JP2022024868A - Non-aqueous secondary battery - Google Patents

Abstract

To provide a non-aqueous secondary battery having high reliability.SOLUTION: A non-aqueous secondary battery includes a positive electrode, a negative electrode, an insulating layer which is a single layer whose one surface comes in contact with the positive electrode and the other surface comes in contact with the negative electrode, and contains a polyvinylidene fluoride-based resin and inorganic particles, and an electrolyte. A weight average molecular weight of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 or more and 1,500,000 or less, and a mass ratio of the inorganic particles in the insulating layer is 50 mass% or more and less than 90 mass%.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to non-aqueous secondary batteries.

In a non-aqueous secondary battery, an insulating layer or a separator is used for the purpose of insulating the positive electrode and the negative electrode.
For example, Patent Document 1 or Patent Document 2 describes an active material layer containing a positive electrode active material or a negative electrode active material, and a heat-resistant porous layer containing a heat-resistant polymer and an inorganic filler laminated on the active material layer. Disclosed is an electrode sheet for a non-aqueous electrolyte battery.
For example, Patent Document 3 describes a positive electrode, a negative electrode, a battery element containing a fluororesin and a ceramic separator layer containing insulating inorganic particles, a battery element containing a lithium ion conductive non-aqueous electrolyte, and an exterior body containing the battery element. A lithium ion secondary battery equipped with the above is disclosed.
For example, Patent Document 4 describes a step of coating a separator layer forming composition containing two or more kinds of resin particles having different average particle sizes on an electrode, and a separator layer forming composition coated on the electrode. A secondary battery is constructed by using a step of drying an object from the coated end to form a separator layer integrated with the electrode on an electrode, an electrode on which the separator layer is formed, a counter electrode, and an electrolytic solution. And a method of manufacturing a secondary battery having the above-mentioned steps are disclosed.
For example, Patent Document 5 describes a separator electrode integrated storage device for a lithium ion secondary battery, which is formed by joining and integrating a separator, which is a porous layer containing magnesium hydroxide having an average particle size of 0.5 μm to 3.0 μm, and an electrode. The element is disclosed.
For example, Patent Document 6 describes a battery including a positive electrode, a negative electrode, and an adhesive resin layer arranged between the positive electrode and the negative electrode and adhering at least one of the positive electrode and the negative electrode, wherein the adhesive resin layer is provided. A battery containing a filler having an average diameter of 0.01 μm to 1 μm and a resin is disclosed.
For example, Patent Document 7 describes a step of arranging a separator precursor solution containing a solid granular material and a polymer binder on an electrode by screen printing, and a step of changing the separator precursor solution into a porous separator in the form of a thin film. A method for producing a porous separator having the above is disclosed.
For example, Patent Document 8 discloses a non-aqueous secondary battery using a separator provided with a porous substrate and an adhesive porous layer containing a polyvinylidene fluoride-based resin and having a crystal size of 1 nm to 13 nm. ing.
For example, Patent Document 9 includes a porous substrate and an adhesive porous layer containing a polyvinylidene fluoride-based resin having a weight average molecular weight of 600,000 to 3,000,000 and having a porosity of 30% to 60%. A non-aqueous secondary battery using a separator is disclosed.
For example, Patent Document 10 discloses a power storage device using a separator made of a composite material containing inorganic particles and an organic binder and having a ratio of a pigment volume concentration to a critical pigment volume concentration of 0.7 to 1.15. There is.
For example, Patent Document 11 describes a current collector, an electrode active material layer formed on one surface of the current collector, and a porous layer formed on the electrode active material layer and containing inorganic particles and a binder polymer. Disclosed is a sheet-type secondary battery electrode including a porous first support layer formed on the presence / absence machine porous layer.
For example, Patent Document 12 describes a porous substrate, a binder resin, and an average primary particle size of 0.01 μm or more. A non-aqueous secondary battery using a separator provided with a heat-resistant porous layer containing barium sulfate particles having a size of less than 30 μm and having a volume ratio of barium sulfate particles of 50% by volume to 90% by volume is disclosed.
For example, in Patent Document 13, a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, a separator, an electrolytic solution, and a positive electrode active material layer or a negative electrode active material layer and a separator are arranged. A lithium ion secondary battery having an inorganic particle layer containing Al ₂ O ₃ and polyvinylidene fluoride is disclosed.
For example, Patent Document 14 describes a porous substrate, an adhesive porous layer containing vinylidene fluoride and an acrylic monomer as monomer components, and a polyvinylidene fluoride resin having a melting point of 130 ° C. to 148 ° C. A non-aqueous secondary battery using a separator provided with the above is disclosed.

Japanese Unexamined Patent Publication No. 2010-056037 Japanese Unexamined Patent Publication No. 2011-108516 JP-A-2015-191710 Japanese Unexamined Patent Publication No. 2016-179962 Japanese Unexamined Patent Publication No. 2017-123269 Japanese Patent No. 4077045 Japanese Patent No. 4790880 Japanese Patent No. 4988972 Japanese Patent No. 5129895 Japanese Patent No. 5880555 Japanese Patent No. 59385523 Japanese Patent No. 6526359 Japanese Patent No. 6597267 International Publication No. 2018/212252

It is desired that the non-aqueous secondary battery has excellent discharge characteristics, coulombic efficiency, and cell strength, that is, high reliability. The insulating layer, which is one of the members constituting the non-aqueous secondary battery, is required to have electrical insulation, ion permeability, adhesion to electrodes, etc. in order to improve the reliability of the non-aqueous secondary battery. ..

The embodiments of the present disclosure have been made under the above circumstances.
An embodiment of the present disclosure aims to provide a highly reliable non-aqueous secondary battery, and an object of the present invention is to achieve this.

Specific means for solving the above-mentioned problems include the following aspects.

