rise of the battery can be suppressed. And, by setting the content of the lithium hydrogen carbonate to 3 to 14 mass% with respect to the total mass of the electrolytic solution, it is possible to exhibit a desired battery temperature rise suppressing effect while suppressing an increase in battery resistance. It is possible to provide a highly safe lithium ion secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which represented typically the whole structure of the flat type (stacked type) non-bipolar type lithium ion secondary battery which concerns on one Embodiment of this invention. FIG. 1 is a perspective view showing the appearance of a flat lithium ion secondary battery according to a representative embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional proportions of the drawings are exaggerated for the convenience of the description, and may differ from the actual proportions. Further, in the present specification, “X to Y” indicating a range means “X or more and Y or less”, and “weight” and “mass”, “weight%” and “mass%” and “weight part” and “ Parts by mass are treated as synonyms.

  FIG. 1 is a cross-sectional view schematically showing the entire structure of a flat (stacked) non-dipolar lithium ion secondary battery 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 generating element 17 in which the charge / discharge reaction actually proceeds is sealed inside a laminate film 22 which is a battery exterior material. In detail, 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 the peripheral portions by heat fusion.

  The power generation element 17 has 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 surface for the lowermost layer and the top layer for the power generation element), the electrolyte layer 13, and the positive electrode current collector 14. And the positive electrode in which the positive electrode active material layer 15 is disposed on both sides of the Specifically, the negative electrode, the electrolyte layer 13 and the positive electrode are stacked in this order so that one negative electrode active material layer 12 and the positive electrode active material layer 15 adjacent thereto face each other through the electrolyte layer 13. There is.

  Thus, the adjacent negative electrode, the electrolyte layer 13 and the positive electrode constitute one unit 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 unit cell layers 16 are stacked and electrically connected in parallel. In addition, a seal portion (insulating layer) (not shown) for insulating between the adjacent negative electrode current collector 11 and positive electrode current collector 14 may be provided on the outer periphery of the unit cell layer 16. . In each of the outermost negative electrode current collectors 11 a located in both outermost layers of the power generation element 17, the negative electrode active material layer 12 is disposed on only one side. The outermost layer positive electrode current collectors are positioned on both outermost layers of the power generation element 17 by reversing the arrangement of the negative electrode and the positive electrode, and the positive electrode active material layer is formed on only one side of the outermost layer positive electrode current collector. It may be arranged.

  A negative electrode current collector plate (negative electrode tab) 18 and a positive electrode current collector plate (positive electrode tab) 19 electrically connected to the respective electrodes (negative electrode and positive electrode) are attached to the negative electrode current collector 11 and the positive electrode current collector 14, respectively. It has a structure led to the outside of the laminate film 22 so as to be sandwiched by the end 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, if necessary, the negative electrode current collector 11 and positive electrode current collector of each electrode via the negative electrode terminal lead 20 and the positive electrode terminal lead 21. 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 derived 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 led out from the battery case 22.

  Although the embodiment of the present invention has been described by taking the flat (stacked) non-bipolar lithium ion secondary battery as an example, the type of lithium ion secondary battery to which the present invention can be applied is particularly It is not restricted. 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 battery layer Can also be applied to so-called bipolar lithium ion secondary batteries of the type in which Hereinafter, each component of the lithium ion secondary battery of the present 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 an electrode of the battery. 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, as the metal, aluminum, nickel, iron, stainless steel, titanium, copper and the like can be mentioned. Besides these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plated material of a combination of these metals can be preferably used. In addition, it may be a foil in which a metal surface is coated with aluminum. Among them, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electron conductivity, battery operation potential, adhesion of the negative electrode active material by sputtering to a current collector, and the like.

  Moreover, as a resin which has the latter electroconductivity, the resin in which the electroconductive filler was added as needed to the electroconductive polymeric material or the nonelectroconductive polymeric material is mentioned. Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Such a conductive polymer material has sufficient conductivity even without the addition of a conductive filler, and thus is advantageous in facilitating the manufacturing process or reducing the weight of the current collector.

  As the nonconductive polymer material, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide imide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) And polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent voltage or solvent resistance.

