JP2022116891A - Electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide means for enhancing the output characteristic of a nonaqueous electrolyte secondary battery.SOLUTION: An electrode for a nonaqueous electrolyte secondary battery comprises: a current collector; and an electrode active material layer disposed on the surface of the current collector. In the electrode for a nonaqueous electrolyte secondary battery, the electrode active material layer includes an electrode active material, a conductive assistant and a binding agent. The binding agent contains poly(vinylidene fluoride)(PVDF) and poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP). The mass ratio of the poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) to the electrode active material is larger than 0 and smaller than 0.015.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to electrodes for non-aqueous electrolyte secondary batteries.

2. Description of the Related Art In recent years, various electric vehicles are expected to spread toward solving environmental and energy problems. Development of a secondary battery is earnestly carried out as an in-vehicle power source such as a power source for driving a motor, which holds the key to popularization of these electric vehicles. As a secondary battery, attention is focused on a non-aqueous electrolyte secondary battery that can be expected to have high energy density and high output.

Here, Patent Literature 1 discloses a technique aimed at improving the safety of non-aqueous electrolyte secondary batteries. Specifically, the technique described in Patent Document 1 uses a composite PTC binder containing polyvinylidene fluoride (PVDF) and a PTC (Positive Temperature Coefficient) function imparting component as the binder for the electrode active material layer. characterized by Thereby, when the temperature of the non-aqueous electrolyte secondary battery rises, the binder melts and the resistance of the electrode active material layer increases, thereby suppressing the heat generation of the electrode active material layer.

WO2018/128139

However, as a result of studies by the present inventors, the non-aqueous electrolyte secondary battery using the technology described in Patent Document 1 has insufficient output characteristics (particularly, sufficient output characteristics during discharge at a high discharge rate). It turned out that there was a problem that the capacity could not be taken out.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide means for improving the output characteristics of a non-aqueous electrolyte secondary battery.

The present inventors have made intensive studies to solve the above problems. In the process, polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) are used as binders in the electrode active material layer, and the mass ratio of the PVDF-HFP to the electrode active material is set to a specific value. The inventors have found that the output characteristics of a non-aqueous electrolyte secondary battery can be improved by controlling it within a range, and have completed the present invention.

That is, according to one aspect of the present invention, there is provided an electrode for a non-aqueous electrolyte secondary battery including a current collector and an electrode active material layer disposed on the surface of the current collector. Here, the electrode active material layer contains an electrode active material, a conductive aid and a binder, and the binder is polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). include. A mass ratio of the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to the electrode active material is more than 0 and less than 0.015.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to improve an output characteristic in a non-aqueous electrolyte secondary battery.

1 is a cross-sectional view schematically showing a laminated (flat) non-bipolar (internal parallel connection type) secondary battery that is an embodiment of the present invention. FIG. FIG. 2 is a cross-sectional view schematically showing a bipolar secondary battery that is another embodiment of the present invention;

Hereinafter, the embodiments of the present embodiment described above 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 claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios. In this 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.

<Electrodes for non-aqueous electrolyte secondary batteries>
One aspect of the present invention is an electrode for a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "electrode") including a current collector and an electrode active material layer disposed on the surface of the current collector. Here, the electrode active material layer contains an electrode active material, a conductive aid and a binder, and the binder is polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). include. A mass ratio of the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to the electrode active material is more than 0 and less than 0.015. According to the non-aqueous electrolyte secondary battery electrode of this embodiment, it is possible to improve output characteristics.

FIG. 1 schematically shows a flat (laminated) non-bipolar (internal parallel connection type) secondary battery (hereinafter also simply referred to as a “laminated secondary battery”) that is an embodiment of the present invention. It is a cross-sectional view.

As shown in FIG. 1, the laminated secondary battery 10a of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which charge/discharge reactions actually progress is sealed inside a laminate film 29. As shown in FIG. Here, the power generation element 21 includes a positive electrode in which the positive electrode active material layer 13 is arranged on both sides of the positive electrode current collector 11 ′, an electrolyte layer 17 made of a separator containing an electrolytic solution, and both sides of the negative electrode current collector 12 It has the structure which laminated|stacked the negative electrode with which the negative electrode active material layer 15 was arrange|positioned. Specifically, the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order such that one positive electrode active material layer 13 and the adjacent negative electrode active material layer 15 face each other with the electrolyte layer 17 interposed therebetween. .

Thereby, the positive electrode, the electrolyte layer, and the negative electrode form one cell layer 19 . Therefore, it can be said that the stacked secondary battery 10a shown in FIG. 1 has a configuration in which a plurality of cell layers 19 are stacked and electrically connected in parallel. The positive electrode current collectors of the outermost layers located on both outermost layers of the power generating element 21 have the positive electrode active material layer 13 only on one side, but the active material layer may be provided on both sides. . That is, a current collector having active material layers on both sides may be used as it is as the current collector for the outermost layer, instead of using a current collector exclusively for the outermost layer having an active material layer on only one side. In addition, by reversing the arrangement of the positive electrode and the negative electrode from FIG. 1, the outermost negative electrode current collector is positioned on both outermost layers of the power generation element 21, A negative electrode active material layer may be arranged on both sides.

A positive electrode current collector 25 and a negative electrode current collector 27 electrically connected to each electrode (positive electrode and negative electrode) are attached to the positive electrode current collector 11 ′ and the negative electrode current collector 12 , respectively. It has a structure in which it is led out to the outside of the laminate film 29 so as to be The positive electrode current collector 25 and the negative electrode current collector 27 are connected to the positive electrode current collector 11′ and the negative electrode current collector 12 of each electrode via a positive electrode terminal lead and a negative electrode terminal lead (not shown), respectively, as necessary. It may be attached by ultrasonic welding, resistance welding, or the like.

