WO2013051416A1

WO2013051416A1 - Electrical device

Info

Publication number: WO2013051416A1
Application number: PCT/JP2012/074425
Authority: WO
Inventors: 一希宮竹; 宏信村松; 本田　崇; 治之齊藤; 文博三木
Original assignee: 日産自動車株式会社
Priority date: 2011-10-07
Filing date: 2012-09-24
Publication date: 2013-04-11
Also published as: JP2013084416A

Abstract

Provided is a means for enhancing lifespan characteristics while minimizing the decrease in cell energy density in an electrical device obtained using a separator with a heat-resistant insulating layer configured by layering a heat-resistant insulating layer on the surface of a porous substrate. An electrical device having at least one single cell in which a positive electrode, an electrolyte layer comprising a non-aqueous electrolyte being held in a separator, and a negative electrode are layered in the sequence listed; wherein the separator has a porous substrate layer and a heat-resistant insulating layer formed on one or both surfaces of the porous substrate layer, the heat-resistant insulating layer including inorganic particles and a binder; and wherein formula (1) is satisfied. y ≤ 0.145x + 0.075 (1) In the formula, x is the ratio (L/V) of the amount of non-aqueous electrolyte (L) relative to the total void volume (V) of the positive electrode, negative electrode, and separator, where x ≥ 1; and y is the ratio (Vs/V) of the void volume (Vs) of the separator relative to the total void volume (V) of the positive electrode, negative electrode, and separator, where y > 0.

Description

Electrical device

The present invention relates to an electric device such as a lithium ion secondary battery or an electric double layer capacitor. More particularly, the present invention relates to improvements for improving the durability of electrical devices.

In recent years, a reduction in the amount of carbon dioxide has been strongly desired in order to cope with global warming. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electric devices such as secondary batteries for motor drive that hold the key to their practical application. Is being actively developed.

Motor drive secondary batteries are required to have extremely high output characteristics and high energy compared to consumer secondary batteries used in mobile phones, laptop computers, and the like. Therefore, lithium ion secondary batteries having a relatively high theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

Lithium-ion secondary batteries are considered suitable for electric vehicles because of their high energy density and durability against repeated charging and discharging, which will further increase the capacity and ensure safety. It has become increasingly important.

A lithium ion secondary battery generally includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector. Or it has the structure connected through the electrolyte layer holding nonaqueous electrolyte gel, and accommodated in a battery case. The lithium ion is occluded / released in the electrode active material, thereby causing a charge / discharge reaction of the battery.

The separator is required to have both a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode and a function as a partition wall. As such a separator, usually, a microporous film composed of an electrically insulating thermoplastic resin such as polyethylene (PE) or polypropylene (PP) is often used.

However, it is known that a separator made of such a thermoplastic resin has a problem in mechanical strength due to its flexibility. In particular, under a high temperature condition, the separator is thermally contracted, and an internal short circuit may occur due to contact between the positive electrode and the negative electrode facing each other through the separator. Therefore, a heat resistant porous layer containing a filler of inorganic particles is laminated on the surface of the resin microporous film in order to suppress heat shrinkage due to heat treatment during battery fabrication or reaction heat during charge / discharge reaction. A separator with an insulating layer has been developed (for example, Patent Document 1).

On the other hand, in order to improve the safety of the battery, the non-aqueous electrolyte retained in the separator has also been improved. For example, in Patent Document 2, in a non-aqueous electrolyte secondary battery using a separator made of a thermoplastic resin, the injection amount of the non-aqueous electrolyte with respect to the total pore volume of the positive electrode, the negative electrode, and the separator is controlled. Discloses a method for improving battery safety. According to this document, by regulating the amount of electrolyte injected into the battery, it is possible to suppress an increase in the internal pressure of the battery due to the decomposition gas of the non-aqueous electrolyte generated when an abnormality occurs, resulting in excellent cycle life performance and The company says it can provide batteries with safety.

International Publication No. 2007/066768 Pamphlet Japanese Patent Laid-Open No. 2001-196094

The separator with a heat-resistant insulating layer as described in Patent Document 1 is likely to absorb the electrolyte on the surface of the inorganic particles constituting the heat-resistant porous layer, and absorbs the electrolyte more easily than the thermoplastic resin separator. For this reason, when the electrolytic mass control technology as described in Patent Document 2 is applied to a separator with a heat-resistant insulating layer as in Patent Document 1, the electrolyte for the entire cell is insufficient with charge and discharge, There is a problem that the life characteristics are deteriorated.

In order to cope with this problem, when the electrolytic mass in the separator with a heat-resistant insulating layer is increased, the life characteristics are improved, but the cell weight is increased and the charge / discharge efficiency is decreased, and the energy density of the cell is decreased. To do.

Therefore, the present invention provides means for improving the life characteristics while suppressing a decrease in the energy density of a cell in an electrical device using a separator with a heat-resistant insulating layer in which a heat-resistant insulating layer is laminated on the surface of a porous substrate layer. The purpose is to do.

The inventors of the present invention have made extensive studies in view of the above problems. As a result, by controlling the ratio of the nonaqueous electrolytic mass to the total pore volume of the cell (x) and the ratio of the pore volume of the separator to the total pore volume of the cell (y) to a specific relationship, Has been found to be resolved.

