TW201941483A - Nonaqueous electrolyte secondary battery and method for producing nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte secondary battery including: a positive electrode 1 including a positive electrode current collector 11 and a positive electrode active material layer 12 located on one or both surfaces of the positive electrode current collector 11; a negative electrode 3 including a negative electrode current collector 31 and a negative electrode active material layer 32 located on one of both surfaces of the negative electrode current collector 31; a nonaqueous electrolyte containing lithium ions located between the positive electrode active material layer 12 and the negative electrode active material layer 32; a separator 2 located between the positive electrode active material layer 12 and the negative electrode active material layer 32; and a particle layer 4 located on a surface of one or both of the positive electrode active material layer 12 and the negative electrode active material layer 32, wherein a ratio of a specific surface area A of particles contained in the particle layer 4 to a specific surface area B of particles contained in the positive electrode active material layer 12, A/B, is more than 0.2 and less than 1.5.

Description

Nonaqueous electrolyte secondary battery and method for manufacturing nonaqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the non-aqueous electrolyte secondary battery.
This case claims priority based on Japanese Patent Application No. 2018-058199, filed in Japan on March 26, 2018, the contents of which are incorporated herein by reference.

Compared with lead storage batteries and nickel-metal hydride batteries, lithium ion secondary batteries have the characteristics of higher energy density and higher electromotive force. Therefore, it is widely used as a power source for mobile phones, notebook computers, etc., which require small size and light weight. In the lithium ion secondary battery, a non-aqueous electrolytic solution obtained by dissolving a lithium salt in an organic solvent is mainly used as an electrolyte.
A lithium ion secondary battery has, for example, an exterior body: a positive electrode provided with a positive electrode active material layer on a positive electrode current collector, a negative electrode provided with a negative electrode active material layer on a negative electrode current collector, and a partition between the positive electrode and the negative electrode. And non-aqueous electrolyte.

A lithium ion secondary battery having a porous insulating layer on the surface of the electrode already exists. For example, in the example of Patent Document 1, a non-aqueous electrolyte secondary battery including a particle layer having a thickness of 2 μm on the surface of the positive electrode is described. The particle layer contains inorganic particles, a polycarboxylate, and a styrene-butadiene rubber.
The particle layer provided on the surface of the positive electrode functions as a filter that captures decomposed matter of the non-aqueous electrolyte generated by the reaction in the positive electrode, or an element (element other than lithium) eluted from the positive electrode active material. Therefore, by having the particle layer, it is possible to prevent the above-mentioned decomposed matter or elements other than lithium from being deposited on the surface of the negative electrode or the separator.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] Japanese Patent No. 5213534

[Problems to be Solved by the Invention]

The inventors conducted research, and as a result, found that if the particle layer described in Patent Document 1 is provided on the surface of the electrode, the lithium ion secondary battery has low mechanical strength and poor cycle characteristics.
An object of the present invention is to provide a nonaqueous electrolyte secondary battery having a particle layer on the surface of an electrode, high mechanical strength, and excellent cycle characteristics, and a method for manufacturing the above nonaqueous electrolyte secondary battery.
[Technical means to solve the problem]

The present invention has the following aspects.
[1] A non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode current collector and a positive electrode active material layer on a surface of the positive electrode current collector, a negative electrode current collector and a surface of the negative electrode current collector. A negative electrode of a negative electrode active material layer, a non-aqueous electrolyte containing lithium ions, a separator located between the positive electrode and the negative electrode, and a particle layer on the surface of one or both of the positive electrode and the negative electrode, the particles The ratio of the specific surface area A of the particles contained in the layer to the specific surface area B of the particles contained in the positive electrode active material layer, that is, A / B exceeds 0.2 and does not reach 1.5.
[2] The non-aqueous electrolyte secondary battery according to [1], wherein the particle layer contains inorganic particles.
[3] The non-aqueous electrolyte secondary battery according to [2], wherein the inorganic particles are selected from the group consisting of magnesium oxide particles, titanium oxide particles, aluminum oxide particles, silicon oxide particles, and lithium phosphate particles. At least one.
[4] The non-aqueous electrolyte secondary battery according to [2] or [3], wherein the average particle diameter of the inorganic particles is 1.3 μm or less.
[5] The non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein at least a part of the particle layer is present on a surface of the positive electrode current collector.
[6] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein at least a part of the particle layer is present on a surface of the negative electrode current collector.
[7] The non-aqueous electrolyte secondary battery according to any one of [1] to [6], wherein a thickness of the particle layer is 2 to 20 μm.
[8] The non-aqueous electrolyte secondary battery according to any one of [1] to [7], wherein the particle layer is located on a surface of the positive electrode.
[9] A method for producing a non-aqueous electrolyte secondary battery, which is the method for producing a non-aqueous electrolyte secondary battery according to any one of [1] to [8], which has a coating containing particles and a binder The liquid is applied on the surface of one or both of the positive electrode and the negative electrode, and is dried. The specific surface area A ′ of the particles contained in the coating solution with respect to the specific surface area B of the particles contained in the positive electrode active material layer is dried. The ratio of A '/ B exceeds 0.2 and does not reach 1.5.
[Effect of the invention]

The non-aqueous electrolyte secondary battery of the present invention has high mechanical strength and excellent cycle characteristics.

Hereinafter, embodiments of the non-aqueous electrolyte secondary battery of the present invention will be described with reference to the drawings. In addition, the drawings used in the following description may be enlarged for the sake of convenience to make the feature easier to understand, and the size ratio of each component may be different from the actual one. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be implemented by appropriately changing the scope without changing the gist thereof.

