JP2017220380A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery improved in durability as a battery having a high capacity, a high density and a large area.SOLUTION: A nonaqueous electrolyte secondary battery comprises a power-generating element 21 including a positive electrode having a positive electrode active material layer 15 formed on a surface of a positive electrode current collector 12 and including a positive electrode active material, a negative electrode having a negative electrode active material layer 13 formed on a surface of a negative electrode current collector 11 and including a negative electrode active material, and a separator 17. In the nonaqueous electrolyte secondary battery, the rate of a rating capacity to a pore volume of the negative electrode active material layer 13 is 1.12 Ah/cc or more; the rate of a battery area to the rating capacity is 4.0 cm/Ah or more; and the rating capacity is 30 Ah or more. The rate (Ra/Rct) of Ra determined from an equivalent circuit of an electrochemical impedance at 25°C to a reaction resistance component Rct is less than 0.35.SELECTED DRAWING: Figure 1

Description

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

  Currently, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries that are used for mobile devices such as mobile phones have been commercialized. A nonaqueous electrolyte secondary battery generally includes a positive electrode obtained by applying a positive electrode active material or the like to a current collector, and a negative electrode obtained by applying a negative electrode active material or the like to a current collector. It has the structure connected through the electrolyte layer holding electrolyte gel. Then, when ions such as lithium ions are occluded / released in the electrode active material, a charge / discharge reaction of the battery occurs.

  Incidentally, in recent years, it has been required to reduce the amount of carbon dioxide in order to cope with global warming. Thus, non-aqueous electrolyte secondary batteries with a low environmental load are being used not only for portable devices, but also for power supply devices for electric vehicles such as hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. .

  Non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have high output and high capacity. Furthermore, non-aqueous electrolyte secondary batteries intended for application to electric vehicles are required to have cycle characteristics capable of maintaining capacity even when charge / discharge cycles are repeated for a long period of time.

For example, to increase the capacity of a lithium ion secondary battery, it is particularly effective to increase the charge / discharge capacity per volume of the negative electrode. However, when the pressure at the time of pressing the electrode plate is increased to increase the density of the negative electrode (1.6 g / cm ³ or more), the negative electrode active material particles tend to break. Such cracking of the negative electrode active material particles may deteriorate the charge / discharge characteristics.

In Patent Document 1, hydrophilic graphite particles formed by adhering carbonaceous or graphite particles having an average particle diameter of more than 100 nm and not more than 1 μm are used as the negative electrode active material. By adopting such a configuration, a negative electrode with high discharge capacity and initial charge / discharge efficiency and high density (1.6 g / cm ³ or more) can be produced. When the negative electrode of a lithium ion secondary battery is obtained, It shows good rapid charge / discharge efficiency.

JP 2005-243447 A JP 2013-65468 A

  By the way, in particular, non-aqueous electrolyte secondary batteries for electric vehicles (that is, high capacity, high density, and large area) are required to have high capacity and high output in order to extend the cruising distance in one charge. It has been. In addition to the above, improvement in battery durability (cycle characteristics in repeated charge / discharge) is also required so that a sufficient cruising distance can be secured even after repeated charge / discharge. However, the lithium ion secondary battery described in Patent Document 1 makes no mention of this cycle characteristic, and further improvement is required.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the durability of the battery is improved in a battery having a high capacity, a high density, and a large area.

  In the present invention, in a high capacity, high density, and large area battery, the ratio (Ra / Rct) of Ra to the reaction resistance component Rct obtained from an equivalent circuit of electrochemical impedance at 25 ° C. is less than 0.35. It has the characteristics.

  In the present invention, the ratio of Ra to the reaction resistance component Rct (Ra / Rct) obtained from the equivalent circuit of the electrochemical impedance at 25 ° C. is less than 0.35, so that the nonaqueous electrolyte secondary with improved durability is obtained. It becomes a battery.

FIG. 1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat type (stacked type) bipolar type, which is an embodiment of a non-aqueous electrolyte secondary battery. FIG. 2 is a diagram showing an equivalent circuit of electrochemical impedance for measuring the Ra / Rct ratio. FIG. 3 is a call-core plot output from the electrochemical impedance for measuring the Ra / Rct ratio. FIG. 4 is a diagram showing changes in the positive electrode potential and the negative electrode potential with respect to the state of charge (SOC). In FIG. 4, the horizontal axis indicates the state of charge (SOC), and the vertical axis indicates the potential with reference to the standard electrode potential of Li / Li ⁺ .

The first embodiment of the present invention includes a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of a positive electrode current collector, and a negative electrode active material layer containing a negative electrode active material on the surface of the negative electrode current collector. The power generation element includes a negative electrode formed and a separator, the ratio of the rated capacity to the pore volume of the negative electrode active material layer is 1.12 Ah / cc or more, and the ratio of the battery area to the rated capacity is 4 A nonaqueous electrolyte secondary battery having a capacity of 0.0 cm ² / Ah or more and a rated capacity of 30 Ah or more, and a ratio of Ra to a reaction resistance component Rct obtained from an equivalent circuit of electrochemical impedance at 25 ° C. ( It is a nonaqueous electrolyte secondary battery in which (Ra / Rct) is less than 0.35. In this specification, “the ratio of the rated capacity to the pore volume of the negative electrode active material layer” is simply referred to as “rated capacity / hole volume ratio of negative electrode active material layer” or “rated capacity / hole volume ratio”. Called. Similarly, the “ratio of Ra to reaction resistance component Rct determined from an equivalent circuit of electrochemical impedance at 25 ° C. (Ra / Rct)” is also simply referred to as “Ra / Rct ratio”. The “nonaqueous electrolyte secondary battery” is also simply referred to as “battery”.

  In recent years, electric vehicles have been attracting attention as being environmentally friendly. However, the cruising distance is shorter than that of a gasoline vehicle, and the cruising distance is particularly short when air conditioning (cooling or heating) is used. For this reason, non-aqueous electrolyte secondary batteries, particularly non-aqueous electrolyte secondary batteries for electric vehicles, are required to have high output and high capacity in order to increase the cruising distance in one charge. In addition, improvement of durability (cycle characteristics) is an important issue for batteries mounted on electric vehicles so that high output and high capacity do not deteriorate even after repeated charging and discharging with a large current for a short time. Longer life is required for the popularization of electric vehicles.

  In general, in a non-aqueous electrolyte secondary battery having a large area, it is difficult to pressurize the electrode surface uniformly, and a pressure distribution is generated in the surface. Due to such a uniform pressure distribution, the overvoltage varies in the electrode plane. Under such circumstances, the negative electrode active material is likely to be burdened during charge and discharge, and the life is likely to deteriorate. The above-described problem is particularly noticeable when a battery unit in which a cell unit is housed in a metal case to form an assembled battery.

The present inventor has intensively studied in view of the above problems. As a result, the ratio of the rated capacity to the pore volume of the negative electrode active material layer is 1.40 Ah / cc (Ah / cm ³ ) or more, and the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more. In addition, in a high capacity density, large area, high capacity non-aqueous electrolyte secondary battery having a rated capacity of 30 Ah or more, by setting the Ra / Rct ratio to less than 0.35, the durability of the battery (cycle characteristics) Has been found to be significantly improved. Although the detailed mechanism which has the said effect is unknown, it estimates as follows. The technical scope of the present invention is not limited to the following mechanism.

  That is, as shown in FIG. 4, during charging (as the SOC increases), the potential of the positive electrode increases and the potential of the negative electrode decreases. When the potential of the negative electrode falls below 0 V (decreases to the negative side), metal ions (for example, lithium ions) are locally deposited on the negative electrode, thereby deteriorating the battery life and improving the battery durability. It will decrease. As a result of intensive studies on the above problems, the present inventor speculated that the problem can be solved by appropriately setting the resistance of the negative electrode. Specifically, in FIG. 4, when the difference (Vb−Va) between the positive electrode potential (Vb) and the negative electrode potential (Va) is fully charged (SOC = 100%, 4.2 V), the negative electrode potential is If (Va) is 0 V or more, metal ions (for example, lithium ions) are not deposited on the negative electrode. For this purpose, it was considered that it is an effective means to set a low ratio of the negative electrode resistance in the overall battery resistance. As a result of further intensive studies on the above, as a result of lowering the Ra / Rct ratio representing the above ratio to less than 0.35, the charging curve of the negative electrode is entirely shifted upward, so that the negative electrode is not fully charged. The potential of the metal exceeds 0 V, and no metal ions can be deposited. Note that Ra is an index of resistance of the negative electrode, Rb is an index of resistance of the positive electrode, and Rct is an index of resistance of the entire battery (Ra + Rb + resistance of the separator). For this reason, the Ra / Rct ratio represents the ratio of the resistance of the negative electrode to the resistance of the entire battery. On the other hand, when the Ra / Rct ratio is 0.35 or more, the capacity retention rate after repeated charge / discharge is significantly reduced (see Comparative Examples 1 and 2 described later). Such a remarkable effect of setting the Ra / Rct ratio to less than 0.35 is not observed in a small battery or a low capacity density battery (in a small battery or a low capacity density battery, Ra Even when the / Rct ratio is 0.35 or more, a high capacity retention ratio is obtained; see Comparative Examples 4 to 5 described later). Therefore, the present invention can be said to be a problem solving means specialized for high capacity density, large area, high capacity non-aqueous electrolyte secondary batteries.