That is, the present invention relates to an electric device having a positive electrode, an electrolyte layer in which a nonaqueous electrolyte is held in a separator, and at least one single cell layer in which a negative electrode is laminated in this order. The separator has a porous substrate layer and a heat-resistant insulating layer containing inorganic particles and a binder formed on one or both surfaces of the porous substrate layer, and satisfies the following formula (1).

In the above formula, x is the ratio (L / V) of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, the negative electrode, and the separator, and x ≧ 1; y is the positive electrode, negative electrode, and separator The ratio (Vs / V) of the void volume Vs of the separator to the total void volume V, where y> 0.

1 is a schematic diagram illustrating a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (stacked battery) that is a representative embodiment of the present invention. It is the cross-sectional schematic which represented typically the separator with a heat resistant insulating layer used for one Embodiment of this invention. It is a graph which shows the relationship between parameter x and y of each cell for evaluation obtained by the Example and the comparative example, and capacity | capacitance maintenance ratio (lifetime characteristic).

Hereinafter, the present embodiment will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following forms. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

The electric device according to one embodiment of the present invention is a lithium ion secondary battery. That is, according to one embodiment of the present invention, in a lithium ion secondary battery having a positive electrode, an electrolyte layer in which a nonaqueous electrolyte is held in a separator, and at least one single cell layer in which a negative electrode is laminated in this order. The separator has a porous base layer and a heat-resistant insulating layer containing inorganic particles and a binder formed on one or both sides of the porous base layer, and satisfies the following formula (1): An ion secondary battery is provided.

According to the present invention, it is possible to prevent a shortage of cell electrolyte accompanying charge / discharge while reducing the increase in electrolytic mass in the separator, which is required when using a separator with a heat-resistant insulating layer. This makes it possible to improve the life characteristics while suppressing a decrease in the energy density of the cell.

The structure and form of the lithium ion secondary battery are not particularly limited, and can be applied to various conventionally known structures. A stacked (flat) battery is preferred. In the following description, a case where the battery of the present invention is a laminated (flat) lithium ion secondary battery will be described as an example as a representative embodiment, but the technical scope of the present invention is as follows. Is not limited to only.

FIG. 1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) according to an embodiment of the present invention. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. .

Here, the power generation element 21 includes a negative electrode in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11, a separator 17, and a positive electrode in which the positive electrode active material layer 15 is disposed on both surfaces of the positive electrode current collector 12. Are stacked. Specifically, the negative electrode, the separator, and the positive electrode are laminated in this order so that one negative electrode active material layer 13 and the positive electrode active material layer 15 adjacent to the negative electrode active material layer 13 face each other with the separator 17 therebetween. Thereby, the adjacent negative electrode, separator, and positive electrode constitute one single battery layer (single cell) 19. Therefore, it can be said that the stacked battery 10 of the present embodiment has a configuration in which a plurality of the single battery layers 19 are stacked and electrically connected in parallel.

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

The negative electrode current collector 11 and the positive electrode current collector 12 are attached to a negative electrode current collector plate 25 and a positive electrode current collector plate 27 that are electrically connected to the respective electrodes (negative electrode and positive electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 are ultrasonically welded to the negative electrode current collector 11 and the positive electrode current collector 12 of each electrode via a negative electrode lead and a positive electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

In the stacked battery 1, at least one of the separators 17 includes a porous substrate layer and a heat-resistant insulating layer containing inorganic particles and a binder formed on one side or both sides of the porous substrate layer (hereinafter referred to as “a separator”). , Also referred to as “separator with heat-resistant insulating layer”). That is, the multilayer battery 1 includes a separator with a heat-resistant insulating layer interposed between a positive electrode and the negative electrode. Thereby, the laminated battery 1 can be a highly safe lithium ion secondary battery that suppresses thermal shrinkage while ensuring a shutdown function. In addition, separators other than the separator with a heat resistant insulating layer may be a conventional separator, for example, a microporous film made of a thermoplastic resin. Preferably, all of the separators 17 shown in FIG. 1 are constituted by a separator with a heat-resistant insulating layer.

In the stacked battery 1, the power generation element 21 is usually disposed inside a laminate sheet 29 that is an exterior body, and then a nonaqueous electrolyte is injected into the laminate sheet 29, and the electrolyte is placed in the pores existing inside the power generation element 21. And the ends are sealed under vacuum. Therefore, the non-aqueous electrolyte exists in pores existing in the power generation element 21 (positive electrode, negative electrode, and separator) and in the external space 20 of the power generation element 21 in the laminate sheet 29, and moves between the positive and negative electrodes during charging and discharging. It will serve as a lithium ion carrier.

In the present invention, the ratio (x) of the nonaqueous electrolysis mass to the pore volume (total pore volume of the cell) existing inside the power generation element 21 (positive electrode, negative electrode, and separator) and the separator to the total pore volume of the cell. The ratio (y) of the pore volume is in a specific relationship.

Conventionally, a battery using a separator with a heat-resistant insulating layer has a problem that a life characteristic is deteriorated due to insufficient electrolyte for the whole cell with charge / discharge. Further, when the electrolytic mass is simply increased, the life characteristics are improved, but the cell weight is increased and the charge / discharge efficiency is decreased, and the energy density of the cell is decreased. Thus, it has been difficult to achieve both life characteristics and high energy density.