  A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material as required. In particular, when the resin to be the base of the current collector is made of only a non-conductive polymer, the conductive filler is necessarily essential 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 and the like can be mentioned as materials excellent in conductivity, potential resistance, or lithium ion blocking properties. 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 a metal thereof Preferably, it contains an alloy or a metal oxide. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it contains at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofibers, ketjen black, carbon nanotubes, carbon nanohorns, carbon nanoballoons, and fullerenes.

  The amount of the conductive filler added is not particularly limited as long as it can impart 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 formed of a single material, or may have a stacked structure in which layers formed 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 unit cell layers, a metal layer may be provided on part of the current collector.

[Electrode active material layer]
The lithium ion secondary battery of the present embodiment essentially contains an active material, and may further contain an additive such as a conductive aid and a binder as required.

(Active material)
The active material occludes and releases ions during charge and discharge to generate electrical energy. Active materials include a positive electrode active material having a composition that occludes ions during discharge and releases ions during charge, and a negative electrode active material having a composition capable of releasing ions during discharge and occluding ions during charge. The electrode active material layer of this embodiment functions as a positive electrode active material layer when using a positive electrode active material as an active material, and conversely functions as a negative electrode active material layer when using a negative electrode active material. In the present specification, matters common to the positive electrode active material and the negative electrode active material are simply described as “active material”.

As the positive electrode active material, for example, lithium such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Mn-Co) O ₂ and those in which a part of these transition metals is substituted by another element Transition metal complex oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds and the like can be mentioned. In some cases, two or more positive electrode active materials may be used in combination. Preferably, in view of capacity and output characteristics, a lithium-transition metal complex oxide is used as a positive electrode active material. Among them, from the viewpoint of battery capacity, it is preferable to contain at least one lithium-nickel composite oxide containing lithium and nickel and having a layered structure as a positive electrode active material. More preferably, Li (Ni-Mn-Co ) O 2 , and in which a part of these transition metals are replaced by other elements (hereinafter, simply referred to as "NMC composite oxide") is used.

The lithium-nickel composite oxide includes not only composite oxides containing only lithium and nickel as metal elements, but also composite oxides in which a part of Ni is substituted with an element such as Co, Mn, or Al. Specific examples of such 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 etc. are illustrated.

  The NMC complex oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are properly arranged) atomic layers are alternately stacked via an oxygen atomic layer, and one atom of a transition metal M One Li atom is contained, and the amount of Li that can be extracted is twice that of spinel lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

  As described above, the NMC composite oxide also includes composite oxides in which part of the transition metal element is replaced by another metal element. As other elements in that case, Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu And Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, Cr, and from the viewpoint of improving cycle characteristics, more preferably Ti, Zr, Al, Mg, Cr.

The NMC composite oxide preferably has a general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (wherein, a, b, c, d, x) because the theoretical discharge capacity is high. A 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. At least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr). Here, a represents an atomic ratio of Li, b represents an atomic ratio of Ni, c represents an atomic ratio of Co, d represents an atomic ratio of Mn, and x represents an atomic ratio of M. Represents From the viewpoint of cycle characteristics, in the general formula (1), it is preferable that 0.4 ≦ b ≦ 0.6. The composition of each element can be measured, for example, by inductively coupled plasma (ICP) emission analysis.

  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 the material and the electron conductivity. Ti and the like partially replace transition metals in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted by another metal element, and in particular in the general formula (1), it is preferable that 0 <x ≦ 0.3. The crystal structure is stabilized by solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr, and as a result, charge and discharge It is considered that the battery capacity can be prevented from being reduced even by repeating the above, and excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d satisfy 0.49 ≦ b ≦ 0.51, 0.29 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.21. Is preferable from the viewpoint of improving the balance between the capacity and the 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., which are proven in common consumer batteries. As compared with the above, it has an advantage that the capacity per unit weight is large and the energy density can be improved so that a compact and high capacity battery can be manufactured, which is preferable also from the viewpoint of the cruising distance. Although LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in that the capacity is larger, the life characteristics are difficult. 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 TiO, Ti ₂ O ₃ , TiO ₂ , or metal oxides such as SiO ₂ , SiO, SnO ₂ , Li _4/3 Ti _5/3 O ₄ or complex oxide of lithium and transition metal such as Li ₇ MnN, Li-Pb alloy, Li-Al alloy, Li, or graphite (natural graphite, artificial graphite), carbon black, activated carbon, carbon fiber, coke And carbon materials such as soft carbon and hard carbon. In addition, the negative electrode active material preferably contains an element which is alloyed with lithium. By using an element to be alloyed with lithium, it is possible to obtain a battery having a high energy density and a high output characteristic with a high energy density as compared with a carbon material. One of these negative electrode active materials may be used alone, or two or more thereof may be used in combination.