[Non-aqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view of one embodiment of a non-aqueous electrolyte secondary battery (hereinafter, sometimes also simply referred to as a secondary battery) of the present invention. The secondary battery 10 shown in FIG. 1 includes a positive electrode 1, a separator 2, a negative electrode 3, a particle layer 4, and an exterior body 5.
The positive electrode 1 and the negative electrode 3 are rectangular flat plates in a plan view. The positive electrode 1 and the negative electrode 3 face each other. The separator 2 is located between the opposite positive electrode 1 and negative electrode 3. In this way, the negative electrode 3, the separator 2, the positive electrode 1, the separator 2, and the negative electrode 3 are arranged in this order to form the laminated body 20.
The laminated body 20 and the non-aqueous electrolyte are located inside the exterior body 5. The particle layer 4 is located on the surface of the positive electrode 1. The particle layer 4 is preferably located on a surface of the positive electrode 1 opposite to the negative electrode 3.

The positive electrode 1 includes a plate-shaped positive electrode current collector 11 and positive electrode active material layers 12 on both surfaces thereof. The positive electrode active material layer 12 is located on a part of the surface of the positive electrode current collector 11. The positive electrode current collector exposed portion 13 in which the positive electrode active material layer 12 is not present is located on the edge portion of the surface of the positive electrode current collector 11. Lead wires (tabs) (not shown) are connected to the positive electrode current collector 11 at any part of the exposed edges. The particle layer 4 covers the positive electrode active material layer 12, and a part of the particle layer 4 is located on the surface of the positive electrode current collector exposed portion 13.

The negative electrode 3 includes a plate-shaped negative electrode current collector 31 and negative electrode active material layers 32 on both surfaces thereof. The negative electrode active material layer 32 is located on a part of the surface of the negative electrode current collector 31. The negative electrode current collector exposed portion 33 in which the negative electrode active material layer 32 is not present is located on the edge portion of the surface of the negative electrode current collector 31. Lead wires (lead plates) (not shown) are connected to the negative electrode current collector 31 at any portion of the exposed edges.

The laminated body 20 and the non-aqueous electrolyte (not shown) of the secondary battery 10 in this embodiment are housed in the exterior body 5 and sealed.

＜ Particle layer ＞
The particle layer contains particles and a binder. When the particle layer does not contain other components to be described later, the particles are referred to as particles A, and when the particle layer contains other components to be described later, a mixture of the particles and other components is referred to as particles A.
The particle layer 4 in the secondary battery 10 is impregnated with the electrolytic solution. The particle layer 4 is wetted by the electrolytic solution, and a small gap is formed between the adhesive and the particles. Since lithium ions and the like pass through the particle layer 4 through the gap, the particle layer 4 has ion conductivity.

(particle)
The particles contained in the particle layer are preferably particles that do not occlude or release lithium ions. The "occlusion or release of lithium ions" refers to the storage or release of lithium ions in a lithium ion secondary battery having a positive electrode 1 and a negative electrode 3 to the extent that it interferes with its charging and discharging operation. The particles may be inorganic particles or organic particles.

The ratio of the specific surface area A of the particles A to the specific surface area B of the particles (hereinafter, also referred to as “particles B”) contained in the positive electrode active material layer described later, that is, A / B is preferably more than 0.2 and less than 1.5, more It is preferably more than 0.3 and less than 1.1, and more preferably more than 0.3 and less than 0.8. If the A / B exceeds the lower limit of the above range, the mechanical strength and cycle characteristics of the secondary battery are improved, and the increase in internal resistance is suppressed. If the A / B does not reach the upper limit of the above range, the mechanical strength and cycle characteristics of the secondary battery will be improved.
In the present specification, the "specific surface area" refers to a BET specific surface area measured by a BET type gas adsorption method using nitrogen as an adsorption gas.

The specific surface area of the particle A is not particularly limited as long as it has the effect of the present invention, preferably 1 to 30 m ² / g, more preferably ² to 25 m ² / g, and still more preferably 3 to 20 m ² / g, particularly preferably ³ to 8 m ² / g.

From the viewpoint that the peel strength of the particle layer and the mechanical strength of the secondary battery become higher, it is preferable to include inorganic particles as the particles A.

The inorganic particles may be particles composed of an inorganic material that does not occlude or release lithium ions. The inorganic particles in the particle layer may be used alone or in combination of two or more.
The inorganic particles are preferably, for example, inorganic oxide particles. The inorganic oxide particles are preferably selected from the group consisting of magnesium oxide (MgO) particles, titanium oxide (TiO ₂ ) particles, aluminum oxide (Al ₂ O ₃ ) particles, silicon oxide (SiO ₂ ) particles, and lithium phosphate particles. One or more members of the group, more preferably one or more members selected from the group consisting of magnesium oxide particles, titanium oxide particles, aluminum oxide particles, and lithium phosphate particles, and further preferably selected from the group consisting of magnesium oxide particles and titanium oxide particles One or more of the group consisting of alumina particles.

From the viewpoint of improving the mechanical strength of the secondary battery and suppressing the increase in internal resistance, the average particle diameter of the inorganic particles is preferably 1.3 μm or less, more preferably 1.0 μm or less, still more preferably 0.8 μm or less, and particularly preferably It is 0.7 μm or less, and most preferably 0.6 μm or less.
The lower limit of the average particle diameter of the inorganic particles is not particularly limited as long as it has the effect of the present invention, and is preferably 0.1 μm or more, and more preferably 0.3 μm or more.
In addition, the above upper limit value and lower limit value can be arbitrarily combined.
The combination of the upper limit value and the lower limit value is preferably 0.1 μm or more and 1.3 μm or less, more preferably 0.1 μm or more and 1.0 μm or less, still more preferably 0.3 μm or more and 0.8 μm or less, and particularly preferably 0.3 μm. It is more than 0.7 μm, and more preferably 0.3 μm or more and 0.6 μm or less.

