JP7040364B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

In recent years, various electric vehicles are expected to become widespread in order to solve environmental and energy problems. Secondary batteries are being enthusiastically developed as in-vehicle power sources such as motor drive power sources that hold the key to the spread of these electric vehicles. A non-aqueous electrolyte secondary battery intended for application to an in-vehicle power source is required to have a high capacity and excellent output characteristics.

As a technique for obtaining a battery having a high capacity, Patent Document 1 states that by increasing the thickness of the electrode, the relative ratio of the current collector and the separator is reduced to increase the energy density of the battery. The means are disclosed.

Japanese Unexamined Patent Publication No. 9-20436

However, as in Patent Document 1, if the film thickness of the electrode is increased, the internal resistance of the battery increases, which causes a problem that the output characteristics are deteriorated.

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

The present inventors have made diligent studies to solve the above problems. As a result, in a non-aqueous electrolyte secondary battery using an electrode having an electrode active material layer containing a gel-forming polymer and an electrolytic solution, the pore volume of the electrode, the volume of the gel-forming polymer, and the gel-forming property with respect to the electrolytic solution are obtained. We have found that it is effective to control the liquid absorption rate of the polymer so as to satisfy a predetermined relationship, and have completed the present invention.

That is, in the non-aqueous electrolyte secondary battery according to the present invention, the electrode active material layer containing the electrode active material and the gel-forming polymer is arranged on the surface of the current collector, and the separator is arranged between the electrodes. Has an electrolyte layer impregnated with an electrolytic solution. Here, the volume of pores per 1 m ³ of the electrode is x [m ³ ], the volume of the gel-forming polymer contained in 1 m ³ of the electrode is y [m ³ ], and the gel-forming polymer with respect to the electrolytic solution is used. When the liquid absorption rate of is z [%],

It is characterized by satisfying.

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

It is sectional drawing which represented typically the bipolar type secondary battery which is one Embodiment of this invention. It is a perspective view which showed the appearance of the flat lithium ion secondary battery which is a typical embodiment of a secondary battery.

In one embodiment of the present invention, an electrode 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 and a separator arranged between the electrodes are impregnated with an electrolytic solution. It is a non-aqueous electrolyte secondary battery having an electrolyte layer. Here, the volume of pores per 1 m ³ of the electrode is x [m ³ ], the volume of the gel-forming polymer contained in 1 m ³ of the electrode is y [m ³ ], and the gel-forming polymer with respect to the electrolytic solution is used. When the liquid absorption rate of is z [%],

It is characterized by satisfying. According to the non-aqueous electrolyte secondary battery of this embodiment, excellent output characteristics can be exhibited by reducing the internal resistance of the battery.

The detailed mechanism that exerts the above effect is unknown, but it 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 suspended in the pores of the electrode is suppressed. Thereby, electron conduction can be improved. Further, since the gel-forming polymer absorbs the electrolytic solution and takes charge of ionic conduction, effective ionic conduction can be improved. Therefore, the DC resistance value can be reduced. Further, by controlling the value of yz / x to 1.06 or less, it is possible to prevent the gel-forming polymer from excessively covering the electrode active material. As a result, it is possible to suppress a decrease in electron conduction. In addition, the gel-forming polymer suppresses the excessive occupation of the pores of the electrode, the decrease in the amount of the electrolytic solution, and the decrease in the amount of ions (for example, the amount of Li ions), thereby reducing the effective ion conduction. Can be suppressed. Therefore, the DC resistance value can be reduced. By controlling the value of yz / x within a predetermined range in this way, 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 will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. .. Hereinafter, the present invention will be described by taking as an example a bipolar lithium ion secondary battery, which is a form of a non-aqueous electrolyte secondary battery. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. In the present specification, "XY" indicating a range means "X or more and Y or less". Unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) and relative humidity of 40 to 50% RH.

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

<Bipolar secondary battery>
FIG. 1 is a cross-sectional view schematically showing a bipolar secondary battery according to an 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 laminated film 29 which is a battery exterior body.

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

The adjacent positive electrode active material layer 13, the electrolyte layer 17, and the negative electrode active material layer 15 constitute one cell cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 19 are laminated. Further, a seal portion (insulation layer) 31 is arranged on the outer peripheral portion of the cell cell layer 19. As a result, liquid leakage due to leakage of the electrolytic solution from the electrolyte layer 17 is prevented, the adjacent current collectors 11 in the battery come into contact with each other, and the end portions of the cell cell layer 19 in the power generation element 21 are slightly uneven. It prevents short circuits caused by the above. The positive electrode active material layer 13 is formed on only one side of the outermost layer current collector 11a on the positive electrode side located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed on only one side of the outermost layer current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21.