FIG. 2 is a cross-sectional view schematically showing a bipolar secondary battery that is another embodiment of the present invention. A bipolar secondary battery 10b shown in FIG. 2 has a structure in which a substantially rectangular power generation element 21 in which charge/discharge reactions actually progress is sealed inside a laminate film 29 that is a battery exterior body. In this specification, a bipolar lithium ion secondary battery may be simply referred to as a "bipolar secondary battery", and an electrode for a bipolar lithium ion secondary battery may be simply referred to as a "bipolar electrode".

As shown in FIG. 2, in the power generation element 21 of the bipolar secondary battery 10b of the present embodiment, the positive electrode active material layer 13 electrically coupled to one surface of the current collector 11 is formed. It has a plurality of bipolar electrodes 23 with a negative electrode active material layer 15 electrically coupled to the opposite surface. Each bipolar electrode 23 is laminated via the electrolyte layer 17 to form the power generation 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 the other bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other with the electrolyte layer 17 interposed therebetween. Each bipolar electrode 23 and electrolyte layer 17 are alternately stacked. That is, the electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of 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.

Adjacent positive electrode active material layer 13 , electrolyte layer 17 , and negative electrode active material layer 15 constitute one cell layer 19 . Therefore, it can be said that the bipolar secondary battery 10b has a structure in which the cell layers 19 are stacked. A sealing portion (insulating layer) 31 is arranged on the outer peripheral portion of the cell layer 19 . This prevents a liquid junction due to leakage of the electrolyte from the electrolyte layer 17, contact between adjacent current collectors 11 in the battery, and slight unevenness at the end of the cell layer 19 in the power generation element 21. This prevents short circuits caused by The positive electrode active material layer 13 is formed only on one side of the outermost current collector 11 a on the positive electrode side located in the outermost layer of the power generation element 21 . In addition, the negative electrode active material layer 15 is formed only on one side of the outermost current collector 11b on the negative electrode side located in the outermost layer of the power generating element 21 .

Furthermore, in the bipolar secondary battery 10b shown in FIG. 2, a positive electrode current collector plate (positive electrode tab) 25 is arranged adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery outer package. It is led out from the laminate film 29 . On the other hand, a negative electrode current collector plate (negative electrode tab) 27 is arranged adjacent to the outermost layer current collector 11 b on the negative electrode side, and is similarly extended to lead out from the laminate film 29 .

Note that the number of times the single cell layer 19 is stacked is adjusted according to the desired voltage. Further, in the bipolar secondary battery 10b, the number of stacking of the cell layers 19 may be reduced if a sufficient output can be secured even if the thickness of the battery is made as thin as possible. In the bipolar secondary battery 10b as well, in order to prevent external shocks and environmental deterioration during use, the power generation element 21 is enclosed under reduced pressure in a laminate film 29, which is a battery outer body, and a positive electrode collector plate 25 and a negative electrode collector are enclosed. A structure in which the electric plate 27 is taken out of the laminate film 29 is preferable.

Main constituent members of the electrode for a non-aqueous electrolyte secondary battery according to this embodiment will be described below.

[Current collector]
The current collector has a function of mediating transfer of electrons from the electrode active material layer. There are no particular restrictions on the material that constitutes the current collector. As the constituent material of the current collector, for example, a metal or a conductive resin can be used.

Specifically, examples of metals 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 plated material of a combination of these metals can be preferably used. It may also be a foil in which a metal surface is coated with aluminum, or a carbon-coated aluminum foil. Among them, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electronic conductivity and battery operating potential.

The latter resin having conductivity includes a resin obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as necessary.

Examples of conductive polymer materials include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Such a conductive polymer material has sufficient conductivity without adding a conductive filler, and is therefore advantageous in terms of facilitating the manufacturing process and reducing the weight of the current collector.

Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), and polyimide. (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA) , polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent electrical potential or solvent resistance.

Conductive fillers may be added to the conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin serving as the base material of the current collector consists of only a non-conductive polymer, a conductive filler is inevitably essential in order to impart conductivity to the resin.

Any electrically conductive filler can be used without particular limitation. Examples of materials that are excellent in conductivity, potential resistance, or lithium ion blocking properties include metals and conductive carbon. The metal is not particularly limited, but includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or these metals. It preferably contains alloys or metal oxides. Also, 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, Ketjenblack (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one.

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.

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 at least a conductive resin layer made of a resin having conductivity. Moreover, from the viewpoint of blocking movement of lithium ions between the single cell layers, 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, a conductive aid and a binder. When the electrode according to this embodiment is a positive electrode, the electrode active material is a positive electrode active material, and when the electrode according to this embodiment is a negative electrode, the electrode active material is a negative electrode active material. In this specification, items common to the positive electrode and the negative electrode are referred to as "electrode" unless otherwise specified.

(Positive electrode active material)
The positive electrode active material has a function of releasing ions such as lithium ions during charging and absorbing ions such as lithium ions during discharging.

Examples of positive electrode active materials include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li(Ni—Mn—Co)O ₂ , Li(Ni—Co—Al)O ₂ and some of these transition metals. Lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, etc., such as those substituted by elements of. In some cases, two or more positive electrode active materials may be used together. From the viewpoint of capacity and output characteristics, lithium-transition metal composite oxides are preferably used as the positive electrode active material. A composite oxide containing lithium and nickel is more preferably used. More preferably, Li(Ni--Mn--Co) O ₂ and those in which a portion of these transition metals are replaced with other elements (hereinafter simply referred to as "NMC composite oxide"), or Li(Ni--Co —Al)O ₂ and those in which a part of these transition metals are replaced with other elements (hereinafter simply referred to as “NCA composite oxide”) are used. NMC composite oxide is particularly preferably used. NMC composite oxides and NCA composite oxides have a layered crystal structure in which lithium atomic layers and transition metal atomic layers are alternately stacked via oxygen atomic layers. One Li atom is included in one atom of the transition metal M, and the amount of Li that can be taken out is double that of the spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and a high capacity can be obtained.