<1> A positive electrode, a negative electrode, a single layer having one surface in contact with the positive electrode and the other surface in contact with the negative electrode, an insulating layer containing a polyvinylidene fluoride-based resin and inorganic particles, and an electrolytic solution. Prepare,
The weight average molecular weight of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 or more and 1.5 million or less.
The mass ratio of the inorganic particles to the insulating layer is 50% by mass or more and less than 90% by mass.
Non-water-based secondary battery.
<2> The non-aqueous secondary battery according to <1>, wherein the inorganic particles contain at least one selected from the group consisting of metal hydroxide particles and metal sulfate particles.
<3> The non-aqueous secondary battery according to <1> or <2>, wherein the average primary particle size of the inorganic particles contained in the insulating layer is 0.01 μm or more and less than 1.00 μm.
<4> The non-aqueous secondary battery according to any one of <1> to <3>, wherein the thickness of the insulating layer is 5 μm or more and 30 μm or less.
<5> The non-aqueous secondary battery according to any one of <1> to <4>, wherein the insulating layer has a porosity of 40% or more and less than 80%.
<6> The non-aqueous secondary battery according to any one of <1> to <5>, wherein the mass of the insulating layer per unit area is 4 g / m ² or more and less than 40 g / m ² .
<7> The non-aqueous secondary battery according to any one of <1> to <6>, which obtains an electromotive force by doping and dedoping lithium ions.

According to the present disclosure, a highly reliable non-aqueous secondary battery is provided.

It is a schematic diagram which shows the embodiment of the non-aqueous secondary battery of this disclosure.

Hereinafter, embodiments of the present disclosure will be described. These explanations and examples illustrate the embodiments and do not limit the scope of the embodiments.

In the present disclosure, "A and / or B" is synonymous with "at least one of A and B". That is, "A and / or B" means that it may be only A, it may be only B, or it may be a combination of A and B.

The numerical range indicated by using "-" in the present disclosure indicates a range including the numerical values before and after "-" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.

When the embodiments are described in the present disclosure with reference to the drawings, the configuration of the embodiments is not limited to the configurations shown in the drawings. Further, the size of the members in each figure is conceptual, and the relative relationship between the sizes of the members is not limited to this.

When referring to the amount of each component in the composition in the present disclosure, if a plurality of substances corresponding to each component are present in the composition, unless otherwise specified, the plurality of species present in the composition. It means the total amount of substances.

In the present disclosure, a plurality of types of particles corresponding to each component may be contained. When a plurality of particles corresponding to each component are present in the composition, the particle size of each component means a value for a mixture of the plurality of particles present in the composition, unless otherwise specified.

<Non-water-based secondary battery>
The technique of the present disclosure relates to a secondary battery that does not contain water in the electrolytic solution, that is, a non-aqueous secondary battery. An example of an embodiment of the non-aqueous secondary battery of the present disclosure is a lithium ion secondary battery that obtains an electromotive force by doping and dedoping lithium ions.

The non-aqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, an insulating layer, and an electrolytic solution. The insulating layer is a single layer in which one surface is in contact with the positive electrode and the other surface is in contact with the negative electrode, and contains a polyvinylidene fluoride-based resin and inorganic particles. The weight average molecular weight of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 or more and 1.5 million or less, and the mass ratio of the inorganic particles in the insulating layer is 50% by mass or more and less than 90% by mass.

Hereinafter, the "positive electrode" and the "negative electrode" are collectively referred to as an "electrode". Further, the "non-aqueous secondary battery" is also simply referred to as a "battery".

In the battery of the present disclosure, since the insulating layer is a single layer, (1) since there is no boundary between the layers inside the insulating layer, the electric resistance of the insulating layer can be suppressed low, and the discharge characteristics and the Coulomb efficiency of the battery can be improved. It can be enhanced, and (2) delamination does not occur inside the insulating layer, so that the Coulomb efficiency and cell strength of the battery can be enhanced.

In the battery of the present disclosure, the weight average molecular weight (Mw) of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 or more and 1.5 million or less.
Mw of the polyvinylidene fluoride-based resin is 90 from the viewpoint of enhancing the electrical insulation of the insulating layer and suppressing the blockage of the pores of the insulating layer to improve the ion permeability and improve the discharge characteristics of the battery. It is over 10,000. If the Mw of the polyvinylidene fluoride-based resin is less than 900,000, the electrical insulating property of the insulating layer may be insufficient. Further, if the Mw of the polyvinylidene fluoride-based resin is less than 900,000, the pores of the insulating layer may be closed when heat is applied to the insulating layer during the manufacturing of the battery, and the discharge characteristics of the battery are inferior.
The Mw of the polyvinylidene fluoride-based resin is 1.5 million or less from the viewpoint of improving the adhesion between the insulating layer and the electrode and increasing the coulombic efficiency and cell strength of the battery. If the Mw of the polyvinylidene fluoride-based resin is more than 1.5 million, the polyvinylidene fluoride-based resin is difficult to soften when heat is applied to the insulating layer during battery manufacturing, so that the insulating layer does not sufficiently adhere to the electrode and is insulated. Voids may form between the layer and the electrodes, resulting in poor battery Coulomb efficiency and cell strength.

