JP2021153022A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a non-aqueous electrolyte secondary battery in which short circuit is suppressed while maintaining high energy density and discharge rate characteristics.SOLUTION: In a non-aqueous electrolyte secondary battery, a positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and a negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector are arranged such that the positive electrode active material layer and the negative electrode active material layer face each other via a non-woven separator. In particle size distribution of the positive electrode active material layer, D50 is 0.5 μm or more and 1.5 μm or less, and the peel strength of the positive electrode active material layer measured by the 180° method is 1.0 N/cm or more and 10.0 N/cm or less.SELECTED DRAWING: Figure 1

Description

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

Lithium-ion secondary batteries are characterized by higher energy density and electromotive force than lead-acid batteries and nickel-hydrogen batteries, and are therefore used in a wide variety of applications from mobile devices to vehicles and aircraft. Most of these lithium ion secondary batteries use a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent as an electrolyte. In a lithium ion secondary battery using such a non-aqueous electrolyte, a positive electrode having a positive electrode active material layer provided on a positive electrode current collector and a negative electrode having a negative electrode active material layer provided on a negative electrode current collector are provided. It has a structure in which a laminated body laminated via a separator is housed in an outer body, filled with a non-aqueous electrolyte solution, and sealed.

In a lithium ion secondary battery, lithium ions are released from the positive electrode and moved into the negative electrode during charging, and lithium ions are released from the negative electrode and moved into the positive electrode during discharging. Therefore, the separator is required to have ion permeability such as lithium ion. Therefore, as a separator for a lithium ion secondary battery using a non-aqueous electrolyte, a porous resin film, which is a material having insulating properties and ion permeability, is used. For example, in Patent Document 1 and the like, a polyolefin microporous membrane having an average pore diameter of 0.05 to 0.5 μm determined by a mercury press-fitting method is used as a separator for a non-aqueous secondary battery, and the polyolefin microporous membrane is used. A configuration has been proposed in which a porous layer made of a heat-resistant resin is provided on the surface.

However, in a conventional non-aqueous electrolyte secondary battery, if the particle size of the positive electrode active material is large in relation to the thickness of the separator, the positive electrode active material may penetrate the separator during charging and discharging and short-circuit to the negative electrode side. Are known. Further, even if the particle size of the positive electrode active material is large enough not to penetrate the separator, a plurality of positive electrode active materials form large-sized aggregates, and the aggregates penetrate the separator and short-circuit to the negative electrode side. There is also the risk of doing so. In particular, when a separator having a high porosity such as a non-woven fabric separator is used, the risk of such a short circuit is considered to be high.

Japanese Unexamined Patent Publication No. 2011-23162

In a non-aqueous electrolyte secondary battery provided with a separator having a high porosity such as a non-woven fabric separator,
If the particle size of the positive electrode active material is large in relation to the thickness of the separator, the separator may be pierced, and as a result, a short circuit may occur to the negative electrode side. In particular, when a separator such as a non-woven fabric separator having a high porosity is used, there is a problem that the risk is even higher. It is conceivable to reduce the thickness of the positive electrode active material layer in order to solve such a problem, but in that case, another problem such as a decrease in energy density occurs.

Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery in which short circuits are suppressed while maintaining high energy density and discharge rate characteristics.

As a result of diligent studies to solve the above problems, the present inventors have combined a positive electrode active material in which D50 in the particle size distribution satisfies a specific numerical range and a positive electrode active material layer in which the peel strength satisfies a specific numerical range. It was found that a non-aqueous electrolyte secondary battery in which short circuits are suppressed can be obtained while maintaining high energy density and discharge rate characteristics. The present invention is based on such findings. That is, the gist of the present invention is as follows.