  In the case of using an active material other than the above carbon material (hereinafter also referred to as "non-carbon based active material"), the non-carbon based active material coated with a carbon material may be used as the active material preferable. According to such a configuration, a conductive network is constructed between the active materials or between the active material and the conductive support agent described later, and even when the active material having a large expansion and contraction is used, the conductivity in the electrode is obtained. You can secure the path. As a result, even when charge and discharge are repeated, it is possible to suppress an increase in resistance. More preferably, from the viewpoint of improving the energy density of the electrode, a material in which a material to be alloyed with high capacity lithium is coated with a carbon material is used as the active material. In this case, the amount of coating of the carbon material used is such an amount that the electrical contact between the active materials or between the active material and the conductive aid becomes good according to the particle diameter of the non-carbon active material (particles). 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, in addition to the form in which the entire surface of the active material is covered with the carbon material, “coating” also includes the form in which the carbon material is present (adhered) on part of the surface of the active material. It shall be

  The average particle size of the active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the capacity of the battery, reactivity, and cycle durability. Within such a range, an increase in internal resistance of the secondary battery during charge and discharge under high power conditions is suppressed, and a sufficient current can be extracted. When the active material is a secondary particle, it can be said that the average particle diameter of primary particles constituting the secondary particle is preferably in the range of 10 nm to 1 μm. It is not limited. However, it goes without saying that the active material may not be formed into secondary particles by aggregation, block formation, etc., although it depends on the production method. The particle size of such an active material and the particle size of primary particles can use the median diameter obtained by using a laser diffraction method. The shape of the active material differs depending on the type and manufacturing method, and examples thereof include, but are not limited to, spherical (powdery), plate-like, needle-like, columnar and angular shapes. Instead, it can be used without any problem in any shape. Preferably, it is desirable to appropriately select an optimal shape that can improve battery characteristics such as charge and discharge characteristics.

(Conduction agent)
The conductive aid refers to an additive compounded to improve the conductivity of the active material layer. Examples of the conductive additive 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 aid, a conductive network inside the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

(Binder)
The binder binds the active material, the conductive additive, and the like to each other, and has a function of holding the structure of the electrode active material layer and the conductive network. 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 to include a water-based binder. The water-based binder has high binding power, and it is easy to procure water as a raw material, and water is generated at the time of drying, so equipment investment in the production line can be greatly suppressed, and the environmental load Has the advantage of being able to reduce the

  The aqueous binder refers to a binder using water as a solvent or dispersion medium, and specifically, a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or the like, or a mixture thereof is applicable. Here, the binder using water as a dispersion medium refers to water and an emulsion or a polymer suspended in water including all expressed as a latex or an emulsion, for example, a polymer latex which is emulsion-polymerized by a system such as self-emulsification. And the like.

  Specific examples of the aqueous binder include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meth ) 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 Polyvinylpyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, saponification degree is preferably 80 Mol% or more, more preferably 90 mol% or more and its modified product (ethylene / vinyl acetate = 2/98 to 30/70 molar ratio of 1 to 80 mol% saponified vinyl acetate unit of the copolymer) , Polybi 1 to 50% by mole partially acetalized with alcohol), starch and its modified products (oxidized starch, phosphated starch, cationized starch etc.), cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, And their salts), polyvinyl pyrrolidone, polyacrylic acid (salt), polyethylene glycol, copolymers of (meth) acrylamide and / or (meth) acrylate [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, (meth) acrylate alkyl (C1-C4) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, Mannich of polyacrylamide Denatured body, Lumarin condensation resin (urea-formalin resin, melamine-formalin resin etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, and water-soluble polymer such as mannan galactan derivative etc. Can be mentioned. One of these aqueous binders may be used alone, or two or more of these aqueous binders may be used in combination.

  The water-based binder may include at least one rubber-based 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 aqueous binder contains a styrene-butadiene rubber because the binding property is good.