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

The number of times the cell cell layer 19 is laminated is adjusted according to a desired voltage. Further, in the bipolar type secondary battery 10, the number of times the single battery layer 19 is laminated may be reduced as long as a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar type secondary battery 10, in order to prevent external impact and environmental deterioration during use, the power generation element 21 is vacuum-enclosed in the laminated film 29 which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode collector are collected. It is preferable to have a structure in which the electric plate 27 is taken out from the laminated film 29. Although the embodiment of the present invention has been described here by taking a bipolar secondary battery as an example, the type of non-aqueous electrolyte battery to which the present invention can be applied is not particularly limited, and the single battery layer is used as a power generation element. It can be applied to any conventionally known non-aqueous electrolyte secondary battery such as a so-called parallel laminated battery in the form of being connected in parallel.

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

[electrode]
The electrode has a structure 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 movement 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. The material constituting the current collector is not particularly limited, but for example, a metal or a resin having conductivity may be adopted.

Specific examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Further, it may be a foil obtained by coating a metal surface with aluminum, or a carbon-coated aluminum foil. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electron conductivity and battery operating potential.

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

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), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials may have excellent potential or solvent resistance.

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

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or a metal thereof. It is preferable to contain an alloy containing or a metal oxide. 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 species.

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

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

[Electrode active material layer]
The electrode active material layer is arranged on the surface of the current collector and contains an electrode active material and a gel-forming polymer.

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

The content (in terms of solid content) of the gel-forming polymer 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 0.5 to 10.0% by mass, more preferably 1.0 to 6.0% by mass from the viewpoint of output characteristics.

The thickness of the electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 950 μm, and further preferably 200 to 800 μm for the positive electrode active material layer. The thickness of the negative electrode active material layer is preferably 150 to 1500 μm, more preferably 180 to 1200 μm, and further preferably 200 to 1000 μm. When the thickness of the electrode active material layer is at least the above-mentioned lower limit value, the energy density of the battery can be sufficiently increased. On the other hand, if the thickness of the electrode active material layer is not more than the above-mentioned upper limit value, 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 film 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 such as those in which some of these transition metals are replaced by other elements. Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more kinds of positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used. More preferably, Li (Ni-Mn-Co) O ₂ and a part of these transition metals are substituted with other elements (hereinafter, also simply referred to as "NMC composite oxide"), or 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 a lithium atomic layer and a transition metal (Mn, Ni and Co are arranged in an orderly manner) atomic layer are alternately stacked via an oxygen atomic layer. Then, one Li atom is contained in each 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, and a high capacity can be obtained.

As described above, the NMC composite oxide also includes a composite oxide in which a part of the transition metal element is replaced 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 and the like, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, and more preferably Ti, Zr, P, Al, Mg, It is Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable to use the general formula (1): Li _a Ni _b Mn _{c Code} M _x O ₂ (however, 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, b + c + d = 1. It has a composition represented by (at least one kind of 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, nickel (Ni), cobalt (Co) and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electron 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 substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). The crystal structure is stabilized by solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. As a result, it is considered that the capacity of the battery can be prevented from decreasing even if charging and discharging are repeated, and excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31 and 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 includes LiCo O ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , etc., which have been proven in general consumer batteries. Compared with, the capacity per unit mass is large. This has the advantage that the energy density can be improved and a compact and high-capacity battery can be manufactured, which is preferable from the viewpoint of cruising range.

Further, as a more preferable embodiment, LiNi _0.8 Co _0.1 Al _0.1 O ₂ and LiNi _0.8 Co _0.15 Al _0.05 O ₂ are preferable from the viewpoint of a 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 size is measured by a particle size distribution measuring device of 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 (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials (tin, silicon), and lithium. Examples thereof include alloy-based negative electrode materials (for example, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.). In some cases, two or more kinds of negative electrode active materials may be used in combination. Preferably, from the viewpoint 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. Of course, a negative electrode active material other than the above may be used.

The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

(Gel-forming polymer)
The gel-forming polymer is an ionic conductive polymer and can form a structure together with the electrode active material to play a role of ionic conduction. Examples of the gel-forming polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP), and the like from the viewpoint of output characteristics. At least one selected from the group consisting of polymethylmethacrylate (PMMA), polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polymethylmethacrylate, and polymers thereof.

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

The volume of the gel-forming polymer contained in 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. The volume of the gel-forming polymer contained in 1 m ³ of the electrode is, for example, 0.006 to 0.038 m ³ , preferably 0.009 to 0.035 m ³ , and more preferably 0.015 to 0.028 m ³ . be. The volume of the gel-forming polymer contained in 1 m ³ of the electrodes can be controlled by the amount charged or the like.

The gel-forming polymer has a liquid absorption rate of preferably 10% or more, more preferably 50% or more with respect to the electrolytic solution. The upper limit of the liquid absorption rate 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 liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is 10% or more, the gel-forming polymer can sufficiently retain the electrolytic solution, and thus can be responsible for ion conduction. When the liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is 200% or less, the structure with the electrode active material can be maintained.