[1] A positive electrode provided with a positive electrode active material layer provided on at least one surface of the positive electrode current collector and the positive electrode current collector, and provided on at least one surface of the negative electrode current collector and the negative electrode current collector. A non-aqueous electrolyte secondary battery in which a negative electrode provided with a negative electrode active material layer is arranged such that the positive electrode active material layer and the negative electrode active material layer face each other via a non-woven separator.
In the particle size distribution of the positive electrode active material, D50 is 0.5 μm or more and 1.5 μm or less.
A non-aqueous electrolyte secondary battery characterized in that the peel strength of the positive electrode active material layer measured by the 180 ° method is 1.0 N / cm or more and 10.0 N / cm or less.
[2] The non-aqueous electrolyte secondary battery according to [1], wherein the peel strength of the positive electrode active material layer is 2.0 N / cm or more and 4.0 N / cm or less.
[3] The non-aqueous electrolyte secondary battery according to [1] or [2], wherein the positive electrode active material contains lithium iron phosphate.
[4] The non-aqueous electrolyte secondary battery according to any one of [1] to [3], wherein the density of the positive electrode active material layer is 1.8 g / cc or more and 2.5 g / cc.
[5] The non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the non-woven fabric separator has a thickness of 8 μm or more and 30 μm or less.
[6] The non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein the positive electrode active material layer contains a binder resin.
[7] The non-aqueous electrolyte secondary battery according to [6], wherein the content of the binder resin is 0.5% by mass or more and 1.5% by mass with respect to the total mass of the positive electrode active material layer.

According to the present invention, a positive electrode active material in which D50 in the particle size distribution satisfies a specific numerical range and a positive electrode active material layer in which the peel strength satisfies a specific numerical range are used in combination to achieve high energy density and discharge rate characteristics. It is possible to realize a non-aqueous electrolyte secondary battery in which short circuits are suppressed while maintaining the above.

FIG. 6 is a schematic cross-sectional view schematically showing an embodiment of the non-aqueous electrolyte secondary battery of the present invention. The figure which schematically showed the peeling test of the positive electrode active material layer of the non-aqueous electrolyte secondary battery in this invention.

The non-aqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing an embodiment of the non-aqueous electrolyte secondary battery of the present invention. In the non-aqueous electrolyte secondary battery 1 according to the present invention, one plate-shaped positive electrode 10, two plate-shaped negative electrodes 20, and two non-woven electrode separators 30 are composed of a negative electrode / non-woven electrode separator / positive electrode / non-woven electrode separator. The laminated body laminated in the order of / negative electrode is housed in the outer body 40, and the non-aqueous electrolyte (not shown) is filled in the outer body 40 and sealed. In the present embodiment, the positive electrode 10, the negative electrode 20, and the non-woven fabric separator 30 are all rectangular in a plan view.

The positive electrode 10 of the non-aqueous electrolyte secondary battery 1 includes a plate-shaped positive electrode current collector 11 and positive electrode active material layers 12 provided on both sides thereof. Although not shown, when the positive electrode and the negative electrode are paired, the positive electrode active material layer 12 may be provided on at least one surface of the positive electrode current collector 11 on the opposite negative electrode side. At the edge of one end of the positive electrode current collector 11, a positive electrode current collector exposed portion 13 in which the positive electrode active material layer 12 does not exist is provided. A leader line (not shown) is provided at an arbitrary portion of the exposed portion 13.

The negative electrode 20 of the non-aqueous electrolyte secondary battery 1 includes a plate-shaped negative electrode current collector 21 and negative electrode active material layers 22 provided on both sides thereof. Although not shown, when the positive electrode and the negative electrode are paired, the negative electrode active material layer 22 may be provided on at least one surface of the negative electrode current collector 21 on the opposite positive electrode side. A negative electrode current collector exposed portion 23 in which the negative electrode active material layer 22 does not exist is provided at the edge of one end of the negative electrode current collector 21. A leader line (not shown) is provided at an arbitrary portion of the exposed portion 23.

In addition to the structure shown in FIG. 1, the non-aqueous electrolyte secondary battery according to the present invention may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated. In this case, the negative electrode and the positive electrode may be provided alternately along the stacking direction. Further, the non-woven fabric separator may be arranged between each negative electrode and each positive electrode.

