JP2020035634A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a nonaqueous electrolyte secondary battery capable of exhibiting excellent output characteristics by reducing the internal resistance of a battery.SOLUTION: A nonaqueous electrolyte secondary battery includes: an electrode including a collector and an electrode active material layer arranged on a surface of the collector, the electrode active material layer containing an electrode active material and a gel-forming polymer; and an electrolyte layer arranged between the electrodes, the electrolyte layer comprising a separator impregnated with an electrolyte. When x [m] represents a pore volume per 1 mof the electrode, y [m] represents a volume of a gel-forming polymer contained per 1 mof the electrode, and z [%] represents a liquid-absorption rate of a gel-forming polymer with respect to the electrolyte, 0.30≤yz/x≤1.06 is satisfied.SELECTED DRAWING: None

Description

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

  2. Description of the Related Art In recent years, the spread of various electric vehicles has been expected to solve environmental and energy problems. Development of secondary batteries has been earnestly carried out as a vehicle-mounted power supply such as a motor drive power supply that holds the key to the spread of these electric vehicles. Non-aqueous electrolyte secondary batteries intended for application to in-vehicle power supplies are required to have high capacity and excellent output characteristics.

  As a technique for obtaining a battery with a high capacity, Patent Document 1 discloses that by increasing the thickness of an electrode, the relative proportion of a current collector or a separator is reduced to increase the energy density of the battery. Means are disclosed.

JP-A-9-204936

  However, when the thickness of the electrode is increased as in Patent Literature 1, a problem arises in that the internal resistance of the battery increases and output characteristics deteriorate.

  Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that can exhibit excellent output characteristics by reducing the internal resistance of the battery.

  The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, in a nonaqueous electrolyte secondary battery using an electrode having an electrode active material layer containing a gel-forming polymer and an electrolyte, the pore volume of the electrode, the volume of the gel-forming polymer, and the It has been found that it is effective to control the liquid absorption of the polymer so as to satisfy a predetermined relationship, and the present invention has been completed.

That is, the nonaqueous electrolyte secondary battery according to the present invention is an electrode in which an electrode active material layer containing an electrode active material and a gel-forming polymer is disposed on the surface of a current collector, and a separator disposed between the electrodes. And an electrolyte layer impregnated with an electrolytic solution. Here, the volume of pores per m ^{3 of the} electrode is x [m ³ ], the volume of the gel-forming polymer contained per m ^{3 of the} electrode is y [m ³ ], and the gel-forming polymer with respect to the electrolytic solution is When the liquid absorption rate of z is z [%],

Is satisfied.

  According to the nonaqueous electrolyte secondary battery of one embodiment of the present invention, excellent output characteristics can be exhibited by reducing the internal resistance of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which represented typically the bipolar secondary battery which is one Embodiment of this invention. FIG. 1 is a perspective view illustrating an appearance of a flat lithium ion secondary battery which is a typical embodiment of a secondary battery.

One embodiment of the present invention is an electrode in which an electrode active material layer including an electrode active material and a gel-forming polymer is disposed on a surface of a current collector, and a separator disposed between the electrodes is impregnated with an electrolytic solution. And a non-aqueous electrolyte secondary battery having an electrolyte layer. Here, the volume of pores per m ^{3 of the} electrode is x [m ³ ], the volume of the gel-forming polymer contained per m ^{3 of the} electrode is y [m ³ ], and the gel-forming polymer with respect to the electrolytic solution is When the liquid absorption rate of z is z [%],

Is satisfied. According to the nonaqueous electrolyte secondary battery of the present embodiment, excellent output characteristics can be exhibited by reducing the internal resistance of the battery.

  The detailed mechanism of the above effect is unknown, but is presumed as follows. The technical scope of the present invention is not limited to the following mechanism.

  In this embodiment, the electrode active material layer contains the electrode active material and the gel-forming polymer, and at this time, the electrode active material and the gel-forming polymer are structured. When the value of yz / x is controlled to 0.30 or more, the electrode active material and the gel-forming polymer are structured, and the generation of the electrode active material floating in the pores of the electrode is suppressed. Thereby, electron conduction can be improved. In addition, since the gel-forming polymer absorbs the electrolytic solution and plays a role in ion conduction, effective ion conduction can be improved. Therefore, the DC resistance can be reduced. Further, by controlling the value of yz / x to 1.06 or less, it is possible to suppress the gel-forming polymer from excessively covering the electrode active material. Thereby, a decrease in electron conduction can be suppressed. In addition, the gel-forming polymer excessively occupies the pores of the electrode, reduces the amount of the electrolyte solution, and suppresses the decrease in the amount of ions (eg, the amount of Li ions), thereby reducing the effective ion conduction. Can be suppressed. Therefore, the DC resistance can be reduced. As described above, by controlling the value of yz / x within a predetermined range, it is considered that the non-aqueous electrolyte secondary battery of the present embodiment can reduce the DC resistance value and exhibit excellent output characteristics. .

  Hereinafter, embodiments of the present invention described above will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited to only the following embodiments. . Hereinafter, the present invention will be described using a bipolar lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery. Note that the dimensional ratios in the drawings are exaggerated for the sake of explanation, and may differ from the actual ratios. In the present specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20 to 25 ° C.) and relative humidity of 40 to 50% RH.

  In this specification, the bipolar lithium ion secondary battery may be simply referred to as “bipolar secondary battery”, and the electrode for the bipolar lithium ion secondary battery may be simply referred to as “bipolar electrode”.

<Bipolar secondary battery>
FIG. 1 is a cross-sectional view schematically showing a bipolar secondary battery according to one embodiment of the present invention. The bipolar secondary battery 10 shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 29 which is a battery exterior body.