  When using a styrene-butadiene rubber as an aqueous binder, it is preferable to use the said water soluble polymer together from a viewpoint of a coating property improvement. Examples of water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and its modified product, starch and its modified product, cellulose derivatives (such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose and salts thereof), polyvinyl There may be mentioned pyrrolidone, polyacrylic acid (salt) or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethylcellulose (salt) as a binder. The content weight ratio of the styrene-butadiene rubber to the water-soluble polymer is not particularly limited, but it is preferable that styrene-butadiene rubber: water-soluble polymer = 1: 0.1 to 10, 0 It is more preferable that it is .5-2.

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

  The binder material other than the above aqueous binder is not particularly limited, but, for example, polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamide imide, 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 Copolymers and their hydrogenated substances, styrene / isoprene / styrene block copolymers and thermoplastic polymers such as their hydrogenated substances, polyvinylidene fluoride (PVdF), polyethers Lafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychloro Fluororesins such as trifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF) PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE) And vinylidene fluoride-based fluororubbers such as-TFE-based fluororubber) and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), epoxy resin and the like. Among them, 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, and furthermore, the potential window is very wide and stable to 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 or more.

  The content of the binder is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 15% by mass, more preferably 1 with respect to the active material. And 10% by mass.

[Electrolyte layer]
The electrolyte used in the electrolyte layer of the present embodiment is not particularly limited, but from the viewpoint of securing the ion conductivity of the electrode active material layer, a liquid electrolyte, a gel polymer electrolyte, or an ionic liquid electrolyte is used.

The liquid electrolyte has a function as a lithium ion carrier. The liquid electrolyte constituting the electrolyte layer has a form in which a lithium salt as a support salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent to be 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 Compounds such as ₃ (C ₂ F ₅ ) may be employed. The liquid electrolyte may further contain an additive other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate 1-Methyl-1-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-1-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyl Oxymethyl ethylene carbonate, Allyloxy methyl ethylene carbonate, Acryloxy methyl ethylene carbonate, Methane 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, methylvinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. One of these cyclic carbonates may be used alone, or two or more of these cyclic carbonates may be used in combination.

  The amount of the liquid electrolyte contained in the lithium ion secondary battery of the present embodiment is not particularly limited, and can be appropriately set by those skilled in the art. Generally, the amount of liquid electrolyte is 1.0 times to 2.5 times, preferably 1.5 times to 2.0 times, the volume of all pores in the battery. The content of the support salt in the liquid electrolyte is also not particularly limited, but is usually 0.5 to 2.0 M, preferably 0.7 to 1.8 M, and more preferably 0.8 to 1 .2M.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte described above 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 excellent in that the fluidity of the electrolyte is lost and the ion conductivity between the layers is easily cut off. As an ion conductive polymer used as a matrix polymer (host polymer), for example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA) and copolymers of these, etc. may be mentioned.

  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. may be performed on a polymerizable polymer (eg, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be applied.

  The ionic liquid electrolyte is one in which a lithium salt is dissolved in an ionic liquid. The ionic liquid is a salt composed of only a cation and an anion, and refers to a series of compounds which are liquid at normal temperature.

  The cationic 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 triatria Preferably, it is 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 fluoride ion, chloride ion, bromide ion, halide ion such as 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 ⁻ ), methane sulfone acid ion _{(CH 3} SO 3 ^-), trifluoromethanesulfonate ion _(CF 3 SO ₃ ^-), bis (trifluoromethanesulfonyl) imide ion _{((CF 3 SO 2) 2} N -), bis (pentafluoroethyl sulfonyl) imide ion ((C ₂ F ₅ SO ₂ ) ₂ N ⁻ ), BF ₃ C ₂ F ₅ ⁻ , Tris (trifluoromethanesulfonyl) carbonate 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 ⁻ (in this case, R ¹ is a substituent and is an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, And aromatic hydrocarbon groups, ether groups, ester groups, and acyl groups, and the aforementioned substituents may contain a fluorine atom) and the like.

  Examples of preferred ionic liquids include 1-methyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide, N-methyl-N-propyl pyrrolidinium bis (trifluoromethanesulfonyl) imide. One of these ionic liquids may be used alone, or two or more thereof may be used in combination.