In the present specification, the "liquid 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 rate (%) = [(mass of gel-forming polymer after immersion in electrolytic solution-mass of gel-forming polymer before immersion in electrolytic solution) / mass of gel-forming polymer before immersion in electrolytic solution] × 100.

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

The electrolytic solution for determining the liquid absorption rate was obtained by dissolving 22 mol / L of LiN ₍ FSO ₂ ) in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC). Use an electrolytic solution.

(Conductive aid)
The electrode active material layer can further contain a conductive auxiliary agent.

The conductive auxiliary agent has a function of forming an electron conduction 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 the improvement of output characteristics at a high rate. In particular, at least a part of the conductive auxiliary agent forms a conductive passage that electrically connects the two main surfaces of the electrode active material layer (in the present embodiment, it contacts the electrolyte layer side of the electrode active material layer). It is preferable to form a conductive passage that electrically connects from the first main surface to the second main surface in contact with the current collector side). 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. At least a part of the conductive auxiliary agent forms a conductive passage that electrically connects the two main surfaces of the electrode active material layer (in the present embodiment, it is in contact with the electrolyte layer side of the electrode active material layer). Whether or not a conductive passage is formed that electrically connects from the first main surface to the second main surface in contact with the current collector side) is determined by using an SEM or an optical microscope to determine the cross section of the electrode active material layer. It can be confirmed by observing.

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 in which a metal having good conductivity or graphite is uniformly dispersed in synthetic fibers, and a metal such as stainless steel are used as fibers. Examples thereof include carbonized metal fibers, conductive fibers in which the surface of organic fibers is coated with metal, and conductive fibers in which the surface of organic fibers is coated with a resin containing a conductive substance. Of these, carbon fiber is preferable because it has excellent conductivity and is lightweight.

However, of course, a conductive auxiliary agent that does not have a fibrous form may be used. For example, a conductive auxiliary agent having a particulate (for example, spherical) morphology 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 powder, sphere, plate, columnar, amorphous, fluffy, and spindle-shaped. The average particle size (primary particle size) when the conductive auxiliary agent is in the form of particles is not particularly limited, but is preferably about 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery. In the present specification, the “particle diameter” means the maximum distance L among the distances between arbitrary two points on the contour line of the conductive auxiliary agent. As the value of the "average particle size", an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used, and the average value of the particle size of the particles observed in several to several tens of fields is used. The calculated value shall be adopted.

Conductive aids having a particulate (eg, spherical) morphology include, for example, metals such as aluminum, stainless steel (SUS), silver, gold, copper, titanium, alloys or metal oxides containing these metals; carbon nanotubes. (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark), furnace black, channel black, thermal lamp black, etc.) and the like, but are not limited thereto. Further, a particulate ceramic material or a resin material coated with the above metal material by plating or the like can also be used as a conductive auxiliary agent. Among these conductive auxiliaries, from the viewpoint of electrical stability, it is preferable to contain at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, and aluminum, stainless steel. It is more preferable to contain at least one selected from the group consisting of silver, gold, and carbon, and even more preferably to contain at least one carbon. Only one kind of these conductive auxiliary agents may be used alone, or two or more kinds thereof may be used in combination.

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

(Structure consisting of electrode active material, gel-forming polymer and conductive additive)
In a preferred embodiment of the invention, the electrode active material layer comprises a structure consisting of an electrode active material, a gel-forming polymer and a conductive additive. As a result, the electrode active material can be in good contact with the conductive auxiliary agent, and the electrode active material is in an active state, so that electron conduction can be further improved. Further, by structuring the conductive auxiliary agent around the electrode active material, excellent conductivity can be ensured, so that the output and the capacity can be improved. Further, by structuring the conductive auxiliary agent around the electrode active material, percolation in the pores is formed. Therefore, the effective ion conductivity can be further improved. In addition, by forming such a structure, the electrode active material layer can be made into a self-standing film, and the strength of the electrode can be further increased.

[Calculation method of electrode pore volume]
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 obtained from the compounding ratio of the materials used.
(2) Measure the thickness [A] of the electrode.
(3) Using the mass of each material obtained in (1) and the density of each material, the electrode thickness [B] when the porosity is 0% is calculated.
(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. The pore volume per 1 m ³ of the electrode is, for example, 0.180 m ³ to 0.445 m ³ , preferably 0.190 m ³ to 0.435 m ³ . The pore volume per 1 m ³ of the electrode can be adjusted by adjusting the particle size of the electrode active material, the amount of the gel-forming polymer charged, the film thickness of the electrode active material layer, and the like. Further, as described later, it can be adjusted by pressing at the time of manufacturing the electrode.