The particles A may also include particles other than inorganic particles, such as organic particles. If the particle layer contains organic particles, the internal resistance of the secondary battery can be further reduced.
The organic particles may be particles composed of an organic material that does not occlude or release lithium ions. One type of organic particles may be used in the particle layer, or two or more types may be used in combination.
Examples of the organic material constituting the organic particles include poly-α-olefin, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polysilicone (polymethylsilicone), and the like. Sesquioxane, etc.), polystyrene, polydivinylbenzene, styrene-divinylbenzene copolymer, polyamidoamine, polyimide, polycarbonate, urea resin, urethane resin, melamine Resin, phenol resin, benzoguanidine -Formaldehyde condensates, polyfluorene, polyacrylonitrile, polyacetal, thermoplastic polyimide, and the like.
Considering the preferable thickness of the particle layer, the upper limit of the average particle diameter of the organic particles is preferably 2 μm or less, and more preferably 1 μm or less. In terms of dispersibility in a dispersion medium, the lower limit of the average particle diameter of the organic particles is preferably 0.01 μm or more, and more preferably 0.1 μm or more.
In addition, the above upper limit value and lower limit value can be arbitrarily combined.
The combination of the upper limit value and the lower limit value is preferably 0.01 μm or more and 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less.

The average particle diameters of the inorganic particles and organic particles are measured by a laser diffraction particle size distribution measuring device (for example, Partica LA-960 manufactured by Horiba, SALD-3000J manufactured by Shimadzu Corporation). The particle diameter when the volume from the small-diameter side reaches 50% cumulatively (that is, the volume average particle diameter). The details of the measurement conditions are described in the following examples.

The content of the inorganic particles with respect to all particles (100 parts by mass) contained in the particle layer is preferably 50 to 100 parts by mass, more preferably 60 to 100 parts by mass, still more preferably 70 to 100 parts by mass, and particularly preferably 80 ~ 100 parts by mass.
When the content of the inorganic particles is above the lower limit of the above range, the mechanical strength of the secondary battery and the adhesion strength to the separator are further improved. When the content of the inorganic particles is equal to or less than the upper limit of the above range, the liquid-retaining property of the insulating layer is improved, and the increase in the internal resistance of the secondary battery can be further reduced.

When the particle layer includes not only inorganic particles but also organic particles, the content of the organic particles with respect to all particles (100 parts by mass) contained in the particle layer is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and It is preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.
If the content of the organic particles is equal to or less than the above upper limit value, the internal resistance of the secondary battery can be further reduced while maintaining the peeling strength of the particle layer and the mechanical strength of the secondary battery.
The lower limit of the content of the organic particles is not particularly limited as long as it has the effect of the present invention, and is, for example, more than 0 parts by mass.
That is, the content of the organic particles is preferably more than 0 parts by mass and 50 parts by mass or less, more preferably more than 0 parts by mass and 40 parts by mass or less, still more preferably more than 0 parts by mass and 30 parts by mass or less, particularly preferably more than 0 parts by mass. 0 to 20 parts by mass.

The total content of the particles in the particle layer is preferably 70 to 98% by mass, and more preferably 85 to 95% by mass relative to the total mass of the particle layer (100% by mass).
If the total content of the particles is above the lower limit of the above range, the mechanical strength and ion conductivity of the secondary battery will be improved, and the increase in battery resistance will be reduced. When the total content of the particles is equal to or less than the upper limit of the above range, the peel strength of the particle layer is further increased.

(Adhesive)
A binder is a polymer in a particle layer that binds particles to each other.
As a binder constituting the particle layer, it can be used as a binder for electrodes of non-aqueous secondary batteries. For example, polyacrylic acid (PAA), lithium polyacrylate (PAALi), and polyvinylidene fluoride (PVDF) can be exemplified. ), Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene glycol (PEG), carboxymethyl cellulose (CMC), polyacrylonitrile (PAN), polyimide (PI), etc.
The molecular weight of the binder is appropriately set in consideration of particle dispersibility, adhesiveness, and the like.
The adhesive may be used singly or in combination of two or more kinds. When two or more types are used in combination, the combination and ratio can be appropriately selected according to the purpose.

As the adhesive, a water-based adhesive capable of being dispersed in water is preferred. Specific examples of the water-based adhesive include CMC, PAA, PAALi, PVA, PEO, PEG, and the like.
When a water-based adhesive is used, the particle layer has improved resistance to dissolution in a non-aqueous electrolyte solution, and the peel strength of the particle layer when the electrolyte solution is immersed is further improved.

The content of the binder is preferably 1.5 to 20 parts by mass, and more preferably 4 to 20 parts by mass with respect to 100 parts by mass of the particles in the particle layer.
When the content of the binder is at least the lower limit of the above range, the cohesive force and the peeling strength of the particles are further improved. If the content of the binder is below the upper limit of the above range, the battery resistance is reduced, and the mechanical strength of the secondary battery is improved.

As the thickness of the particle layer increases to a certain thickness, the peel strength of the particle layer increases. On the other hand, when the particle layer exceeds a certain thickness, the peeling strength of the particle layer tends to decrease and the battery resistance tends to increase.
The thickness of the particle layer is preferably 1.5 to 20 μm, more preferably 2 to 15 μm, and particularly preferably 2 to 10 μm.
In the present specification, the "thickness of the particle layer" is a value obtained by observing the thickness of any 10 locations in the cross section of the particle layer with a scanning electron microscope (SEM) and calculating the average value.

When the particle layer contains inorganic particles, the relationship between the thickness T (μm) of the particle layer and the average particle diameter D (μm) of the inorganic particles is expressed by (average particle diameter D) / (thickness of the particle layer T). The ratio (D / T) is, for example, preferably 0.02 to 0.50, more preferably 0.04 to 0.40, and still more preferably 0.05 to 0.30.
When the ratio (D / T) is within the above range, the mechanical strength of the secondary battery is further improved.

The particle layer may contain components other than particles and a binder within a range that does not impair the effects of the present invention. Examples of other components include polyvinylpyrrolidone.
When the particle layer contains other components, the total content of other components relative to the total mass of the particle layer (100% by mass) is preferably more than 0% by mass and less than 5% by mass, more preferably more than 0% by mass and 3% by mass. %the following.