On the other hand, when the x and y are in a specific relationship, the present inventors can prevent the lack of electrolyte and reduce the energy of the cell even when the separator with a heat-resistant insulating layer is used. It was found that a decrease in density can be suppressed, and a battery having excellent battery performance and durability can be obtained.

Specifically, the stacked battery 10 satisfies the following formula (1).

More preferably, in order to further improve the durability, the laminated battery 10 satisfies the following formula (2).

Particularly preferably, the stacked battery 10 satisfies the following formula (3). The laminated battery 1 satisfying the following formula (3) has particularly excellent durability.

In the above formulas (1) to (3), x is the ratio (L / V) of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, negative electrode, and separator; y is the positive electrode, negative electrode, and separator This is the ratio (Vs / V) of the pore volume Vs of the separator to the total pore volume V.

The parameter x is a ratio (L / V) of the nonaqueous electrolytic mass L to the total pore volume V of the cell. When x is 1, it means that the total pore volume V of the cell and the nonaqueous electrolytic mass L are equal, and all of the nonaqueous electrolyte can be retained in the positive electrode, the negative electrode, and the pores in the separator. To do. In order to improve the utilization efficiency of the active material, it is preferable that the pores in the cell are filled with the electrolyte. From such a point, x ≧ 1.

When x exceeds 1, there is a nonaqueous electrolyte in an amount exceeding the pore volume in the cell. In this case, an excessive amount that is not absorbed by the pores existing inside the power generation element 21 (positive electrode, negative electrode, and separator). The non-aqueous electrolyte is present in the external space 20 of the power generation element 21. Therefore, the amount of excess electrolyte increases as x increases, so that the shortage of electrolyte that occurs when charging and discharging are repeated can be prevented, and the life characteristics can be improved. From such a viewpoint, x ≧ 1.2 is more preferable, and x ≧ 1.4 is more preferable.

On the other hand, an increase in x, that is, an increase in excessive nonaqueous electrolytic mass leads to a decrease in the energy density of the cell. Therefore, from the viewpoint of suppressing a decrease in energy density, x ≦ 2 is preferable, and x ≦ 1.8 is more preferable.

The parameter y is a ratio (Vs / V) of the pore volume Vs of the separator to the total pore volume V of the positive electrode, the negative electrode, and the separator, and the electrolyte held in the separator with respect to the electrolyte present in the cell. It means the ratio (occupation ratio of the electrolyte in the separator).

Parameter y satisfies y> 0. The upper limit of the parameter y is not particularly limited. However, the larger the parameter y, the greater the volume of the separator that does not contribute to power generation, leading to a decrease in energy density. Therefore, y ≦ 0.30 is preferable, and y ≦ 0.28 is more preferable.

On the other hand, the smaller the parameter y, the smaller the size of the separator and the higher the energy density, but it becomes difficult to manufacture a separator having a thickness that satisfies the desired parameter y value. Therefore, from the viewpoint of ease of production, for example, when a polyolefin-based resin is used as the porous substrate layer, y ≧ 0.24 is preferable, and y ≧ 0.25 is more preferable.

The larger the pore volume Vs of the separator, the easier the electrolyte shortage occurs due to the liquid absorption of the separator with the heat-resistant insulating layer, and the total electrolytic mass L needs to be increased. In the present invention, the cell is set so that the parameter y indicating the ratio (Vs / V) retained in the separator and the parameter x indicating the electrolytic mass ratio (L / V) to the cell pore volume have the above specific relationship. The electrolyte inside is controlled. Accordingly, it is possible to inject an electrolyte in which an electrolyte shortage due to liquid absorption of the separator is prevented while minimizing a decrease in energy density accompanying an increase in electrolytic mass.

The parameter x is calculated by dividing the nonaqueous electrolytic mass L by the total pore volume V of the positive electrode, the negative electrode, and the separator, and the parameter y is the total pore volume of the positive electrode, the negative electrode, and the separator. Calculated by dividing by V.

Here, the non-aqueous electrolyte mass L means the volume of the liquid electrolyte when a liquid electrolyte is used as the non-aqueous electrolyte. When a solid electrolyte such as a polymer electrolyte is used as the non-aqueous electrolyte, the volume of the solid electrolyte calculated by dividing the weight of the solid electrolyte by the true density of the solid electrolyte (= weight of the solid electrolyte / solid electrolyte True density). The “true density” refers to a theoretical density that does not consider the vacancies in the raw material.

The pore volume Vs of the separator is calculated using the following formula from the volume of the separator, the weight of the separator, and the true density of the raw materials constituting the separator. The volume, weight, and true density of the raw material of the separator are the volume, weight, and true density of the raw material of the entire separator including the porous substrate layer and the heat-resistant insulating layer.