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

The electrolytic solution has a function as a carrier of lithium ions. The electrolytic solution constituting the electrolytic solution 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) and the like. Among them, the non-aqueous solvents are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). ), And preferably contains ethylene carbonate. As the non-aqueous 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. Of these, 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 electrolytic solution is preferably 0.1 to 3.0 mol / L, more preferably 0.8 to 2.2 mol / L.

The electrolytic solution may be further mixed with additives other than the above-mentioned components. Further, the additive may be contained in the electrolytic solution. Specific examples of such compounds include, for example, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-divinylethylene carbonate. , 1-Methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylenecarbonate, 1-ethyl-1-vinylethylenecarbonate, 1-ethyl-2-vinylethylenecarbonate, vinylvinylene carbonate, allylethylenecarbonate, vinyl Oxymethylethylene carbonate, allyloxymethylethylene carbonate, acrylicoxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1,1- Examples thereof include dimethyl-2-methyleneethylene carbonate. Only one of these additives may be used alone, or two or more of these additives may be used in combination. When the additive is used in the electrolytic solution, the amount used is preferably 0.5 to 10% by mass, more preferably 0.5 to 5 with respect to 100% by mass of the electrolytic solution before the additive is added. It is mass%.

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

Examples of the form of the separator include a separator of a porous sheet made of a polymer or fiber that absorbs and retains the electrolytic solution, a non-woven fabric separator, and the like.

As the separator of the porous sheet made of a polymer or a fiber, for example, a microporous (microporous membrane) can be used. Specific forms of the porous sheet made of the polymer or fiber include, for example, a polyolefin 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). Examples thereof include a microporous (microporous film) separator made of a (structured laminate, etc.), a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and glass fiber.

The thickness of the microporous (microporous membrane) separator cannot be uniquely specified because it varies depending on the intended use. To give an example, in applications 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 length is 4 to 60 μm in a single layer or a multilayer. Is desirable. It is desirable that the fine pore size of the microporous (microporous membrane) separator is 1 μm or less at the maximum (usually, the pore size is about several tens of nm).

As the non-woven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. Further, 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.

Further, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (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 separator having a melting point or a thermal softening point of 150 ° C. or higher, preferably 200 ° C. or higher, having high heat resistance is used. By having the heat-resistant insulating layer, the internal stress of the separator, which increases when the temperature rises, is relaxed, so that the effect of suppressing heat 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 less likely to cause performance deterioration due to a temperature rise. Further, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the film breakage of the separator is less likely to occur. Further, due to the effect of suppressing heat shrinkage and high mechanical strength, the separator is less likely to curl in the battery manufacturing process.

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. For example, silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al _{2O 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. Further, only one kind of these inorganic particles may be used alone, or two or more kinds thereof may be used in combination. Of these, from the viewpoint of cost, it is preferable to use silica (SiO ₂ ) or alumina (Al ₂ O ₃ ), and it is more preferable to use alumina (Al ₂ O ₃ ).

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

The binder in the heat-resistant insulating layer has a role of adhering the inorganic particles to each other 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 substrate layer and the heat-resistant insulating layer.

The binder used for the heat-resistant insulating layer is not particularly limited, and is, for example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber. , Butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), methyl acrylate and the like can be used as the binder. Of these, carboxymethyl cellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. Only one of these compounds may be used alone, or two or more of these compounds may be used in combination.

The content of the binder in the heat-resistant insulating layer is preferably 2 to 20% by mass with respect to 100% by mass of the heat-resistant insulating layer. When the binder content is 2% by mass 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 mass or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

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 under the conditions of 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 shrinking even when the heat generation amount becomes high 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 less likely to cause performance deterioration due to a temperature rise.

[Positive current collector plate and negative electrode current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used. As the 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. The same material may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25, or different materials may be used.

[Positive lead and negative electrode lead]
Although not shown, the current collector 11 and the current collector plates (25, 27) may be electrically connected to each other via a positive electrode lead or a negative electrode lead. As the constituent material of the positive electrode and the negative electrode lead, a material used in a known lithium ion secondary battery can be similarly adopted. The part taken out from the exterior is heat-shrinkable with heat-resistant insulation so that it does not affect the product (for example, automobile parts, especially electronic devices) by contacting peripheral devices and wiring and causing electric leakage. It is preferable to cover with a tube or the like.

[Seal part]
The seal portion (insulating layer) 31 has a function of preventing contact between current collectors and a short circuit at the end of the cell cell layer. As the material constituting the sealing portion, if it has insulating property, sealing property against falling off of solid electrolyte, sealing property against moisture permeation from the outside (sealing property), heat resistance under battery operating temperature, etc. 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 may be used, or a hot-melt adhesive (urethane resin, polyamide resin, polyolefin resin) or the like may be used. Among them, polyethylene resin and polypropylene resin are preferably used as constituent materials of the insulating layer from the viewpoints of corrosion resistance, chemical resistance, ease of production (film formation), economy, etc., and mainly non-crystalline polypropylene resin. It is preferable to use a resin obtained by copolymerizing ethylene, propylene, and butene as components.