NMC composite oxides and NCA composite oxides also include composite oxides in which a portion of the transition metal element is replaced with another metal element, as described above. 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, and Cu. , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, Cr, more preferably Ti, Zr, Al, Mg, or Cr from the viewpoint of improving cycle characteristics. However, other metal elements that can replace the transition metal elements of the NCA composite oxide are those other than Al.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferably represented by the general formula (1): _{LiaNibMncCodMxO2 (} wherein 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+x=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 general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

Nickel (Ni), cobalt (Co) and manganese (Mn) are generally known to contribute to capacity and output characteristics from the viewpoint of improving material purity and electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is replaced with another metal element, and it is particularly preferable that 0<x≦0.3 in general formula (1). A solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr stabilizes the crystal structure. As a result, even if charging and discharging are repeated, the capacity of the battery can be prevented from decreasing, and excellent cycle characteristics can be realized.

As a more preferred embodiment, in 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 is LiCoO 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. Large capacity per unit mass compared to As a result, the energy density can be improved, and there is an advantage that a compact and high-capacity battery can be produced, which is also preferable from the viewpoint of cruising distance.

As a more preferred 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 higher 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 high output. In the present specification, the average particle diameter of particles is defined as the dian diameter (D50) measured by a particle size distribution analyzer based on the laser diffraction/scattering method.

(Negative electrode active material)
The negative electrode active material has a function of releasing ions such as lithium ions during discharging and absorbing ions such as lithium ions during charging.

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), silicon containing alloy-based negative electrode materials (eg, Si ₆₀ Sn ₁₀ Ti ₃₀ ), lithium alloy-based negative electrode materials (eg, lithium-tin alloys, lithium-silicon alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.), and the like. . In some cases, two or more kinds of negative electrode active materials may be used together. Silicon-containing alloy negative electrode materials, carbon materials, lithium-transition metal composite oxides, and lithium alloy negative electrode materials are preferably used as negative electrode active materials from the viewpoint of capacity and output characteristics. Needless to say, negative electrode active materials other than those described above may be used.

Although the average particle size 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.

The content of the electrode active material in the electrode active material layer is, for example, 60% by mass or more and less than 100% by mass, preferably 80% by mass or more and 99.5% or less, relative to 100% by mass of the total solid content. It is preferably more than 95% by mass and 99.0% by mass or less, more preferably 97% by mass or more and 98.5% by mass or less. If the content of the electrode active material is within the above range, both battery capacity and output characteristics can be achieved.

(Conductivity aid)
The conductive aid has the function of forming an electron conductive path (conductive path) in the electrode active material layer. Formation of such an electron conduction path in the electrode active material layer can reduce the internal resistance of the battery and improve the output characteristics at a high rate. In particular, at least part of the conductive aid forms a conductive path that electrically connects the two main surfaces of the electrode active material layer (in this embodiment, the electrode active material layer is in contact with the electrolyte layer side). It is preferable that a conductive path is formed that electrically connects the first main surface that contacts the current collector side to the second main surface that contacts the current collector side. With such a configuration, the electron transfer resistance in the thickness direction in the electrode active material layer is further reduced, so that the high-rate output characteristics of the battery can be further improved. At least part of the conductive aid forms a conductive path that electrically connects the two main surfaces of the electrode active material layer (in this embodiment, the conductive path is in contact with the electrolyte layer side of the electrode active material layer). The cross section of the electrode active material layer is examined using an SEM or an optical microscope to determine whether or not a conductive path is formed that electrically connects the first main surface to the second main surface that contacts the current collector side. It can be confirmed by observation.

Conductive aids include particulate carbon materials and fibrous carbon materials. In this specification, a particulate carbon material refers to a carbon material whose primary particles have an aspect ratio of 20 or less. Moreover, in this specification, the fibrous carbon material refers to a carbon material having an aspect ratio of 1000 or more. In this specification, the aspect ratios of the particulate carbon material and the fibrous carbon material refer to the length of the long axis to the length of the short axis of 100 carbon materials arbitrarily selected by a scanning electron microscope (SEM). means the mean value for the ratio of the lengths of

Examples of particulate carbon materials include carbon powders such as acetylene black, carbon black, channel black, thermal black, and Ketjenblack (registered trademark). Among them, acetylene black is preferable from the viewpoint of conductivity. The average particle size (primary particle size) of the particulate carbon material (preferably acetylene black) is not particularly limited, but is preferably 10 to 500 nm, more preferably 10 to 100 nm, still more preferably 15 to 75 nm, Especially preferred is 20 to 60 nm. In addition, the aspect ratio (the aspect ratio of the primary particles) of the particulate carbon material (preferably acetylene black) is 20 or less as described above, preferably 10 or less, more preferably 5 or less, and still more preferably It is 2 or less, and particularly preferably 1.5 or less (the lower limit is 1).

Examples of fibrous carbon materials include carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes), carbon nanofibers, vapor-grown carbon fibers, electrospun carbon fibers, polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, and the like. be done. Among them, carbon nanotubes are preferable from the viewpoint of conductivity. The diameter (minor axis) of the fibrous carbon material (preferably carbon nanotubes) is not particularly limited, but is preferably 1-100 nm, more preferably 2-50 nm, and still more preferably 5-20 nm. The length (major axis) of the fibrous carbon material (preferably carbon nanotube) is not particularly limited, but is preferably 1 to 100 μm, more preferably 2 to 50 μm, still more preferably 5 to 30 μm. The aspect ratio of the fibrous carbon material (preferably carbon nanotube) is 1000 or more as described above, preferably 1500 or more, more preferably 1800 or more. Although the upper limit of the aspect ratio of the fibrous carbon material (preferably carbon nanotubes) is not particularly limited, it is, for example, 20,000 or less, and may be 10,000 or less, 5,000 or less, or 4,000 or less.