The non-aqueous electrolyte secondary battery according to the present invention is characterized in that D50 in the particle size distribution of the positive electrode active material constituting the positive electrode active material layer 12 is 0.5 μm or more and 1.5 μm or less. D50 in the particle size distribution of the positive electrode active material means the particle size when the cumulative volume is 50% in the particle size distribution (particle size distribution) based on the volume of the positive electrode active material. In the non-aqueous electrolyte secondary battery according to the present invention, even when the positive electrode active material D50 constituting the positive electrode active material layer 12 satisfies the above numerical range, the positive electrode active material is easily penetrated even when combined with a non-woven separator. It is possible to prevent the positive electrode active material from penetrating the non-woven sheet separator 30 and short-circuiting. The particle size distribution of the positive electrode active material on a volume basis can be measured using a particle size (particle size) analyzer that uses the laser diffraction / scattering method as a principle. The particle size of the positive electrode active substance can be appropriately adjusted depending on the crushing conditions when the raw material is crushed (crushed). When the crushing time is short, the particle size of the object to be crushed tends to be large, and when the crushing time is long, the particle size tends to be small.

The range of D50 of the positive electrode active material is preferably 0.6 μm or more and 1.4 μm or less, more preferably 0.7 μm or more and 1.3 μm or less, and even more preferably 1.0 μm.

The non-aqueous electrolyte secondary battery according to the present invention is characterized in that the peel strength of the positive electrode active material layer 12 is 1.0 N / cm or more and 10.0 N / cm or less. The peel strength of the positive electrode active material layer 12 means the strength to resist peeling from the positive electrode current collector 11 when the positive electrode active material layer 12 is peeled in the 180 ° direction using an autograph (180 ° method). do. In the non-aqueous electrolyte secondary battery according to the present invention, the positive electrode active material is a non-woven electrode even when combined with a non-woven separator in which the positive electrode active material easily penetrates because the peel strength of the positive electrode active material layer 12 satisfies the above numerical range. It is possible to prevent short-circuiting through the separator 30. The peel strength of the positive electrode active material layer 12 can be measured by the following method using an autograph. A specific method for measuring the peel strength of the positive electrode active material layer will be described with reference to FIG.
First, a double-sided tape 50 having a length of 25 mm and a width of 120 mm is prepared. The release paper on one side of the prepared double-sided tape 50 is peeled off to expose the glue surface. The double-sided tape 50 is bent so that the glue surface and the glue surface adhere to each other at a portion about 10 cm from the end in the lateral direction (hereinafter, referred to as "bent end").
Next, the positive electrode active material layer 60 and the double-sided tape 50 are attached so that the entire surface of the glue surface of the double-sided tape 50 is in contact with the positive electrode active material layer to obtain a composite.
Next, the composite is cut out along the outer edge of the double-sided tape 50, and the crimping roller is reciprocated twice in the lateral direction of the cut-out composite to crimp the double-sided tape 50 constituting the composite and the positive electrode active material layer 60.
Next, the surface of the composite on the double-sided tape 50 side is brought into contact with the stainless plate 70, and the end of the composite on the side different from the bent end is fixed to the stainless plate 70 with mending tape. At this time, the composite is arranged so that the end of the composite on the side different from the bent end is located at a position of about 5 mm from the end of the stainless steel plate, and one end of the mending tape having a length of about 30 mm is composite. Attach it so that it is 5 mm from the above end of the body, and weave another end of the mending tape (the remaining 20 mm) into the back side of the stainless steel plate 70 (the side that is not in contact with the complex) and attach it. Fix.
Next, the positive electrode active material layer 60 is slowly peeled off from the double-sided tape 50 in parallel with the lateral direction of the double-sided tape from the bent end side of the composite, and the end portion of the positive electrode active material layer 60 on the bent end side (hereinafter, hereinafter, Slowly peel off until the "peeling edge") protrudes from the stainless steel plate 70.
Next, the stainless plate 70 to which the composite is fixed is installed on a tensile tester 80 (EZ-LX, manufactured by Shimadzu Corporation), the bent end of the double-sided tape 50 is fixed, and the peeled end of the positive electrode active material layer 60 is fixed. The peel strength is measured by pulling with a stroke of 7 cm at a tensile speed of 60 mm / min and a test force of 50,000 mN in the direction opposite to the bent end (180 ° direction with respect to the bent end).
The average value of the peel strength at a stroke of 20 to 50 mm at this time is taken as the peel strength of the positive electrode active material.