  By the way, as a structure of the electrode, there is a flat rectangular structure in addition to a wound type. Among these, in the winding type battery, the pressure distribution hardly occurs in the electrode surface as described above due to its structure. On the other hand, the flat rectangular electrode has a larger surface area and a shorter distance between the battery surface and the center than the wound electrode. For this reason, the heat generated inside the battery can be easily released to the outside, and the heat can be prevented from staying in the center of the battery. In an electric vehicle, charging and discharging are performed with a large current, and thus high heat dissipation is required. However, by using a flat rectangular electrode, a rise in battery temperature can be suppressed and deterioration in battery performance can be suppressed. be able to. On the other hand, in order to increase the capacity of the battery using the flat rectangular electrode, the area of the non-aqueous electrolyte secondary battery used for the electric vehicle is very large compared to the consumer battery. In addition, in order to secure a living space, it is also required to reduce the volume of the battery mounted on the electric vehicle, so that the capacity of the battery having a small capacity and a high capacity is increased. In such a high-capacity, high-capacity density, large-area flat rectangular battery, further improvement in battery durability is required. As described above, in a flat rectangular battery, the problem of deterioration in cycle characteristics due to pressure distribution in the electrode surface due to the size of the area becomes obvious. However, according to the present invention, even in the case of a flat rectangular nonaqueous electrolyte secondary battery, cycle characteristics during repeated charging and discharging with a large current for a short time can be improved. Therefore, the nonaqueous electrolyte secondary battery of the present invention can be particularly suitably used for a flat type nonaqueous electrolyte secondary battery.

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

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing an outline of a flat laminated battery which is an embodiment of the battery of the present invention. By adopting the stacked type, the battery can be made compact and have a high capacity. In this specification, the flat-stacked lithium ion secondary battery shown in FIG. 1 that is not a bipolar type battery will be described in detail as an example.

  In addition, the lithium ion secondary battery is not limited to a stacked flat shape, but the pressure in the surface direction is likely to be non-uniform, and the effects of the present invention are more easily exhibited. A flat shape is preferable, and since a high capacity can be easily achieved, a laminated type is more preferable. 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.

  First, the overall structure of the nonaqueous electrolyte secondary battery of the present invention will be described with reference to the drawings.

[Battery overall structure]
FIG. 1 is a schematic cross-sectional view schematically illustrating a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat stacked bipolar type. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a flat, substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 that is an exterior body. Have Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer negative electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 1 so that the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the single-sided positive electrode active material of the outermost layer positive electrode current collector Layers may be arranged.

  The positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out of the battery exterior material 29 so that it may be pinched | interposed into the edge part. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

Note that FIG. 1 shows a flat battery that is not a flat stacked bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and a surface opposite to the current collector. A bipolar battery including a bipolar electrode having a negative electrode active material layer that is electrically coupled may be used. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Hereinafter, each member which comprises the nonaqueous electrolyte lithium ion secondary battery which is one Embodiment of this invention is demonstrated.

[Negative electrode]
The negative electrode has a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material formed on the surface of the negative electrode current collector.

(Negative electrode current collector)
There is no particular limitation on the material constituting the negative electrode current collector, but a metal is preferably used. Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. 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, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

(Negative electrode active material layer)
The negative electrode active material layer preferably contains a negative electrode active material, a binder, and a conductive additive. If necessary, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), a lithium salt for increasing ion conductivity, etc. Other additives may be further included.

The density of the negative electrode active material layer is preferably 1.0 to 2.0 g / cm ³ and more preferably 1.2 to 1.8 g / cm ³ from the viewpoint of increasing the density.

  There is no restriction | limiting in particular also about the thickness of a negative electrode active material layer, The conventionally well-known knowledge about a battery can be referred suitably. For example, the thickness of the negative electrode active material layer is about 2 to 100 μm.

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

  The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 30 μm from the viewpoint of increasing the output. In this specification, the average particle diameter is measured by a particle size distribution measuring apparatus using a laser diffraction / scattering method.

  In the negative electrode active material layer, the content (in terms of solid content) of the negative electrode active material is preferably 80 to 99.5% by weight, and more preferably 85 to 99.5% by weight.

(binder)
The negative electrode active material layer preferably contains at least an aqueous binder. A water-based binder has a high binding power. In addition, it is easy to procure water as a raw material, and since steam is generated at the time of drying, the capital investment in the production line can be greatly suppressed, and the environmental load can be reduced. There is. The negative electrode active material layer may contain a binder other than the aqueous binder. The binder when the negative electrode active material layer contains a binder other than the aqueous binder is not particularly limited, and examples thereof include those described in the column of the following positive electrode active material layer.

  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 using 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 (SBR), styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, and 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, Polyra Yl methacrylate), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer Polymer, 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, saponification degree is preferably 80 mol% or more, more preferably 90 mol% or more) and a modified product thereof (ethylene / vinyl acetate = 2/98 to 30/70 mol ratio of vinyl acetate units of 1 to 80 mol% of vinyl acetate units). , Polyvinyl alcohol 1-50 mol% partially acetalized product), starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxy) Ethyl cellulose, and salts thereof), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) Acrylamide- (meth) acrylate copolymer, alkyl (meth) acrylate (carbon number 1 to 4) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Manni Dech, modified formalin resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, mannangalactan derivative, etc. And water-soluble polymers. These aqueous binders may be used alone or in combination of two or more.

The water-based binder may contain 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, since the binding property is good, the aqueous binder preferably contains styrene-butadiene rubber (SBR).

  When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving 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 (carboxymethylcellulose (CMC), methylcellulose, hydroxyethylcellulose, and salts thereof, etc. ), Polyvinylpyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose (CMC) (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 = 0.1 to 10: 1. It is more preferably 5 to 3: 1, more preferably 1 or more and less than 2.8: 1, further preferably 1.5 to 2.5: 1.

  The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material. However, adjusting the amount of binder and the amount of conductive aid is one of the important means for controlling Ra / Rct. That is, when the amount of the binder is increased, the resistance of the electrode is increased. For this reason, when the amount of the binder in the negative electrode active material layer is increased, Ra increases and the Ra / Rct ratio increases. For this reason, in order to lower the Ra / Rct ratio, it is preferable to reduce the amount of the binder contained in the negative electrode active material layer. Specifically, the binder amount is preferably 0.5% by weight or more and less than 3.8% by weight, more preferably 1 to 3.7% by weight with respect to the negative electrode active material layer (in terms of solid content). It is particularly preferably 1.5 to 3.5% by weight. In addition, in this specification, when using 2 or more types of aqueous binders, let these total amount be a binder amount. Moreover, when using together styrene-butadiene rubber and water-soluble polymer, let the total amount of styrene-butadiene rubber and water-soluble polymer be a binder amount.

  Moreover, it is preferable that content of an aqueous | water-based binder is 80-100 weight% among the binders used for a negative electrode active material layer, It is preferable that it is 90-100 weight%, It is preferable that it is 100 weight%.

(Conductive aid)
The negative electrode active material layer preferably contains a conductive additive. Here, the conductive auxiliary agent refers to an additive blended to improve the conductivity of the negative electrode 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, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  The amount of the conductive auxiliary agent contained in the active material layer is not particularly limited. However, as described above, adjusting the amount of the conductive additive is one of important means for controlling Ra / Rct. That is, when the amount of the conductive aid is increased, the resistance of the electrode is reduced. For this reason, when the amount of the conductive additive in the negative electrode active material layer is increased, Ra is decreased and the Ra / Rct ratio is decreased. For this reason, in order to lower the Ra / Rct ratio, it is preferable to increase the amount of the conductive auxiliary agent contained in the negative electrode active material layer. Specifically, the amount of the conductive auxiliary is preferably 0.05% by weight or more and less than 15% by weight, more preferably 0.1 to 10% by weight with respect to the negative electrode active material layer (in terms of solid content). It is particularly preferably 0.2 to 5% by weight.