[Battery exterior]
As the battery exterior, a known metal can case can be used, or a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generation element as shown in FIG. 1, can be used. As the laminated film, for example, a laminated film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminated film is not limited thereto. A laminated film is desirable from the viewpoint of high output, excellent cooling performance, and suitable use for batteries for large equipment for EVs and HEVs. Further, since the group pressure applied to the power generation element from the outside can be easily adjusted and the thickness of the electrolytic solution layer can be easily adjusted, an aluminumate laminate is more preferable for the exterior body.

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

[Volume of pores in the electrode, volume of gel-forming polymer and liquid absorption rate of gel-forming polymer]
In the non-aqueous electrolyte secondary battery of the present embodiment, the pore volume per 1 m ³ of the electrode is x [m ³ ], and the volume of the gel-forming polymer contained in the electrode 1 m ³ is y [m ³ ]. When the liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is z [%],

It is characterized by satisfying. The present inventors have found that there is an appropriate range between the ratio of the gel-forming polymer in the pores of the electrode and the liquid absorption rate of the gel-forming polymer, and quantified the findings by the above relational expression. ..

According to the non-aqueous electrolyte secondary battery having such a structure, 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 suspended in the pores of the electrode is suppressed. Thereby, electron conduction can be improved. Further, since the gel-forming polymer absorbs the electrolytic solution and takes charge of ionic conduction, effective ionic conduction can be improved. Therefore, the DC resistance value can be reduced. Further, by controlling the value of yz / x to 1.06 or less, it is possible to prevent the gel-forming polymer from excessively covering the electrode active material. As a result, it is possible to suppress a decrease in electron conduction. Further, by suppressing the gel-forming polymer from occupying the pores of the electrode excessively, reducing the amount of the electrolytic solution, and suppressing the decrease in the amount of Li ions, it is possible to suppress the decrease in effective ion conduction. Therefore, the DC resistance value can be reduced. In this way, 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 preferably satisfy 0.50 ≦ yz / x ≦ 0.86. Is more preferable.

[Manufacturing method of non-aqueous electrolyte secondary battery]
In one embodiment of the present invention, an electrode active material slurry containing an electrode active material, a gel-forming polymer, a conductive auxiliary agent and a solvent is applied to the surface of a current collector to form an electrode active material layer to obtain an electrode. It is a step of laminating the electrode and the separator to obtain a power generation element, a step of covering the power generation element with an exterior body and injecting an electrolytic solution, and a method of manufacturing a non-aqueous electrolyte secondary battery having the step. At this time, the liquid absorption rate of the gel-forming polymer with respect to the electrolytic solution is 10% or more. According to the method for producing a non-aqueous electrolyte secondary battery of this embodiment, electron conduction is performed by structuring the gel-forming polymer with an electrode active material and a conductive auxiliary agent, and by causing the gel-forming polymer to hold an electrolytic solution. And by optimizing the ion conduction and reducing the DC resistance value, it is possible to obtain a non-aqueous electrolyte secondary battery exhibiting excellent output characteristics.

(A step of forming an electrode active material layer by applying an electrode active material slurry containing an electrode active material, a gel-forming polymer, a conductive auxiliary agent and a solvent to the surface of a current collector to obtain an electrode)
First, the above-mentioned electrode active material, gel-forming polymer and conductive auxiliary agent are mixed with a solvent to prepare an electrode active material slurry.

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 findings such as the order of addition of members and the mixing method are 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, 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 onto the current collector and dried. After coating, pressing may be performed if necessary. As described above, by mixing the electrode active material, the gel-forming polymer, and the conductive auxiliary agent at the time of preparing the electrode active material slurry, the electrode active material has a structure composed of the electrode active material, the gel-forming polymer, and the conductive auxiliary agent. 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 inkjet 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, more preferably 400 to 1000 μm.

The drying method after applying the electrode active material slurry on the current collector is not particularly limited, and at least a part of the solvent may be removed. Examples of the drying method include heating. The drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the volatilization rate of the solvent contained in the electrode active material slurry to be applied, the coating amount of the electrode active material slurry, and the like.

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

In this way, an electrode (positive electrode or negative electrode) can be obtained.

(Process of laminating electrodes and separators to obtain power generation elements)
After manufacturing the electrodes as described above, the electrodes and the separator are laminated to manufacture a power generation element. The method for producing the power generation element is not particularly limited, and conventionally known findings are appropriately referred to. As an example, a positive electrode and a negative electrode are laminated so as to face each other via a separator to prepare a single battery layer. A power generation element can be obtained by laminating the cell cells to a desired number.