In the battery of the present disclosure, the mass ratio of the inorganic particles in the insulating layer is 50% by mass or more and less than 90% by mass.
The mass ratio of the inorganic particles in the insulating layer is 50 from the viewpoint of enhancing the electrical insulating property of the insulating layer and increasing the pore ratio of the insulating layer to improve the ion permeability and the discharge characteristics of the battery. It is mass% or more. If the mass ratio of the inorganic particles to the insulating layer is less than 50% by mass, the electrical insulating property of the insulating layer may be insufficient. Further, when the mass ratio of the inorganic particles to the insulating layer is less than 50% by mass, the porosity of the insulating layer is not sufficient and the discharge characteristics of the battery are inferior.
The mass ratio of the inorganic particles to the insulating layer is less than 90% by mass from the viewpoint of increasing the mechanical strength of the insulating layer, improving the adhesion between the insulating layer and the electrode, and increasing the Coulomb efficiency and cell strength of the battery. If the mass ratio of the inorganic particles to the insulating layer is 90% by mass or more, voids may be formed between the insulating layer and the electrodes, and the Coulomb efficiency and cell strength of the battery are inferior. In addition, if the mass ratio of the inorganic particles to the insulating layer is 90% by mass or more, the insulating layer may become brittle.

The actions of each of the above configurations are synergistic, and the non-aqueous secondary battery of the present disclosure is excellent in discharge characteristics, Coulomb efficiency and cell strength, and is therefore highly reliable.

Hereinafter, the configuration included in the non-aqueous secondary battery of the present disclosure will be described in detail.

[Positive electrode]
The positive electrode includes, for example, a current collector and a positive electrode active material layer arranged on one side or both sides of the current collector.

Examples of the current collector of the positive electrode include a metal foil. Examples of the metal foil include aluminum foil, titanium foil, stainless steel foil and the like. The thickness of the current collector of the positive electrode is preferably 5 μm to 20 μm.

The positive electrode active material layer preferably contains a positive electrode active material and a resin. The positive electrode active material layer may further contain a conductive auxiliary agent.

Examples of the positive electrode active material include lithium-containing transition metal oxides. Examples of the lithium-containing transition metal oxides include LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , LiMn ₂ O ₄ , and LiFePO ₄ . , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O ₂ , and the like.

Examples of the resin include polyvinylidene fluoride-based resin, alginate and the like.

Examples of the conductive auxiliary agent include carbon materials. Examples of the carbon material include acetylene black, ketjen black, carbon fiber and the like.

[Negative electrode]
The negative electrode includes, for example, a current collector and a negative electrode active material layer arranged on one side or both sides of the current collector.

Examples of the current collector of the negative electrode include a metal foil. Examples of the metal foil include copper foil, nickel foil, stainless steel foil and the like. The thickness of the current collector of the negative electrode is preferably 5 μm to 20 μm.

The negative electrode active material layer preferably contains a negative electrode active material and a resin. The negative electrode active material layer may further contain a conductive auxiliary agent.

Examples of the negative electrode active material include a material capable of electrochemically occluding lithium ions. Examples of the material include a carbon material; an alloy of silicon, a silicon compound, tin, aluminum and the like and lithium; a wood alloy; and the like.

Examples of the resin include polyvinylidene fluoride-based resins, styrene-butadiene copolymers, carboxymethyl cellulose and the like.

Examples of the conductive auxiliary agent include carbon materials. Examples of the carbon material include acetylene black, ketjen black, carbon fiber and the like.

[Insulation layer]
The insulating layer is a single layer that has a large number of micropores inside and has a porous structure in which these micropores are connected so that gas or liquid can pass from one surface to the other. be.

In one example of the insulating layer embodiment, one surface is in contact with the positive electrode active material layer and the other surface is in contact with the negative electrode active material layer.

The insulating layer contains a polyvinylidene fluoride-based resin and inorganic particles. The insulating layer may contain a resin other than the polyvinylidene fluoride-based resin, an organic filler, and the like.

-Polyvinylidene fluoride resin-
Examples of the polyvinylidene fluoride-based resin include homopolymers of vinylidene fluoride (that is, polyvinylidene fluoride); vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and the like. Polymers with halogen-containing monomers such as trichloroethylene; mixtures thereof; can be mentioned. As the polyvinylidene fluoride-based resin, one type may be used alone, or two or more types may be used in combination.

As the polyvinylidene fluoride-based resin, a copolymer (VDF-HFP copolymer) of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) is preferable from the viewpoint of adhesiveness of the insulating layer to the electrode. In the present disclosure, the VDF-HFP copolymer includes a copolymer obtained by polymerizing only VDF and HFP (referred to as a VDF-HFP binary copolymer), and a copolymer obtained by polymerizing VDF, HFP and other monomers. Any of the polymers are included. Examples of other monomers here include halogen-containing monomers such as tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichlorethylene.

By increasing or decreasing the content of the HFP unit, the VDF-HFP copolymer can control the crystallinity of the copolymer, the adhesiveness to the electrode active material layer, the solubility resistance to the electrolytic solution, and the like within an appropriate range.
In the VDF-HFP copolymer, the ratio of HFP to the total polymer components is preferably more than 1.0 mol%, more preferably more than 1.5 mol%, still more preferably 2.0 mol% or more, 2.2. More preferably, it is more than mol%, more preferably 7.0 mol% or less, more preferably 6.5 mol% or less, still more preferably 6.0 mol% or less.

The weight average molecular weight (Mw) of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 to 1,500,000.
When the Mw of the polyvinylidene fluoride-based resin is 900,000 or more, the electrical insulation of the insulating layer is good, and when heat is applied to the insulating layer during manufacturing of the battery, the pores of the insulating layer are closed. Is hard to occur. From this viewpoint, the Mw of the polyvinylidene fluoride-based resin is 900,000 or more, preferably 1 million or more, and more preferably 1.1 million or more.
When the Mw of the polyvinylidene fluoride resin is 1.5 million or less, the insulating layer and the electrode adhere well when heat is applied to the insulating layer during the manufacturing of the battery, and a gap is formed between the insulating layer and the electrode. It is unlikely to occur. From this viewpoint, the Mw of the polyvinylidene fluoride-based resin is 1.5 million or less, preferably 1.4 million or less, and more preferably 1.3 million or less.