The electrode of the present embodiment preferably contains both the particulate carbon material and the fibrous carbon material as conductive aids. That is, in an electrode for a non-aqueous electrolyte secondary battery according to a preferred embodiment, the conductive aid contains a particulate carbon material with an aspect ratio of 20 or less and a fibrous carbon material with an aspect ratio of 1000 or more. By including both the particulate carbon material and the fibrous carbon material in the conductive aid, an electron conduction path is well formed. More specifically, the presence of the particulate carbon material near the surface of the electrode active material forms a short-distance electron conduction path, while the fibrous carbon material is dispersed in the electrode active material layer to form a medium- or long-distance electron conduction path. of electronic motor paths are formed. Thereby, an electron conduction path can be efficiently formed from the electrode active material to the current collector. As a result, in the non-aqueous electrolyte secondary battery having the electrode according to the present embodiment, the output characteristics can be further improved (in particular, more capacity can be extracted during discharge at a high discharge rate). Furthermore, the amount of conductive aid in the electrode active material layer can be reduced by forming an electron conduction path well. As a result, it becomes possible to further improve the energy density of the non-aqueous electrolyte secondary battery.

From the viewpoint of better formation of the electron conduction path described above, the mass ratio of the particulate carbon material and the fibrous carbon material (particulate carbon material:particulate carbon material) is 1:10 to 1:1. 1:6 to 1:2 is more preferred, and 1:5 to 1:3 is even more preferred. When the mass ratio is within the above range, an electron conduction path is formed more satisfactorily, so that the output characteristics can be further improved (in particular, more capacity can be extracted during discharge at a high discharge rate). can). Moreover, it is possible to further improve the energy density of the non-aqueous electrolyte secondary battery.

The content of the conductive aid contained in the electrode active material layer (the total amount if the particulate carbon material and the fibrous carbon material are included) is 2% by mass with respect to 100% by mass of the total solid content of the electrode active material layer. % or less, more preferably 1 mass % or less, and even more preferably 0.5 mass % or less. At such an upper limit value, the electron conduction path is well formed by suppressing the aggregation of the conductive aids, so that the output characteristics can be further improved (especially, discharge at a high discharge rate (more capacity can be extracted when Moreover, it is possible to further improve the energy density of the non-aqueous electrolyte secondary battery. Although the lower limit of the content of the conductive aid is not particularly limited, it exceeds 0% by mass, preferably 0.1% by mass or more, preferably 0.2% by mass or more, and 0.3 % by mass or more is more preferable. At such a lower limit, there is sufficient conductive aid to form an electron conduction path, so that the output characteristics can be further improved (especially, when discharging at a high discharge rate, more capacity can be taken out).

Incidentally, as long as the effect of the present invention is not impaired, it is a matter of course that conductive aids other than those described above may be used.

(Binder)
The binding agent (binder) has a function of maintaining the structure of the electrode active material layer by binding the members included in the electrode active material layer to each other. The electrode according to this embodiment contains polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as binders, and polyvinylidene fluoride-hexafluoropropylene (PVDF- HFP) is more than 0 and less than 0.015. With such a configuration, the output characteristics can be improved in the non-aqueous electrolyte secondary battery having the electrode according to the present embodiment (in particular, a large amount of capacity can be extracted during discharge at a high discharge rate. can be done). Although the detailed mechanism by which the above effects are exhibited is unknown, the present inventors presume as follows. The technical scope of the present invention is not limited to the following mechanisms.

According to the study of the present inventors, it was found that the combined use of PVDF and PVDF-HFP significantly improved the output characteristics rather than the use of PVDF alone. This is because PVDF-HFP has a higher swellability in an electrolytic solution than PVDF, and by using PVDF and PVDF-HFP in combination, ion conductivity such as lithium ions in the electrode active material layer is improved. It is considered to be Furthermore, since PVDF-HFP has high flexibility, it is assumed that it enters the gaps of other members (electrode active material, conductive aid, etc.) contained in the electrode active material layer and improves their dispersibility. . As a result, it is considered that electron conduction paths are well formed and excellent output characteristics can be exhibited. Further, the present inventors have found that when the mass ratio of PVDF-HFP to the electrode active material is 0.015 or more, the above effect cannot be sufficiently obtained. This is probably because the excessive PVDF-HFP content inhibits the electron conduction path in the electrode active material layer.

In the electrode of this embodiment, PVDF is not particularly limited as long as it is a homopolymer of vinylidene fluoride. The molecular weight of PVDF is preferably 100,000 or more and 1,000,000 or less, more preferably 300,000 or more and 800,000 or less, still more preferably 500,000 or more and 700, 000 or less.

In the electrode of this embodiment, PVDF-HFP is not particularly limited as long as it is a comonomer of vinylidene fluoride and hexafluoropropylene. The ratio of hexafluoropropylene-derived structural units contained in PVDF-HFP is preferably 6 mol% or more and 20 mol% or less, and 6.5 mol% or more and 10 mol, with respect to all structural units of PVDF-HFP. % or less, and particularly preferably 6.9 mol % or more and 8 mol % or less. When the ratio of the structural unit derived from hexafluoropropylene is within the above range, the swelling property to the electrolytic solution and the flexibility can be improved. As a result, the ionic conductivity and electronic conductivity in the electrode active material layer are improved, and excellent output characteristics can be exhibited (in particular, a large amount of capacity can be extracted during discharge at a high discharge rate). ).