[Partition method of particle A for measuring specific surface area]
By cutting out a part of the particle layer that does not overlap with the positive electrode active material in the positive electrode of the secondary battery, a sample containing particles A can be obtained. In addition, as for the portion overlapping with the positive electrode active material, only a portion of the particle layer was cut off under the visual observation, thereby obtaining a sample containing particles A.

Since the above sample contains particles A and a binder, the binder needs to be removed. The method for removing the adhesive is not limited. For example, the adhesive can be removed from the sample by performing ultrasonic cleaning and solid-liquid separation in an organic solvent capable of dissolving the adhesive, followed by drying. Examples of the organic solvent include N-methylpyrrolidone. If the steps of ultrasonic cleaning in an organic solvent and including solid-liquid separation are regarded as one cleaning, the cleaning is usually performed 1 to 10 times, preferably 2 to 5 times. The temperature of the organic solvent during cleaning is usually 20 to 80 ° C, and more preferably 40 to 70 ° C.

The above-mentioned drying after the solid-liquid separation can be performed under normal pressure or under reduced pressure. The drying temperature is not particularly limited, but is usually 20 to 200 ° C.
In short, from the above-mentioned conditions, the particles A are fractionated by appropriately selecting conditions that can substantially completely remove the binder.

The particle layer used to perform the above-mentioned particle A classification and measurement of the specific surface area may be a particle layer in a secondary battery immediately after the secondary battery is manufactured, or may be charged and discharged as described in Examples described later. Particle layer in the secondary battery. Among them, it is preferable to use a particle layer in a secondary battery after charging and discharging.
In addition, it was confirmed separately that the value of the specific surface area of the particles A did not change before and after charging and discharging.

[Formation method of particle layer]
The particle layer can be formed by applying a coating solution (slurry) on the surface of at least one of the positive electrode and the negative electrode and then drying to remove the diluent solvent. In addition to the particles and the binder, the coating liquid further contains a diluent solvent and any other components as necessary.
The coating method is not particularly limited, and for example, a doctor blade method, various coating methods, printing methods, and the like can be applied.
As the particles contained in the coating liquid, the above-mentioned inorganic particles and organic particles are used. In addition, as the binder, the binder used as an electrode of a non-aqueous secondary battery is used.
The diluting solvent may be any one capable of dispersing the particles and the binder. The amount of the diluent solvent to be used can be appropriately adjusted according to coating workability and the like. Examples of the diluting solvent include N-methylpyrrolidone.

The ratio of the specific surface area A 'of the particles (hereinafter also referred to as "particles A'") contained in the coating solution to the specific surface area B of the particles (particles B) contained in the positive electrode active material layer described later is A '/ B It is preferably more than 0.2 and less than 1.5, more preferably more than 0.3 and less than 1.1, and still more preferably more than 0.3 and less than 0.8. If the A '/ B exceeds the lower limit of the above range, the mechanical strength and cycle characteristics of the secondary battery are improved, and the increase in internal resistance is suppressed. If the A '/ B does not reach the upper limit of the above range, the mechanical strength and cycle characteristics of the secondary battery will be improved.

The content of the particles with respect to 100 parts by mass of the coating liquid is preferably 3 to 60 parts by mass, more preferably 8 to 50 parts by mass, and even more preferably 10 to 50 parts by mass.
The content of the binder relative to 100 parts by mass of the coating liquid is preferably 1 to 40 parts by mass, and more preferably 1 to 30 parts by mass.
From the viewpoint of workability, the viscosity of the coating liquid is preferably 30 to 3000 cps, more preferably 30 to 2000 cps, and still more preferably 100 to 1800 cps.

The drying temperature and drying time are not particularly limited. The drying temperature is usually 60 to 200 ° C, preferably 60 to 150 ° C.

＜ Positive electrode ＞
The positive electrode current collector and the positive electrode active material layer are not particularly limited as long as they have the effects of the present invention, and known materials can be used.
As the positive electrode current collector, a conductive metal foil can be used. For example, aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used.
The positive electrode active material layer contains particles (particles B) and a binder. Examples of the particles B include a positive electrode active material and a conductive auxiliary agent. When a plurality of particles are contained, a mixture thereof is used as the particles B.
The specific surface area of the particles B is preferably 5 to 20 m ² / g, and more preferably 10 to 15 m ² / g. When the specific surface area is at least the lower limit of the above range, the load characteristics as a battery are further improved. When the specific surface area is equal to or less than the upper limit of the above range, the adhesiveness is further improved.

Examples of the positive electrode active material include layered rock salt type lithium cobaltate, lithium nickelate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum compound, spinel type lithium manganate, lithium nickel manganese oxide, and olivine type. The transition metal compound such as lithium iron phosphate is preferably one or more selected from the group consisting of these transition metal compounds.
Examples of the conductive auxiliary agent include acetylene black, Ketjen black, and carbon fiber.
Examples of the binder include a fluororesin such as polyvinylidene fluoride.
The positive electrode active material layer is formed by, for example, coating a surface of a positive electrode current collector with a positive electrode slurry obtained by dispersing a positive electrode active material, a conductive auxiliary agent, and a binder in a solvent. Examples of the solvent include N-methylpyrrolidone.