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

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

  The mixing ratio of the other additives contained in the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

[Positive electrode]
The positive electrode has a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material formed on the surface of the positive electrode current collector.

(Positive electrode current collector)
There are no particular restrictions on the material and size of the positive electrode current collector. Specifically, the same negative electrode current collector can be used.

(Positive electrode active material layer)
The positive electrode active material layer includes a positive electrode active material, and further includes an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and other additives such as a lithium salt for increasing ion conductivity, if necessary. But you can. Here, about other additives, such as a conductive support agent, a binder, electrolyte (polymer matrix, an ion conductive polymer, electrolyte solution, etc.), lithium salt for improving ion conductivity, in the column of the above-mentioned negative electrode active material layer The same as described.

The density of the positive electrode active material layer is preferably 2.5 to 3.8 g / cm ³ , more preferably 2.6 to 3.7 g / cm ³ from the viewpoint of increasing the density.

  The thickness of the positive electrode active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. For example, the thickness of the positive electrode active material layer is about 2 to 100 μm.

(Positive electrode active material)
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. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. In some cases, two or more positive electrode active materials may be used in combination.

More preferably, Li (Ni—Mn—Co) O ₂ and those in which some of these transition metals are substituted with other elements (hereinafter, also simply referred to as “NMC composite oxide”) are used. The NMC composite oxide has a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co are arranged in order) atomic layers are alternately stacked via oxygen atomic layers. In addition, one Li atom is contained per one atom of the transition metal, and the amount of Li that can be taken out is twice that of the spinel-based 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. are mentioned. Preferred are Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. More preferred are Ti, Zr, P, Al, Mg, and Cr. 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, and 0 ≦ x ≦ 0.3, where M is Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. In the general formula (1), the relationship between b, c, and d is not particularly limited and varies depending on the valence of M, but preferably satisfies b + c + d = 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, a part of the transition element may be substituted with another metal element. In this case, it is 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.

  The NMC composite oxide can be prepared by selecting various known methods such as a coprecipitation method and a spray drying method. The coprecipitation method is preferably used because the composite oxide is easy to prepare. Specifically, for example, a nickel-cobalt-manganese composite hydroxide is produced by a coprecipitation method as in the method described in JP2011-105588A. Thereafter, the NMC composite oxide can be obtained by mixing and baking the nickel-cobalt-manganese composite hydroxide and the lithium compound.

  Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 25 μm from the viewpoint of increasing the output.

  In the positive electrode active material layer, the content of the positive electrode active material (in terms of solid content) is preferably 80 to 99.5% by weight, and more preferably 85 to 99.5% by weight.

(binder)
The positive electrode active material layer preferably contains a binder. The binder used for the positive electrode active material layer is not particularly limited. For example, polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and a salt thereof, Ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and Its hydrogenated product, thermoplastic polymer such as styrene / isoprene / styrene block copolymer and its hydrogenated product, polyvinylidene fluoride (PVdF), polytetrafluoroethylene ( TFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene ( PCTFE), fluoropolymers such as ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride- Hexafluoropropylene-tetrafluoroethylene fluoro rubber (VDF-HFP-TFE fluoro rubber), vinylidene fluoride-pentafluoropropylene fluoro rubber (VDF-PFP fluoro rubber) Vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber) And vinylidene fluoride-based fluororubber such as vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 1 to 15% by weight with respect to the active material layer. More preferably, it is more than 1.5% by weight and 10% by weight or less. As described above, when a relatively large amount of binder is used in the positive electrode active material layer, the resistance of the positive electrode increases. Therefore, by setting the amount as described above, the resistance of the entire battery is increased, and the Ra / Rct ratio can be lowered.

(Conductive aid)
The positive electrode active material layer preferably contains a conductive additive. Here, the conductive assistant refers to an additive blended to improve the conductivity of the positive electrode active material layer. Since it is the same as the definition in the said negative electrode active material layer as a conductive support agent, description is abbreviate | omitted here.

  The amount of the conductive auxiliary agent contained in the positive electrode active material layer is not particularly limited, but is preferably 0.5 to 10% by weight, more preferably 1% by weight or more and 4% with respect to the active material layer. Less than% by weight. As described above, when a relatively small amount of conductive additive is used in the positive electrode active material layer, the resistance of the positive electrode increases. Therefore, by setting the amount as described above, the resistance of the entire battery is increased, and the Ra / Rct ratio can be lowered.

(Other additives)
Since the electrolyte salt (lithium salt) and the ion conductive polymer that can be included in the positive electrode active material layer are the same as those defined in the negative electrode active material layer, the description thereof is omitted here.

  The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

[Ra / Rct ratio]
In the first embodiment, the Ra / Rct ratio is less than 0.35. Here, when the Ra / Rct ratio is 0.35 or more, the capacity retention rate after repeated charge / discharge is significantly reduced (Comparative Examples 1 and 2 described later). Considering further improvement in durability (cycle characteristics), it is preferably 0.34 or less, and more preferably 0.33 or less. Here, the lower limit of the Ra / Rct ratio is not particularly limited, but is, for example, 0.20 or more. However, when the battery temperature rises, the charging curves of the negative electrode and the positive electrode in FIG. 4 shift upward. For this reason, the potential of the negative electrode at the time of full charge is 0 V or more, and precipitation of metal ions at the negative electrode is difficult to occur. On the other hand, due to the upward shift in the charging curve of the positive electrode, the potential of the positive electrode at the time of full charge rises, and accordingly, the electrolyte solution is oxidized and decomposed on the positive electrode side to generate gas, In some cases, cracks may occur, causing the battery life to deteriorate and the battery durability to decrease. From such a viewpoint, the Ra / Rct ratio is preferably more than 0.28. That is, according to the preferred embodiment of the present invention, the ratio of Ra to the reaction resistance component Rct (Ra / Rct) obtained from an equivalent circuit of electrochemical impedance at 25 ° C. exceeds 0.28. Ra / Rct is preferably 0.29 or more. When such a lower limit is satisfied, the durability of the battery at a high temperature can be more effectively improved while ensuring the durability of the battery at room temperature (25 ° C.) (Examples 8 to 9 and Examples 1 to 3 described later). And contrast). In a preferred embodiment of the present invention, the ratio of Ra to the reaction resistance component Rct (Ra / Rct) obtained from an equivalent circuit of electrochemical impedance at 5 ° C. is preferably 0.20 or more and less than 0.35, more preferably It is more than 0.28 and less than 0.35, still more preferably 0.29 or more and 0.34 or less, and particularly preferably 0.29 or more and 0.33 or less. Within such a range, the durability of the battery at a high temperature can be further effectively improved while ensuring the durability of the battery at room temperature (25 ° C.).

As described above, the present invention is a problem solving means specialized for high capacity density, large area, high capacity non-aqueous electrolyte secondary batteries. For this reason, it is also preferable to set the capacity density higher (for example, the ratio of the rated capacity to the pore volume of the negative electrode active material layer = 1.4 Ah / cc or more). Normally, as the capacity density increases, the negative electrode potential drop (negative charge curve) tends to shift downward, and the above phenomenon appears more prominently. For this reason, in such a battery having a higher capacity density, in order to further improve the durability of the battery, it is preferable to set the upper limit of the Ra / Rct ratio further lower. That is, according to a preferred embodiment of the present invention, the ratio of the rated capacity to the void volume of the negative electrode active material layer is 1.4 Ah / cc or more, the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more, and the rated capacity Is 30 Ah or more, the Ra / Rct ratio is preferably less than 0.33. This reduces the negative electrode potential (Va) to less than 0 V (deposition of metal ions at the negative electrode) when fully charged (SOC = 100%, 4.2 V) in a higher capacity density battery. This can be prevented more effectively. More preferably, the ratio of the rated capacity to the void volume of the negative electrode active material layer is 1.4 Ah / cc or more, the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more, and the rated capacity is 30 Ah or more. In the water electrolyte secondary battery, the Ra / Rct ratio is more preferably 0.20 or more and less than 0.33, still more preferably 0.20 or more and 0.32 or less, and particularly preferably 0.29 or more. 0.31 or less. With such a configuration, even a non-aqueous electrolyte secondary battery having a higher capacity density can more effectively improve the durability (comparison between Example 5 and Examples 6 to 7 described later).