  The lithium salt used for the ionic liquid electrolyte is similar to the lithium salt used for the above-mentioned liquid electrolyte. The concentration of the lithium salt is preferably 0.1 to 2.0 M, and more preferably 0.8 to 1.2 M.

  Further, the following additives may be added to the ionic liquid. By including the additive, charge and discharge characteristics at high rates and cycle characteristics can be further improved. Specific examples of the additive include, for example, vinylene carbonate, ethylene carbonate, propylene carbonate, γ-butyl lactone, γ-valerolactone, methyl diglyme, sulfolane, trimethyl phosphate, triethyl phosphate, methoxymethyl ethyl carbonate, A fluorinated ethylene carbonate etc. are mentioned. These may be used alone or in combination of two or more. The amount of the additive to be used is preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass, based on the ionic liquid.

  In the lithium ion secondary battery of this embodiment, a separator may be used in the electrolyte layer. The separator has a function of holding an electrolyte to secure lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition between the positive electrode and the negative electrode. In particular, in the case of using a liquid electrolyte as the electrolyte, it is preferable to use a separator.

  As a form of a separator, the separator of the porous sheet which consists of a polymer which absorbs and holds the said electrolyte, and a fiber, a nonwoven fabric separator, etc. can be mentioned, for example.

  As a separator of the porous sheet which consists of a polymer thru | or a fiber, microporous (microporous membrane) can be used, for example. Specific examples of the porous sheet comprising the polymer or fiber include, for example, polyolefins such as polyethylene (PE) and polypropylene (PP); laminates obtained by laminating a plurality of these (for example, three layers of PP / PE / PP) A microporous (microporous membrane) separator made of a structured laminate or the like), a hydrocarbon based resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, etc. may be mentioned.

  The thickness of the microporous (microporous membrane) separator can not be uniquely defined because it varies depending on the application. If one example is shown, in applications such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and motor-driven secondary batteries such as fuel cell vehicles (FCVs), it is 4 to 60 μm in single layer or multilayer Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is preferably at most 1 μm or less (usually a pore diameter of about several tens of nm).

  As the non-woven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefin such as PP, PE, etc .; polyimide, aramid and the like known in the prior art are used singly or in combination. The bulk density of the non-woven 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 non-woven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

  The separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (a separator with a heat-resistant insulating layer). The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the heat-resistant insulating layer-provided separator, a highly heat-resistant separator having a melting point or a heat softening point of 150 ° C. or more, preferably 200 ° C. or more is used. By having the heat-resistant insulating layer, the internal stress of the separator, which increases at the time of temperature rise, is relaxed, so that the thermal contraction suppressing effect can be obtained. As a result, since it is possible to prevent the induction of a short circuit between the electrodes of the battery, it becomes a battery configuration in which the performance decrease due to the temperature rise hardly occurs. Further, by having the heat-resistant insulating layer, the mechanical strength of the heat-resistant insulating layer-provided separator is improved, and breakage of the separator hardly occurs. Furthermore, due to the heat shrinkage suppressing effect and the high mechanical strength, the separator is less likely to curl in the battery manufacturing process.

The inorganic particles in the heat-resistant insulating layer contribute to the mechanical strength and the thermal contraction suppressing effect of the heat-resistant insulating layer. The material used as the inorganic particles is not particularly limited. Examples include oxides of silicon, aluminum, zirconium, titanium (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 of these inorganic particles may be used independently, and 2 or more types may be used together. Among these, from the viewpoint of cost, it is preferable to use silica (SiO ₂ ) or alumina (Al ₂ O ₃ ), and it is more preferable to use alumina (Al ₂ O ₃ ).

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 obtained and it is preferable at the point which maintains heat resistance.

  The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles and the inorganic particles and the resin porous substrate layer. By the binder, the heat-resistant insulating layer is stably formed, and the 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, carboxymethylcellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber Compounds such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), methyl acrylate and the like may be used as the binder. Among these, carboxymethyl cellulose (CMC), methyl acrylate or polyvinylidene fluoride (PVDF) is preferably used. One of these compounds may be used alone, or two or more may be used in combination.

  The content of the binder 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 content of the binder is 2% by weight or more, the peel strength between the heat-resistant insulating layer and the porous base layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the content of the binder is 20% by weight or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be secured.