The total pore volume V of the positive electrode, the negative electrode, and the separator is calculated from the sum of the pore volumes V ₁ and V ₂ of the positive electrode and the negative electrode and the pore volume Vs of the separator. Here, the pore volumes V ₁ and V ₂ of the positive electrode and the negative electrode mean the pore volumes of the positive electrode active material layer and the negative electrode active material layer, and do not include the voids contained in the positive electrode current collector and the negative electrode current collector. . That is, the pore volumes V ₁ and V ₂ of the positive electrode and the negative electrode are expressed by the following formula from the volume and weight of the positive electrode active material layer or the negative electrode active material layer and the true density of the raw materials constituting the positive electrode active material layer or the negative electrode active material layer. Is calculated using

The above V ₁ , V ₂ , and Vs can also be calculated from pore distribution measurement by mercury porosimetry. Furthermore, Vs can also be calculated from the difference between the moisture content of the separator and the dry weight.

Hereinafter, members constituting the battery of this embodiment will be described in detail.

[Separator with heat-resistant insulating layer (separator)]
In FIG. 2, the cross-sectional schematic which represented typically the separator with a heat resistant insulating layer used for one Embodiment of this invention is shown. As shown in FIG. 2, the separator 1 with a heat-resistant insulating layer has a porous substrate layer 31 and a heat-resistant insulating layer 34 containing inorganic particles 32 and a binder 33 formed on one or both surfaces of the porous substrate layer 31. It becomes. The inorganic particles 32 are bonded to the porous substrate layer 31 and the adjacent inorganic particles 32 via the binder 33. As shown in FIG. 2, voids exist in the porous substrate layer 3, and gaps exist between the inorganic particles. A nonaqueous electrolyte is held in these pores, and the separator 1 with a heat-resistant insulating layer functions as an electrolyte layer having ion conductivity as a whole.

In addition, the separator 1 with a heat-resistant insulating layer may have other layers interposed between the porous substrate layer and the heat-resistant insulating layer, and such a form is also included in the technical scope of the present invention. .

(Porous substrate layer)
The porous substrate layer functions as a substrate when the heat-resistant insulating layer is formed. The material constituting the porous substrate layer is not particularly limited, but resin materials such as thermoplastic resins and thermosetting resins, metal materials, cellulosic materials, and the like can be used. Among these, it is preferable to use a porous substrate layer made of a resin material (hereinafter also referred to as “resin porous substrate layer”) from the viewpoint of providing a separator with a heat-resistant insulating layer with a shutdown function.

The material (base material) of the resin porous substrate layer preferably contains a resin having a melting temperature of 120 to 200 ° C., for example, polyethylene (PE), polypropylene (PP), or ethylene and propylene as monomer units. Examples thereof include a copolymer (ethylene-propylene copolymer) obtained by copolymerization. These polyolefin resins are preferable because they have a property of being chemically stable with respect to an organic solvent and can suppress the reactivity with an electrolyte to a low level. In addition to these, rubber materials such as acrylic rubber, butyl rubber, nitrile rubber, ethylene propylene rubber, chlorosulfonated polyethylene rubber, and epichlorohydrin rubber can also be used as the resin material of the resin porous substrate layer.

Furthermore, in addition to the resin having a melting temperature of 120 to 200 ° C., a resin having a melting temperature exceeding 200 ° C. or a thermosetting resin may be included. For example, polystyrene (PS), polyvinyl acetate (PVAc), polyethylene terephthalate (PET), polyvinylidene fluoride (PFDV), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyethersulfone (PES), polyether Examples include ether ketone (PEEK), polyimide (PI), polyamideimide (PAI), aramid, phenol resin, epoxy resin (EP), melamine resin, urea resin (UF), alkyd resin, and polyurethane. At this time, the ratio of the resin having a melting temperature of 120 to 200 ° C. in the entire resin porous substrate layer is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95%. % By mass or more, most preferably 100% by mass.

Alternatively, the resin porous substrate layer may be formed by laminating the above materials. For example, as an example of the laminated form, a resin porous substrate layer having a three-layer structure of PP / PE / PP can be cited.

The shape of the resin porous substrate layer is not particularly limited, and may be at least one selected from the group consisting of a woven fabric, a nonwoven fabric, or a microporous membrane, for example.

Here, since the material (base material) of the porous substrate layer itself has a role of insulating ionic conduction, the shape of the porous substrate layer is a highly porous structure in order to ensure high ionic conductivity. It is preferable that Specifically, the porosity of the porous substrate layer is preferably 50% or more. In order to ensure the mechanical strength of the porous substrate layer, the porosity of the porous substrate layer is preferably 85% or less. Among these, in order to ensure a dense pore structure and mechanical strength, the shape of the porous substrate layer is preferably a microporous film.

The thickness of the porous substrate layer cannot be uniquely defined because it varies depending on the type and form of the substrate. As an example, the thickness of the woven or non-woven fabric is preferably 5 to 200 μm, particularly preferably 5 to 100 μm. If the thickness is 5 μm or more, the electrolyte retainability is good, and if it is 200 μm or less, the resistance is difficult to increase excessively. The thickness of the microporous film is preferably 4 to 60 μm for a single layer or multiple layers.

The above-mentioned porous substrate layer can be manufactured by a known method. For example, a stretch opening method and a phase separation method for producing a microporous membrane, an electrospinning method for producing a nonwoven fabric, and the like can be mentioned.