  As described above, Ra is an indicator of the resistance of the negative electrode, Rb is an indicator of the resistance of the positive electrode, Rct is an indicator of the resistance of the entire battery (Ra + Rb + resistance of the separator), and the Ra / Rct ratio is It represents the ratio of the negative electrode resistance to the overall resistance. In this specification, the Ra / Rct ratio is measured by the following method.

(Measurement of Ra / Rct ratio)
Electrochemical impedance measurement is performed at 25 ° C. (measurement temperature), SOC (battery charge state) 50% (charge state of about 50% of rated capacity), measurement frequency range of 100 kHz to 10 mHz, applied voltage amplitude ± 10 mV, The measurement point is 10 points / decade. As shown in FIG. 3, in electrochemical impedance measurement, inductance components (R _L , L), electrolyte resistance (Rsol), charge transfer resistance (Ra, Rb), electric double layer capacitance components (CPEa, CPEb), An equivalent circuit represented by the diffusion component (Zw) and the limit capacity (C) is used. In this equivalent circuit, the electrochemical impedance Z is expressed by the following formula (A).

  Various parameters of the equivalent circuit are calculated by referring to the real component of the resistance, the imaginary component of the resistance, and the frequency obtained from the electrochemical impedance measurement.

  Further, Rct is a difference value between the resistance value intersecting the horizontal axis of the arc in the colle-coll plot (Nyquist plot) shown in FIG. 4 and the resistance value at the position on the lower frequency side of the arc. In FIG. 4, the vertical axis represents the reciprocal of the real component of the resistance output from the electrochemical impedance, and the horizontal axis represents the imaginary component of the resistance output from the electrochemical impedance on the horizontal axis.

The Ra and Rct of the battery are not particularly limited as long as the Ra / Rct ratio is less than 0.35. For example, Ra is preferably less than 5.6 (Ohm · cm ² ), more preferably 5.5 (Ohm · cm ² ) or less, and particularly preferably less than 5.4 (Ohm · cm ² ). In general, the lower the resistance, the greater the battery capacity, which is preferable. For this reason, the lower limit of Ra is preferable, but if Ra is 2 (Ohm · cm ² ) or more, it is practically acceptable. Rct is preferably 25 (Ohm · cm ² ) or less, more preferably 24 (Ohm · cm ² ) or less. In addition, although the lower limit of Rct is so preferable that it is low, if Rct is 6 (Ohm · cm ² ) or more, it is practically acceptable. Within such a range, the potential (Va) of the negative electrode at full charge can be more effectively prevented from decreasing to less than 0 V (deposition of metal ions at the negative electrode).

[Separator (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.

  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.

  In addition, as described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

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

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

  The matrix polymer of gel electrolyte can express 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.

Moreover, as a separator, the separator (separator with a heat-resistant insulating layer) by which the heat-resistant insulating layer was laminated | stacked on the porous base | substrate may be sufficient. 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 inorganic 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. With 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 a 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 gaps between the inorganic particles are 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.

[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 material (battery exterior body)]
As the battery exterior material (battery exterior body) 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 of high output and excellent cooling performance, and can be suitably used for a battery for large-size equipment for EV and HEV, and an aluminum laminate film is more preferable from the viewpoint of weight reduction.

[Ratio of rated capacity to pore volume of negative electrode active material layer]
In the first embodiment, the ratio of the rated capacity to the pore volume of the negative electrode active material layer is 1.12 Ah / cc (Ah / cm ³ ) or more. The ratio of the rated capacity to the pore volume of the negative electrode active material layer is an index indicating an increase in capacity density of the negative electrode active material layer. Here, in g / cc which shows the active material density of a negative electrode active material layer, the density of negative electrode active material itself needs to be considered. For example, in a material with a low active material density, even if the same volume of active material is filled in the same volume, the density of the negative electrode active material layer is smaller than that of a material with a high active material density. Or whether the weight of the negative electrode active material is small. Therefore, in this specification, the capacity | capacitance per void | hole volume is prescribed | regulated and it is set as the parameter | index of the height of capacity density. Furthermore, by setting the capacity per pore volume, it becomes an index of the density of how much gap is filled with the negative electrode active material.

  In addition, by increasing the capacity of the battery, the Li ions in the active material layer increase, while the diffusivity of Li ions decreases when the pore volume in the active material layer decreases. Therefore, the ratio of the capacity to the vacancy volume of the negative electrode is an indicator of the diffusibility of Li ions, and the ratio of the capacity to the vacancy volume of the negative electrode is 1.12 Ah / cc or more, in an environment where the diffusivity of Li ions is low. Even if it exists, cycling characteristics will improve notably by setting Ra / Rct ratio to less than 0.35.

  The upper limit of the ratio of the rated capacity to the void volume of the negative electrode active material layer is not particularly limited, but considering the diffusibility of Li ions, the ratio of the capacity to the negative electrode void volume is 2.5 Ah / cc. Or less, more preferably 2.0 Ah / cc or less, and even more preferably 1.8 Ah / cc or less. Further, from the viewpoint of higher density, it is preferably 1.25 Ah / cc or more, more preferably 1.4 Ah / cc or more, since the effects of the present invention are more easily exhibited. More preferably, it is 5 Ah / cc or more, and preferably 1.65 Ah / cc or more.

The pore volume of the negative electrode active material layer is measured as follows; the negative electrode active material layer is extracted from the nonaqueous electrolyte secondary battery and cut into a 10 cm × 10 cm sample. The volume of pores (micropores) existing inside the sample is measured by measuring the pore distribution by a mercury intrusion method using a mercury intrusion porosimeter. When a capillary is erected in the liquid, the liquid that wets the wall rises in the capillary, and the liquid that does not wet the liquid falls. Needless to say, this capillary phenomenon is caused by pressure acting at the meniscus due to surface tension. Mercury and other substances that do not get wet with ordinary substances do not enter the capillary unless pressure is applied. The mercury porosimeter utilizes this, and mercury is injected into the pores, the pore diameter is determined from the required pressure, and the pore volume (pore volume) of the sample is determined from the amount of injection. From the pore volume of this sample, the pore volume of the negative electrode active material layer is calculated in consideration of the area of the negative electrode active material layer and the number of stacked layers.

  The rated capacity is measured as follows by the following procedures 1 and 2 at a temperature of 25 ° C. and a predetermined voltage range.

  Procedure 1: After reaching the upper limit voltage by constant current charge of 0.2 C, charge for 2.5 hours by constant voltage charge, and then rest for 10 seconds.

  Procedure 2: After reaching the lower limit voltage by constant current discharge of 0.2 C, stop for 10 seconds.

  Rated capacity: The discharge capacity in constant current discharge in procedure 2 is defined as the rated capacity.

[Ratio of battery area to rated capacity and rated capacity]
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. Further, as described above, the effect of the present invention is exhibited in a large battery. Specifically, in this embodiment, the enlargement of the battery is defined from the relationship between the battery area and the battery capacity. Specifically, in the nonaqueous electrolyte secondary battery according to this embodiment, the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more. In the present invention, since the rated capacity is as large as 30 Ah or more, the battery area inevitably becomes as large as 120 cm ² or more. From the viewpoint of high capacity, the ratio of the battery area to the rated capacity is preferably as large as possible, but is usually 18 cm ² / Ah or less because of the in-vehicle capacity. The value of the ratio of the battery area to the rated capacity is preferably 5.0 to 15 cm ² / Ah.

  Here, the battery area refers to the area (in the surface direction) of the positive electrode. When there are a plurality of positive electrodes and their areas are different, the maximum positive electrode area is defined as the battery area.

In this embodiment, the rated capacity is 30 Ah or more. In the case of a large-area and large-capacity battery having a ratio of the battery area to the rated capacity of 4.0 cm ² / Ah or more and a rated capacity of 30 Ah or more, a high capacity can be maintained by repeating charge and discharge cycles. It becomes even more difficult, and the problem of improving cycle characteristics can be even more pronounced. On the other hand, in a battery having a large area and not having a large capacity as described above, such as a conventional consumer battery, occurrence of such a problem is difficult to manifest (Comparative Examples 4 to 5 described later). The rated capacity is preferably as large as possible, and the upper limit is not particularly limited. The rated capacity is preferably 30 to 150 Ah, and more preferably 40 to 100 Ah. In addition, the value measured by the method as described in the following Example is employ | adopted for a rated capacity.

  Moreover, as for the size of the physical electrode, the length of the short side of the 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 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. The size of the electrode is defined as the size of the negative electrode. Further, the positive electrode and the negative electrode may be the same size or different sizes, but it is preferable that both are the sizes described above.