The range of peel strength of the positive electrode active material layer 12 is preferably 2.0 N / cm or more and 4.5 N / cm or less, more preferably 2.0 N / cm or more and 4.0 N / cm or less, and even more preferably 3.0 N. / Cm.

<Non-woven separator>
The fiber material that can be used for the non-woven fabric separator is not particularly limited as long as it is an insulating material, and either an inorganic fiber or an organic fiber can be used. Examples of inorganic fibers include microglass (small diameter glass fiber) and rock wool. Examples of organic fibers include cellulose esters such as cellulose, carboxymethyl cellulose and cellulose acetate, cellulose fiber materials such as lignocellulose, neutral mucopolysaccharide fiber materials such as chitin and chitosan, and aliphatic nylons. Examples thereof include polyamides such as aromatic nylon (aramid), polyolefins such as polyethylene and polypropylene, and synthetic resin-based fiber materials such as vinylon, polyester, polyimide, polyamideimide, and vinylidene fluoride. Among these, since it is easy to prepare and obtain a fiber material of a preferable size and it is easy to obtain a fiber material that is well dispersed in a dispersion medium by a modification treatment such as hydrophobicization, cellulose, carboxymethyl cellulose, cellulose acetate, etc. Cellulose-based fibers such as cellulose ester and lignocellulosic can be preferably used. Further, the cellulosic fiber is advantageous from the viewpoint of widening the selectivity of the electrolytic solution and heat resistance as compared with the conventional porous separator made of a polyolefin resin film.

The non-woven fabric is a cloth obtained by joining or entwining fibers with each other using a mechanical, chemical, solvent or the like without weaving or knitting the above-mentioned fiber materials. The non-woven fabric is a conventionally known method such as a dry method, a wet method, a thermal bond method, a chemical bond method, a needle punch method, a spunlace method (water flow entanglement method), a stitch bond method, a steam jet method, a spunbond method, and a melt blow method. Can be manufactured by. By appropriately adjusting the shape of the fiber material to be used, such as the fiber length and the fiber diameter, and the entanglement conditions when producing the non-woven fabric, the non-woven fabric separator can be obtained so as to satisfy the above-mentioned Garley value.

In the non-aqueous electrolyte secondary battery of the present invention, an insulating layer may be provided on either or both of the separator surfaces in order to effectively prevent a short circuit between the positive electrode and the negative electrode. The insulating layer is preferably a layer having a porous structure formed by binding insulating fine particles with a binder resin for an insulating layer. However, by providing the insulating layer having the porous structure as described above on the surface of the non-woven fabric separator, the pore volume and the porosity of the non-woven fabric separator as a whole are greatly affected. Therefore, in the present invention, it is important to adjust the void amount ratios X and Z so as to be within the above ranges even when the insulating layer is provided on the surface of the non-woven fabric separator.

The thickness of the non-woven fabric separator is preferably 8 μm or more and 30 μm or less, and more preferably 12 μm or more and 24 μm or less from the viewpoint of mechanical strength.

The non-woven fabric separator may contain various plasticizers, antioxidants, flame retardants, and the fiber surface may be coated with a metal oxide or the like. For example, the antioxidants include hindered phenolic antioxidants, monophenolic antioxidants, bisphenolic antioxidants, and phenolic antioxidants such as polyphenolic antioxidants, hindered amines, and phosphorus. Examples include phenol-based antioxidants, sulfur-based antioxidants, benzotriazole-based antioxidants, benzophenone-based antioxidants, triazine-based antioxidants, salicylate-based antioxidants, and phenol-based antioxidants and phosphorus-based antioxidants. Antioxidants can be preferably used.

<Positive electrode>
The positive electrode constituting the non-aqueous electrolyte secondary battery according to the present invention has a structure in which a positive electrode active material layer is provided on a positive electrode current collector, and includes, for example, a positive electrode active material, a binder resin, a conductive auxiliary agent, and a solvent. It can be prepared by preparing a composition, applying it on a positive electrode current collector, and drying it.

The positive electrode active material is not particularly limited as long as it is a lithium transition metal compound, but is a layered rock salt type compound represented by lithium cobalt oxide, _{an olivine type compound represented by lithium iron phosphate (LiFePO 4} ), and a spinel type manganese. Lithium oxide is more preferred.