The separation of the particles B used for the measurement of the specific surface area (the collection of the sample and the removal of the binder) can be performed by the same method as the above [the method of the separation of the particles A for the measurement of the specific surface area]. That is, a portion of the positive electrode in the positive electrode of the secondary battery that does not overlap with the particle layer is cut out, whereby a sample containing particles B can be obtained. In addition, as for the portion overlapping with the particle layer, only the portion of the positive electrode active material layer was cut off under the visual observation, thereby obtaining a sample containing particles B.
The removal of the adhesive from the above-mentioned sample can be performed by the same method as the removal of the adhesive described in the above [Partition Method of Particle A for Measurement of Specific Surface Area].
The positive electrode active material layer used to measure the particle B and measure the specific surface area may be the positive electrode active material layer in the secondary battery immediately after the secondary battery is manufactured, or may be the one described in the examples described later. The positive electrode active material layer in the secondary battery after charging and discharging. Among them, it is preferable to use a positive electrode active material layer in a secondary battery after charging and discharging.
In addition, it was confirmed separately that the value of the specific surface area of the particles B did not change before and after charging and discharging.

＜ negative electrode ＞
The negative electrode current collector and the negative electrode active material layer are not particularly limited, and known materials can be used.
As the negative electrode current collector, a conductive metal foil can be used. For example, copper, stainless steel, nickel, titanium, or an alloy thereof can be used.
The negative electrode active material layer is formed by, for example, coating a surface of a negative electrode current collector with a negative electrode active material, a binder, and a slurry for a negative electrode obtained by dispersing a conductive additive added as necessary in a solvent.
Examples of the negative electrode active material include metallic lithium, lithium alloys, carbon-based materials (carbon powder, graphite powder, etc.) capable of occluding and releasing lithium ions, and metal oxides, and are preferably selected from the group consisting of these materials One or more of the group.
As the conductive aid, for example, acetylene black, carbon nanotube, or the like can be used.
Examples of the binder include fluororesins such as polyvinylidene fluoride, styrene-butadiene rubber, and carboxymethyl cellulose.

<Dividers>
The material of the separator is not particularly limited, and examples thereof include an olefin-based resin (polyolefin), a microporous polymer film or a non-woven fabric made of a cellulose-based material, and a woven fabric made of glass fiber. Cloth or non-woven cloth, etc. Among these, from the viewpoint of improving the adhesion to the particle layer, an olefin-based resin or a cellulose-based material is preferred, and an olefin-based resin is more preferred.

The olefin-based resin may be a single polyolefin or a mixture of two or more different polyolefins (for example, a mixture of polyethylene and polypropylene), or a copolymer of different olefins. Particularly preferred are polyethylene and polypropylene.

The mass average molecular weight (Mw) of the olefin-based resin is not particularly limited. From the viewpoint of obtaining sufficient mechanical strength, for example, 1 × 10 ^{4 to} 1 × 10 ^{7 is} preferred, and 1 × 10 ^{4 to} 15 is more preferred. × 10 ⁶ , and more preferably 1 × 10 ^{5 to} 5 × 10 ⁶ .
In this specification, "mass average molecular weight" means the polystyrene conversion value measured by the gel permeation chromatography (GPC) method.

The air permeability of the separator followed by the particle layer is preferably 50 to 200 seconds / 100 cc, and more preferably 120 to 180 seconds / 100 cc.
When the air permeability of the separator is greater than or equal to the lower limit of the above range, the permeability and permeability of the electrolytic solution can be sufficiently obtained. If the air permeability of the separator is below the upper limit of the above range, the adhesion strength of the particle layer to the separator is further improved.
The said air permeability can be calculated | required by measuring with a Gurley type densometer (made by Toyo Seiki etc.).

The thickness of the separator is not particularly limited, and from the viewpoint of obtaining sufficient mechanical strength, for example, it can be set to 5 μm to 30 μm.
The vertical × horizontal size of the separator is preferably greater than the size of the electrode current collector, and more preferably one circle larger than the size of the electrode current collector, for example, about 0.1 cm to 5 cm larger.

＜ Non-aqueous electrolyte ＞
Non-aqueous electrolytes known in the field of non-aqueous electrolyte secondary batteries can be used.
It can be a mixture of electrolyte and non-aqueous solvent, that is, a non-aqueous electrolyte, or a mixture of electrolyte and polymer, that is, a polymer solid electrolyte. Polymer solid electrolytes also include those containing a non-aqueous solvent as a plasticizer.
As the electrolyte, those known for use in lithium ion secondary batteries can be applied. Examples include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and lithium bis (fluorosulfonyl) phosphonium imide (LiN ( SO ₂ F) ₂ , LiFSI), known lithium salts such as lithium bis (trifluoromethanesulfonyl) fluorenimide (LiN (SO ₂ CF ₃ ) ₂ , LiTFSI). The electrolyte may be used singly or in combination of two or more kinds.

As the non-aqueous solvent, for example, carbonates, esters, ethers, lactones, nitriles, amidines, amidines, and the like can be used. The non-aqueous solvent may be used singly or in a mixture of two or more kinds.
Specific examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethoxyethane, and dioxolane. Ring (dioxolane), tetrahydrofuran, 2-methyltetrahydrofuran, di Alkane, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethylmethylene, cyclobutane, and γ-butyrolactone.

[Manufacturing method of non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention includes the step of forming a particle layer described in the above [Method for forming a particle layer]. The step of assembling the components constituting the non-aqueous electrolyte secondary battery may employ a known assembling step except that at least one of the positive electrode having the particle layer and the negative electrode having the particle layer is used. The assembly steps are, for example, an operation of laminating a negative electrode, a separator, and a positive electrode, an operation of accommodating a laminate in an exterior body, an operation of filling a non-aqueous electrolyte into an exterior body, and an operation of sealing an exterior body.

＜ Action and effect ＞
In the secondary battery of this embodiment, the ratio of the specific surface area A of the particles contained in the particle layer to the specific surface area B of the particles contained in the positive electrode active material layer, that is, A / B exceeds 0.2 and does not reach 1.5. High and excellent cycle characteristics.

The internal impedance of the non-aqueous electrolyte secondary battery of this embodiment measured by the method described in the examples described later is preferably 90 to 250 mΩ, more preferably 90 to 180 mΩ, and even more preferably 90 to 130 mΩ.
The capacity retention rate measured by the method described in the examples described later is preferably 80 to 95%, more preferably 85 to 95%, and even more preferably 90 to 95%.
The puncture strength measured by the method described in the examples described later is preferably 20 to 100 N, more preferably 40 to 100 N, and even more preferably 60 to 100 N.