  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.

A cell unit in which a plurality of batteries are stacked in this way may be accommodated in upper and lower cases (for example, metal cases) to form an assembled battery. At this time, normally, the battery case is accommodated in the case by fastening the metal case with the fastening member. Therefore, the battery is pressurized in the stacking direction within the case. Due to such pressurization, in-plane pressure distribution is likely to occur in a large-sized battery, which imposes a burden on the electrode active material during charge and discharge and tends to deteriorate the battery life. On the other hand, according to the configuration of the present embodiment, it is considered that durability (cycle characteristics) can be improved because precipitation of metal ions (particularly, Li ⁺ ) during full charge is suppressed.

[vehicle]
The nonaqueous electrolyte secondary battery of this embodiment maintains a discharge capacity even when used for a long period of time, and has good cycle characteristics. 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 nonaqueous electrolyte secondary battery can be suitably used as a vehicle power source, for example, 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 this embodiment, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charging mileage can be formed by installing such a battery. it can. 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.

[Production method]
The production of the active material layer and the assembly of the battery can be produced by a conventionally known method. Next, although an example is demonstrated about the manufacturing method of the nonaqueous electrolyte secondary battery of this invention, this invention is not limited only to this example.

  Although preferable embodiment of manufacture of a negative electrode active material layer is described below, this invention is not limited to the following form.

  For example, a step (mixing step) of obtaining a negative electrode active material layer constituent by mixing a negative electrode active material, a binder and a conductive additive, and other additives if necessary, and a slurry viscosity of the negative active material layer constituent A step of preparing a slurry composition by mixing an aqueous solvent that is an adjustment solvent (slurry composition preparation step), a step of coating the slurry composition on a negative electrode current collector, and drying to obtain a negative electrode ( Drying step). Furthermore, it is preferable to perform a press work after the drying step, and in this case, a hot press step is more preferable.

  As described above, adjusting the amount of binder and the amount of conductive assistant is one of the important means for controlling Ra / Rct. For this reason, it is preferable to mix the negative electrode active material, the binder, and the conductive additive in the mixing step so that the amounts are as described above.

  In the slurry composition preparation step, the slurry viscosity adjusting solvent is not particularly limited, and a conventionally known solvent can be used. However, when an aqueous binder is used, an aqueous solvent is used. preferable. Examples of the aqueous solvent include water (pure water, ultrapure water, distilled water, ion exchange water, ground water, well water, tap water (tap water), etc.), water and alcohol (eg, ethyl alcohol, methyl alcohol, isopropyl alcohol, etc.) ) And a mixed solvent can be used. However, in this embodiment, it is not restricted to these, A conventionally well-known aqueous solvent can be selected suitably and used as long as the effect of this embodiment is not impaired.

  The amount of the aqueous solvent is not particularly limited, and an appropriate amount may be added so that the slurry composition is within a desired viscosity range. The solid content concentration of the slurry composition is not particularly limited, but is preferably 45 to 65% by weight in consideration of ease of coating.

In the drying step, the (coating amount) basis weight when applying (applying) the slurry composition to the current collector is not particularly limited, but is preferably 1 to 20 g / m ² , more preferably 5 to 15 g. / M ² , particularly preferably 6 to 15 g / m ² . If it is the said range, the negative electrode active material layer which has suitable thickness can be obtained. The coating method is not particularly limited, and examples thereof include a knife coater method, a gravure coater method, a screen printing method, a wire bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method.

  The method for drying the slurry composition after application is not particularly limited. For example, warm air, hot air, infrared rays, far infrared rays, microwaves, high frequencies, or a combination thereof can be used. You may dry with the heat which discharge | released the metal roller and metal sheet which support or press a collector in a drying process. In addition, after drying, the active material layer can also be obtained by irradiating an electron beam or radiation to cause a crosslinking reaction of the binder. Application and drying may be repeated a plurality of times. Drying conditions are not particularly limited. For example, the drying temperature is 30 to 100 ° C. The drying time is, for example, 2 seconds to 1 hour.

Although the thickness of the negative electrode active material layer thus obtained is not particularly limited, for example, 2 to 10
0 μm.

  A negative electrode can be manufactured by such a process.

  Next, although preferable embodiment of manufacture of a positive electrode active material layer is described, this invention is not limited to the following form. Note that the positive electrode active material layer can also be manufactured by the same method as that for the negative electrode active material layer.

  For example, a step of mixing a positive electrode active material, a binder, a conductive additive and a solvent, and, if necessary, other additives and the like to obtain a mixture (mixing step), and further adding a solvent to the mixture for mixing Thus, the method includes a step of obtaining a slurry composition (slurry composition preparation step) and a step of drying the slurry composition after coating the slurry composition on the positive electrode current collector (drying step). Furthermore, it is preferable to perform press working after the drying step, and in this case, a hot pressing step is more preferable.

  In the mixing step, the mixture may be mixed by any method, but it is preferably by solidification. Thereby, it can mix more uniformly. Here, the kneading method is not limited to the following, but for example, it is preferable to carry out as follows. That is, a positive electrode active material, a binder, and other compounding components (for example, a conductive auxiliary agent) are placed in an appropriate solvent, and mixed and dispersed by a disperser to prepare a paste. The term “kneading” refers to kneading in a state where the solid content rate is higher than that of the final slurry for forming an active material layer. By kneading in such a high solid content state, a composition in which each material is uniformly dispersed can be obtained. By such uniform dispersion, the components are brought into close contact with each other, and the active material layer can be densified.

  The solvent used in the mixing step is not particularly limited. For example, ketones such as acetone, aromatic hydrocarbon solvents such as toluene and xylene, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), Polar solvents such as dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), acetonitrile, and the like can be used. These may be used alone or in combination of two or more.

  Although the mixer used for mixing in a mixing process is not specifically limited, A planetary mixer, a biaxial kneader, a triaxial kneader etc. are mentioned. The order of addition to the mixer is not particularly limited, and after adding powder such as active material to the mixer, the solvent is added: powder such as active material and solvent are charged almost simultaneously. Either may be sufficient.

  The solid concentration in the mixing step is preferably 75 to 90% by weight in the mixture because a high tensile force can be applied.

  The mixing conditions in the mixing step are not particularly limited. Specifically, the mixing time is preferably 100 minutes or more, more preferably more than 100 minutes, and more preferably 110 minutes or more. The upper limit of the mixing time is not particularly limited, but is preferably 200 minutes or less in consideration of production efficiency and effect saturation. Moreover, it is preferable that the temperature at the time of mixing is 15-40 degreeC from the point of coating property.

  Next, a solvent is added to obtain a slurry composition (slurry composition preparation step). As the solvent, the solvent used in the mixing step can be used. The solid content concentration of the slurry composition is not particularly limited, but is preferably 45 to 65% by weight in consideration of ease of coating.

  In the drying step, the method of applying the slurry composition to the negative electrode current collector is not particularly limited, but a thick coating layer can be formed, such as die coating such as slide die coating, comma direct coating, comma reverse coating, and the like. The method is suitable. However, depending on the coating weight, it may be applied by gravure coating or gravure reverse coating.

The basis weight (one-side coating amount) when applying (applying) the slurry composition to the current collector is not particularly limited, but is preferably 10.0 to 30.0 g / m from the viewpoint of high capacity and light weight. ² , more preferably 13.0 to 25.0 g / m ² . If it is the said range, the negative electrode active material layer which has suitable thickness can be obtained.

  As a heat source in the drying process, hot air, hot air, infrared rays, far infrared rays, microwaves, high frequencies, or a combination thereof can be used. You may dry with the heat which discharge | released the metal roller and metal sheet which support or press a collector in a drying process. In addition, after drying, the active material layer can also be obtained by irradiating an electron beam or radiation to cause a crosslinking reaction of the binder. Application and drying may be repeated a plurality of times.

  The electrode drying conditions are not particularly limited. For example, the electrode drying temperature is preferably 120 ° C. or lower, preferably 118 ° C. or lower, more preferably 115 ° C. or lower, and particularly preferably 110 ° C. or lower. Moreover, although drying time is suitably set by the time which drying completes at the said temperature, it is 2 second-1 hour, for example. Under such conditions, a uniform positive electrode active material layer can be formed.

  Furthermore, the density of the active material layer, the adhesion to the current collector, and the homogeneity can be improved by pressing the obtained negative electrode active material layer.