[Heat resistant insulation layer]
The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the mechanical strength of the separator with the heat-resistant insulating layer is improved, and the effect of suppressing thermal shrinkage is obtained by relaxing the internal stress of the separator that increases when the temperature rises. Further, since the mechanical strength is high, the separator is unlikely to break. Furthermore, due to the high mechanical strength and the effect of suppressing thermal shrinkage, the separator is less likely to curl during the manufacturing process. Since the heat-resistant insulating layer also has oxidation resistance, the stability of the surface in contact with the positive electrode is high.

(Inorganic particles)
The inorganic particles are a constituent element of the heat-resistant insulating layer and impart mechanical strength and a heat shrinkage suppressing effect to the heat-resistant insulating layer.

The inorganic particles are not particularly limited, and known particles can be used. Examples include oxides, hydroxides, and nitrides of zirconium, aluminum, silicon, and titanium, and mixtures or composites thereof. For example, the oxide of silicon, aluminum, zirconium, or titanium can be silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), or titania (TiO ₂ ). These inorganic particles can be used alone or in combination of two or more. Of these, silica or alumina is preferably used from the viewpoint of cost.

Each inorganic particle has a specific density. For example, the density of zirconia is about 5.7 g / cm ³ , the density of alumina is about 4.0 g / cm ³ , the density of titania is about 3.9 to 4.3 g / cm ³ , and the density of silica The density is about 2.2 g / cm ³ . The amount of inorganic particles required varies depending on the type of inorganic particles used, and when compared with a constant weight, the higher the density of the inorganic particles, the better the thermal shrinkage suppression effect. Thus, in another embodiment, the inorganic particles are preferably zirconia.

The particle diameter of the inorganic particles is not particularly limited and can be adjusted as appropriate.

(binder)
The binder is a constituent element of the heat-resistant insulating layer, and has a function of adhering adjacent inorganic particles, and the inorganic particles and the resin porous substrate layer. With the binder, the heat-resistant insulating layer is stably formed, and the peel strength between the porous substrate layer and the heat-resistant insulating layer is improved.

The binder is not particularly limited, and known binders can be used. For example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), and methyl acrylate. These may be used alone or in combination of two or more. Of these binders, carboxymethyl cellulose (CMC), methyl acrylate, and polyvinylidene fluoride (PVDF) are preferred.

The binder contributes to adhesion between inorganic particles and adhesion between the porous substrate layer and the heat-resistant insulating layer. Therefore, the binder is essential as a component of the heat resistant insulating layer. The addition amount of the binder is preferably 2 to 10% by mass with respect to 100% by mass of the heat-resistant insulating layer. When the addition amount of the binder is 2% by mass or more, it is preferable because the peel strength of the separator with a heat-resistant insulating layer is increased and vibration resistance is improved. On the other hand, when the addition amount of the binder is 10% by mass or less, the adhesiveness is appropriately maintained, and the possibility of inhibiting the ionic conductivity can be reduced.

The thickness of the heat-resistant insulating layer is appropriately determined according to the type and application of the battery, and should not be particularly limited. For example, the heat-resistant insulating layer formed on one side or both sides of the porous substrate. The total thickness is about 5 to 200 μm. In addition, in applications such as motor-driven secondary batteries such as electric vehicles (EV) and hybrid electric vehicles (HEV), the total thickness of the heat-resistant insulating layers formed on both surfaces of the porous substrate is, for example, 5 to 200 μm. The thickness is preferably 5 to 20 μm, more preferably 6 to 10 μm. When the thickness of the heat-resistant insulating layer is within such a range, high output performance can be secured while increasing the mechanical strength in the thickness direction.

The porosity of the heat-resistant insulating layer is not particularly limited, but is preferably 40% or more, more preferably 50% or more from the viewpoint of ion conductivity. Moreover, if the porosity is 40% or more, the retainability of the electrolyte (electrolytic solution, electrolyte gel) is improved, and a high-power battery can be obtained. The porosity of the heat-resistant insulating layer is preferably 70% or less, more preferably 60% or less. When the porosity of the heat-resistant insulating layer is 70% or less, sufficient mechanical strength is obtained, and the effect of preventing a short circuit due to foreign matter is high.

The total thickness of the separator with a heat-resistant insulating layer is not particularly limited, but can be generally used if it is about 5 to 30 μm. In order to obtain a compact battery, it is preferable to make it as thin as possible within a range in which the function as an electrolyte layer can be ensured, and in order to contribute to improvement of battery output by reducing the film thickness, the total thickness of the separator is preferably 20 to It is 30 μm, more preferably 20 to 25 μm.

The manufacturing method of the separator with a heat-resistant insulating layer is not particularly limited, and a known method can be used. For example, a separator with a heat-resistant insulating layer can be manufactured by applying a solution in which inorganic particles and a binder are dispersed in a solvent to a porous substrate layer, removing the solvent, and drying.

The solvent used at this time is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like are used. When adopting polyvinylidene fluoride (PVDF) as a binder, it is preferable to use NMP as a solvent. The temperature at which the solvent is removed is not particularly limited and can be appropriately set depending on the solvent used. For example, when water is used as a solvent, the temperature may be 50 to 70 ° C., and when NMP is used as a solvent, the temperature may be 70 to 90 ° C. If necessary, drying may be performed under reduced pressure. Further, a part of the solvent may be left without being completely removed.