The heat shrinkage ratio of the heat-resistant insulating layer-provided separator is preferably 10% or less for both MD and TD after holding at 150 ° C. and ² gf / cm ² for 1 hour. By using such a material having high heat resistance, it is possible to effectively prevent the contraction of the separator even if the heat generation amount of the positive electrode is increased and the internal temperature of the battery reaches 150 ° C. As a result, since it is possible to prevent the induction of a short circuit between the electrodes of the battery, it becomes a battery configuration in which the performance decrease due to the temperature rise hardly occurs.

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

It has been confirmed that lithium hydrogen carbonate is thermally decomposed into carbon dioxide (CO ₂ ), water (H ₂ O) and lithium oxide (Li ₂ O) at a temperature of 170 ° C. or higher. The lithium hydrogen carbonate thermal decomposition temperature (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. to generate water. The water hydrolyses the support salt. The hydrolysis reaction when the supporting salt is LiPF ₆ is as follows.

  By 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 electrolytic solution can be suppressed, it is possible to obtain a lithium ion secondary battery with high safety.

  In this embodiment, lithium hydrogen carbonate may be present in at least a part of the positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer, and, for example, any one of the positive electrode active material layer, the negative electrode active material layer, and the electrolytic solution It may be present only partially or may be present throughout them. When the battery has a plurality of unit cell layers, lithium hydrogen carbonate may be present in at least one unit cell layer, and may be present in only some unit cell layers, or all unit cell layers. However, in order to suppress heat generation more effectively, lithium hydrogen carbonate is preferably present in all unit cell layers.

  As a preferable form, a form in which lithium hydrogen carbonate is present on at least a part of the surface of the positive electrode active material can be mentioned. In other words, lithium hydrogen carbonate preferably covers at least a part of the surface of the positive electrode active material. When a lithium-transition metal complex oxide such as a lithium-nickel complex oxide as 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 hydrogencarbonate is formed on the surface A film containing can be formed.

  By manufacturing the battery using the positive electrode active material on which such a film containing lithium hydrogen carbonate is formed, it is not necessary to separately carry out the step of 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 the present 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 content of lithium hydrogen carbonate is 3% by mass or more, an increase in battery temperature can be effectively suppressed, and when it 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, content of the said lithium hydrogen carbonate is preferably 1.3-4.3 mass% with respect to the total amount of an active material, More preferably, it is 2.0-3.7 mass%. An increase in battery temperature can be effectively suppressed when the content of lithium hydrogen carbonate is 1% by mass or more, and an increase in battery resistance can be suppressed when the content is 5% by mass or less.

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

[Positive electrode lead and negative electrode lead]
Further, although not shown, the current collector 11 and the current collector plate (25, 27) may be electrically connected via the positive electrode lead or the 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 adopted. The heat-shrinkable heat-shrinkage so that the part taken out from the exterior does not affect products (for example, automobile parts, especially electronic equipment, etc.) by contacting peripheral devices, wiring, etc. and causing an electric leakage. It is preferable to coat with a tube or the like.

[Battery body]
As the battery outer package 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum, which can cover the power generation element, can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but it is not limited thereto. A laminate film is desirable from the viewpoint of being excellent in high output and cooling performance and being suitably usable for a battery for large-sized devices for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be easily adjusted and adjustment to the desired electrolyte layer thickness is easy, the outer package 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 a secondary battery.

  As shown in FIG. 3, the flat lithium ion secondary battery 50 has a rectangular flat shape, and positive and negative tabs 58 and 59 for extracting electric power are drawn from both sides thereof. There is. The power generation element 57 is wrapped by the battery exterior material (laminated film 52) of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed, and the power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. It is sealed tightly. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 2 described above. The power generation element 57 is formed by stacking a plurality of unit cell layers (single cells) 19 configured of the positive electrode (positive electrode active material layer) 15, the electrolyte layer 17, and the negative electrode (negative electrode active material layer) 13.

  In addition, the said lithium ion secondary battery is not restrict | limited to the thing of the laminated | stacked flat shape. The wound lithium ion secondary battery may have a cylindrical shape, or may have such a cylindrical shape deformed into a rectangular flat shape. There is no particular restriction. In the case of the cylindrical shape, a laminate film may be used as the exterior material, or a conventional cylindrical can (metal can) may be used, and the like, and is not particularly limited. Preferably, the power generation element is coated with an aluminum laminate film. Weight reduction can be achieved by the form.