In the electrode active material layer, the mass ratio of PVDF-HFP to the electrode active material is more than 0 and less than 0.015, preferably 0.002 or more and 0.009 or less, more preferably 0.003 or more and 0 0.007 or less, and particularly preferably 0.004 or more and 0.006 or less. When the mass ratio is 0 (that is, the electrode active material layer does not contain PVDF-HFP) or when the mass ratio is 0.015 or more, the effect of improving the output characteristics as described in the mechanism above. is not obtained.

In the electrode active material layer, the content of the binder is preferably less than 3% by mass, more preferably 2% by mass or less, still more preferably 100% by mass of the total solid content of the electrode active material layer. is 1% by mass or less, more preferably less than 1% by mass, particularly preferably 0.9% by mass or less, and most preferably 0.8% by mass or less. Since the binder does not directly contribute to the charging/discharging reaction, it is possible to further improve the energy density of the non-aqueous electrolyte secondary battery by reducing its content as described above. The lower limit is not particularly limited as long as the structure of the electrode active material layer can be maintained, but is preferably 0.3% by mass or more, more preferably 0.5% by mass or more.

In the electrode active material layer, the mass ratio (PVDF: PVDF-HFP) of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is preferably 1:5 to 5:1. , more preferably 1:4 to 4:1, more preferably 1:2 to 2:1, particularly preferably 1:1.5 to 1.5:1, most preferably 1:1 .2 to 1.2:1. When the mass ratio is within the above range, even when the content of the binder in the electrode active material layer is relatively small (especially preferably 1% by mass or less, more preferably less than 1% by mass, and even more preferably is 0.9% by mass or less, particularly preferably 0.8% by mass or less) While maintaining the binding property of PVDF, the effect of improving ion conductivity and / or electronic conductivity by PVDF-HFP is well balanced. Become. On the other hand, when the content of the binder in the electrode active material layer is relatively large (especially preferably 1% by mass or more, more preferably more than 1% by mass, still more preferably 1.1% by mass or more, particularly preferably 1.2% by mass or more), the mass ratio (PVDF: PVDF-HFP) is preferably 1:1.1 to 1:10, more preferably 1:1.5 to 1:6, It is more preferably 1:2 to 1:5. When the mass ratio is within the above range, the swellability to the electrolytic solution and the flexibility can be improved. As a result, the ionic conductivity and electronic conductivity in the electrode active material layer are improved, and excellent output characteristics can be exhibited (in particular, a large amount of capacity can be extracted during discharge at a high discharge rate). ).

The electrode active material layer may contain a binder other than PVDF and PVDF-HFP (hereinafter also referred to as "another binder"). However, from the viewpoint of further exerting the effect of the present invention, the content of the other binder in the electrode active material layer is preferably 10% by mass or less, more preferably 10% by mass or less, relative to the total amount of the binder. is 5% by mass or less, more preferably 3% by mass or less, particularly preferably 1% by mass or less, and most preferably 0% by mass (that is, the electrode active material layer contains another binder Not included). Other binders are not particularly limited, and known materials can be used as appropriate.

In the electrode for a non-aqueous electrolyte secondary battery of the present embodiment, the thickness of the electrode active material layer is not particularly limited, and conventionally known knowledge about batteries can be appropriately referred to. For example, the thickness of the electrode active material layer is usually about 1 to 1000 μm, preferably 20 to 800 μm, more preferably 30 to 500 μm, still more preferably 40 to 200 μm. As the thickness of the electrode active material layer increases, it becomes possible to hold the electrode active material for exhibiting a sufficient capacity (energy density). On the other hand, the smaller the thickness of the electrode active material layer, the better the output characteristics (especially, the more capacity can be extracted during discharge at a high discharge rate).

(Electrolyte)
The electrode active material layer may further include an electrolyte. The electrolyte has a function as a carrier of lithium ions. The electrolytic solution has a form in which a lithium salt is dissolved in a non-aqueous solvent.

Non-aqueous solvents are, 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), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO ), and γ-butyrolactone (GBL). Among them, the non-aqueous solvent is preferably a chain carbonate, more preferably diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate ( DMC), more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

Lithium salts include Li(FSO ₂ ) ₂ N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF _{3 SO3} and the like. Among them, the lithium salt is preferably Li(FSO ₂ ) ₂ N from the viewpoint of battery output and charge/discharge cycle characteristics.

The concentration of the lithium salt in the electrolytic solution is preferably 0.1-3.0 mol/L, more preferably 0.8-2.2 mol/L.

The electrolytic solution may further contain additives other than the components described above. Specific examples of such compounds include ethylene carbonate, 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-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxymethylethylene carbonate, allyloxymethylethylene carbonate, acryloxymethylethylene carbonate, methacryloxymethylethylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, ethynyloxymethylethylene carbonate, propargyloxyethylene carbonate, methyleneethylene carbonate, 1 , 1-dimethyl-2-methylene ethylene carbonate and the like. These additives may be used alone or in combination of two or more. In addition, when the additive is used in the electrolytic solution, the amount used can be appropriately adjusted.

[Method for producing electrode for non-aqueous electrolyte secondary battery]
The method for producing the electrode for a non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and conventionally known methods can be appropriately adopted. For example, the electrode active material, conductive aid, and binder are mixed with a solvent to prepare an electrode slurry (positive electrode slurry, negative electrode slurry). Then, the electrode slurry is applied to the surface of the current collector, and the solvent is dried to form a coating film.

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 mixing the electrode active material, the conductive aid and the binder with the solvent is not particularly limited, but as shown in the examples below, the electrode active material and the conductive aid are dispersed in the solvent. It is preferable to add a binder and mix. More specifically, a solvent is added to a kneaded mixture of an electrode active material and a conductive aid, and then a binder is added and mixed. By mixing in this order, the electrode active material, conductive aid and binder are sufficiently dispersed in the electrode slurry, and electron conduction paths are well formed in the electrode active material layer.