The basis weight when applying the heat-resistant insulating layer forming composition to the porous substrate is not particularly limited, but is preferably 5 to 20 g / m ² , more preferably 9 to 13 g / m ² . If it is the said range, the heat-resistant insulating layer which has a suitable porosity and thickness can be obtained. There are no particular restrictions on the coating method, for example, blade coater method, knife coater method, gravure coater method, screen printing method, Mayer bar method, die coater method, reverse roll coater method, ink jet method, spray method, roll coater method, etc. Is mentioned.

[Nonaqueous electrolyte]
The non-aqueous electrolyte is present in pores in the separator and the active material layer (holes in the power generation element 21) or in the external space 20 of the power generation element 21, and is a lithium ion carrier that moves between the positive and negative electrodes during charge and discharge. Serves as a function. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte may be used.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). As the supporting salt (lithium _{_{salt), Li (CF 3 SO 2}} ) 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 Compounds that can be added to the electrode mixture layer such as SO ₃ can be similarly employed.

The polymer electrolyte is classified into a gel polymer electrolyte (gel electrolyte) containing an electrolytic solution (liquid electrolyte) and an intrinsic polymer electrolyte containing no electrolytic solution.

The gel polymer electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), polyacrylonitrile (PAN), Examples thereof include polymethyl methacrylate (PMMA) and copolymers thereof.

The intrinsic polymer electrolyte has a structure in which a lithium salt is dissolved in the above matrix polymer and does not contain an organic solvent. Therefore, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

These nonaqueous electrolytes may be used alone or in combination of two or more.

[electrode]
(Current collector)
As the current collectors (the negative electrode current collector 11 and the positive electrode current collector 12), any member conventionally used as a current collector material for a battery can be appropriately employed. As an example, examples of the positive electrode current collector and the negative electrode current collector include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. Among these, from the viewpoints of electron conductivity and battery operating potential, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector. A typical thickness of the current collector is 10 to 20 μm. However, a current collector having a thickness outside this range may be used. The current collector plate can also be formed of the same material as the current collector. In addition to the current collector, a resin current collector material obtained by adding a conductive filler (metal particles or carbon material) to the resin material can also be applied as the bipolar battery current collector. If an example of resin material is given, materials, such as polyethylene, a polypropylene, a polystyrene, a polyimide, polyamide, will be mentioned.

(Active material layer)
The active material layers (the positive electrode active material layer 15 and the negative electrode active material layer 13) include an active material (a negative electrode active material, a positive electrode active material). If necessary, a binder, a conductive auxiliary agent for increasing electrical conductivity, and the like are included. Including. Moreover, the non-aqueous electrolyte may be contained in the pores of the active material layer.

The average particle diameter of each active material contained in each active material layer (13, 15) is not particularly limited, but is usually about 0.1 to 100 μm from the viewpoint of increasing capacity, reactivity, and cycle durability. The thickness is preferably 1 to 20 μm.

The compounding ratio of the components contained in each active material layer (13, 15) is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries or lithium ion batteries. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a lithium ion secondary battery or a lithium ion battery can be referred suitably. For example, the thickness of the active material layer is about 2 to 100 μm.

(A) Active Material (i) Positive Electrode Active Material The positive electrode active material is not limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used for lithium ion secondary batteries can be used. Specifically, lithium-manganese composite oxide (such as LiMn ₂ O ₄ ), lithium-nickel composite oxide (such as LiNiO ₂ ), lithium-cobalt composite oxide (such as LiCoO ₂ ), lithium-iron composite oxide (such as LiFeO ₂ etc.), lithium-nickel-manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ etc.), lithium-nickel-cobalt composite oxide (LiNi _0.8 Co _0.2 O ₂ etc.), lithium-transition metal phosphate compound (LiFePO ₄ ), and lithium-transition metal sulfate compounds (Li _x Fe ₂ (SO ₄ ) ₃ ). The positive electrode active material may be used alone or in the form of a mixture of two or more. Of course, positive electrode active materials other than those described above may be used.

(Ii) Negative electrode active material The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and any conventionally known negative electrode active material can be used. For example, high crystalline carbon graphite (natural graphite, artificial graphite, etc.), low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, Carbon materials such as thermal black, fullerene, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon fibrils; silicon monoxide (SiO), SiO _x (0 <x <2), tin dioxide (SnO ₂ ), SnO _x (0 <x <2), SnSiO ₃ , negative electrode materials such as silicon carbide (SiC); metal materials such as lithium metal; lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ), etc. Lithium-transition metal composite An oxide etc. are mentioned. The negative electrode active material may be used alone or in the form of a mixture of two or more. Of course, negative electrode active materials other than those described above may be used.

(B) Binder The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector.

As such a binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polymethyl acrylate (PMA), Thermosetting resins such as polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN), epoxy resins, polyurethane resins, and urea resins And rubber-based materials such as styrene butadiene rubber (SBR).

(C) Conductive aid The conductive aid refers to a conductive additive blended to improve conductivity. The conductive auxiliary agent that can be used in the present embodiment is not particularly limited, and conventionally known ones can be used. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the conductive assistant is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery and improvement of reliability due to improvement of liquid retention of the electrolytic solution.