  As shown in FIG. 1, the power generating element 21 of the bipolar secondary battery 10 of the present embodiment has the positive electrode active material layer 13 electrically connected to one surface of the current collector 11, and It has a plurality of bipolar electrodes 23 having a negative electrode active material layer 15 electrically coupled to the opposite surface. Each bipolar electrode 23 is laminated via an electrolyte layer (separator) 17 to form a power generating element 21. At this time, the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other with the electrolyte layer 17 interposed therebetween. The bipolar electrodes 23 and the electrolyte layers 17 are alternately stacked. That is, the electrolyte layer 17 is disposed between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. ing.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the unit cell layers 19 are stacked. In addition, a seal portion (insulating layer) 31 is arranged on the outer peripheral portion of the unit cell layer 19. This prevents a liquid junction due to leakage of the electrolyte from the electrolyte layer 17, causes adjacent current collectors 11 to come into contact with each other in the battery, or causes a slight irregularity in the end of the unit cell layer 19 in the power generation element 21. To prevent a short circuit caused by the above. The positive electrode active material layer 13 is formed only on one surface of the outermost layer current collector 11a on the positive electrode side located on the outermost layer of the power generation element 21. The negative electrode active material layer 15 is formed only on one surface of the outermost layer current collector 11b on the negative electrode side located on the outermost layer of the power generating element 21.

  Further, in the bipolar secondary battery 10 shown in FIG. 1, a positive electrode current collector plate (positive tab) 25 is disposed adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior body. It is derived from the laminate film 29. On the other hand, a negative electrode current collector (negative electrode tab) 27 is arranged adjacent to the outermost layer current collector 11 b on the negative electrode side, and is similarly extended and led out of the laminate film 29.

  Note that the number of laminations of the unit cell layer 19 is adjusted according to a desired voltage. In the bipolar secondary battery 10, the number of stacks of the unit cell layer 19 may be reduced as long as a sufficient output can be ensured even if the thickness of the battery is made as thin as possible. In the bipolar secondary battery 10 as well, in order to prevent external impact and environmental degradation during use, the power generating element 21 is sealed under reduced pressure in a laminate film 29 as a battery exterior body, and the positive electrode current collector plate 25 and the negative electrode current collector 25 are sealed. It is preferable that the electric plate 27 is taken out of the laminate film 29. Note that, here, the embodiment of the present invention has been described by taking a bipolar secondary battery as an example, but the type of nonaqueous electrolyte battery to which the present invention can be applied is not particularly limited, and the unit cell layer in the power generation element is not limited. The present invention can be applied to any conventionally known non-aqueous electrolyte secondary battery such as a so-called parallel stacked battery of a type connected in parallel.

  Hereinafter, main components of the above-described bipolar secondary battery will be described.

[electrode]
The electrode has a configuration in which an electrode active material layer containing an electrode active material and a gel-forming polymer is arranged on the surface of a current collector.

(Current collector)
The current collector has a function of mediating the transfer of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There is no particular limitation on the material constituting the current collector, but, for example, a metal or a resin having conductivity may be employed.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plated material of a combination of these metals can be preferably used. Further, a foil having a metal surface coated with aluminum or a carbon-coated aluminum foil may be used. Among them, aluminum, stainless steel, copper, and nickel are preferred from the viewpoint of electron conductivity and battery operating potential.

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

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

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

  The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, as a material excellent in conductivity, potential resistance, or lithium ion blocking property, metal, conductive carbon, and the like can be given. The metal is not particularly limited, but is at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to include an alloy or metal oxide containing Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one kind.

  The amount of the conductive filler to be added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally about 5 to 80% by mass.

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

(Electrode active material layer)
The electrode active material layer is disposed on the surface of the current collector, and includes an electrode active material and a gel-forming polymer.

  The content (in terms of solid content) of the electrode active material in the electrode active material layer is preferably from 60 to 95% by mass, and more preferably from 80 to 95% by mass, from the viewpoint of output characteristics.

  The content of the gel-forming polymer (in terms of solid content) in the electrode active material layer can be appropriately adjusted so as to satisfy the above range of yz / x. The content (in terms of solid content) of the gel-forming polymer is preferably from 0.5 to 10.0% by mass, more preferably from 1.0 to 6.0% by mass, from the viewpoint of output characteristics.

  The thickness of the electrode active material layer for the positive electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 950 μm, and still more preferably 200 to 800 μm. Further, the thickness of the negative electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 1200 μm, and still more preferably 200 to 1000 μm. When the thickness of the electrode active material layer is equal to or greater than the lower limit described above, the energy density of the battery can be sufficiently increased. On the other hand, when the thickness of the electrode active material layer is equal to or less than the above upper limit, the structure of the electrode active material layer can be sufficiently maintained.

  In the present embodiment, in the electrode active material layer, the mechanical strength can be improved by structuring the electrode active material and the gel-forming polymer. Therefore, even if the thickness of the electrode is increased, the mechanical strength of the electrode can be improved while maintaining excellent output characteristics.

(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-based materials such as those in which some of these transition metals are replaced by other elements. A transition metal composite oxide, a lithium-transition metal phosphate compound, a lithium-transition metal sulfate compound, and the like can be given. In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. More preferably, a composite oxide containing lithium and nickel is used. More preferably Li (Ni-Mn-Co) O 2 , and in which a part of these transition metals are replaced by other elements (hereinafter, simply referred to as "NMC composite oxide"), or a lithium - nickel - cobalt -Aluminum composite oxide (hereinafter, also simply referred to as "NCA composite oxide") or the like is 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 an orderly) atomic layer are alternately stacked via an oxygen atomic layer. Then, one Li atom is contained per atom of the transition metal M, 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 also includes a composite oxide in which part of a transition metal element is replaced by another metal element. Other elements in this case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably, Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably, Ti, Zr, P, Al, Mg, Cr, and more preferably, Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

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

  Generally, it is known that nickel (Ni), cobalt (Co) and manganese (Mn) contribute to capacity and output characteristics from the viewpoint of improving the purity of a material and improving electronic conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is replaced by another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). The crystal structure is stabilized by the solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. As a result, it is considered that the capacity of the battery can be prevented from lowering even when charge and discharge are repeated, and excellent cycle characteristics can be realized.

In a more preferred embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26 Is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _{2 which} has been used in general consumer batteries. The capacity per unit mass is larger than that of. This has the advantage that the energy density can be improved and that a compact and high-capacity battery can be manufactured, which is preferable from the viewpoint of the cruising distance.

Moreover, as a more preferable embodiment, LiNi _0.8 Co _0.1 Al _0.1 O ₂ or LiNi _0.8 Co _0.15 Al _0.05 O ₂ is preferable from the viewpoint of larger capacity.

  The average particle size of the positive electrode active material is preferably 1 to 100 μm, more preferably 1 to 20 μm, from the viewpoint of increasing the output. In the present specification, the average particle diameter used is a value measured by a particle size distribution analyzer using a laser diffraction / scattering method.