The mass ratio of the polyvinylidene fluoride-based resin to the insulating layer is preferably 10% by mass to 50% by mass, more preferably 15% by mass to 50% by mass, still more preferably 20% by mass to 50% by mass.

The content of the polyvinylidene fluoride-based resin contained in the insulating layer is preferably 85% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and 95% by mass, based on the total amount of the total resin contained in the insulating layer. More preferably, it is from% by mass to 100% by mass.

-Other resins-
The insulating layer may contain other resins other than the polyvinylidene fluoride-based resin. Examples of other resins include acrylic resins, fluororubbers, styrene-butadiene copolymers, homopolymers or copolymers of vinylnitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, and the like. Polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.), polyamide, total aromatic polyamide (also referred to as aramid), polyimide, polyamideimide, polysulfone, polyketone, polyetherketone, polyethersulfone, Polyetherimides and mixtures thereof can be mentioned.

The content of the resin other than the polyvinylidene fluoride-based resin contained in the insulating layer is preferably 0% by mass to 15% by mass, preferably 0% by mass to 10% by mass, based on the total amount of the total resin contained in the insulating layer. Is more preferable, and 0% by mass to 5% by mass is further preferable.

-Inorganic particles-
The particle shape of the inorganic particles is not limited, and may be spherical, plate-shaped, needle-shaped, or indefinite. The inorganic particles are preferably spherical or plate-shaped particles from the viewpoint of suppressing short circuits in the battery or from the viewpoint of being easily filled in the insulating layer.

The material of the inorganic particles is not limited. Examples of the inorganic particles include metal hydroxide particles, metal sulfate particles, metal oxide particles, metal carbonate particles, metal nitride particles, metal fluoride particles, and clay mineral particles. As the inorganic particles, one kind may be used alone, or two or more kinds of different materials may be used in combination.

Examples of the metal hydroxide particles include magnesium hydroxide (Mg (OH) ₂ ), aluminum hydroxide (Al (OH) ₃ ), calcium hydroxide (Ca (OH) ₂ ), and nickel hydroxide (Ni (OH) 2). ) ₂ ) and other particles can be mentioned. As the metal hydroxide particles, magnesium hydroxide particles are preferable.

Examples of the metal sulfate particles include barium sulfate (BaSO ₄ ), strontium sulfate (SrSO ₄ ), calcium sulfate (CaSO ₄ ), calcium sulfate dihydrate (CaSO _{4.2H 2} O), and myoban stone (KAl ₃ ). Particles such as (SO ₄ ) ₂ (OH) ₆ ) and jarosite (KFe ₃ (SO ₄ ) ₂ (OH) ₆ ) can be mentioned. As the metal sulfate particles, barium sulfate particles are preferable.

Examples of the metal oxide particles include magnesium oxide, alumina (Al ₂ O ₃ ), boehmite (AlOOH, alumina monohydrate), titania (TiO ₂ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), and titanium. Examples include particles such as barium acid (BaTIO ₃ ) and zinc oxide.

Examples of the metal carbonate particles include particles such as magnesium carbonate and calcium carbonate.

Examples of the metal nitride particles include particles such as magnesium nitride, aluminum nitride, calcium nitride, and titanium nitride.

Examples of the metal fluoride particles include particles such as magnesium fluoride and calcium fluoride.

Examples of the clay mineral particles include particles such as calcium silicate, calcium phosphate, apatite, and talc.

As the inorganic particles, metal hydroxide particles are preferable from the viewpoint of flame retardancy, and metal sulfate particles are preferable from the viewpoint of being stable with respect to the electrolytic solution and suppressing gas generation. The inorganic particles preferably contain at least one selected from the group consisting of metal hydroxide particles and metal sulfate particles.

The average primary particle size of the inorganic particles contained in the insulating layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, and further preferably 0.03 μm or more, from the viewpoint of making the insulating layer porous and enhancing ion permeability. preferable.
The average primary particle size of the inorganic particles contained in the insulating layer is preferably less than 1.00 μm, more preferably less than 0.95 μm, and further less than 0.90 μm from the viewpoint of thinning the insulating layer and increasing the energy density of the battery. preferable.

Two or more kinds of inorganic particles having different average primary particle sizes may be used in combination as the inorganic particles. In that case, the average primary particle size of each is preferably in the above range, and the overall average primary particle size is in the above range. Is preferable.

The average primary particle size of the inorganic particles is determined by measuring the major axis of 100 primary particles randomly selected in observation with a scanning electron microscope (SEM) and averaging the major axis of 100 particles. If the primary particle size of the inorganic particles is small and it is difficult to measure the major axis of the primary particles with SEM and / or if the aggregation of the inorganic particles is remarkable and the major axis of the primary particles is difficult to measure with SEM, the BET specific surface area of the inorganic particles ( m ² / g) is measured, assuming that the inorganic particles are true spheres, and the average primary particle size is obtained according to the following formula.
Average primary particle size (μm) = 6 ÷ [specific gravity (g / cm ³ ) x BET specific surface area (m ² / g)]
The BET specific surface area (m ² / g) is a gas adsorption method using nitrogen gas and is obtained by the BET multipoint method. During the measurement by the gas adsorption method, nitrogen gas is adsorbed on inorganic particles at the boiling point (-196 ° C.) of liquid nitrogen.

The sample to be used for observation by SEM or measurement of the BET specific surface area is inorganic particles which are materials for forming the insulating layer or inorganic particles taken out from the insulating layer. There is no limitation on the method of extracting the inorganic particles from the insulating layer, for example, a method of heating the insulating layer to about 800 ° C. to eliminate the binder resin and extracting the inorganic particles, a method of immersing the insulating layer in an organic solvent and using an organic solvent for the binder resin. A method of dissolving the inorganic particles and taking out the inorganic particles can be mentioned.