(D) Electrolyte The nonaqueous electrolyte present in the active material layer is preferably the same as the nonaqueous electrolyte present in the separator or in the external space of the power generation element, but may be different. When the non-aqueous electrolyte present in the active material layer is different from the non-aqueous electrolyte present in the separator or in the external space of the power generation element, the liquid electrolyte and / or gel polymer electrolyte described above as the non-aqueous electrolyte in the active material layer Alternatively, or in addition, an intrinsic polymer electrolyte may be used.

[Exterior body]
In a lithium ion secondary battery, it is desirable to accommodate the entire power generating element in an exterior body in order to prevent external impact and environmental degradation during use. As the exterior body, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

In the above embodiment, a lithium ion secondary battery (laminated battery 1) using a laminate film as an exterior material is illustrated as an electrical device, but the present invention is not limited to this. It can be applied to other types of secondary batteries and even primary batteries. Moreover, it can be applied not only to batteries but also to electric double layer capacitors.

The effect of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

[Example 1]
1. Production of Positive Electrode LiMn ₂ O ₄ (85% by mass) as a positive electrode active material, acetylene black (5% by mass) as a conductive additive, and polyvinylidene fluoride (PVDF) (10% by mass) as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, to prepare a positive electrode active material slurry. This positive electrode active material slurry was applied to one side of an aluminum current collector foil (thickness: 20 μm) as a positive electrode current collector, dried and pressed to produce a positive electrode having a single-side active material layer thickness of 60 μm. Note that the porosity of the positive electrode (positive electrode active material layer) was 30%.

2. Production of Negative Electrode Hard carbon (90% by mass) as a negative electrode active material and polyvinylidene fluoride (PVDF) (10% by mass) as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, to prepare a negative electrode active material slurry. This negative electrode active material slurry is applied to one side of a copper current collector punching metal (thickness: 20 μm) as a negative electrode current collector, dried and pressed to produce a negative electrode having a thickness of 50 μm on one side of the active material layer did. The porosity of the negative electrode (negative electrode active material layer) was 35%.

3. Production of separator with heat-resistant insulating layer Alumina particles 1 (average particle size: 0.5 μm, specific surface area 5 g / m ² ) (95% by mass) as inorganic particles and polyvinylidene fluoride (PVDF) (5% by mass) as a binder Was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, to prepare a heat-resistant insulating layer slurry.

The heat-resistant insulating layer slurry is applied to both sides of a polyethylene (PE) microporous membrane (porosity 50%, film thickness 15 μm), which is a porous resin substrate, by a blade coater, dried and pressed to obtain a PE microporous membrane. A separator with a heat-resistant insulating layer in which a heat-resistant insulating layer was formed on both sides was prepared. At this time, the thickness of the heat-resistant insulating layer was adjusted so that the ratio of the pore volume Vs of the separator to the total pore volume V of the positive electrode, the negative electrode, and the separator (y = Vs / V) was 0.250. In addition, the porosity of the separator with a heat-resistant insulating layer was 50%.

3. Production of Evaluation Cell The positive electrode, negative electrode, and separator with a heat-resistant insulating layer produced above were cut into a size of 10 cm in length and 10 cm in width, and the positive electrode active material layer and the negative electrode active material layer were interposed via the separator with a heat-resistant insulating layer. The power generation element for evaluation was manufactured by stacking so as to face each other. The nickel tab lead was connected to the negative electrode, and the aluminum tab lead was connected to the positive electrode by ultrasonic welding.

Next, the power generation element for evaluation was placed inside a pair of laminate sheaths, and an electrolyte was injected, followed by vacuum sealing to produce an evaluation cell. Incidentally, the electrolyte, a 1M LiPF ₆ ethylene carbonate (EC): diethyl carbonate (DEC) = 1: 1 were used as dissolved in a solvent (volume ratio). At this time, the amount of the electrolyte was adjusted so that the ratio of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, the negative electrode, and the separator (x = L / V) was 1.25.

[Examples 2 to 3, Comparative Examples 1 to 3]
Example 1 except that the amount of the electrolyte was changed so that the ratio of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, the negative electrode, and the separator (x = L / V) became the value shown in Table 1 An evaluation cell was produced in the same manner.

[Example 4]
As the inorganic particles constituting the heat-resistant insulating layer, alumina particles 1 (average particle size: 0.5 μm, specific surface area 5 g / m ² ) and alumina particles 2 (average particle size: 0.5 μm, specific surface area 50 g) are used instead of alumina particles 1. / M ² ), and the amount of the electrolyte was changed so that the ratio of the pore volume Vs of the separator to the total pore volume V of the positive electrode, the negative electrode, and the separator (y = Vs / V) was 0.275. . Except for this, an evaluation cell was produced in the same manner as in Example 1.

[Examples 5 to 6, Comparative Examples 4 to 6]
Example 4 except that the amount of the electrolytic solution was changed so that the ratio (x = L / V) of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, the negative electrode, and the separator became the value shown in Table 1. An evaluation cell was produced in the same manner.

[Example 7]
The mixing ratio of alumina particles 1 and alumina particles 2 as inorganic particles constituting the heat-resistant insulating layer was changed, and the ratio of the separator pore volume Vs to the total pore volume V of the positive electrode, the negative electrode, and the separator (y = Vs / V) was set to 0.310. Other than this, an evaluation cell was produced in the same manner as in Example 4.