(Negative electrode active material)
Examples of the negative electrode active material include carbon materials such as graphite (graphite), soft carbon, and hard carbon; lithium-transition metal composite oxides (eg, Li ₄ Ti ₅ O ₁₂ ); metal materials (tin, silicon); Alloy-based negative electrode materials (for example, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, and the like) and the like. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoints of capacity and output characteristics, a carbon material, a lithium-transition metal composite oxide, and a lithium alloy-based negative electrode material are preferably used as the negative electrode active material. In addition, it goes without saying that a negative electrode active material other than the above may be used.

  Although the average particle diameter of the negative electrode active material is not particularly limited, it is preferably 1 to 100 μm, more preferably 1 to 20 μm, from the viewpoint of high output.

(Gel-forming polymer)
The gel-forming polymer is an ion-conductive polymer, and can form a structure together with the electrode active material and play a role of ion conduction. As the gel-forming polymer, from the viewpoint of output characteristics, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP), It is at least one selected from the group consisting of polymethyl methacrylate (PMMA), polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polymethyl methacrylate, and a copolymer thereof.

  The gel-forming polymer is preferably polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (EPO) from the viewpoint of further enhancing output characteristics. (PVdF-HEP) and polymethyl methacrylate (PMMA), more preferably polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP).

The volume of the gel-forming polymer contained per electrode 1 m ³ is not particularly limited, can be appropriately adjusted so as to satisfy the relationship of 0.30 ≦ yz / x ≦ 1.06. The volume of the gel-forming polymer contained per electrode 1 m ³ is, for example, 0.006～0.038M ^3, preferably 0.009～0.035M ^3, more preferably 0.015～0.028M ³ is there. The volume of the gel-forming polymer contained per electrode 1 m ³ can be controlled by such charged amount.

  The gel-forming polymer preferably has a liquid absorption of 10% or more, more preferably 50% or more, with respect to the electrolytic solution. The upper limit of the liquid absorption of the gel-forming polymer with respect to the electrolytic solution is not particularly limited, but is, for example, 200% or less, preferably 120% or less, and more preferably 90% or less. When the absorption rate of the gel-forming polymer with respect to the electrolytic solution is 10% or more, the gel-forming polymer can sufficiently hold the electrolytic solution, and thus can perform ion conduction. When the absorption rate of the gel-forming polymer with respect to the electrolyte is 200% or less, the structure with the electrode active material can be maintained.

  In the present specification, the “absorption rate of the gel-forming polymer with respect to the electrolytic solution” is calculated by the following formula by measuring the mass of the gel-forming polymer before and after immersion in the electrolytic solution.

  Liquid absorption (%) = [(mass of gel-forming polymer after immersion in electrolyte−mass of gel-forming polymer before immersion in electrolyte) / mass of gel-forming polymer before immersion in electrolyte] × 100.

  As a sample, the gel-forming polymer is dissolved in N-methyl-2-pyrrolidone to prepare a cast film. The immersion of the cast film in the electrolytic solution is performed at 25 ° C. to 50 ° C. for 24 hours.

As an electrolytic solution for obtaining the liquid absorption rate, a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1: 1) to _LiN obtained by dissolving the _(FSO 2) 2 2mol / L Use electrolyte.

(Conduction aid)
The electrode active material layer may further include a conductive additive.

  The conductive additive has a function of forming an electron conductive path (conductive path) in the electrode active material layer. When such an electron conduction path is formed in the electrode active material layer, the internal resistance of the battery is reduced, which can contribute to an improvement in output characteristics at a high rate. In particular, at least a part of the conductive additive forms a conductive path that electrically connects the two main surfaces of the electrode active material layer (in the present embodiment, the conductive path contacts the electrolyte layer side of the electrode active material layer). It is preferable to form a conductive path that electrically connects the first main surface to the second main surface that contacts the current collector. By having such a form, the electron transfer resistance in the thickness direction in the electrode active material layer is further reduced, so that the output characteristics at a high rate of the battery can be further improved. Note that at least a part of the conductive additive forms a conductive path that electrically connects the two main surfaces of the electrode active material layer (in the present embodiment, the conductive path is in contact with the electrolyte layer side of the electrode active material layer). (A conductive path for electrically connecting the first main surface to the second main surface contacting the current collector side is formed) using a SEM or an optical microscope to determine the cross section of the electrode active material layer. It can be confirmed by observation.

  From the viewpoint of reliably forming such a conductive passage, the conductive auxiliary agent is preferably a conductive fiber having a fibrous form. Specifically, carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers obtained by uniformly dispersing a highly conductive metal or graphite in synthetic fibers, and metals such as stainless steel are used. Metal fibers, conductive fibers in which the surfaces of organic fibers are coated with a metal, and conductive fibers in which the surfaces of organic fibers are coated with a resin containing a conductive substance. Among them, carbon fibers are preferred because they have excellent conductivity and are lightweight.

  However, a conductive auxiliary agent having no fibrous form may be used. For example, a conductive auxiliary having a particulate (for example, spherical) form can be used. When the conductive auxiliary agent is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as a powder, a sphere, a plate, a column, an irregular shape, a scale, and a spindle. The average particle diameter (primary particle diameter) when the conductive additive is in the form of particles is not particularly limited, but is preferably about 0.01 to 10 μm from the viewpoint of the electric characteristics of the battery. In addition, in this specification, "particle diameter" means the largest distance L among the distances between any two points on the outline of the conductive additive. The value of the “average particle diameter” is determined by using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) as an average value of particle diameters of particles observed in several to several tens of visual fields. It is assumed that the calculated value is adopted.

  Examples of the conductive assistant having a particulate (eg, spherical) form include, for example, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium; alloys or metal oxides containing these metals; (CNT), carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), but are not limited thereto. Further, a material obtained by coating the above-described metal material around a particulate ceramic material or resin material by plating or the like can also be used as the conductive assistant. Among these conductive aids, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon. , Silver, gold, and carbon, and more preferably at least one carbon. One of these conductive assistants may be used alone, or two or more thereof may be used in combination.

  The content of the conductive additive in the electrode active material layer is preferably 4 to 8% by mass based on 100% by mass of the total solid content of the electrode active material layer (the sum of the solid contents of all members). When the content of the conductive auxiliary agent is in the above range, there is an advantage that an electron conduction path can be favorably formed in the electrode active material layer and a decrease in energy density of the battery can be suppressed.