As an aspect of the present invention, it is preferable that the capacity retention rate of the secondary battery is 90 to 95%, and the puncture strength is 35 to 80 N, and more preferably, the capacity retention rate is 90 to 95%, and the above The puncture strength is 40 ~ 60 N.
As another aspect of the present invention, the internal resistance of the secondary battery is preferably 90 to 130 mΩ, and the capacity retention rate is 85 to 95%, and more preferably, the internal resistance is 90 to 130 mΩ, and the above Capacity maintenance rate is 90 ~ 95%.

The secondary battery of this embodiment is on the surface of the positive electrode current collector provided with the positive electrode active material layer, and the particle layer exists not only on the positive electrode active material layer but also on the surface of the positive electrode current collector. That is, as shown in FIG. 1, a part of the particle layer 4 exists on the surface of the positive electrode current collector exposed portion 13. There may be a state where the separator does not exist between the opposed negative electrode active material layer 32 and the positive electrode current collector exposed portion 13 due to thermal contraction or positional displacement of the separator. In such a case, the particle layer 4 existing between these can prevent the negative electrode active material layer 32 from coming into contact with the positive electrode current collector exposed portion 13 to cause a short circuit.
The larger the area where the particle layer 4 exists in the surface of the positive electrode current collector exposed portion 13, the better the above-mentioned short-circuit prevention effect. For example, the distance from the edge of the positive electrode active material layer 12 to the edge of the particle layer 4 (indicated by x in the figure) is preferably 1 mm or more, and more preferably 2 mm or more. The upper limit of x is not particularly limited as long as it has the effects described above, and may be, for example, 20 mm or less and 8 mm or less.
The combination of the upper limit value and the lower limit value is preferably 1 mm or more and 20 mm or less, and more preferably 2 mm or more and 8 mm or less.

＜ Modifications ＞
In this embodiment, the particle layer 4 is provided on the surface of the positive electrode 1. However, the same particle layer may be provided on the surface of the negative electrode 3, or the same particle layer may be provided on both surfaces of the surface of the positive electrode 1 and the surface of the negative electrode 3. FIG. 3 shows a secondary battery 10 having a particle layer 4 on the surface of the negative electrode 3 and no particle layer on the surface of the positive electrode 1. FIG. 4 shows a particle battery 4 having both the surface of the positive electrode 1 and the surface of the negative electrode 3 on both surfaces. Secondary battery 10.
The description of the symbols in FIGS. 3 and 4 is the same as the description of the symbols in FIG. 1 described above.
When the surface of the negative electrode has a particle layer, as in the case of the positive electrode, a part of the particle layer may exist on the surface of the exposed portion of the negative electrode current collector. The larger the area where the particle layer exists in the surface of the exposed portion of the negative electrode current collector, the better the above-mentioned short-circuit prevention effect. For example, the distance from the edge of the negative electrode active material layer to the edge of the particle layer (x in FIGS. 3 and 4) is preferably 1 mm or more, and more preferably 2 mm or more. In addition, the upper limit of the distance from the edge of the negative electrode active material layer to the edge of the particle layer is not particularly limited as long as it has the above-mentioned effects, and may be, for example, 20 mm or less and 8 mm or less.
The combination of the upper limit value and the lower limit value is preferably 1 mm or more and 20 mm or less, and more preferably 2 mm or more and 8 mm or less.
The secondary battery 10 of this embodiment is a laminate of one positive electrode 1, two negative electrodes 3, and two separators 2 as shown in FIG. 1, but as long as it has a unit that is laminated in the order of the negative electrode, separator, and positive electrode, Yes, the number of the above units can be arbitrarily changed.
In the secondary battery 10 of this embodiment, the positive electrode current collector 11 has both the positive electrode active material layer 12 and the particle layer 4 on both sides, and the positive electrode current collector 11 may have the positive electrode active material layer 12 and the particles only on one side. Layer 4. When the surface of the negative electrode has a particle layer, a negative electrode active material layer and a particle layer may be provided on both sides of the negative electrode current collector, or a negative electrode active material layer and a particle layer may be provided on only one side of the negative electrode current collector.
In general, in most cases, conductivity is a factor determining reaction rate in a positive electrode, and ion conductivity is a factor determining reaction rate in a negative electrode. Therefore, a particle layer on the surface of the positive electrode is better than a particle layer on the surface of the negative electrode in terms of smoothly promoting the electrochemical reaction of the secondary battery and suppressing the increase in internal resistance.
The shape of the secondary battery is not limited to the shape of the present embodiment, and can be adjusted to various shapes such as a cylindrical shape, a square shape, a coin shape, and a sheet shape.
[Example]

Hereinafter, the present invention will be described in more detail with examples. However, the present invention is not limited to these examples.

[Manufacturing example 1]
90 parts by mass of a solid component containing a positive electrode active material, 5 parts by mass of acetylene black as a conductive aid, 5 parts by mass of polyvinylidene fluoride (# 7200 by KUREHA) as a binder, and NMP (N -Methylpyrrolidone) to obtain a slurry having a solid content adjusted to 45%. This slurry was applied to both sides of an aluminum foil, pre-dried, and then vacuum-dried at 120 ° C. The electrode was press-stamped at 4 kN, and then punched to an electrode size of 40 mm square to produce a positive electrode.
98 parts by mass of a solid component containing a negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, 1 part by mass of carboxymethyl cellulose Na (CMC), and water as a solvent were mixed To obtain a slurry with a solid content adjusted to 50%. This slurry was applied to both sides of a copper foil and vacuum dried at 100 ° C.
The electrode was press-pressed at 2 kN, and then punched to an electrode size of 42 mm square, to produce a negative electrode.