A positive electrode tab and a negative electrode tab are joined to the obtained power generation element by welding. If necessary, it is desirable to remove excess tabs and the like by trimming after welding. The joining method is not particularly limited, but the ultrasonic welding machine does not generate heat (heating) at the time of joining and can be joined in an extremely short time. Therefore, the electrode active material layer (negative electrode active material) by heat is used. It is excellent in that it can prevent deterioration of the 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 face each other on the same side (same extraction side). As a result, the positive electrode tabs of each positive electrode can be bundled into one and taken out from the exterior body 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 exterior body as one negative electrode current collector plate. Further, the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) may be arranged so as to be opposite sides (different extraction sides).

(The process of covering the power generation element with an exterior body and injecting the electrolytic solution)
Cover the obtained power generation element with an exterior body. The method of covering the power generation element with the exterior body is not limited, and conventionally known findings are appropriately referred to. As an example, it is a laminated film that uses a power generation element for the battery exterior, so that the positive electrode current collector plate (positive electrode current collector tab) and the negative electrode current collector plate (negative electrode current collector tab) can be taken out from the top and bottom of the battery exterior body. And sandwich it.

Next, three sides of the outer peripheral portions (sealing portions) of the upper and lower laminated films are thermocompression bonded to be sealed. A three-sided sealed body is obtained by thermocompression-bonding three sides of the outer peripheral portion to seal the outer peripheral portion. At this time, it is preferable to seal the heat-sealed portion on the side where 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. This is because if these positive electrode current collector plates and negative electrode current collector plates are located at the openings during subsequent liquid injection, the electrolytic solution may scatter during liquid injection.

Although the battery having a laminated structure has been described above, the battery is not limited to the laminated type, and various shapes such as a square type, a paper type, a cylindrical type, and a coin type can be adopted as the battery configuration. can.

Next, the electrolytic solution is injected into the inside of the three-sided encapsulant from the opening on the remaining one side of the three-sided encapsulant by the liquid injection device. As a result, an electrolyte layer in which the separator is impregnated with an electrolyte is formed. At this time, the three-sided sealant may be housed in a vacuum box connected to a vacuum pump so that the electrolyte can be impregnated into the laminate inside the three-sided sealant, particularly the separator and the electrode active material layer 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 in a high vacuum state. After the injection, the three-sided encapsulant is taken out from the vacuum box, and the remaining one side of the three-sided encapsulant is temporarily sealed to obtain a laminated type (laminated structure) non-aqueous 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 positive electrode tabs 58 and negative electrode tabs 59 for extracting electric power are pulled out from both sides thereof. There is. The power generation element 57 is wrapped by a battery exterior (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. It is sealed in a closed state. 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 generation element 57 is formed by stacking a plurality of bipolar electrodes 23 via the electrolyte layer 17.

The lithium ion secondary battery is not limited to a laminated flat battery. The wound lithium-ion secondary battery may have a cylindrical shape, or may be formed by deforming such a cylindrical shape into a rectangular flat shape. There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminated film. By this form, weight reduction can be achieved.

Further, the removal of the tabs (58, 59) shown in FIG. 2 is not particularly limited. 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 each and taken out from each side, as shown in FIG. It is not limited to. Further, in the winding type lithium ion battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

In a general electric vehicle, the battery storage space is about 170 L. Since the cell and auxiliary equipment such as charge / discharge control equipment are stored in this space, the storage space efficiency of the normal cell is about 50%. The loading efficiency of the cell in this space is a factor that controls the cruising range of the electric vehicle. If the size of the single cell becomes small, the above loading efficiency is impaired, so that the cruising range 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 exterior body is large. Specifically, the length of the short side of the laminated cell battery is preferably 100 mm or more. Such large batteries can be used in vehicle applications. Here, the length of the short side of the laminated cell battery refers to the side having 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, how to lengthen the mileage (cruising range) by one charge is an important development goal. Considering these points, the volume energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Wh or more.

Further, from the viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to specify the size of the battery from the viewpoint of the battery area and the battery capacity. For example, in the case of a flat laminated laminated battery, the value of the ratio of the battery area (projected area of the battery including the battery exterior) to the rated capacity is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. It is preferable that the present invention is applied to a certain battery. Further, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The aspect ratio of the electrodes is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio within such a range, there is an advantage that both vehicle required performance and mounting space can be achieved.

[Battery set]
An assembled battery is configured by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By serializing and parallelizing, it becomes possible to freely adjust the capacity and voltage.