  Also, the removal of the tabs 58 and 59 shown in FIG. 3 is not particularly limited. As shown in FIG. 3, 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 and taken out from each side. It is not limited to Further, in the wound type lithium ion battery, the terminal may be formed using, for example, a cylindrical can (metal can) instead of the tab.

  In a general electric vehicle, the battery storage space is about 170 liters. In order to store the cells and accessories such as charge / discharge control devices in this space, the storage space efficiency of the normal cells is about 50%. The loading efficiency of cells into this space is a factor that controls the range of the electric vehicle. If the size of the single cell is reduced, the loading efficiency is lost, and the cruising distance can not be secured.

  Therefore, in the present invention, the battery structure in which the power generation element is covered with the outer package is preferably large. Specifically, the length of the short side of the laminate cell battery is preferably 100 mm or more. Such large batteries can be used for vehicle applications. Here, the short side length of the laminate cell battery refers to the side with 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 the case of a general electric vehicle, the market requirement is 100 km for a single charge (running distance). In consideration of such a cruising distance, the volumetric energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Wh or more.

In addition, the size of the battery can also be defined from the relationship between the battery area and the battery capacity as a viewpoint of the size-increased battery, which is different from the viewpoint of the physical size of the electrode. For example, in the case of a flat laminate type laminated battery, the value of the ratio of the battery area (the 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 the deterioration of the battery characteristics (cycle characteristics) due to the collapse of the crystal structure accompanying the expansion and contraction of the active material is more likely to be 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, in that the merit due to 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 aspect ratio of the electrode is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio to such a range, there is an advantage that both the vehicle required performance and the mounting space can be compatible.

[Battery pack]
An assembled battery is a thing which connected and comprised two or more batteries. Specifically, at least two or more of them are used to constitute serialization and / or parallelization. By connecting in series and in parallel, it is possible to freely adjust the capacity and voltage.

  A plurality of cells can be connected in series or in parallel to form a compact battery pack that can be loaded and removed. Then, by connecting a plurality of such small detachable battery packs in series or in parallel, a large capacity suitable for a vehicle drive power source or an auxiliary power source requiring high volume energy density and high volume output density is required. An assembled battery having an output can also be formed. How many batteries are connected to make a battery pack, and how many small battery packs are stacked to produce a large capacity battery pack depends on the battery capacity of the vehicle (electric vehicle) and It should be decided according to the output.

[vehicle]
The lithium ion secondary battery of the present invention maintains its discharge capacity even after long-term use, and has excellent cycle characteristics. Furthermore, the volumetric energy density, the volumetric output density are high, and it is superior to Anne. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles and hybrid fuel cell vehicles, higher capacity and larger size are required compared with electric and portable electronic devices applications, and longer life is required. . Therefore, the lithium ion secondary battery can be suitably used as a vehicle power supply, for example, a vehicle drive power supply or an auxiliary power supply.

  Specifically, a battery or an assembled battery formed by combining a plurality of these can be mounted on a vehicle. In the present invention, since a battery with excellent safety, long-term reliability and output characteristics can be configured with a long life, a plug-in hybrid electric vehicle with a long EV travel distance or a long charge travel distance when such a battery is mounted It can constitute an electric car. For example, in addition to hybrid vehicles, fuel cell vehicles, and electric vehicles (all four-wheel vehicles (cars, trucks, buses, commercial vehicles such as cars, mini vehicles, etc.), etc. And a three-wheeled vehicle (including a two-wheeled vehicle (bicycle) and a three-wheeled vehicle), the vehicle has a long life and high reliability. However, the application is not limited to automobiles. For example, application is possible to various power supplies of other vehicles, for example, moving objects such as trains, and mounting power supplies such as uninterruptible power supplies It is also possible to use as.

The invention is further described in detail by means of the following examples. However, the technical scope of the present invention is not limited to the following examples.