In Production Example 1, the following materials were used.
As the positive electrode active material, olivine-type lithium iron phosphate (specific surface area: 10 m ² / g) was used, and mixed in the following mass ratio.
Positive electrode active material: Adhesive (PVdF): Conductive additive = 90: 5: 5
As the negative electrode active material, graphite was used and mixed in the following mass ratio.
Negative electrode active material: Adhesive (CMC): Adhesive (SBR) = 98: 1: 1
Electrolyte: prepared by dissolving LiPF ₆ as an electrolyte in a solvent prepared by mixing ethyl carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7. Non-aqueous electrolyte.

[Manufacturing example 2]
In Production Example 1, the olivine-type lithium iron phosphate was pulverized by a planetary ball mill for 1 hour, and the specific surface area was adjusted to 13 m ² / g. Other than that, it carried out similarly to the manufacture example 1, and produced the positive electrode.

[Manufacturing example 3]
In Production Example 1, the olivine-type lithium iron phosphate was pulverized by a planetary ball mill for 6 hours, and the specific surface area was adjusted to 15 m ² / g. Other than that, it carried out similarly to the manufacture example 1, and produced the positive electrode.

As the inorganic particles forming the particle layer, the following materials were used.
• Al ₂ O ₃ -1 (specific surface area: 4 m ² / g, average particle size: 0.3 μm)
• Al ₂ O ₃ -2 (specific surface area: 10 m ² / g, average particle size: 0.3 μm)
• Al ₂ O ₃ -3 (specific surface area: 11 m ² / g, average particle size: 0.3 μm)
• Al ₂ O ₃ -4 (specific surface area: 17 m ² / g, average particle size: 0.3 μm)
• Al ₂ O ₃ -5 (specific surface area: 3 m ² / g, average particle size: 0.3 μm)
• Al ₂ O ₃ -6 (specific surface area: 4 m ² / g, average particle size: 1.2 μm)
• Al ₂ O ₃ -7 (specific surface area: 4 m ² / g, average particle size: 2.0 μm)
• Al ₂ O ₃ -8 (specific surface area: 2 m ² / g, average particle size: 0.3 μm)
• TiO ₂ -1 (specific surface area: 4 m ² / g, average particle size: 0.4 μm)
• MgO-1 (specific surface area: 4 m ² / g, average particle size: 0.7 μm)
• Li ₃ PO ₄ -1 (specific surface area: 5 m ² / g, average particle size: 0.3 μm)

[Example 1]
(Formation of particle layer)
100 parts by mass of inorganic particles, 10 parts by mass of polyvinylidene fluoride (KUREHA, # 7200), and 500 parts by mass of N-methylpyrrolidone were uniformly mixed to prepare a coating solution. As the inorganic particles, Al ₂ O ₃ -1 was used.
The obtained coating solution was applied to both sides of the positive electrode obtained in Production Example 1 and dried to form a particle layer on both sides of the positive electrode. The thickness of each particle layer after drying was 5 μm.
As shown in FIG. 1, the particle layer 4 is continuously formed on the positive electrode active material layer 12 of the positive electrode and the positive electrode current collector exposed portion 13 adjacent thereto. The distance (x) from the edge of the positive electrode active material layer 12 to the edge of the particle layer 4 is 5 mm.
The solid content of the binder in the particle layer is 10 parts by mass based on 100 parts by mass of all the particles.

(Manufacturing of batteries)
As the separator, a polyethylene porous film (melting point: 128 ° C) was used.
As shown in FIG. 1, the two negative electrodes obtained in Production Example 1, the one positive electrode on which the particle layer was formed, and the two separators were laminated in the order of a negative electrode, a separator, a positive electrode, a separator and a negative electrode. The terminal lead plates were electrically connected to the positive electrode current collector exposed portion and the negative electrode current collector exposed portion, respectively, and the laminated body was sandwiched by an aluminum laminate film so that the terminal lead plate protruded to the outside. Edge seal. The secondary battery (laminated battery) was manufactured by injecting the electrolytic solution obtained in Production Example 1 from the remaining unsealed one and vacuum-sealing it.