[Example 8, Comparative Examples 7 to 9]
The same as Example 7 except that the electrolytic mass was changed so that the ratio of the non-aqueous electrolyte amount L to the total pore volume V of the positive electrode, negative electrode, and separator (x = L / V) was the value shown in Table 1. An evaluation cell was prepared by the method described above.

[Example 9]
Instead of alumina particles 1, alumina (Al ₂ O ₃ ) particles 1 (average particle diameter: 0.5 μm, specific surface area 5 g / m ² ) and silica (SiO ₂ ) particles (average particles) are used as inorganic particles constituting the heat-resistant insulating layer. Diameter: 0.5 μm, specific surface area 5 g / m ² ) was used. Except for this, an evaluation cell was produced in the same manner as in Example 1.

[Example 10]
As inorganic particles constituting the heat-resistant insulating layer, alumina (Al ₂ O ₃ ) particles 1 (average particle diameter: 0.5 μm, specific surface area 5 g / m ² ) and zirconia (ZrO ₂ ) particles (average particles) instead of alumina particles 1 Diameter: 0.5 μm, specific surface area 5 g / m ² ) was used. Except for this, an evaluation cell was produced in the same manner as in Example 1.

(Evaluation)
About each cell for an evaluation of the Example and comparative example which were produced by said method, initial charge discharge was performed for 5 hours at 0.5 C in 25 degreeC atmosphere.

Next, after degassing each evaluation cell, a cycle test of 100 cycles was performed at a constant current of 1 C in an atmosphere of 45 ° C. The capacity measurement after the test is performed under the condition of 1C after full charge, and the discharge capacity after 100 cycles of each evaluation cell is the relative value when the discharge capacity after 100 cycles of the evaluation cell of Comparative Example 1 is 1. It is shown in Table 1 as (capacity maintenance ratio). FIG. 3 shows the relationship between the parameters x and y of each evaluation cell obtained in the examples and comparative examples and the capacity maintenance ratio (life characteristics). Shown in parentheses in FIG. 3 are the capacity retention ratios of the cells in each example and comparative example.

From Table 1 and FIG. 3, it is confirmed that in the evaluation cell of the example satisfying the formula (1), the capacity maintenance ratio after the cycle test is high and the life characteristics are maintained high. In particular, in the region that does not satisfy Expression (1) from FIG. 3 (Comparative Example), the capacity retention ratio changes (increases) greatly as x and y change (increase), whereas the area that satisfies Expression (1) In (Example), it is confirmed that the change in the capacity maintenance ratio accompanying the change in x and y is moderate. That is, it can be seen that the capacity retention rate is maintained significantly high when Expression (1) is satisfied with y = 0.145x + 0.075 as the boundary.

Furthermore, it is confirmed that in the evaluation cell of the example satisfying the formulas (2) and (3), the capacity retention rate after the cycle test is further improved and the life characteristics are further improved.

As mentioned above, although the present invention has been described using the embodiments, the present invention is not limited to the above embodiments.

In the present specification, “mass” and “weight”, “mass%” and “wt%”, “mass part” and “part by weight” are synonymous, and there is no particular notice regarding measurement of physical properties and the like. In this case, measurement is performed at room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

This application is based on Japanese Patent Application No. 2011-222937 filed on October 07, 2011, the disclosure of which is referenced and incorporated as a whole.

1 Separator with heat-resistant insulating layer,
10 stacked battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer (negative electrode),
15 positive electrode active material layer (positive electrode),
17 electrolyte layer,
19 Single battery layer (single cell),
20 external space,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 exterior body (laminate sheet),
31 (resin) porous substrate layer,
32 inorganic particles,
33 binder,
34 Heat-resistant insulating layer.

Claims

An electrical device having a positive electrode, an electrolyte layer in which a nonaqueous electrolyte is held in a separator, and at least one single cell layer in which a negative electrode is laminated in this order,
The separator has a porous substrate layer and a heat-resistant insulating layer containing inorganic particles and a binder formed on one or both surfaces of the porous substrate layer, and
An electrical device that satisfies the following formula (1).

In the above formula, x is the ratio (L / V) of the nonaqueous electrolytic mass L to the total pore volume V of the positive electrode, the negative electrode, and the separator, and x ≧ 1; y is the positive electrode, negative electrode, and separator The ratio (Vs / V) of the void volume Vs of the separator to the total void volume V, where y> 0.
The electric device according to claim 1, wherein x ≦ 2.
Furthermore, the electrical device of Claim 1 or 2 which satisfy | fills following formula (2).

In the above formula, x and y have the same definitions as above.
Furthermore, the electrical device of Claim 3 which satisfy | fills following formula (3).

In the above formula, x and y have the same definitions as above.
The inorganic particles include at least one selected from the group consisting of oxides, hydroxides, and nitrides of zirconium, aluminum, silicon, and titanium, and mixtures or composites thereof. The electrical device according to any one of the above.
The electrical device according to any one of claims 1 to 5, wherein the material constituting the porous substrate layer includes at least one selected from the group consisting of polyethylene, polypropylene, or ethylene-propylene copolymer. .