The concentration of the electrode slurry is not particularly limited. However, from the viewpoint of facilitating application of the electrode slurry, which will be described later, the concentration of the total solid content relative to 100% by mass of the electrode 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.

The electrode slurry is then applied onto the current collector and dried. After application, pressing may be performed as necessary.

The method of applying the electrode slurry to the current collector is not particularly limited, and includes screen printing, spray coating, electrostatic spray coating, inkjet, doctor blade, and the like.

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

The drying method after coating the electrode active material slurry on the current collector is not particularly limited as long as at least part of the solvent is removed. Heating is mentioned as the said drying method. The drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the volatilization rate of the solvent contained in the applied electrode active material slurry, 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.

Through the steps described above, the electrodes (positive electrode, negative electrode) for a non-aqueous electrolyte secondary battery of the present embodiment can be obtained.

<Non-aqueous electrolyte secondary battery>
According to another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") having the electrode for a non-aqueous electrolyte secondary battery. Since the secondary battery includes the electrode, it has excellent output characteristics. In this embodiment, there are an embodiment in which the positive electrode is the above electrode, an embodiment in which the negative electrode is the above electrode, and an embodiment in which the positive electrode and the negative electrode are the above electrodes. Especially, it is preferable that it is embodiment whose positive electrode is the said electrode. When the secondary battery of the present embodiment includes electrodes other than the electrodes described above, conventionally known electrodes can be appropriately employed as the electrodes other than the electrodes described above. Main constituent members other than the electrodes of the non-aqueous electrolyte secondary battery according to the present embodiment will be described below.

[Electrolyte layer]
The electrolyte layer preferably has a structure in which a separator is impregnated with an electrolytic solution (liquid electrolyte). The specific configuration and preferred embodiments of the electrolytic solution have been described in the above section (Electrolyte solution), and detailed description thereof will be omitted here. The electrolytic solution contained in the electrolyte layer may be the same as or different from the electrolytic solution contained in the electrode active material layer, but is preferably the same.

The separator that constitutes the electrolyte layer has a function of retaining the electrolyte to ensure lithium ion conductivity between the positive electrode and the negative electrode, and a function of a partition wall between the positive electrode and the negative electrode.

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

As a porous sheet separator made of polymer or 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, polyolefins such as polyethylene (PE) and polypropylene (PP); structural laminates, etc.), hydrocarbon resins such as polyimide, aramid, and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and microporous (microporous membrane) separators made of glass fibers.

The thickness of the microporous (microporous membrane) separator cannot be defined uniquely because it varies depending on the intended use. As an example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), the single layer or multiple layers may have a thickness of 4 to 60 μm. desirable. The fine pore size of the microporous (microporous membrane) separator is desirably 1 μm or less at maximum (usually, the pore size is about several tens of nanometers).

As the non-woven fabric separator, conventionally known materials such as cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; polyimide and aramid are used singly or in combination. Also, the bulk density of the non-woven fabric is not particularly limited as long as the impregnated polymer gel electrolyte provides sufficient battery characteristics. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

The separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (separator with a heat-resistant insulating layer). A heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, one having a high heat resistance with a melting point or 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 relieved, so that the effect of suppressing thermal shrinkage can be obtained. As a result, it is possible to prevent short-circuiting between the electrodes of the battery, so that the battery configuration is such that the deterioration of performance due to temperature rise is unlikely to occur. Moreover, by having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the breakage of the separator hardly occurs. Furthermore, due to the effect of suppressing heat shrinkage and high mechanical strength, the separator is less likely to curl during the battery manufacturing process.

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 thermal shrinkage. Materials used as inorganic particles are not particularly limited. Examples include oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides, and nitrides of silicon, aluminum, zirconium, titanium, 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, these inorganic particles may be used alone or in combination of two or more. Among these, silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) is preferably used from the viewpoint of cost, and alumina (Al ₂ O ₃ ) is more preferably used.

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 is obtained and heat resistance strength is maintained, which is preferable.

The binder in the heat-resistant insulating layer has a role of bonding the inorganic particles to each other and bonding the inorganic particles to the resin porous substrate layer. The binder stably forms the heat-resistant insulating layer and prevents separation 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 examples thereof include carboxymethylcellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), and isoprene rubber. , butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), methyl acrylate, and other compounds can be used as binders. Among these, it is preferable to use carboxymethyl cellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF). These compounds may be used alone or in combination of two or more.

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 content of the binder 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 content of the binder is 20% by mass or less, the gaps between the inorganic particles are appropriately maintained, so sufficient lithium ion conductivity can be ensured.

The heat shrinkage rate of the separator with a heat-resistant insulating layer is preferably 10% or less in both MD and TD after holding for 1 hour under conditions of 150° C. and 2 gf/cm ² . By using such a highly heat-resistant material, the shrinkage of the separator can be effectively prevented even when the heat value increases and the internal temperature of the battery reaches 150°C. As a result, it is possible to prevent the induction of short-circuiting between the electrodes of the battery, so that the battery configuration is such that performance degradation due to temperature rise is unlikely to occur.

[Positive collector plate and negative collector plate]
The material constituting the current collectors (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collectors for lithium ion secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable as the constituent material of the current collector plate. From the viewpoint of light weight, corrosion resistance and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The same material or different materials may be used for the positive collector plate 25 and the negative collector plate 27 .

[Positive lead and negative lead]
Although not shown, the current collector 11 and the current collector plates (25, 27) may be electrically connected via a positive lead or a negative lead. Materials used in known lithium-ion secondary batteries can also be employed as the constituent materials of the positive and negative electrode leads. In addition, the part taken out from the exterior body should be heat-resistant and insulative so that it does not affect the product (for example, automobile parts, especially electronic equipment, etc.) by contacting peripheral equipment or wiring and causing electric leakage. Covering with a shrinkable tube or the like is preferable.