(Structure composed of electrode active material, gel-forming polymer and conductive aid)
In a preferred embodiment of the present invention, the electrode active material layer includes a structure composed of the electrode active material, the gel-forming polymer, and the conductive auxiliary. Thereby, the electrode active material can be brought into good contact with the conductive auxiliary agent, and the electrode active material is activated, so that the electron conduction can be further improved. In addition, since the conductive auxiliary agent is structured around the electrode active material, excellent conductivity can be ensured, so that output and capacity can be improved. Further, by structuring the conductive additive around the electrode active material, percolation in the pores is formed. Therefore, the effective ionic conductivity can be further improved. In addition, with such a structure, the electrode active material layer can be a free-standing film, and the strength of the electrode can be further increased.

[Method of calculating pore volume of electrode]
The pore volume of the electrode is calculated as follows.
(1) The mass per unit area of the electrode is measured, and the mass of each material per unit area is determined from the mixing ratio of the materials used.
(2) The thickness [A] of the electrode is measured.
(3) Using the mass of each material obtained in (1) and the density of each material, calculate the electrode thickness [B] when the porosity is 0%.
(4) The pore volume of the electrode is calculated from the difference (AB) between the measured electrode thickness [A] and the calculated electrode thickness [B].

The pore volume per 1 m ^{3 of the} electrode is not particularly limited, and can be appropriately adjusted so as to satisfy the relational expression of 0.30 ≦ yz / x ≦ 1.06. Pore volume per electrode 1 m ³ is, for example, 0.180m ³ ~0.445m ^3, preferably 0.190m ³ ~0.435m ^3. Pore volume per electrode 1 m ³ can be adjusted particle diameter of the electrode active material, the charged amount of the gel forming polymer, such as by the thickness of the electrode active material layer. In addition, as described later, it can be adjusted by pressing at the time of manufacturing the electrode.

[Electrolyte layer]
The electrolyte layer is disposed between the electrodes, and has a configuration in which the separator is impregnated with the electrolytic solution.

  The electrolyte has a function as a carrier for lithium ions. The electrolyte constituting the electrolyte layer has a form in which a lithium salt is dissolved in a non-aqueous solvent.

  Non-aqueous solvents include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF) ), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) ), And γ-butyrolactone (GBL). Among them, non-aqueous solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) ) Is preferable, and preferably contains ethylene carbonate. As the nonaqueous solvent to be added, only one kind may be used alone, or two or more kinds may be used in combination.

Examples of the lithium salt include LiN (FSO ₂ ) ₂ , Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like. Among them, LiN (FSO ₂ ) ₂ is preferable from the viewpoint of battery output and charge / discharge cycle characteristics.

  The concentration of the lithium salt in the electrolyte is preferably from 0.1 to 3.0 mol / L, and more preferably from 0.8 to 2.2 mol / L.

  The electrolyte may further include additives other than the above-described components. Further, the additive may be contained in the electrolytic solution. 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, and 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 Oxymethylethylene carbonate, allyloxymethylethylene carbonate, acryloxymethylethylene carbonate, Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. One of these additives may be used alone, or two or more thereof may be used in combination. When the additive is used in the electrolytic solution, the amount is preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass, based on 100% by mass of the electrolytic solution before adding the additive. % By mass.

  In this embodiment, a separator is used for the electrolyte layer. The separator has a function of retaining electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition between the positive electrode and the negative electrode.

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

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

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. As an example, in a use such as a secondary battery for driving a motor such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV), the thickness is 4 to 60 μm in a single layer or a multilayer. Is desirable. It is desirable that the micropore diameter of the microporous (microporous membrane) separator is 1 μm or less at maximum (usually, the pore diameter is about several tens nm).

  As the nonwoven fabric separator, conventionally known materials such as cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; polyimides and aramids 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. Further, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, and particularly preferably 10 to 100 μm.

  The separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (a separator with a heat-resistant insulating layer). The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a high heat-resistant separator having a melting point or a thermal 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, which increases when the temperature rises, is reduced, so that the effect of suppressing heat shrinkage can be obtained. As a result, induction of a short circuit between the electrodes of the battery can be prevented, so that a battery configuration in which performance degradation due to a rise in temperature hardly occurs is obtained. In addition, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the separator is hardly broken. Further, the separator is unlikely to curl in the battery manufacturing process due to the effect of suppressing heat shrinkage and the high mechanical strength.

The inorganic particles in the heat-resistant insulating layer contribute to the mechanical strength of the heat-resistant insulating layer and the effect of suppressing heat shrinkage. The material used as the inorganic particles is not particularly limited. Examples include oxides of silicon, aluminum, zirconium, and titanium (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides, and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. In addition, one kind of these inorganic particles may be used alone, or two or more kinds may be used in combination. Among these, from the viewpoint of cost, it is preferable to use silica (SiO ₂ ) or alumina (Al ₂ O ₃ ), and it is more preferable to use alumina (Al ₂ O ₃ ).

The weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . Within this range, sufficient ion conductivity is obtained, and the heat resistance is preferably maintained.

  The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles and the inorganic particles and the resin porous substrate layer. The binder stably forms the heat-resistant insulating layer and prevents peeling between the porous base layer and the heat-resistant insulating layer.

  There is no particular limitation on the binder used for the heat-resistant insulating layer. For example, carboxymethylcellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber Compounds such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), and methyl acrylate can be used as the binder. Among them, carboxymethyl cellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. One of these compounds may be used alone, or two or more of them may be used in combination.

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

The heat shrinkage 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, the heat generation becomes high, and even when the battery internal temperature reaches 150 ° C., the contraction of the separator can be effectively prevented. As a result, induction of a short circuit between the electrodes of the battery can be prevented, so that a battery configuration in which performance degradation due to a rise in temperature hardly occurs is obtained.

[Positive current collector and negative current collector]
The material constituting the current collectors (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector for a lithium ion secondary battery can be used. As a constituent material of the current collector, for example, a metal material such as aluminum, copper, titanium, nickel, stainless steel (SUS), or an alloy thereof is 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 collector 27 and the negative electrode current collector 25, or different materials may be used.