  The press working is performed using, for example, a metal roll, an elastic roll, a heating roll (heat roll), a sheet press machine, or the like. In this embodiment, the pressing temperature may be performed at room temperature or under heating conditions as long as the temperature is lower than the temperature for drying the coating film of the active material layer, but it is performed under heating conditions. It is preferable. A uniform positive electrode active material layer can be formed by pressing (hot pressing) under heating conditions. The temperature during hot pressing (the temperature of the processing machine (for example, roll)) is preferably 100 to 150 ° C, more preferably 110 to 140 ° C, and particularly preferably 115 to 130 ° C. .

  The positive electrode can be manufactured by such a process.

  The effects of the present invention will be described using the following examples and comparative examples. In the examples, “part” or “%” may be used, but “part by weight” or “% by weight” is expressed unless otherwise specified. Unless otherwise specified, each operation is performed at room temperature (25 ° C.).

Example 1
1. Preparation of Electrolyte Solution A mixed solvent (30:30:40 (volume ratio)) of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as a solvent. Further, 1.0M LiPF ₆ was used as a lithium salt. Furthermore, 2.0% by weight of vinylene carbonate was added to 100% by weight of the total of the solvent and the lithium salt to prepare an electrolytic solution. Note that “1.0 M LiPF ₆ ” means that the lithium salt (LiPF ₆ ) concentration in the mixture of the mixed solvent and the lithium salt is 1.0 M.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 91.5% by weight as a positive electrode active material, 4% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (PVdF) A solid content (1-1) consisting of 4.5% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content (1-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. Thus, a positive electrode having a positive electrode active material layer density of 2.8 g / cm ³ , a single-sided coating amount of the positive electrode active material layer of 17.5 mg / cm ² , and a positive electrode active material layer thickness of about 62.5 μm was produced.

3. Production of negative electrode 95.1% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.5% by weight of acetylene black as a conductive additive, 2.4% by weight of styrene-butadiene rubber (SBR) as a binder, and carboxy A solid content (1-2) consisting of 1% by weight of methylcellulose (CMC) was prepared. An appropriate amount of ion-exchanged water as a slurry viscosity adjusting solvent was added to the solid content (1-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. This produced a negative electrode having a negative electrode active material layer density of 1.5 g / cm ³ , a negative electrode active material layer coated on one side of 8.7 mg / cm ² , and a negative electrode active material layer thickness of about 58 μm.

4). Step of Completing Single Cell The positive electrode produced above was cut into a 200 mm × 210 mm rectangular shape, and the negative electrode was cut into a 205 × 215 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed. The battery thus manufactured had a rated capacity (cell capacity) of 50 Ah, and the ratio of the battery area to the rated capacity was 8.4 cm ² / Ah. Here, the battery area refers to the area (in the plane direction) of the positive electrode. Further, the rated capacity of the battery was determined as follows.

≪Measurement of rated capacity≫
The rated capacity is measured as follows by the following procedures 1 and 2 at a temperature of 25 ° C. and a voltage range of 3.0 V to 4.15 V.

  Procedure 1: After reaching 4.15 V by constant current charging at 0.2 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.

  Procedure 2: After reaching 3.0 V by constant current discharge of 0.2 C, stop for 10 seconds.

  Rated capacity: The discharge capacity in the discharge from the constant current discharge to the constant voltage discharge in the procedure 2 is defined as the rated capacity.

  Further, with respect to the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined according to the following method and found to be 1.25 Ah / cc.

  In addition, the void | hole volume of the negative electrode active material layer was calculated | required by the following. That is, the pore volume of the negative electrode active material layer is measured as follows; the negative electrode active material layer is extracted from the nonaqueous electrolyte secondary battery and cut into a 10 cm × 10 cm sample. The volume of pores (micropores) existing inside the sample is measured by measuring the pore distribution by a mercury intrusion method using a mercury intrusion porosimeter. When a capillary is erected in the liquid, the liquid that wets the wall rises in the capillary, and the liquid that does not wet the liquid falls. Needless to say, this capillary phenomenon is caused by pressure acting at the meniscus due to surface tension. Mercury and other substances that do not get wet with ordinary substances do not enter the capillary unless pressure is applied. The mercury porosimeter utilizes this, and mercury is injected into the pores, and the pore diameter is determined from the required pressure, and the pore volume is determined from the amount of injection.

  The rated capacity determined above was divided by the pore volume determined above, and the ratio of the rated capacity to the pore volume of the negative electrode active material layer was calculated.

(Example 2)
In Example 1, instead of the solid content (1-1), the following solid content (2-1) was used to produce a positive electrode, and instead of the solid content (1-2), the following solid content ( A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that a negative electrode was produced using 2-2).

(Preparation of solid content (2-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle diameter: 15 μm) 91.7% by weight as the positive electrode active material, 3.8% by weight acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride ( PVdF) A solid content (2-1) consisting of 4.5% by weight was prepared.

(Preparation of solid content (2-2))
Natural graphite (average particle size: 20 μm) 95.2% by weight as a negative electrode active material, acetylene black 1.5% by weight as a conductive assistant, styrene-butadiene rubber (SBR) 2.3% by weight and carboxymethyl cellulose (CMC) ) A solid content (2-2) consisting of 1% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

(Example 3)
In Example 1, instead of the solid content (1-1), the following solid content (3-1) was used to produce a positive electrode, and instead of the solid content (1-2), the following solid content ( A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that a negative electrode was produced using 3-2).

(Preparation of solid content (3-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 92.1 wt% as a positive electrode active material, 3.4 wt% acetylene black as a conductive additive, and polyvinylidene fluoride ( PVdF) A solid content (3-1) consisting of 4.5% by weight was prepared.

(Preparation of solid content (3-2))
Natural graphite (average particle size: 20 μm) 95.5% by weight as a negative electrode active material, acetylene black 1.5% by weight as a conductive assistant, styrene-butadiene rubber (SBR) 2% by weight and carboxymethyl cellulose (CMC) 1 A solid content (3-2) consisting of% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

(Comparative Example 1)
In Example 1, the following comparative solid content (1-1) was used instead of the solid content (1-1) to produce a positive electrode, and the following comparative solid content was used instead of the solid content (1-2). A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode was produced using the minute (1-2).

(Preparation of comparative solid content (1-1))
92% by weight of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) as a positive electrode active material, 4% by weight of acetylene black as a conductive assistant, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder A comparative solid content (1-1) comprising% was prepared.

(Preparation of comparative solid content (1-2))
Natural graphite (average particle size: 20 μm) 94.5% by weight as a negative electrode active material, 1.5% by weight of acetylene black as a conductive assistant, 3% by weight of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) 1 A comparative solid content (1-2) consisting of% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

(Comparative Example 2)
In Example 1, the following comparative solid content (2-1) was used instead of the solid content (1-1) to produce a positive electrode, and the following comparative solid content was used instead of the solid content (1-2). A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode was produced using the minute (2-2).

(Preparation of comparative solid content (2-1))
92% by weight of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) as a positive electrode active material, 4% by weight of acetylene black as a conductive assistant, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder A comparative solid content (2-1) consisting of% was prepared.

(Preparation of comparative solid content (2-2))
Natural graphite (average particle size: 20 μm) 94.7% by weight as a negative electrode active material, acetylene black 1.5% by weight as a conductive assistant, 2.8% by weight styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) ) A comparative solid content (2-2) consisting of 1% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

Example 4
1. Production of Electrolytic Solution An electrolytic solution was produced in the same manner as in Example 1.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle diameter: 15 μm) 92% by weight as a positive electrode active material, 4% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder ) A solid content (4-1) consisting of 4% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content (4-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. As a result, a positive electrode having a positive electrode active material layer density of 2.8 g / cm ³ , a single-sided coating amount of the positive electrode active material layer of 14.5 mg / cm ² , and a positive electrode active material layer thickness of about 51.8 μm was produced.

3. Production of negative electrode 95.5% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.5% by weight of acetylene black as a conductive additive, 2% by weight of styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose ( CMC) A solid content (4-2) consisting of 1% by weight was prepared. An appropriate amount of ion-exchanged water as a slurry viscosity adjusting solvent was added to the solid content (4-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. As a result, a negative electrode having a negative electrode active material layer density of 1.4 g / cm ³ , a negative electrode active material layer coating amount of 7.2 mg / cm ² , and a negative electrode active material layer thickness of about 51.4 μm was produced.

4). Step of Completing Single Cell The positive electrode produced above was cut into a 200 mm × 204 mm rectangular shape, and the negative electrode was cut into a 205 × 209 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

  A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 40 Ah. The ratio of the positive electrode area to the rated capacity was 10.2 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.12 Ah / cc.