[Seal part]
The sealing portion (insulating layer) 31 is a member unique to a bipolar secondary battery (series stacked battery) and has a function of preventing leakage of electrolyte from the electrolyte layer. In addition, the sealing portion 31 has a function of preventing contact between current collectors and short circuiting at the ends of the cell layers. The material constituting the sealing portion should have insulating properties, sealing properties against dropout of the solid electrolyte, sealing properties (sealing properties) against permeation of moisture from the outside, and heat resistance under the battery operating temperature. 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. Alternatively, 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, from the viewpoint of corrosion resistance, chemical resistance, ease of production (film forming property), economic efficiency, etc., polyethylene resin and polypropylene resin are preferably used as the constituent material of the seal part, and amorphous polypropylene resin is the main component. It is more preferable to use a resin obtained by copolymerizing ethylene, propylene, and butene.

[Battery exterior body]
As the battery exterior body, a known metal can case can be used, and as shown in FIGS. 1 and 2, a bag-like case using a laminate film 29 containing aluminum that can cover the power generation element is used. can be The laminated film may be, for example, a laminated film having a three-layer structure in which PP, aluminum and nylon are laminated in this order, but is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high power output and cooling performance and can be suitably used for batteries for large equipment for EV and HEV. Further, the exterior body is more preferably an aluminate laminate because the group pressure applied to the power generating element from the outside can be easily adjusted, and the thickness of the electrolytic solution layer can be easily adjusted to a desired thickness.

The non-aqueous electrolyte secondary battery according to this embodiment can exhibit excellent output characteristics. Therefore, the non-aqueous electrolyte secondary battery according to this embodiment is suitably used as a power source for driving EVs and HEVs.

[Assembled battery]
An assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and serialization or parallelization or both of them are used. By connecting in series and in parallel, it is possible to freely adjust the capacity and voltage.

A plurality of batteries can be connected in series or in parallel to form a small detachable assembled battery. A plurality of these detachable small battery packs are further connected in series or in parallel to form a large-capacity, large-capacity battery suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density. It is also possible to form assembled batteries (battery modules, battery packs, etc.) with 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) in which it is installed. It should be decided according to the output.

[vehicle]
The non-aqueous electrolyte secondary battery of this embodiment has excellent output characteristics (in particular, sufficient capacity can be obtained during discharge at a high discharge rate). Furthermore, it has a high volumetric energy density. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require high capacity and large current compared to electrical and portable electronic device applications. Therefore, the non-aqueous electrolyte secondary battery can be suitably used as a power source for vehicles, for example, a power source for driving a vehicle or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, a battery having a large capacity and excellent output characteristics can be configured. Therefore, when such a battery is mounted on a vehicle, a plug-in hybrid electric vehicle with a long EV driving range or an electric vehicle with a long driving distance per charge can be configured. Examples of vehicles include hybrid vehicles, fuel cell vehicles, and electric vehicles (both of which include four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, and buses, light vehicles, etc.), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles. ). However, the application is not limited to automobiles, and it can be applied to various power sources for other vehicles such as trains and other moving bodies, and can be used as a power source for installation such as an uninterruptible power supply. It is also possible to

EXAMPLES Hereinafter, the present invention will be described in more detail using examples and comparative examples, but the present invention is not limited to the examples below.

[Manufacturing example]
<Production of negative electrode>
A solid content of 95.5% by mass of graphite (average particle size: 20 μm) as a negative electrode active material, 0.5% by mass of carbon black as a conductive aid, and 4% by mass of PVDF as a binder was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to this solid content, and a planetary stirring type mixing and kneading device "Awatori Mixer" (ARE-310, manufactured by Thinky Co., Ltd.) is used at 2000 rpm for 6 minutes. They were mixed to prepare a negative electrode slurry. The negative electrode slurry was applied evenly on a Cu foil placed on a smooth plate using a doctor blade so that the negative electrode active material layer had a thickness of 86 μm. Then, the negative electrode was produced by drying on the hot plate heated at 80 degreeC for 2 hours.

[Example 1]
<Preparation of positive electrode>
LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (abbreviation: NMC811, average particle diameter: 10 μm) 98.5% by mass, which is a positive electrode active material, carbon nanotubes (abbreviation: CNT, fiber diameter : 10 nm, fiber length: 20 μm, aspect ratio: 2000) 0.4% by mass, acetylene black (abbreviation: AB, HS-100, manufactured by Denka, average primary particle size: 48 nm, aspect ratio: 1) 0.1% by mass, PVDF as a binder (Kureha KF Polymer W#7200, manufactured by Kureha) 0.8% by mass, PVDF-HFP as a binder (Kyner Flex 2501-10, manufactured by Arkema, hexafluoropropylene A solid content of 0.2% by mass (ratio of structural units derived from 6.9 mol%) was prepared. First, the positive electrode active material (whole amount) and the conductive aid (whole amount of carbon nanotubes and acetylene black) were kneaded. N-Methyl-2-pyrrolidone (NMP) was added to this so that the solid content concentration was 85%, and a planetary stirring type mixing and kneading device "Awatori Mixer" (ARE-310, manufactured by Thinky Co., Ltd.) was used. and mixed at 2000 rpm for 5 minutes. N-Methyl-2-pyrrolidone (NMP) was added thereto so that the solid content concentration was 80%, and the mixture was mixed at 2000 rpm for 5 minutes using the above-described mixing and kneading apparatus. A binder (the total amount of PVDF and PVDF-HFP) was added thereto, and mixed for 2 minutes at 2000 rpm using the above-mentioned mixing and kneading device. To this, N-methyl-2-pyrrolidone (NMP) was added so that the solid content concentration was 70%, the viscosity was adjusted, and positive electrode slurry was produced. The positive electrode slurry was applied evenly on an Al foil placed on a smooth board using a doctor blade so that the positive electrode active material layer had a thickness of 62 μm. Then, it was dried on a hot plate heated to 80° C. for 30 minutes, moved to a vacuum dryer, and dried under vacuum at 130° C. for 8 hours to prepare a positive electrode.