[Positive electrode lead and negative electrode lead]
Although not shown, the current collector 11 and the current collector (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, the parts removed from the exterior may be in contact with peripheral equipment or wiring, etc., causing a short circuit, which will not affect products (for example, automobile parts, especially electronic equipment, etc.). It is preferable to coat with a tube or the like.

[Seal part]
The seal portion (insulating layer) 31 has a function of preventing contact between current collectors and short-circuiting at an end of the unit cell layer. As a material constituting the seal portion, any material having an insulating property, a seal property against falling off of the solid electrolyte, a seal property against moisture permeation from the outside (sealing property), heat resistance at a battery operating temperature, and the like can be used. Good. For example, acrylic resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber (ethylene-propylene-diene rubber: EPDM), and the like can be used. Further, an isocyanate-based adhesive, an acrylic resin-based adhesive, a cyanoacrylate-based adhesive, or the like, or a hot-melt adhesive (urethane resin, polyamide resin, polyolefin resin), or the like may be used. Among them, polyethylene resin or polypropylene resin is preferably used as a constituent material of the insulating layer from the viewpoint of corrosion resistance, chemical resistance, easiness of production (film forming property), economy, etc., and amorphous polypropylene resin is mainly used. It is preferable to use a resin obtained by copolymerizing ethylene, propylene and butene as components.

[Battery exterior]
As the battery outer case, a known metal can case can be used, and a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generating element as shown in FIG. 1, can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the present invention is not limited thereto. Laminated films are desirable from the viewpoint that they are excellent in high output and cooling performance and can be suitably used for batteries for large-sized devices for EV and HEV. In addition, since the group pressure applied to the power generation element from the outside can be easily adjusted and the thickness of the electrolyte layer can be easily adjusted to a desired value, the exterior body is more preferably an aluminate laminate.

  The bipolar secondary battery of the present embodiment can exhibit excellent output characteristics. Therefore, the bipolar secondary battery of the present embodiment is suitably used as a power supply for driving EVs and HEVs.

[Pore volume of electrode, volume of gel-forming polymer, and liquid absorption of gel-forming polymer]
In the nonaqueous electrolyte secondary battery of the present embodiment, the volume of pores per m ^{3 of the} electrode is x [m ³ ], and the volume of the gel-forming polymer contained per m ^{3 of the} electrode is y [m ³ ]. When the absorption rate of the gel-forming polymer with respect to the electrolyte is z [%],

Is satisfied. The present inventors have found that there is an appropriate range between the ratio of the gel-forming polymer to the pores of the electrode and the liquid absorption of the gel-forming polymer, and quantified the finding with the above relational expression. .

  According to the nonaqueous electrolyte secondary battery having such a configuration, the electrode active material layer contains the electrode active material and the gel-forming polymer, and at this time, the electrode active material and the gel-forming polymer are structured. When the value of yz / x is controlled to 0.30 or more, the electrode active material and the gel-forming polymer are structured, and the generation of the electrode active material floating in the pores of the electrode is suppressed. Thereby, electron conduction can be improved. In addition, since the gel-forming polymer absorbs the electrolytic solution and plays a role in ion conduction, effective ion conduction can be improved. Therefore, the DC resistance can be reduced. Further, by controlling the value of yz / x to 1.06 or less, it is possible to suppress the gel-forming polymer from excessively covering the electrode active material. Thereby, a decrease in electron conduction can be suppressed. Further, by suppressing the gel-forming polymer from excessively occupying the pores of the electrode, decreasing the amount of the electrolytic solution and decreasing the amount of Li ions, a decrease in effective ion conduction can be suppressed. Therefore, the DC resistance can be reduced. As described above, by controlling the value of yz / x within a predetermined range, the non-aqueous electrolyte secondary battery of the present embodiment can exhibit excellent output characteristics by reducing the DC resistance value. Conceivable.

  From the viewpoint of further improving the output characteristics, the above x, y and z preferably satisfy 0.45 ≦ yz / x ≦ 0.86, and satisfy 0.50 ≦ yz / x ≦ 0.86. Is more preferred.

[Method for producing non-aqueous electrolyte secondary battery]
One embodiment of the present invention provides an electrode by forming an electrode active material layer by applying an electrode active material slurry containing an electrode active material, a gel-forming polymer, a conductive additive, and a solvent to the surface of a current collector. And a step of laminating the electrode and the separator to obtain a power generating element, and a step of covering the power generating element with an exterior body and injecting an electrolytic solution. At this time, the absorption rate of the gel-forming polymer with respect to the electrolyte is 10% or more. According to the method for manufacturing a nonaqueous electrolyte secondary battery of the present embodiment, the gel-forming polymer is structured with an electrode active material and a conductive auxiliary, and the gel-forming polymer holds an electrolytic solution, so that the electronic conductivity is improved. By optimizing ion conduction and reducing the DC resistance value, a non-aqueous electrolyte secondary battery exhibiting excellent output characteristics can be obtained.

(Step of obtaining an electrode by forming an electrode active material layer by applying an electrode active material slurry containing an electrode active material, a gel-forming polymer, a conductive additive and a solvent to the surface of the current collector)
First, an electrode active material slurry is prepared by mixing the above-mentioned electrode active material, gel-forming polymer and conductive additive together with a solvent.

  The solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used.

  The method for preparing the electrode active material slurry by mixing the electrode active material, the gel-forming polymer, the conductive auxiliary agent and the solvent is not particularly limited, and conventionally known knowledge such as the order of addition of the members and the mixing method is appropriately referred to. .

  The concentration of the electrode active material slurry is not particularly limited. However, from the viewpoint of facilitating the application of the slurry described later, the concentration of the total solid content with respect to 100% by mass of the electrode active material slurry is preferably 35 to 75% by mass, and more preferably 40 to 70% by mass. When the concentration is within the above range, an electrode active material layer having a sufficient thickness can be easily formed by coating.

  Next, the electrode active material slurry is applied on the current collector and dried. After the application, pressing may be performed as necessary. As described above, by mixing the electrode active material, the gel-forming polymer, and the conductive auxiliary at the time of preparing the electrode active material slurry, the electrode active material having the structure including the electrode active material, the gel-forming polymer, and the conductive auxiliary can be mixed. A material layer can be formed.

  The method for applying the electrode active material slurry to the current collector is not particularly limited, and examples thereof include a screen printing method, a spray coating method, an electrostatic spray coating method, an ink jet method, and a doctor blade method.