The layered rock salt type compound means a compound having a layered rock salt type structure, and is not particularly limited, and is _{a lithium nickel composite oxide represented by LiMeO 2} (Me is a transition metal) (for example, LiNiO ₂ ). , lithium-cobalt composite oxide (e.g., LiCoO _2), lithium nickel cobalt composite oxide (e.g., _{LiNi 1-y Co y O 2} ), lithium-nickel-cobalt-manganese composite oxide (e.g., _{LiNi x Co y Mn 1-y} -z O _2. However, x + y + z = 1), for example _{, a solid solution of LiMnO 3} and Li ₂ MnO ₃ and LixMeO ₂ in excess of lithium can be used, but since structural deterioration due to long-term use is smaller, LiCoO _{2 can be used. , LiNi 0.8 Co 0.15 Al 0.05 O} 2, LiNi x Co y Mn 1-y-z O 2 ( where, x + y + z = 1 ) are preferred.

The olivine-type compound means a compound having an olivine-type structure, and is not particularly limited, and _{LiFePO 4} , LiMn _1-x Fe _x PO ₄ , _{represented by LiMePO 4} (Me is a transition metal), LiMnPO ₄ , LiCoPO ₄ , LiNiPO _{4, and the} like can be used.

_{In the present invention, LiFePO 4} (lithium iron phosphate) can be preferably used as the positive electrode active material from the viewpoint of battery characteristics such as durability and charge / discharge. Further, as the positive electrode active material, a material having a granular form in which D50 is in the above-mentioned numerical range is used. The positive electrode active material D50 can be appropriately adjusted depending on the crushing conditions when crushing (crushing) the raw material. When the crushing time is short, the particle size of the object to be crushed tends to be large, and when the crushing time is long, the particle size tends to be small.

When the granular form of lithium iron phosphate is used, at least a part of the particle surface is coated with an organic substance such as polyethylene glycol, an inorganic substance such as aluminum oxide, magnesium oxide, zirconium oxide or titanium oxide, or a carbon material. May be. In particular, lithium iron phosphate particles in which at least a part of the particle surface is coated with carbon can be preferably used. The amount of carbon coated is preferably 4% or more and 8% or less with respect to the mass of the lithium iron phosphate particles.

Examples of the conductive auxiliary agent include carbon materials such as graphite, graphene, hard carbon, Ketjen black, and acetylene black.

Examples of the binder resin include polyacrylic acid, lithium polyacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene butadiene rubber, polyvinyl alcohol, polyvinyl acetal, polyethylene oxide, polyethylene glycol, carboxymethyl cellulose, and poly. Acrylic nitrile, polyimide and the like can be mentioned. The content of the binder resin is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 0.5% by mass or more and 1.5% by mass or less with respect to the total mass of the positive electrode active material layer.

The solvent is preferably a non-aqueous solvent, for example, alcohols such as methanol, ethanol, 1-propanol and 2-propanol; chain or cyclic amides such as N-methylpyrrolidone, N, N-dimethylformamide; and ketones such as acetone. Can be mentioned.

Examples of the material constituting the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel.

The above-mentioned positive electrode active material, binder resin, conductive auxiliary agent and solvent may be used alone or in combination of two or more.

In the non-aqueous electrolyte secondary battery according to the present invention, the positive electrode active material layer preferably contains a positive electrode active material and a binder resin, and particularly preferably contains a positive electrode active material and polyvinylidene fluoride.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% or more and 99% or less, and more preferably 60% or more and 98% or less on a mass basis with respect to the entire positive electrode active material layer.

The positive electrode active material layer produced as described above preferably has a density of 1.8 g / cc or more and 2.5 g / cc or less from the viewpoint of increasing the electrode density.

The thickness of the positive electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, and can be appropriately set from the viewpoint of maintaining the energy density and the like.