Example 1
LiNiO ₂ and a conductive support agent 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 of 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-tight sealed measurement container was used for the measurement. The electrode powder was 1 mg, and the electrolyte was 0.5 mg. DSC measurement was performed from room temperature to 400.degree. The total calorific value (room temperature to 400 ° C) when using an electrolyte solution to which lithium hydrogen carbonate is not added is 1 (blank) and an electrolyte solution to which 10 mass% of lithium hydrogen carbonate is added based on the amount of the electrolyte is used The rate of change of the total calorific value (room temperature to 400 ° C.) was determined. In addition, an electrolytic solution in which lithium hydrogen carbonate is added at 10% by mass with respect to the amount of electrolytic solution with respect to IR (cell voltage 4.2 V, current value 2 mA) (blank) of coin cell manufactured using the electrolytic solution to which lithium hydrogen carbonate is not added The percentage of increase in IR (cell voltage 4.2 V, current value 2 mA) was calculated as a percentage [%]. In addition, IR was computed from (DELTA) V when an electric current was sent for 1 second.

Comparative Example 1
LiNiO ₂ and a conductive support agent 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 of 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-tight sealed measurement container was used for the measurement. The electrode powder was 1 mg, and the electrolyte was 0.5 mg. DSC measurement was performed from room temperature (25 ° C.) to 400 ° C. The total calorific value (room temperature to 400 ° C) when using an electrolyte solution to which lithium hydrogen carbonate is not added is 1 (blank) and an electrolyte solution to which 2 mass% of lithium hydrogen carbonate is added with respect to the amount of electrolyte solution is used The rate of change of the total calorific value (room temperature to 400 ° C.) was determined.

Comparative Example 2
LiNiO ₂ and a conductive support agent 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 of 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-tight sealed measurement container was used for the measurement. The electrode powder was 1 mg, and the electrolyte was 0.5 mg. DSC measurement was performed from room temperature to 400.degree. Use of an electrolyte solution in which lithium hydrogen carbonate is added at 20% by mass with respect to the amount of electrolyte with respect to IR (cell voltage 4.2 V, current value 2 mA) (blank) of coin cell in the case of using electrolyte without addition of lithium hydrogen carbonate The rate of increase of IR (cell voltage 4.2 V, current value 2 mA) in the case where the temperature was on was determined as a percentage [%]. In addition, IR was computed from (DELTA) V when an electric current was sent for 1 second.

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

  The results are shown in the following table.

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 exhibited a sufficient heat generation amount suppressing effect while suppressing the IR increase rate to 8%. Indicated. This is because lithium hydrogen carbonate is thermally decomposed to generate water (H ₂ O) as the temperature rises, and the supporting salt concentration in the electrolytic solution is lowered by hydrolyzing the supporting salt in the electrolytic solution, It was considered that the temperature rise of the battery was suppressed.

  On the other hand, in Comparative Example 1 in which 2% by mass of lithium hydrogen carbonate was added to the electrolytic solution, the effect of suppressing the heat generation was not sufficient. In addition, 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, it was also found that in Example 3 in which the capsule was mixed in the electrolytic solution, the IR increase rate was 15%, and 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 capable of exhibiting a desired battery temperature rise suppression effect while suppressing the rise in battery resistance. .

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
11a Outermost layer current collector,
12 negative electrode active material layer,
13 electrolyte layers,
14 positive electrode current collector,
15 positive electrode active material layer,
16 cell layers,
17, 57 Generating elements,
18, 58 negative electrode current collector plate (negative electrode tab),
19, 59 positive current collector plate (positive electrode tab),
20 negative terminal lead,
21 positive terminal lead,
22, 52 laminated film.

Claims (3)

A positive electrode having a positive electrode active material layer containing a positive electrode active material formed on the surface of a current collector;
An electrolyte layer containing an electrolytic solution,
A negative electrode having a negative electrode active material layer containing a negative electrode active material formed on the surface of a current collector;
In a lithium ion secondary battery having a structure in which a power generation element including at least one unit cell layer in which the plurality of unit cells are sequentially laminated is sealed inside a battery outer package made of a laminate film ,
The positive electrode active material layer, the negative electrode active material layer, or the electrolyte layer contains lithium hydrogen carbonate,
The lithium ion secondary battery, wherein a content of the lithium hydrogen carbonate is 3 to 14% by mass with respect to a total mass of the electrolytic solution.   The lithium ion secondary battery according to claim 1, wherein a content of the lithium hydrogen carbonate is 4 to 13% by mass with respect to a total mass of the electrolytic solution.   The lithium ion secondary battery according to claim 1, wherein the lithium hydrogen carbonate is present on at least a part of the surface of the positive electrode active material.