＜ Evaluation ＞
The performance of the secondary battery manufactured as described above was evaluated by the following method. The results are shown in Table 1.
(1) Internal impedance (battery resistance)
In order to evaluate the internal impedance of the secondary battery manufactured as described above, the resistance (battery resistance) of the laminated battery was measured using Battery Hi-Tester BT3562 (product name, manufactured by Hitachi Electric Co., Ltd.) at room temperature (25 ° C). Measurement (measurement unit: mΩ).
(2) Capacity maintenance rate The manufactured secondary battery is placed in a constant temperature bath at 40 ° C, the charge rate is set to 1C, the discharge rate is set to 1C, and the charge and discharge cycle is repeated. The discharge capacity after the 100th cycle was compared with the discharge capacity after the 10th cycle to determine the capacity retention rate.
(3) Puncture strength The puncture strength was measured using a device having a structure as shown in FIG. 2. The puncture strength is a measure of the mechanical strength of a lithium ion secondary battery. Reference numeral 41 in the figure indicates the negative electrode obtained in Production Example 1, 42 indicates the separator used in Example 1, 43 indicates a small piece of nickel, 44 indicates a particle layer, and 45 indicates an aluminum foil used in Production Example 1. The particle layer 44 is formed on the aluminum foil 45 under the same conditions as in Example 1. The symbol 51 is a pressing jig for applying pressure in a direction in which the negative electrode 41 and the aluminum foil 45 (positive electrode) are close to each other, and the pressure can be measured by an autostereograph. The symbol 52 is a receiving plate made of SUS304. The nickel pieces 43 are those described in the JIS C 8714 forced internal short-circuit test. When the pressing jig 51 is lowered and the pressing force of the negative electrode 41 against the aluminum foil 45 (positive electrode) is increased, the nickel pieces 43 penetrate the separator 42 and the particle layer 44 and cause conduction (short circuit).
The test was performed by applying 2 V between the negative electrode 41 and the aluminum foil 45 (positive electrode), while lowering the pressing jig 51, and measuring the resistance value between the positive electrode and the negative electrode. It was judged when the resistance value became 10 Ω or less. Turn on, and use the pressure at this time as the puncture strength of the particle layer.
(4) Measurement of specific surface area (i) Partition of sample • Partition of particle layer Confirm that the battery is discharged after the first charge and discharge of the manufactured secondary battery, and the OCV (Open Circuit Voltage) changes. 1 V or less. The portion of the particle layer formed between the positive electrode active material layer and the separator that is not overlapped with the positive electrode active material layer and the separator was taken out from the positive electrode. For the portion of the particle layer that overlaps with the positive electrode active material layer, carefully cut only the portion of the particle layer with a spatula to take out the particles in the particle layer.
• The separation of the positive electrode active material layer was confirmed after the first charge and discharge of the manufactured secondary battery, the battery was discharged, and the OCV became 1 V or less. A sample including the positive electrode active material layer was taken out from the positive electrode, and a particle layer formed between the positive electrode active material and the separator was removed by a spatula to obtain particles in the positive electrode active material layer.
(Ii) Pretreatment of the sample The particles in the particle layer taken out above or the particles in the positive electrode active material layer were immersed in NMP at 60 ° C. Next, ultrasonic cleaning was performed for 10 minutes to filter the solid components, and then vacuum drying was performed at 130 ° C for 4 hours to remove 90% of NMP. After performing the above-mentioned washing step using NMP three times, vacuum drying was performed at 130 ° C for 4 hours.
• BET gas adsorption method uses 1 g of the particles in the particle layer after the vacuum drying or the particles in the positive electrode active material layer, and measures the specific surface area with an N ₂ adsorption device (product name BELSORP-miniII manufactured by Microtrac BEL). .
(5) Measurement of average particle diameter of inorganic particles The average particle diameter of inorganic particles was measured using a laser diffraction type particle size distribution measuring device (Partica LA-960 manufactured by Horiba, Ltd.) using NMP as a solvent. The particle diameter (that is, the volume average particle diameter) when the volume reached 50% from the small diameter side in the obtained particle size distribution was taken as the average particle diameter of the inorganic particles. In addition, it was confirmed that the average particle diameter of the inorganic particles did not change from the raw material stage after the secondary battery manufacturing and after the charge and discharge described above.
The results are shown in Table 1.

[Examples 2 to 16, Comparative Examples 1 to 2]
Production and evaluation of the secondary battery were performed in the same manner as in Example 1 except that the inorganic particles and the positive electrode shown in Table 1 were used, and the particle layer on the positive electrode surface was set to the film thickness shown in Table 1 on both sides. The evaluation results are shown in Table 1.

[Table 1]

As shown in the results of Table 1, compared with Comparative Example 1 in which the ratio of the specific surface area A of the particles contained in the particle layer to the specific surface area B of the particles contained in the positive electrode active material layer, that is, A / B was 1.5 or more, The secondary batteries of Examples 1 to 16 were high in capacity retention rate and puncture strength. In addition, compared with Comparative Example 2 in which the A / B is 0.2 or less, the secondary batteries of Examples 1 to 16 not only have a high capacity retention rate, high puncture strength, but also have low internal resistance.

1‧‧‧ positive

2‧‧‧ divider

3‧‧‧ negative

4‧‧‧ particle layer

5‧‧‧ Outer body

10‧‧‧ secondary battery

11‧‧‧Positive collector

12‧‧‧ cathode active material layer

13‧‧‧Positive electrode current collector exposed portion

20‧‧‧Laminated body

31‧‧‧Negative current collector

32‧‧‧ Negative electrode active material layer

33‧‧‧ Negative electrode current collector exposed portion

41‧‧‧ Negative

42‧‧‧ divider

43‧‧‧ Nickel Chips

44‧‧‧ particle layer

45‧‧‧ aluminum foil

51‧‧‧Pressing fixture

52‧‧‧Accepting board

FIG. 1 is a schematic cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a method for measuring puncture strength.

3 is a schematic cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

Claims (9)

A non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer on a surface of the positive electrode current collector, a negative electrode current collector and a negative electrode activity on a surface of the negative electrode current collector. A negative electrode of a material layer, a non-aqueous electrolyte containing lithium ions, a separator between the positive electrode and the negative electrode, and a particle layer on the surface of one or both of the positive electrode and the negative electrode, The ratio of the specific surface area A of the particles contained in the particle layer to the specific surface area B of the particles contained in the positive electrode active material layer, that is, A / B exceeds 0.2 and does not reach 1.5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the particle layer contains inorganic particles. The non-aqueous electrolyte secondary battery according to claim 2, wherein the inorganic particles are at least one selected from the group consisting of magnesium oxide particles, titanium oxide particles, aluminum oxide particles, silicon oxide particles, and lithium phosphate particles. . The non-aqueous electrolyte secondary battery according to claim 2 or 3, wherein the average particle diameter of the inorganic particles is 1.3 μm or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein at least a part of the particle layer is present on a surface of the positive electrode current collector. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein at least a part of the particle layer is present on a surface of the negative electrode current collector. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein a thickness of the particle layer is 2 to 20 μm. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the particle layer is located on a surface of the positive electrode. A method for manufacturing a non-aqueous electrolyte secondary battery, which is the method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, It has a step of applying a coating liquid containing particles and a binder on the surface of one or both of the positive electrode and the negative electrode, and drying the coating liquid. The ratio of the specific surface area A ′ of the particles contained in the coating solution to the specific surface area B of the particles contained in the positive electrode active material layer, that is, A ′ / B is more than 0.2 and less than 1.5.