The mass ratio of the inorganic particles in the insulating layer is 50 from the viewpoint of enhancing the electrical insulating property of the insulating layer and increasing the pore ratio of the insulating layer to improve the ion permeability and the discharge characteristics of the battery. It is 5% by mass or more, preferably 55% by mass or more, and more preferably 60% by mass or more.
The mass ratio of the inorganic particles in the insulating layer is less than 90% by mass, preferably less than 88% by mass, preferably 85, from the viewpoint of improving the adhesion between the insulating layer and the electrode and increasing the coulombic efficiency and cell strength of the battery. More preferably less than% by weight.

-Organic filler-
Examples of the organic filler include crosslinked poly (meth) acrylic acid, crosslinked poly (meth) acrylic acid ester, crosslinked polysilicone, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, melamine resin, and phenol. Particles made of crosslinked polymers such as resins and benzoguanamine-formaldehyde condensates; particles made of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, and polyacetal; and the like. These organic fillers may be used alone or in combination of two or more. In the present disclosure, the notation "(meth) acrylic" means that it may be either "acrylic" or "methacrylic".

-Other ingredients-
The insulating layer may contain an additive such as a dispersant such as a surfactant, a wetting agent, a defoaming agent, and a pH adjuster. These may be added to the coating liquid for forming the insulating layer.

[Characteristics of insulating layer]
The thickness of the insulating layer is preferably 5 μm or more from the viewpoint of electrical insulation and mechanical strength of the insulating layer, preferably 30 μm or less, more preferably 25 μm or less from the viewpoint of ion permeability and energy density of the battery. 20 μm or less is more preferable.

The mass per unit area of the insulating layer is preferably 4 g / m ² or more, more preferably 8 g / m ² or more, still more preferably 10 g / m ² or more, from the viewpoint of electrical insulation and mechanical strength of the insulating layer. From the viewpoint of ion permeability and energy density of the battery, less than 40 g / m ² is preferable, less than 35 g / m ² is more preferable, and less than 30 g / m ² is further preferable.

The porosity of the insulating layer is preferably 40% or more, more preferably 45% or more, further preferably 50% or more from the viewpoint of ion permeability, and further preferably 50% or more, from the viewpoint of electrical insulation and mechanical strength of the insulating layer. Less than 80% is preferred, less than 75% is more preferred, and less than 70% is even more preferred.

The porosity ε (%) of the insulating layer is obtained by the following method.
The mass per unit area of the insulating layer is divided by the thickness of the insulating layer to obtain the bulk density d1 of the insulating layer. The true density d0 of the insulating layer is calculated from the following equation (1). Then, the porosity ε (%) of the insulating layer is calculated from the following equation (2).
Equation (1) ... d0 = 100 / (resin solid content ratio of insulating layer / density of resin + solid content ratio of inorganic particles in insulating layer / density of inorganic particles)
Equation (2) ... ε = (1-d1 / d0) × 100

[Electrolytic solution]
Examples of the electrolytic solution include a solution in which a lithium salt is dissolved in a non-aqueous solvent.
Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , and the like.
Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; and chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and fluorine-substituted products thereof; Cyclic esters such as γ-butyrolactone and γ-valerolactone; and the like. These may be used alone or in combination.

As the electrolytic solution of the lithium ion secondary battery, cyclic carbonate and chain carbonate are mixed at a cyclic carbonate: chain carbonate = 20:80 to 40:60 (mass ratio), and the lithium salt is 0.5 mol / L or more. A solution dissolved in the range of 1.5 mol / L is suitable.

FIG. 1 is an example of an embodiment of the non-aqueous secondary battery of the present disclosure. FIG. 1 is a diagram schematically showing a cross section of a battery. FIG. 1 is an example of an embodiment of a non-aqueous secondary battery, and does not limit the embodiment.

The non-aqueous secondary battery 100 shown in FIG. 1 includes a battery element 10, an electrolytic solution 50, and an exterior material 90. The battery element 10 and the electrolytic solution 50 are housed inside the exterior material 90.

The battery element 10 includes a positive electrode 20, an insulating layer 30, and a negative electrode 40. The battery element 10 has a structure in which a positive electrode 20, an insulating layer 30, and a negative electrode 40 are laminated in this order by at least one layer.

The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 arranged on both sides of the positive electrode current collector 22. The positive electrode active material layer 24 is not arranged at one end of the positive electrode current collector 22, and is in the shape of a tab, for example.

The negative electrode 40 includes a negative electrode current collector 42 and negative electrode active material layers 44 arranged on both sides of the negative electrode current collector 42. The negative electrode active material layer 44 is not arranged at one end of the negative electrode current collector 42, and is in the shape of a tab, for example.

One surface of the insulating layer 30 is in contact with the positive electrode active material layer 24, and the other surface is in contact with the negative electrode active material layer 44. The insulating layer 30 is a porous layer, and the insulating layer 30 is impregnated with the electrolytic solution 50.

Examples of the exterior material 90 include metal cans, aluminum laminated film packs, and the like.

The non-aqueous secondary battery 100 includes a positive electrode terminal (not shown) and a negative electrode terminal (not shown) outside the exterior material 90. A plurality of positive electrode current collectors 22 are connected to the positive electrode terminals, and a plurality of negative electrode current collectors 42 are connected to the negative electrode terminals. A lead tab may be interposed between the positive electrode terminal and the positive electrode current collector 22 (or between the negative electrode terminal and the negative electrode current collector 42).

Examples of the shape of the non-aqueous secondary battery 100 include a square type, a cylindrical type, and a coin type.