(Comparative Example 3)
In Example 4, a positive electrode was prepared using the following comparative solid content (3-1) instead of the solid content (4-1), and the following comparative solid content was used instead of the solid content (4-2). A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 4 except that the negative electrode was produced using the minute (3-2).

(Preparation of comparative solid content (3-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle diameter: 15 μm) 92 layers as positive electrode active material. A comparative solid content (3-1) consisting of 3% by weight, 4.2% by weight of acetylene black as a conductive assistant, and 3.5% by weight of polyvinylidene fluoride (PVdF) as a binder was prepared.

(Preparation of comparative solid content (3-2))
Natural graphite (average particle size: 20 μm) 94.7% by weight as a negative electrode active material, acetylene black 1.5% by weight as a conductive assistant, 2.8% by weight styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) ) A comparative solid content (3-2) comprising 1% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 40 Ah. The ratio of the positive electrode area to the rated capacity was 10.2 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.12 Ah / cc.

(Example 5)
1. Production of Electrolytic Solution An electrolytic solution was produced in the same manner as in Example 1.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 91.5% by weight as a positive electrode active material, 4% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (PVdF) A solid content (5-1) consisting of 4.5% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content (5-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. As a result, a positive electrode having a positive electrode active material layer density of 2.8 g / cm ³ , a positive electrode active material layer coated on one side of 21.5 mg / cm ² , and a positive electrode active material layer thickness of about 76.8 μm was produced.

3. Production of negative electrode 94.9% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.7% by weight of acetylene black as a conductive additive, 2.4% by weight of styrene-butadiene rubber (SBR) as a binder and carboxy A solid content (5-2) comprising 1% by weight of methylcellulose (CMC) was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to the solid content (5-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. Thus, a negative electrode having a negative electrode active material layer density of 1.6 g / cm ³ , a negative electrode active material layer coated on one side of 10.5 mg / cm ² , and a negative electrode active material layer thickness of about 65.6 μm was produced.

4). Step of Completing Single Cell The positive electrode produced above was cut into a 200 mm × 210 mm rectangular shape, and the negative electrode was cut into a 205 × 215 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

  A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 60 Ah. The ratio of the positive electrode area to the rated capacity was 7.0 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.65 Ah / cc.

(Example 6)
In Example 5, a positive electrode was prepared using the following solid content (6-1) instead of the solid content (5-1), and the following solid content (5-2) was used instead of the solid content (5-2). A non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 5 except that the negative electrode was produced using 6-2).

(Preparation of solid content (6-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle diameter: 15 μm) 91.7% by weight as the positive electrode active material, 3.8% by weight acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride ( PVdF) A solid content (6-1) consisting of 4.5% by weight was prepared.

(Preparation of solid content (6-2))
Natural graphite (average particle size: 20 μm) 95.1% by weight as a negative electrode active material, 1.7% by weight acetylene black as a conductive additive, 2.2% by weight styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) ) A solid content (6-2) consisting of 1% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 60 Ah. The ratio of the positive electrode area to the rated capacity was 7.0 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.65 Ah / cc.

(Example 7)
In Example 5, instead of the solid content (5-1), the following solid content (7-1) was used to produce a positive electrode, and instead of the solid content (5-2), the following solid content ( A non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 5 except that the negative electrode was prepared using 7-2).

(Preparation of solid content (7-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle diameter: 15 μm) 91.9% by weight as the positive electrode active material, 3.6% by weight acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride ( PVdF) A solid content (7-1) consisting of 4.5% by weight was prepared.

(Preparation of solid content (7-2))
Natural graphite (average particle size: 20 μm) 95.3% by weight as a negative electrode active material, 1.7% by weight of acetylene black as a conductive assistant, and 2% by weight of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) 1 A solid content (7-2) consisting of% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 60 Ah. The ratio of the positive electrode area to the rated capacity was 7.0 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.65 Ah / cc.

(Example 8)
1. Production of Electrolytic Solution An electrolytic solution was produced in the same manner as in Example 1.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 92.5% by weight as a positive electrode active material, 3% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (PVdF) A solid content (8-1) consisting of 4.5% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content (8-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. Thus, a positive electrode having a positive electrode active material layer density of 2.8 g / cm ³ , a single-sided coating amount of the positive electrode active material layer of 17.5 mg / cm ² , and a positive electrode active material layer thickness of about 62.5 μm was produced.

3. Production of negative electrode 95.2% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.5% by weight of acetylene black as a conductive additive, 2.3% by weight of styrene-butadiene rubber (SBR) as a binder, and carboxy A solid content (8-2) consisting of 1% by weight of methylcellulose (CMC) was prepared. An appropriate amount of ion-exchanged water as a slurry viscosity adjusting solvent was added to the solid content (8-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. This produced a negative electrode having a negative electrode active material layer density of 1.5 g / cm ³ , a negative electrode active material layer coated on one side of 8.7 mg / cm ² , and a negative electrode active material layer thickness of about 58 μm.

4). Step of Completing Single Cell The positive electrode produced above was cut into a 200 mm × 210 mm rectangular shape, and the negative electrode was cut into a 205 × 215 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

  A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

Example 9
In Example 8, a positive electrode was prepared using the following solid content (9-1) instead of the solid content (8-1), and the following solid content ( A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 8 except that the negative electrode was produced using 9-2).

(Preparation of solid content (9-1))
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 92.7% by weight as a positive electrode active material, 2.8% by weight acetylene black as a conductive additive, and polyvinylidene fluoride ( PVdF) A solid content (9-1) consisting of 4.5% by weight was prepared.

(Preparation of solid content (9-2))
Natural graphite (average particle size: 20 μm) 95.2% by weight as a negative electrode active material, acetylene black 1.5% by weight as a conductive assistant, styrene-butadiene rubber (SBR) 2.3% by weight and carboxymethyl cellulose (CMC) ) A solid content (9-2) consisting of 1% by weight was prepared.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 50 Ah. The ratio of the positive electrode area to the rated capacity was 8.4 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

(Comparative Example 4)
1. Production of Electrolytic Solution An electrolytic solution was produced in the same manner as in Example 1.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 91.5% by weight as a positive electrode active material, 4% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (PVdF) A comparative solid content (4-1) consisting of 4.5% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the comparative solid content (4-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. Thereby, the density of the positive electrode active material layer is 2.8 g / cm ³ , and the coating amount on one side of the positive electrode active material layer is 1
A positive electrode having a thickness of 0.03 mg / cm ² and a positive electrode active material layer thickness of about 35.7 μm was produced.

3. Production of negative electrode 94.5% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.5% by weight of acetylene black as a conductive additive, 3% by weight of styrene-butadiene rubber (SBR) as a binder and carboxymethylcellulose ( CMC) A comparative solid content (4-2) consisting of 1% by weight was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to the comparative solid content (4-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. This produced a negative electrode having a negative electrode active material layer density of 1.4 g / cm ³ , a negative electrode active material layer coating amount of 4.9 mg / cm ² , and a negative electrode active material layer thickness of about 35 μm.

4). Step of completing cell The positive electrode produced above was cut into a 200 mm × 226 mm rectangular shape, and the negative electrode was cut into a 205 × 231 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

  A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed.

The battery thus obtained was measured for the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 30 Ah. The ratio of the positive electrode area to the rated capacity was 14.0 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.01 Ah / cc.

(Comparative Example 5)
1. Production of Electrolytic Solution An electrolytic solution was produced in the same manner as in Example 1.

2. Production of positive electrode LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (average particle size: 15 μm) 91.5% by weight as a positive electrode active material, 4% by weight of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (PVdF) A comparative solid content (5-1) consisting of 4.5% by weight was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the comparative solid content (5-1), and the mixture was kneaded with a planetary mixer. Further, an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to prepare a positive electrode slurry composition. Next, the positive electrode slurry composition was applied to both sides of an aluminum foil (thickness 20 μm) as a current collector by a die coater, dried, and then subjected to roll press. As a result, a positive electrode having a positive electrode active material layer density of 2.8 g / cm ³ , a positive electrode active material layer coated on one side of 9.3 mg / cm ² , and a positive electrode active material layer thickness of about 33.2 μm was produced.