It is also possible to connect a plurality of batteries in series or in parallel to form a small assembled battery that can be attached / detached. Then, by connecting a plurality of small detachable batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle drive power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery with an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be mounted. It may be decided according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery of this embodiment maintains the discharge capacity even after long-term use and has good cycle characteristics. In addition, the volumetric energy density is high. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required and longer life is required compared to electric and portable electronic device applications. .. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

Specifically, a battery or a combined battery formed by combining a plurality of batteries can be mounted on the vehicle. In the present invention, a long-life battery having excellent long-term reliability and output characteristics can be configured. Therefore, when such a battery is installed, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long one-charge mileage can be configured. .. For example, in the case of automobiles, hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (passenger cars, trucks, commercial vehicles such as buses, light vehicles, etc.)) can be used as batteries or a combination of multiple batteries. This is because it becomes a highly reliable automobile with a long life by using it for two-wheeled vehicles (including motorcycles) and three-wheeled vehicles. However, the application is not limited to automobiles, and can be applied to various power sources of other vehicles, for example, moving objects such as trains, and power supplies for mounting such as uninterruptible power supplies. It is also possible to use it 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 the following Examples.

[Example 1]
<Manufacturing of positive electrode>
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (Li-containing layered transition metal oxide, average particle size: 9 μm) as a positive electrode active material and acetylene black as a conductive auxiliary agent (Denka Co., Ltd., Denka) Black (registered trademark); average particle size (primary particle size): 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 Archema) and N-methyl-2-pyrrolidone as a solvent so as to have a ratio of 8.28: 0.54: 0.18: 0.06: 6.00 (mass ratio), respectively. The mixture was mixed and mixed at 2000 rpm for 6 minutes using a planetary stirring type mixing and kneading device "Awatori Rentaro" (ARE-310, manufactured by Shinky Co., Ltd.) to prepare a positive electrode slurry. The positive electrode slurry was uniformly applied onto the Al foil placed on the smoothing board using a doctor blade so that the thickness of the positive electrode active material layer was 400 μm. Then, it was dried on a hot plate heated to 80 ° C. for 2 hours to obtain a positive electrode having a porous structure of 94 mg / cm ² in mass of the positive electrode active material (the amount of the positive electrode active material).

<Manufacturing of negative electrode>
Hard carbon as a negative electrode active material (manufactured by Kureha Battery Materials Japan Co., Ltd., Carbotron (registered trademark) PS (F), average particle size: 20 μm) and acetylene black as a conductive auxiliary agent (manufactured by Denka Co., Ltd.) , Denka Black (registered trademark); average particle size (primary particle size): 0.023 μm) and 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 each at 8.28: 0.54: 0.18: 0.21: 9.00 (mass ratio). The mixture was mixed in the above manner at 2000 rpm for 6 minutes using a planetary stirring type mixing and kneading device "Awatori Rentaro" (ARE-310, manufactured by Shinky Co., Ltd.) to prepare a negative electrode slurry. The negative electrode slurry was uniformly applied onto the Cu foil placed on the smoothing board using a doctor blade so that the thickness of the negative electrode active material layer was 420 μm. Then, it was dried on a hot plate heated to 80 ° C. for 2 hours to obtain a negative electrode having a porous structure of 39 mg / cm ² in terms of the mass of the negative electrode active material (the amount of the negative electrode active material).

<Manufacturing of lithium-ion batteries>
The obtained positive electrode was cut to 12 cm ² and the negative electrode was cut to 12.4 cm ² . For the positive electrode, an aluminum foil with an Al terminal was cut and laminated on the current collecting foil side of the positive electrode. For the negative electrode, a copper foil with a Ni terminal was cut and laminated on the collector foil side of the negative electrode. A separator (manufactured by Cellguard, manufactured by Cellguard (registered trademark) 3501 PP) was inserted into the electrode side of the positive electrode and the negative electrode to form a laminated body. This laminate is sandwiched between heat-sealing aluminum laminate films, and LiN (FSO ₂ ) _{2 2} mol / L is dissolved in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC). A pouch-type lithium-ion battery was produced by injecting the obtained non-aqueous electrolytic solution and then vacuum-sealing.

[Example 2]
In the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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: 0.45: 9.00 (mass ratio). ..

[Example 4]
In the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 the production of the porous structure for the positive electrode, the compounding ratio of the members is 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) was changed, and in the production of the porous structure for the negative electrode, the compounding ratio of the members was changed to 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 electrode pore volume]
For the electrodes produced in Examples 1 to 5 and Comparative Examples 1 to 3, the pore volume was calculated as follows.
(1) The mass per unit area was measured. The mass of each material per unit area was calculated from the compounding 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 electrode thickness [B] when the porosity was 0% was calculated.
(4) The pore volume of the electrode was calculated from the difference (AB) between the measured electrode thickness and the calculated electrode thickness, and the pore volume per 1 m ³ of the electrode was obtained.

The results are shown in Table 1.