<Production of lithium ion battery>
The obtained positive electrode was cut into 12 cm ² pieces, and the negative electrode into 13 cm ² pieces. In the positive electrode, an aluminum foil with an Al terminal was laminated on the current collector foil side of the cut positive electrode. For the negative electrode, a copper foil with a Ni terminal was laminated on the collector foil side of the cut negative electrode. A separator (manufactured by Celgard Co., Ltd., manufactured by PP) was inserted into the electrode active material layer side of the positive electrode and the negative electrode to form a laminate. This laminate is sandwiched between heat-sealable aluminum laminate films, and Li(FSO ₂ ) is added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 3:7 (EC:EMC)) as a non-aqueous solvent. After injecting a nonaqueous electrolytic solution obtained by dissolving 2 mol/L of ₂ N (lithium bis(fluorosulfonyl)imide; LiFSI), the chamber was vacuum-sealed. In this way, a pouch-type lithium ion battery was produced in which the positive electrode and the negative electrode were laminated so as to face each other with the separator interposed therebetween.

[Example 2]
A lithium ion battery was produced in the same manner as in Example 1, except that the proportion of PVDF was changed to 0.5% by mass and the proportion of PVDF-HFP was changed to 0.5% by mass in the production of the positive electrode.

[Example 3]
A lithium ion battery was produced in the same manner as in Example 1, except that the proportion of PVDF was changed to 0.2% by mass and the proportion of PVDF-HFP was changed to 0.8% by mass in the production of the positive electrode.

[Comparative Example 1]
In the preparation of the positive electrode, except that the ratio of carbon nanotubes was changed to 0.5% by mass, the ratio of acetylene black to 0% by mass, the ratio of PVDF to 1% by mass, and the ratio of PVDF-HFP to 0% by mass, A lithium ion battery was produced in the same manner as in Example 1.

[Comparative Example 2]
A lithium ion battery was produced in the same manner as in Example 1, except that the proportion of PVDF was changed to 1% by mass and the proportion of PVDF-HFP was changed to 0% by mass in the production of the positive electrode.

[Comparative Example 3]
In the fabrication of the positive electrode, the proportion of LiNi _0.8 Mn _0.1 Co _0.1 O ₂ was increased to 96.5% by mass, the proportion of PVDF to 1.5% by mass, and the proportion of PVDF-HFP to 1.5% by mass. A lithium ion battery was produced in the same manner as in Example 1, except that

[Evaluation of output characteristics]
The output characteristic evaluation was carried out by placing the lithium ion secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 3 in a constant temperature bath (ARSF-0250-10, manufactured by Espec Co., Ltd.) set at 45 ° C. . The lithium ion secondary battery produced above was sandwiched between urethane rubber and silicone sponge sheets with a thickness of 5 mm, and was evaluated in a state where it was restrained at 6 points using a metal plate with a thickness of 10 mm and M6 screws. First, charging and discharging were performed twice at a cell voltage range of 2.5 to 4.3 V and a current value of 0.1 C rate to confirm the capacity at a low rate. The capacity obtained at the 2.5 V cutoff during the first discharge was taken as the reference capacity of the cell. Next, while the charge rate was fixed at 0.1C, the discharge rate was increased stepwise to 0.5C, 1C, and 2C, and charging and discharging were performed. Then, the capacity obtained under the cell voltage cutoff condition of 2.5V when discharging at the 2C rate was defined as the effective capacity. 2C effective capacity/0.1C reference capacity×100 obtained based on these values was defined as 2C/0.1C discharge capacity retention (%). Table 1 shows the results.

From the above results, it was shown that the lithium ion battery using the positive electrode according to the present invention has improved output characteristics compared to the battery of the comparative example.

10a stacked secondary battery,
10b bipolar secondary battery,
11 current collector,
11a outermost current collector on the positive electrode side,
11b outermost current collector on the negative electrode side,
11′ positive electrode current collector 12 negative electrode current collector 13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation element,
23 bipolar electrodes,
25 positive collector plate (positive tab),
27 negative electrode current collector (negative electrode tab),
29 laminate film,
31 seal.

Claims (8)

An electrode for a non-aqueous electrolyte secondary battery comprising a current collector and an electrode active material layer disposed on the surface of the current collector,
The electrode active material layer contains an electrode active material, a conductive aid and a binder,
The binder includes polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP),
An electrode for a non-aqueous electrolyte secondary battery, wherein the mass ratio of the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to the electrode active material is greater than 0 and less than 0.015. 2. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the mass ratio of said polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to said electrode active material is 0.002 or more and 0.009 or less. 3. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of said binder is less than 3% by mass with respect to 100% by mass of the total solid content of said electrode active material layer. Claims 1 to 3, wherein the mass ratio (PVDF: PVDF-HFP) of the polyvinylidene fluoride (PVDF) and the polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is 1:4 to 4:1. The electrode for non-aqueous electrolyte secondary batteries according to any one of the above. The non-aqueous electrolyte secondary according to any one of claims 1 to 4, wherein the conductive aid contains a particulate carbon material having an aspect ratio of 20 or less and a fibrous carbon material having an aspect ratio of 1000 or more. Electrodes for batteries. 6. The non-aqueous electrolyte secondary according to claim 5, wherein the mass ratio of the particulate carbon material to the fibrous carbon material (particulate carbon material:particulate carbon material) is 1:10 to 1:1. Electrodes for batteries. The non-aqueous electrolyte according to any one of claims 1 to 6, wherein the content of the conductive aid is 0.5% by mass or less with respect to 100% by mass of the total solid content of the electrode active material layer. Electrodes for secondary batteries. A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 7.

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