[Manufacturing method of non-aqueous secondary battery]
The non-aqueous secondary battery of the present disclosure can be manufactured by, for example, the following manufacturing method. That is,
Step A of forming an insulating layer on a support by a wet coating method or a dry coating method, and
Step B of manufacturing a laminate in which an insulating layer is arranged between a positive electrode and a negative electrode, and
Step C of performing a wet heat press and / or a dry heat press on the laminate,
It is a manufacturing method including.

-Process A-
The support means a sheet-like material to which a coating liquid for forming an insulating layer is applied. Examples of the support include a positive electrode, a negative electrode, and a release sheet.

The wet coating method means a method of solidifying the coating layer in a coagulating liquid, and the dry coating method means a method of drying and solidifying the coating layer.

As an example of the embodiment of step A, a step of forming an insulating layer on an active material layer of a positive electrode by a wet coating method or a dry coating method; forming an insulating layer on an active material layer of a negative electrode by a wet coating method or a dry coating method. A step; a step of forming an insulating layer on a release sheet by a wet coating method or a dry coating method;

Hereinafter, an example of an embodiment in which the insulating layer is formed on the support by a wet coating method will be described.

As an example of an embodiment of the wet coating method, a coating liquid containing a resin and inorganic particles is applied onto a support, immersed in a coagulating liquid to solidify the coating layer, and then withdrawn from the coagulating liquid to be washed with water and dried. The form is mentioned.

The coating liquid for forming the insulating layer is prepared by dissolving or dispersing the resin and the inorganic particles in a solvent. If necessary, the coating liquid dissolves or disperses other components other than the resin and inorganic particles.

The solvent used for preparing the coating liquid includes a solvent that dissolves the resin (hereinafter, also referred to as “good solvent”). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide and dimethylformamide.

The solvent used for preparing the coating liquid preferably contains a phase separation agent that induces phase separation from the viewpoint of forming an insulating layer having a good porous structure. Therefore, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with a good solvent in an amount that can secure an appropriate viscosity for coating. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butane diol, ethylene glycol, propylene glycol, tripropylene glycol and the like.

The solvent used for preparing the coating liquid is a mixed solvent of a good solvent and a phase separation agent from the viewpoint of forming an insulating layer having a good porous structure, and contains 60% by mass or more of the good solvent for phase separation. A mixed solvent containing 5% by mass to 40% by mass of the agent is preferable.

The resin concentration of the coating liquid is preferably 3% by mass to 10% by mass from the viewpoint of forming an insulating layer having a good porous structure. The concentration of inorganic particles in the coating liquid is preferably 2% by mass to 50% by mass from the viewpoint of forming an insulating layer having a good porous structure.

The coating liquid may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjusting agent and the like. These additives may remain in the insulating layer as long as they are electrochemically stable in the range of use of the non-aqueous secondary battery and do not inhibit the reaction in the battery.

Examples of the means for applying the coating liquid to the support include a Meyer bar, a die coater, a reverse roll coater, a roll coater, a gravure coater, a knife coater and the like.

The solidification of the coating layer is performed by immersing the support on which the coating layer is formed in the coagulating liquid and solidifying the resin while inducing phase separation in the coating layer. As a result, a complex in which an insulating layer is arranged on the support is obtained.

The coagulation liquid generally contains a good solvent and a phase separation agent used for preparing the coating liquid, and water. It is preferable in terms of production that the mixing ratio of the good solvent and the phase separation agent is adjusted to the mixing ratio of the mixed solvent used for preparing the coating liquid. The content of water in the coagulation liquid is preferably 40% by mass to 90% by mass from the viewpoint of forming the porous structure of the insulating layer and productivity. The temperature of the coagulant is, for example, 20 ° C to 50 ° C.

After the coating layer is solidified in the coagulation liquid, the complex is withdrawn from the coagulation liquid and washed with water. The coagulant is removed from the complex by washing with water. In addition, drying removes water from the complex. Water washing is performed, for example, by transporting the complex in a water bath. Drying is performed, for example, by transporting the complex in a high temperature environment, blowing air on the complex, bringing the complex into contact with a heat roll, and the like. The drying temperature is preferably 40 ° C to 80 ° C. In order to prevent the water in the insulating layer from coming into contact with the electrolytic solution, it is preferable to perform vacuum drying at a high temperature (for example, 80 ° C. to 110 ° C.) from the viewpoint of removing water from the insulating layer as much as possible.

The insulating layer can also be formed by a dry coating method. As an example of the embodiment of the dry coating method, there is a mode in which an insulating layer is formed on the support by applying a coating liquid to the support and drying the coating layer to volatilize and remove the solvent.

-Process B-
As an example of the embodiment of step B, an embodiment in which a positive electrode and a negative electrode having an insulating layer formed on a negative electrode active material layer are overlapped; an embodiment in which a negative electrode and a positive electrode having an insulating layer formed on a positive electrode active material layer are overlapped; Examples thereof include an embodiment in which a positive electrode, an insulating layer peeled from a release sheet, and a negative electrode are overlapped with each other.

The method of arranging the insulating layer between the positive electrode and the negative electrode may be a method of stacking at least one layer of the positive electrode, the insulating layer, and the negative electrode in this order (so-called stack method), and the positive electrode, the insulating layer, the negative electrode, and the insulating layer are laminated in this order. A method of stacking them in order and winding them in the length direction may also be used.

-Process C-
Wet heat press means that the insulating layer is impregnated with the electrolytic solution and the hot press treatment is performed, and dry heat press means that the coating layer is not impregnated with the electrolytic solution and the hot press treatment is performed. do.

Examples of the embodiment of the step C include the following (1) to (3).

(1) The laminate is housed in an exterior material (for example, a pack made of an aluminum laminate film; the same applies hereinafter), an electrolytic solution is injected therein, the inside of the exterior material is evacuated, and then the laminate is wetted from above the exterior material. Heat press to bond the electrode to the insulating layer and seal the exterior material.