The coating thickness of the electrode active material slurry is appropriately set in consideration of the thickness of the electrode active material layer to be formed. The coating thickness of the electrode active material slurry is preferably 200 to 2000 μm, and more preferably 400 to 1000 μm.

  The method of drying after applying the electrode active material slurry on the current collector is not particularly limited, and it is sufficient that at least a part of the solvent is removed. Heating is mentioned as the drying method. The drying conditions (drying time, drying temperature, and the like) can be appropriately set according to the volatilization rate of the solvent contained in the applied electrode active material slurry, the applied amount of the electrode active material slurry, and the like.

  When the pressing is performed, the pressing means is not particularly limited, and for example, a calender roll, a flat plate press, or the like can be used.

  Thus, an electrode (a positive electrode or a negative electrode) can be obtained.

(Step of laminating electrode and separator to obtain power generation element)
After producing the electrode as described above, the electrode and the separator are laminated to produce a power generating element. The method for producing the power generating element is not particularly limited, and conventionally known knowledge is appropriately referred to. As an example, a unit cell layer is manufactured by laminating a positive electrode and a negative electrode so as to face each other with a separator interposed therebetween. By stacking the unit cell layers to a desired number, a power generation element can be obtained.

  A positive electrode tab and a negative electrode tab are joined to the obtained power generating element by welding. If necessary, it is desirable to remove extra tabs and the like by welding after welding. Although there is no particular limitation on the joining method, since it is possible to perform the joining in an extremely short time by using an ultrasonic welding machine without generating heat (heating) at the time of joining, the electrode active material layer (negative electrode active material) by heat is used. Layer and the positive electrode active material layer). At this time, the positive electrode tab and the negative electrode tab can be arranged so as to be opposed (facing) on the same side (same extraction side). Thereby, the positive electrode tabs of each positive electrode can be bundled into one and taken out from the package as one positive electrode current collector plate. Similarly, the negative electrode tabs of each negative electrode can be bundled into one and taken out from the package as one negative electrode current collector plate. Further, the positive electrode current collector (positive electrode current collector tab) and the negative electrode current collector (negative electrode current collector tab) may be arranged so as to be on opposite sides (different extraction sides).

(Step of covering the power generation element with an exterior body and injecting the electrolyte)
The obtained power generating element is covered with an exterior body. The method for covering the power generating element with the outer package is not limited, and conventionally known knowledge is appropriately referred to. As an example, a laminate film using a power generation element for a battery outer package is provided so that a positive current collector (a positive current collector tab) and a negative current collector (a negative current collector tab) can be taken out of the battery outer package from above and below. Then, sandwich it.

  Next, three sides of the outer peripheral portions (sealing portions) of the upper and lower laminated films are sealed by thermocompression bonding. A three-side sealed body is obtained by sealing three sides of the outer peripheral portion by thermocompression bonding. At this time, it is preferable that the heat sealing portion on the side from which the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) are taken out is sealed. This is because if the positive electrode current collector plate and the negative electrode current collector plate are in the openings during the subsequent injection, the electrolyte may be scattered during the injection.

  Note that, in the above description, a battery having a stacked structure is described. However, the battery is not limited to a stacked type, and various shapes such as a square, a paper, a cylinder, and a coin can be adopted as the battery configuration. it can.

  Next, an electrolytic solution is injected into the inside of the three-side sealed body from the opening of the remaining one side of the three-side sealed body by the liquid injection device. As a result, an electrolyte layer in which the electrolyte is impregnated in the separator is formed. At this time, the three-sided sealed body may be housed in a vacuum box connected to a vacuum pump so that the electrolyte, particularly the separator and the electrode active material layer, inside the three-sided sealed body can be impregnated as soon as possible. preferable. Further, it is desirable to perform the injection in a state where the pressure is reduced and the inside is set in a high vacuum state. After the injection, the three-side sealed body is taken out of the vacuum box, and the remaining one side of the three-side sealed body is temporarily sealed to obtain a laminate type (laminated structure) nonaqueous electrolyte secondary battery.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery.

  As shown in FIG. 2, the flat bipolar secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for extracting electric power are drawn out from both sides thereof. I have. The power generation element 57 is wrapped by a battery outer casing (laminated film 52) of the bipolar secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. Sealed. Here, the power generation element 57 corresponds to the power generation element 21 of the bipolar secondary battery 10 shown in FIG. 1 described above. The power generating element 57 is formed by stacking a plurality of bipolar electrodes 23 via the electrolyte layer 17.

  Note that the lithium ion secondary battery is not limited to a stacked flat battery. The wound lithium ion secondary battery may have a cylindrical shape, or may have such a cylindrical shape deformed into a rectangular flat shape. It is not particularly limited. In the case of the cylindrical shape, there is no particular limitation, for example, a laminate film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used. Preferably, the power generating element is clad with an aluminum laminated film. With this configuration, weight reduction can be achieved.

  The removal of the tabs (58, 59) shown in FIG. 2 is not particularly limited. As shown in FIG. 2, the positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side. It is not limited to. In a wound lithium ion battery, terminals may be formed using, for example, a cylindrical can (metal can) instead of a tab.

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

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

[Volume energy density and rated discharge capacity]
In a general electric vehicle, an important development target is how to increase the mileage (cruising distance) per charge. In consideration of such points, it is preferable that the volume energy density of the battery is 157 Wh / L or more, and the rated capacity is 20 Wh or more.

In addition, as a viewpoint of a larger battery, which is different from the viewpoint of the physical size of the electrode, the size of the battery can be specified from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated type laminated battery, the value of the ratio of the battery area to the rated capacity (projected area of the battery including the battery exterior body) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. The present invention is preferably applied to a certain battery. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. Note that the aspect ratio of the electrode is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both the required performance of the vehicle and the mounting space can be achieved.

[Battery pack]
An assembled battery is formed by connecting a plurality of batteries. More specifically, at least two or more are used for serialization and / or parallelization. It is possible to freely adjust the capacity and the voltage by making them serial and parallel.

  A plurality of batteries may be connected in series or in parallel to form a detachable small assembled battery. Then, a plurality of the small battery packs which can be attached and detached are further connected in series or in parallel, and a large capacity and a large capacity suitable for a vehicle drive power supply and an auxiliary power supply requiring a high volume energy density and a high volume output density are required. A battery pack having an output can also be formed. How many batteries are connected to create a battery pack, and how many small battery packs are stacked to produce a large capacity battery pack, depends on the battery capacity of the vehicle (electric vehicle) to be mounted. It may be determined according to the output.