[Calculation of gel-forming polymer pore occupancy]
The gel-forming polymer pore occupancy 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 of the gel-forming polymer with respect to the pore volume of the electrode made of a material other than the gel-forming polymer. Means proportion. That is, the gel-forming polymer pore occupancy was calculated by the following formula;
Gel-forming polymer pore occupancy = gel-forming polymer volume / (gel-forming polymer volume + electrode pore volume).

Specifically, the gel-forming polymer pore occupancy was calculated as follows;
(1) The mass per unit area was measured. The mass of each material per unit area was calculated from the compounding 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 is 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 gel-forming polymer pore occupancy was calculated using the volume of the pores of the electrode and the volume of the gel-forming polymer.

The results are shown in Table 1.

[Measurement of liquid absorption rate of gel-forming polymer with respect to electrolytic solution]
The liquid absorption rate 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 rate (%) = [(mass of gel-forming polymer after immersion in electrolytic solution-mass of gel-forming polymer before immersion in electrolytic solution) / mass of gel-forming polymer before immersion in electrolytic solution] × 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 cast membrane was immersed in the electrolytic solution at 25 ° C to 50 ° C for 24 hours.

The electrolytic solution for determining the liquid absorption rate was obtained by dissolving 22 mol / L of LiN ₍ FSO ₂ ) in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC). An electrolytic solution was used.

The results are shown in Table 1.

[Evaluation of output characteristics]
The output evaluation was carried out by installing the lithium ion battery prepared above in a constant temperature bath (ARSF-0250-10, manufactured by Espec Co., Ltd.) set at 25 ° C. The output evaluation was performed with a lithium ion battery sandwiched between a urethane rubber having a thickness of 5 mm and a silicone sponge sheet, and restrained at 6 points using a metal plate having a thickness of 10 mm and an M6 screw. First, as a capacity confirmation at a low rate, charge / discharge evaluation was performed twice with a cell voltage range of 4.2 to 2.5 V and a current value of 0.05 C rate, and the obtained capacity was used as a reference capacity. The C rate was calculated based on the cell discharge capacity obtained at the 2.5 V cutoff. Next, after charging to 4.2V at 0.05C, discharging is performed at 0.05C, 0.1C, 0.2C, 0.33C, and 0.5C rates until the cell voltage reaches 2.5V. rice field. The [effective capacity / reference capacity × 100] at the obtained 0.33C was defined as [0.33C effective capacity ratio (%)]. The results are shown in Table 1.

[DCR resistance measurement]
Similar to the output characteristic evaluation, the SOC was adjusted to 50% after charging and discharging for 2 cycles at a 0.05 C rate. The resistance value was calculated from the voltage obtained by passing a direct current through the adjusted cell for 30 seconds. The ohm resistance was calculated from the voltage difference immediately after the current was applied (0.1 seconds). The reaction resistance was calculated from the voltage difference 1 second after the current was applied. The diffusion resistance was calculated from the voltage difference 30 seconds after the current was applied. The amount of change in the cell OCV due to the application of the current was obtained by correcting the amount of the average voltage fluctuation assigned to the current application time from the voltage fluctuation after the application for 30 seconds and then sufficiently relaxing.

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

10,50 bipolar secondary battery,
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 Single battery layer,
21,57 Power generation element,
23 Bipolar electrode,
25 Positive electrode current collector plate (positive electrode tab),
27 Negative electrode current collector plate (negative electrode tab),
29, 52 Laminating film,
31 Seal part,
58 Positive 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 arranged on the surface of a current collector, and an electrode.
The separator arranged between the electrodes has an electrolyte layer impregnated with an electrolytic solution, and has an electrolyte layer.
The volume of pores per 1 m ³ of the electrode is x [m ³ ], the volume of the gel-forming polymer contained in 1 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 rate is z [%]

Meet, non-aqueous electrolyte secondary battery. The x, y and z are

The non-aqueous electrolyte secondary battery according to claim 1. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the electrode active material layer comprises a structure composed of the electrode active material, the gel-forming polymer, and a conductive auxiliary agent. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the gel-forming polymer has a liquid absorption rate 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), polymethylmethacrylate (PMMA), and the like. The item according to any one of claims 1 to 4, which is at least one selected from the group consisting of polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol dimethacrylate and polypropylene glycol diacrylate, and copolymers thereof. The non-aqueous electrolyte secondary battery described. A step of forming an electrode active material layer by applying an electrode active material slurry containing an electrode active material, a gel-forming polymer, a conductive auxiliary agent and a solvent to the surface of a current collector to obtain an electrode.
The process of laminating the electrode and the separator to obtain a power generation element, and
The process of covering the power generation element with an exterior body and injecting an electrolytic solution,
Have,
A method for producing a non-aqueous electrolyte secondary battery, wherein the gel-forming polymer has a liquid absorption rate of 10% or more with respect to the electrolytic solution.

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