(2) After dry heat pressing the laminate to bond the electrode and the insulating layer, the laminate is housed in the exterior material, an electrolytic solution is injected therein, the inside of the exterior material is evacuated, and then the exterior material is sealed. I do.

(3) After the laminate is dry heat pressed to bond the electrode and the insulating layer, the laminate is housed in the exterior material, an electrolytic solution is injected therein, the inside of the exterior material is evacuated, and then from above the exterior material. Further, the laminate is wet heat-pressed to bond the electrode and the insulating layer and to seal the exterior material.

As the conditions for the hot press in the manufacturing methods (1) to (3) above, the press pressure is preferably 0.1 MPa to 10.0 MPa, and the temperature is preferably 60 ° C. to 100 ° C., respectively, for the dry heat press and the wet heat press. ..

Hereinafter, the non-aqueous secondary battery of the present disclosure will be described in more detail with reference to examples. The materials, amounts, ratios, treatment procedures, etc. shown in the following examples may be appropriately changed as long as they do not deviate from the gist of the present disclosure. Therefore, the scope of the non-aqueous secondary batteries of the present disclosure should not be construed as limiting by the specific examples shown below.

<Measurement method, evaluation method>
The measurement methods and evaluation methods applied to the examples and comparative examples are as follows.

[Thickness of insulating layer]
The thickness of the electrode (μm) and the thickness of the composite in which the insulating layer is arranged on the electrode (μm) are 5 cm × 3 cm with a contact type thickness gauge (Mitutoyo Co., Ltd., LITEMATTIC VL-50). It was calculated by measuring 20 points in the rectangle and averaging them. As the measurement terminal, a columnar terminal having a diameter of 5 mm was used, and the load was adjusted so that a load of 0.01 N was applied during the measurement. Then, the value obtained by subtracting the thickness of the electrode from the thickness of the composite was taken as the thickness of the insulating layer (μm).

[Mass per unit area of insulating layer]
The electrode and the composite in which the insulating layer is arranged on the electrode are cut into rectangles of 5 cm × 3 cm each, the mass (g) is measured, and the mass is divided by the area (0.0015 m ² ) to unit. The mass per area (g / m ² ) was determined. Then, the value obtained by subtracting the mass per unit area of the electrode from the mass per unit area of the composite was taken as the mass per unit area (g / m ² ) of the insulating layer.

[Porosity of insulating layer]
The porosity ε (%) of the insulating layer was determined by the method described above.

[Average primary particle size of inorganic particles]
The average primary particle size of the inorganic particles is 100 primary particles randomly selected for observation with a scanning electron microscope (SEM) using the inorganic particles before addition to the coating liquid for forming the insulating layer as a sample. It was obtained by measuring the major axis and averaging 100 major diameters.

[Weight average molecular weight of polyvinylidene fluoride resin]
The weight average molecular weight (Mw) of the polyvinylidene fluoride-based resin was measured by gel permeation chromatography (GPC). For molecular weight measurement by GPC, a GPC device GPC-900 manufactured by JASCO Corporation was used, two TSKgel SUPER AWM-H manufactured by Tosoh Corporation were used for the column, N, N-dimethylformamide was used as a solvent, and the temperature was 40 ° C. Measurement was performed under the condition of a flow rate of 0.6 mL / min to obtain a polystyrene-equivalent molecular weight.

[Discharge characteristics]
The battery was charged / discharged in the following (a) for 5 cycles, and then charged / discharged in the following (b) for 1 cycle.
(A) Constant current constant voltage charging at 4mA / 4.2V for 15 hours, constant current discharge at 4mA / 2.5V cutoff (b) Constant current constant voltage charging at 8mA / 4.2V for 8 hours, and , Constant current discharge with 200mA / 2.5V cutoff The discharge capacity of the above (b) was divided by the discharge capacity of the fifth cycle of the above (a), and the obtained value was taken as the discharge characteristic of the battery. Using the discharge characteristics of Reference Example 1 as a reference value, the percentages of the discharge characteristics of Examples and Comparative Examples with respect to Reference Example 1 were calculated and classified as follows.
A: 95% or more B: 85% or more and less than 95% C: 70% or more and less than 85% D: less than 70%

[Coulomb efficiency]
The discharge capacity in the first cycle of (a) above was divided by the charge capacity, and the obtained value was taken as the coulombic efficiency of the battery. Using the Coulomb efficiency of Reference Example 1 as a reference value, the percentages of the Coulomb efficiencies of Examples and Comparative Examples with respect to Reference Example 1 were calculated and classified as follows.
A: 95% or more B: 85% or more and less than 95% C: 70% or more and less than 85% D: less than 70%

[Cell strength]
A three-point bending test was performed on the battery according to ISO178, and the maximum load (N) when the battery was destroyed was determined. Using the maximum load of Reference Example 1 as a reference value, the percentages for Reference Example 1 were calculated for each of the maximum loads of Examples and Comparative Examples, and classified as follows.
A: 90% or more B: less than 90%

<Manufacturing of non-aqueous secondary batteries>
[Example 1]
-Preparation of positive electrode-
A slurry was prepared by kneading 94 parts by mass of lithium cobalt oxide powder, 3 parts by mass of acetylene black, 3 parts by mass of polyvinylidene fluoride resin, and an appropriate amount of N-methyl-2-pyrrolidone. The slurry was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode (single-sided coating, basis weight 20.5 mg / cm ² , density 2.95 g / cm ³ ).

-Manufacturing of negative electrode-
A slurry was prepared by kneading 96.2 parts by mass of graphite powder, 2.8 parts by mass of a modified styrene-butadiene copolymer, 1.0 part by mass of carboxymethyl cellulose, and an appropriate amount of water. The slurry was applied onto a copper foil having a thickness of 15 μm, dried and pressed to obtain a negative electrode (single-sided coating, basis weight 10.0 mg / cm ² , density 1.60 g / cm ³ ).