[vehicle]
The nonaqueous electrolyte secondary battery of the present embodiment maintains a discharge capacity even when used for a long time, and has good cycle characteristics. Further, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity and larger size and longer life than electric and portable electronic device applications. . Therefore, the nonaqueous electrolyte secondary battery can be suitably used as a vehicle power supply, for example, as a vehicle drive power supply or an auxiliary power supply.

  Specifically, a battery or an assembled battery obtained by combining a plurality of these batteries can be mounted on a vehicle. According to the present invention, since a long-life battery having excellent long-term reliability and output characteristics can be formed, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed. . For example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (all four-wheel vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) This is because the use in a motorcycle (including a motorcycle) and a three-wheeled vehicle) results in a vehicle having a long life and high reliability. However, the application is not limited to automobiles. For example, other vehicles, for example, various power supplies for moving objects such as trains can be applied, and a mounting power supply such as an uninterruptible power supply. It is also possible to use as.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to only the following Examples.

[Example 1]
<Preparation of positive electrode>
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (Li-containing layered transition metal oxide, average particle diameter: 9 μm) as a positive electrode active material, and acetylene black as a conductive additive (Denka Corporation) Black (registered trademark); average particle diameter (primary particle diameter: 0.023 μm) and carbon fiber (manufactured by Osaka Gas Chemical Co., Ltd.), and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) as a gel-forming polymer (PVdF-HFP) (Kyner Flex 2501-10, manufactured by Arkema) and N-methyl-2-pyrrolidone as a solvent so that the ratio becomes 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio). Mixing and mixing at 2000 rpm using a planetary stirring type mixing and kneading device “Awatori Neritaro” (ARE-310, manufactured by Shinky Corporation) Mixed to prepare a positive electrode slurry minutes. The positive electrode slurry was uniformly applied on an Al foil placed on a smoothing plate using a doctor blade so that the thickness of the positive electrode active material layer was 400 μm. Thereafter, by drying on a hot plate heated to 80 ° C. for 2 hours, a positive electrode having a porous structure with a positive electrode active material mass (weight of the positive electrode active material) of 94 mg / cm ² was obtained.

<Preparation of negative electrode>
Hard carbon (manufactured by Kureha Battery Materials Japan Co., Ltd., Carbotron (registered trademark) PS (F), average particle diameter: 20 μm) as an anode active material, and acetylene black (manufactured by Denka Corporation) as a conductive aid , Denka Black (registered trademark); average particle size (primary particle size: 0.023 μm), carbon fiber (manufactured by Osaka Gas Chemical Co., Ltd.), and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) as a gel-forming polymer. ) (Kyner Flex 2501-10, manufactured by Arkema) and N-methyl-2-pyrrolidone as a solvent are 8.28: 0.54: 0.18: 0.21: 9.00 (mass ratio), respectively. And a planetary agitation type mixing and kneading device “Awatori Neritaro” (ARE-310, Shinki Co., Ltd.) Using Ltd.) were mixed for 6 minutes at 2000 rpm, to prepare a negative electrode slurry. The negative electrode slurry was uniformly applied on a Cu foil placed on a smoothing plate using a doctor blade so that the thickness of the negative electrode active material layer was 420 μm. Thereafter, by drying on a hot plate heated to 80 ° C. for 2 hours, a negative electrode having a porous structure of 39 mg / cm ^{2 in} terms of negative electrode active material mass (basis weight of negative electrode active material) was obtained.

<Production of lithium ion battery>
The resulting 12cm ² a positive electrode was cut negative electrode such that the 12.4 cm ^2. In the positive electrode, the aluminum foil with the Al terminal was laminated on the current collector foil side of the cut positive electrode. In the negative electrode, the copper foil with the Ni terminal was laminated on the current collecting foil side of the cut negative electrode. A separator (manufactured by Celgard Co., Ltd., manufactured by Celgard (registered trademark) 3501 PP) was inserted into the positive electrode side and the negative electrode side to form a laminate. Sandwiching the laminate heat fusion type aluminum laminate film, a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1: 1) to _{LiN (FSO} 2) dissolved 2 2 mol / L to obtain After injecting the obtained non-aqueous electrolyte, it was vacuum-sealed to produce a pouch type lithium ion battery.

[Example 2]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.10: 6.00 (mass ratio), and in the preparation of the porous structure for negative electrode, the mixing ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1, except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.34: 9.00 (mass ratio). .

[Example 3]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.13: 6.00 (mass ratio), and in the production of the porous structure for negative electrode, the mixing ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was fabricated in the same manner as in Example 1, except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.45: 9.00 (mass ratio). .

[Example 4]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.16: 6.00 (mass ratio), and in the production of the porous structure for negative electrode, the compounding ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1 except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.57: 9.00 (mass ratio). .

[Example 5]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.20: 6.00 (mass ratio), and in the production of the porous structure for negative electrode, the mixing ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1 except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.68: 9.00 (mass ratio). .

[Comparative Example 1]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.00: 6.00 (mass ratio), and in the production of the porous structure for a negative electrode, the mixing ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1, except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.00: 9.00 (mass ratio). .

[Comparative Example 2]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.23: 6.00 (mass ratio), and in the production of the porous structure for negative electrode, the mixing ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1, except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.80: 9.00 (mass ratio). .

[Comparative Example 3]
In producing the porous structure for the positive electrode, the compounding ratio of the members was changed from 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio) to 8.28: 0.54: 0.18. : 0.26: 6.00 (mass ratio), and in the production of the porous structure for negative electrode, the compounding ratio of the members was 8.28: 0.54: 0.18: 0.21: 9. A lithium ion battery was produced in the same manner as in Example 1, except that the ratio was changed from 00 (mass ratio) to 8.28: 0.54: 0.18: 0.91: 9.00 (mass ratio). .

[Calculation of pore volume of electrode]
The pore volumes of the electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 3 were calculated as follows.
(1) The mass per unit area was measured. The mass of each material per unit area was determined from the mixing ratio of the materials.
(2) The thickness [A] of the electrode was measured using a micrometer.
(3) The thickness [B] of the electrode when the porosity was 0% was calculated using the mass of each material obtained in (1) and the density of each material.
(4) to calculate the pore volume from the difference (A-B) of the electrode of thickness between the calculated electrode measured electrode was determined pore volume per electrode 1 m ^3.