3. Production of negative electrode 94.5% by weight of natural graphite (average particle size: 20 μm) as a negative electrode active material, 1.5% by weight of acetylene black as a conductive additive, 3% by weight of styrene-butadiene rubber (SBR) as a binder and carboxymethylcellulose ( CMC) A comparative solid content (5-2) consisting of 1% by weight was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to this comparative solid content (5-2) to prepare a negative electrode active material slurry composition. Next, the negative electrode active material slurry composition was applied to both sides of a copper foil (10 μm) as a current collector by a die coater, dried, and roll-pressed. This produced a negative electrode having a negative electrode active material layer density of 1.5 g / cm ³ , a negative electrode active material layer coated on one side of 4.5 mg / cm ² , and a negative electrode active material layer thickness of about 30 μm.

4). Process for Completing Single Cell The positive electrode produced above was cut into a 200 mm × 210 mm rectangular shape, and the negative electrode was cut into a 205 × 115 mm rectangular shape (24 positive electrodes, 25 negative electrodes). The positive electrode and the negative electrode were alternately laminated via a 210 × 214 mm separator (polypropylene microporous film, thickness 25 μm, porosity 53%) to produce a power generation element.

  A tab was welded to the resulting power generation element, and the battery was completed by sealing together with the electrolyte in an exterior made of an aluminum laminate film. Thereafter, the battery was sandwiched between a urethane rubber sheet (thickness 3 mm) larger than the electrode area and an Al plate (thickness 5 mm), and the battery was appropriately pressed from both sides in the stacking direction. Then, the battery thus obtained was charged for the first time over 5 hours (upper limit voltage 4.2 V), then aged at 45 ° C. for 5 days, degassed and discharged, The battery of the example was completed.

For the battery thus obtained, the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity were measured in the same manner as in Example 1. The rated capacity (cell capacity) of the battery was 26 Ah. The ratio of the positive electrode area to the rated capacity was 16 cm ² / Ah. Further, for the obtained battery, the ratio of the rated capacity to the pore volume of the negative electrode active material layer was determined in the same manner as in Example 1, and found to be 1.25 Ah / cc.

  Table 1 below shows the rated capacity (cell capacity) and the ratio of the battery area to the rated capacity of the batteries produced in the above Examples and Comparative Examples, and the ratio of the rated capacity to the pore volume of the negative electrode active material layer. In addition, the amounts of conductive assistant (acetylene black) and binder (PVdF) in the positive electrode active material layers of the above Examples and Comparative Examples, and the amounts of conductive assistant (acetylene black) and binder in the negative electrode active material layer (SBR and CMC). Is shown in Table 1 below. Furthermore, Table 1 below shows the sizes of the positive electrode and the negative electrode, and the coating amount (weight per unit area) and density of the positive electrode and the negative electrode active material layer.

  For the battery obtained above, the Ra / Rct ratio was measured according to the following method, and the results are shown in Table 2 below.

(Measurement of Ra / Rct ratio)
Electrochemical impedance measurement is performed at 25 ° C. (measurement temperature), SOC (battery charge state) 50% (charge state of about 50% of rated capacity), measurement frequency range of 100 kHz to 10 mHz, applied voltage amplitude ± 10 mV, The measurement point is 10 points / decade. As shown in FIG. 3, in electrochemical impedance measurement, inductance components (R _L , L), electrolyte resistance (Rsol), charge transfer resistance (Ra, Rb), electric double layer capacitance components (CPEa, CPEb), An equivalent circuit represented by the diffusion component (Zw) and the limit capacity (C) is used. In this equivalent circuit, the electrochemical impedance Z is expressed by the following formula (A).

  Various parameters of the equivalent circuit are calculated by referring to the real component of the resistance, the imaginary component of the resistance, and the frequency obtained from the electrochemical impedance measurement.

  Further, Rct is a difference value between the resistance value intersecting the horizontal axis of the arc in the colle-coll plot (Nyquist plot) shown in FIG. 4 and the resistance value at the position on the lower frequency side of the arc. In FIG. 4, the vertical axis represents the reciprocal of the real component of the resistance output from the electrochemical impedance, and the horizontal axis represents the imaginary component of the resistance output from the electrochemical impedance on the horizontal axis.

  Ra / Rct ratio is calculated by dividing Ra obtained above by Rct.

  The batteries produced in the above examples and comparative examples were evaluated for durability (cycle characteristics) according to the following method. The results are shown in Table 2 below.

(Cycle characteristics (25 ° C))
The current density with respect to the positive electrode was set to ² mA / cm ² , and the batteries produced in each Example and Comparative Example were charged to a cutoff voltage of 4.15 V to obtain an initial charge capacity, and after a pause of 1 hour, to a cutoff voltage of 3.0 V The capacity when discharged was defined as the initial discharge capacity. This charge / discharge cycle was repeated 500 times. The ratio of the discharge capacity at the 500th cycle to the initial discharge capacity was defined as the capacity retention rate (%), and the cycle characteristics were evaluated. In addition, the said evaluation was performed at 25 degreeC. In the following Table 1, the result is shown in the column of “25 ° C. cycle @ 500 cyc”.

(Cycle characteristics (55 ° C))
The current density with respect to the positive electrode was set to ² mA / cm ² , and the batteries produced in each Example and Comparative Example were charged to a cutoff voltage of 4.15 V to obtain an initial charge capacity, and after a pause of 1 hour, to a cutoff voltage of 3.0 V The capacity when discharged was defined as the initial discharge capacity. This charge / discharge cycle was repeated 500 times. The ratio of the discharge capacity at the 300th cycle to the initial discharge capacity was defined as the capacity retention rate (%), and the cycle characteristics were evaluated. In addition, the said evaluation was performed at 55 degreeC. In the following Table 1, the result is shown in the column of “55 ° C. cycle @ 300 cyc”.

  From the results of Table 1 above, it can be seen that the non-aqueous electrolyte secondary battery of the example is superior in cycle characteristics as compared with the non-aqueous electrolyte secondary battery of the comparative example in which the Ra / Rct ratio is 0.35 or more. . On the other hand, in Comparative Example 5 with a small rated capacity and Comparative Example 4 with a small rated capacity with respect to the pore volume of the negative electrode active material layer, even if the Ra / Rct ratio is 0.35 or more, as in Comparative Examples 1-2 The cycle characteristics are not greatly degraded. From this, it is considered that in a battery having a high capacity, a high capacity density, and a large area, it is particularly important in terms of improving cycle characteristics that the Ra / Rct ratio is less than 0.35.

  Further, from the comparison between Example 5 and Examples 6 to 7, when the ratio of the rated capacity to the pore volume of the negative electrode active material layer is 1.4 Ah / cc or more, the Ra / Rct ratio is less than 0.33. This is considered to be more effective for improving the cycle characteristics. For this reason, it is considered that in a battery having a high capacity, a large area, and a higher capacity density, it is particularly important in terms of improving cycle characteristics that the Ra / Rct ratio is less than 0.33.

  In addition, from comparison between Examples 1 to 3 and Examples 8 to 9, it is considered that the cycle characteristics at a particularly high temperature (55 ° C.) can be further improved by setting the Ra / Rct ratio to more than 0.28. The From this, it is considered that in the case of a battery having a high capacity, a high capacity density and a large area, it is particularly important that the lower limit of the Ra / Rct ratio exceeds 0.28 in terms of improving the cycle characteristics at a high temperature.

10 Lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 Battery exterior material.

Claims (5)

A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of the positive electrode current collector;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the negative electrode current collector;
A separator;
A power generation element including
The ratio of the rated capacity to the void volume of the negative electrode active material layer is 1.12 Ah / cc or more, the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more, and the rated capacity is 30 Ah or more. A non-aqueous electrolyte secondary battery,
A nonaqueous electrolyte secondary battery having a ratio of Ra to a reaction resistance component Rct (Ra / Rct) obtained from an equivalent circuit of electrochemical impedance at 25 ° C. of less than 0.35. The ratio of the rated capacity to the pore volume of the negative electrode active material layer is 1.4 Ah / cc or more, the ratio of the battery area to the rated capacity is 4.0 cm ² / Ah or more, and the rated capacity is 30 Ah or more. ,
The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio (Ra / Rct) of Ra to a reaction resistance component Rct obtained from an equivalent circuit of electrochemical impedance at 25 ° C. is less than 0.33.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a ratio (Ra / Rct) of Ra to a reaction resistance component Rct obtained from an equivalent circuit of electrochemical impedance at 25 ° C exceeds 0.28. The positive electrode active material has a general formula: Li _a Ni _b Mn _c Co _d M _x O ₂
(Where, a, b, c, d, x are 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, where M is at least one selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr) The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, which is an oxide.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, which is a flat type nonaqueous electrolyte secondary battery.