-Preparation of insulating layer-
The VDF-HFP binary copolymer (weight average molecular weight 1.13 million, ratio of HFP to total polymerization components 2.4 mol%) was mixed with dimethylacetamide (DMAc) and tripropylene glycol so that the concentration was 5% by mass. After dissolving in a mixed solvent (DMAc: TPG = 80: 20 [mass ratio]) of (TPG), magnesium hydroxide particles (average primary particle size 0.88 μm) are added and mixed by stirring, and the coating liquid (1) Got The mass ratio of the VDF-HFP binary copolymer to the magnesium hydroxide particles (VDF-HFP binary copolymer: magnesium hydroxide particles) was 20:80.

The coating liquid (1) was applied onto the active material layer of the negative electrode using a knife coater. This was immersed in a coagulating liquid (DMAc: water = 50:50 (mass ratio), liquid temperature 25 ° C.) for 5 minutes to solidify the coating layer, and then washed in a water washing tank at a water temperature of 25 ° C. for 1 minute. This was pulled up from the washing tank, placed in a constant temperature bath at 70 ° C. and dried for 15 minutes, and then dried under reduced pressure at 110 ° C. for 3 hours. In this way, a complex in which an insulating layer was arranged on the negative electrode was obtained.

-Making batteries-
The positive electrode was cut out to 5.0 cm × 3.0 cm, and the complex having the insulating layer arranged on the negative electrode was cut out to 5.2 cm × 3.2 cm, and lead tabs were welded to each. The positive electrode and the composite were laminated so that the positive electrode active material layer and the insulating layer were in contact with each other to obtain a laminated body. The laminate was impregnated with an electrolytic solution and sealed in the exterior material of an aluminum laminate film. A battery was obtained by hot-pressing (85 ° C., 0.5 MPa, 2 minutes) from above the exterior material to bond the electrode and the insulating layer. As the electrolytic solution, 1 mol / L LiPF ₆ -ethylene carbonate: ethylmethyl carbonate (mass ratio 3: 7) was used. The set capacity of the battery was 40 mAh (range 4.2 V-2.5 V).

[Examples 2 to 8, Comparative Examples 1 to 7]
Each battery was manufactured in the same manner as in Example 1, except that the material, composition and thickness of the insulating layer were set to the specifications shown in Table 1.
In Examples 7 to 8, magnesium hydroxide particles and barium sulfate particles were used in combination with magnesium hydroxide particles: barium sulfate particles = 50:50 (mass ratio).

[Reference Example 1]
-Preparation of a separator consisting of 3 layers-
An equal amount of the coating liquid (1) was applied to both sides of a polyethylene microporous membrane (thickness 7 μm, porosity 36%, galley value 120 seconds / 100 mL) using a reverse roll coater. This was immersed in a coagulating liquid (DMAc: water = 50:50 (mass ratio), liquid temperature 40 ° C.) to solidify the coating layer, and then washed in a water washing tank having a water temperature of 40 ° C. and dried. In this way, a separator having a coating layer formed on both sides of the polyethylene microporous film was obtained.

-Making batteries-
The positive electrode and the negative electrode in Example 1 were prepared. The positive electrode was cut out to 5.0 cm × 3.0 cm, the negative electrode was cut out to 5.2 cm × 3.2 cm, and lead tabs were welded to each. The separator was cut out to a size of 5.4 cm × 3.4 cm.
A laminated body was obtained by stacking the positive electrode, the separator, and the negative electrode in this order so that the electrode active material layer and the separator were in contact with each other. The laminate was impregnated with an electrolytic solution (the same electrolytic solution used in Example 1) and sealed in the exterior material of the aluminum laminate film. A battery was obtained by hot-pressing (85 ° C., 0.5 MPa, 2 minutes) from above the exterior material to bond the electrode and the separator.

Table 1 shows the composition, physical characteristics, and evaluation results of the batteries of Examples 1 to 8, Comparative Examples 1 to 7, and Reference Example 1.

100 Non-aqueous secondary battery 10 Battery element 20 Positive electrode 22 Positive electrode current collector 24 Positive electrode active material layer 30 Insulation layer 40 Negative electrode 42 Negative electrode current collector 44 Negative electrode active material layer 50 Electrolyte 90 Exterior material

Claims (7)

With the positive electrode
With the negative electrode
A single layer having one surface in contact with the positive electrode and the other surface in contact with the negative electrode, and an insulating layer containing a polyvinylidene fluoride-based resin and inorganic particles.
With an electrolytic solution,
The weight average molecular weight of the polyvinylidene fluoride-based resin contained in the insulating layer is 900,000 or more and 1.5 million or less.
The mass ratio of the inorganic particles to the insulating layer is 50% by mass or more and less than 90% by mass.
Non-water-based secondary battery. The non-aqueous secondary battery according to claim 1, wherein the inorganic particles contain at least one selected from the group consisting of metal hydroxide particles and metal sulfate particles. The non-aqueous secondary battery according to claim 1 or 2, wherein the average primary particle size of the inorganic particles contained in the insulating layer is 0.01 μm or more and less than 1.00 μm. The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the thickness of the insulating layer is 5 μm or more and 30 μm or less. The non-aqueous secondary battery according to any one of claims 1 to 4, wherein the insulating layer has a porosity of 40% or more and less than 80%. The non-aqueous secondary battery according to any one of claims 1 to 5, wherein the mass of the insulating layer per unit area is 4 g / m ² or more and less than 40 g / m ² . The non-aqueous secondary battery according to any one of claims 1 to 6, wherein an electromotive force is obtained by doping and dedoping lithium ions.

Images