  Table 1 shows the results.

[Calculation of porosity of gel-forming polymer]
The occupancy rate of the gel-forming polymer vacancies in the electrodes prepared in Examples 1 to 5 and Comparative Examples 2 to 3 was calculated.

The gel-forming polymer pore occupancy is the volume of the gel-forming polymer contained in the electrode made using the gel-forming polymer with respect to the pore volume of the electrode made using a material other than the gel-forming polymer. Means percentage. That is, the gel-forming polymer void occupancy was calculated by the following equation:
Gel-forming polymer pore occupancy = gel-forming polymer volume / (gel-forming polymer volume + electrode pore volume).

Specifically, the porosity of the gel-forming polymer was calculated as follows;
(1) The mass per unit area was measured. The mass of each material per unit area was determined from the mixing ratio of the materials.
(2) The thickness [A] of the electrode was measured using a micrometer.
(3) Using the mass of each material obtained in (1) and the density of each material, the thickness [B] of the electrode when the porosity was 0% and the volume of each material were calculated. .
(4) The pore volume of the electrode was calculated from the difference (AB) between the measured electrode thickness and the calculated electrode thickness.
(5) The porosity of the gel-forming polymer was calculated using the pore volume of the electrode and the volume of the gel-forming polymer.

  Table 1 shows the results.

[Measurement of absorption rate of gel-forming polymer to electrolyte]
The liquid absorption of the gel-forming polymer with respect to the electrolytic solution was calculated by the following formula by measuring the mass of the gel-forming polymer before and after immersion in the electrolytic solution;
Liquid absorption (%) = [(mass of gel-forming polymer after immersion in electrolyte−mass of gel-forming polymer before immersion in electrolyte) / mass of gel-forming polymer before immersion in electrolyte] × 100.

  As a sample, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) (Kyner Flex 2501-10, manufactured by Arkema) was dissolved in N-methyl-2-pyrrolidone to prepare a cast film. The immersion of the cast film in the electrolytic solution was performed at 25 ° C to 50 ° C for 24 hours.

As an electrolytic solution for obtaining the liquid absorption rate, a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1: 1) to _LiN obtained by dissolving the _(FSO 2) 2 2mol / L An electrolytic solution was used.

  Table 1 shows the results.

[Output characteristic evaluation]
The output evaluation was performed by installing the lithium ion battery prepared above in a thermostat (ARSF-0250-10, manufactured by Espec Corporation) set at 25 ° C. The output was evaluated in a state where the lithium ion battery was sandwiched between a urethane rubber of 5 mm in thickness and a silicone sponge sheet and restrained at 6 points using a metal plate of 10 mm in thickness and M6 screws. First, as a capacity check at a low rate, charge / discharge evaluation was performed twice at a cell voltage range of 4.2 to 2.5 V and a current value of 0.05 C, and the obtained capacity was used as a reference capacity. The C rate was calculated based on the cell discharge capacity obtained at a 2.5 V cutoff. Next, after charging to 4.2 V at 0.05 C, discharging was performed at a rate of 0.05 C, 0.1 C, 0.2 C, 0.33 C, and 0.5 C until the cell voltage reached 2.5 V. Was. The [effective capacity / reference capacity × 100] at the obtained 0.33C was defined as [0.33C effective capacity ratio (%)]. Table 1 shows the results.

[DCR resistance measurement]
As in the case of the output characteristic evaluation, the SOC was adjusted to 50% after two cycles of charge / discharge at a 0.05 C rate. A resistance value was calculated from a voltage obtained by flowing a direct current for 30 seconds to the adjusted cell. The ohmic resistance was calculated from the voltage difference immediately after the application of the current (0.1 second). The reaction resistance was calculated from the voltage difference one second after current application. The diffusion resistance was calculated from the voltage difference 30 seconds after current application. The change amount of the cell OCV due to the current application was obtained by correcting the average voltage change amount assigned to the current application time from the voltage change amount after sufficiently relaxing after 30 seconds application.

  From the above results, it can be seen that the non-aqueous electrolyte secondary battery of the example according to the present invention has significantly lower DC resistivity and excellent output characteristics as compared with the battery of the comparative example.

10, 50 bipolar secondary batteries,
11 current collector,
11a outermost layer current collector on the positive electrode side,
11b outermost layer current collector on the negative electrode side,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layers,
21, 57 power generation elements,
23 bipolar electrodes,
25 positive electrode current collector plate (positive electrode tab),
27 negative electrode current collector plate (negative electrode tab),
29, 52 laminated film,
31 seal part,
58 positive electrode tab,
59 Negative electrode tab.

Claims (6)

An electrode in which an electrode active material layer containing an electrode active material and a gel-forming polymer is disposed on the surface of the current collector,
Having an electrolyte layer impregnated with an electrolytic solution in a separator disposed between the electrodes,
The volume of pores per m ^{3 of the} electrode is x [m ³ ], the volume of the gel-forming polymer contained per m ^{3 of the} electrode is y [m ³ ], and the absorption of the gel-forming polymer with respect to the electrolytic solution When the ratio is z [%],
Meet the non-aqueous electrolyte secondary battery. Where x, y and z are
The non-aqueous electrolyte secondary battery according to claim 1, which satisfies the following.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode active material layer includes a structure including the electrode active material, the gel-forming polymer, and a conductive auxiliary.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the gel-forming polymer has a liquid absorption of 10% or more.   The gel-forming polymer is polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP), polymethyl methacrylate (PMMA), The polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol dimethacrylate and polypropylene glycol diacrylate, and at least one selected from the group consisting of copolymers thereof, according to any one of claims 1 to 4, The nonaqueous electrolyte secondary battery according to the above. An electrode active material, a gel-forming polymer, an electrode active material slurry containing a conductive additive and a solvent, applied to the surface of the current collector to form an electrode active material layer, and a step of obtaining an electrode;
A step of laminating the electrode and the separator to obtain a power generating element,
A step of covering the power generation element with an exterior body and injecting an electrolytic solution,
Has,
A method for producing a non-aqueous electrolyte secondary battery, wherein a liquid absorption of the gel-forming polymer with respect to the electrolyte is 10% or more.