The porosity (%) of the positive electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 20% or more and 60% or less. The porosity of the positive electrode active material layer can be measured by a mercury injection method using a mercury injection porosimeter. Specifically, a test piece obtained by cutting out each layer to a predetermined size is prepared, the pore distribution of the test piece is measured by the mercury intrusion method using a mercury intrusion porosimeter, and the pore diameter is calculated from the pressure value and the pressure amount is used. The porosity can be calculated by obtaining the pore volume. Specifically, it can be calculated as follows.
First, the sample to be measured is constantly dried at a temperature of 110 ° C. for 12 hours. Subsequently, the pore distribution in the pore diameter range of about 0.0036 μm to 200 μm is measured using a measuring device such as Autopore IV9520 (manufactured by micromerits). The pore diameter is determined by the Washburn formula:
PD = -4σcosθ
(In the formula, P is the pressure, D is the pore diameter, σ is the surface tension of mercury (480 days / cm), and θ is the contact angle between mercury and the sample (140 °).)
It can be calculated from.
The porosity (%) can be calculated by dividing the obtained pore volume by the volume specified by the outer dimensions of the sample (however, the current collector shall have no voids and shall be calculated from the volume of the sample. Calculate by excluding in advance.).

<Negative electrode>
The negative electrode constituting the non-aqueous electrolyte secondary battery according to the present invention has a structure in which a negative electrode active material layer is provided on the negative electrode current collector, and includes, for example, a negative electrode active material, a binder resin, a conductive auxiliary agent, and a solvent. It can be prepared by preparing a composition, applying it on a positive electrode current collector, and drying it.

Examples of the negative electrode active material and the conductive auxiliary agent include carbon materials such as graphite, graphene, hard carbon, Ketjen black, and acetylene black.

Examples of the binder resin, the conductive auxiliary agent, the solvent, and the current collector are the same as those of the above-mentioned positive electrode. As the negative electrode active material, the conductive auxiliary agent, the binder resin, and the solvent, one kind may be used alone, or two or more kinds may be used in combination.

The content of the negative electrode active material in the negative electrode active material layer is preferably 50% or more and 99% or less, and more preferably 60% or more and 98% or less on a mass basis with respect to the entire negative electrode active material layer.

The negative electrode active material layer produced as described above has a density of preferably 1.3 g / cc or more and 1.8 g / cc or less, and more preferably 1.5 g / cc or more and 1.7 g / cc or less.

The thickness of the negative electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, and can be appropriately set.

The porosity (%) of the negative electrode active material layer is not particularly limited as long as the effects of the present invention are exhibited, but is preferably 25% or more and 60% or less, and more preferably 30% or more and 50% or less. The porosity here means a value measured by a mercury injection method using a mercury injection porosimeter, as in the case of the positive electrode active material layer.

The non-aqueous electrolyte secondary battery according to the present invention may include an insulating layer on the negative electrode active material layer or the positive electrode active material layer. The insulating layer effectively prevents short circuits between the positive and negative electrodes. The insulating layer is preferably a layer having a porous structure containing insulating fine particles and a binder resin for an insulating layer, and the insulating fine particles are bound by a binder resin for an insulating layer.

The insulating fine particles are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles. Specific organic particles include, for example, crosslinked polymethyl methacrylate, crosslinked styrene-acrylic acid copolymer, crosslinked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamide-2-methylpropanesulfonate), and the like. Examples thereof include particles composed of organic compounds such as polyacetal resin, epoxy resin, polyester resin, phenol resin, and melamine resin. Inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), potassium fluoride, and foot. Examples thereof include particles composed of inorganic compounds such as lithium pentoxide, clay, zeolite, and calcium carbonate. Further, the inorganic particles may be particles composed of known composite oxides such as niobium-tantalum composite oxide and magnesium-tantalum composite oxide. One type of insulating fine particles may be used alone, or a plurality of types may be used in combination.

The content of the insulating fine particles contained in the insulating layer is not particularly limited as long as the effect of the present invention is exhibited, but is generally 15 to 95% by mass, more preferably 40 to 90% by mass, based on the total amount of the insulating layer. Is. When the content of the insulating fine particles is within the above range, the insulating layer can form a uniform porous structure and is provided with appropriate insulating properties.

As the binder resin for the insulating layer, the same type as the binder resin that can be used for the positive electrode or the negative electrode described above can be used. The content of the binder resin for the insulating layer in the insulating layer is preferably 5% or more and 50% or less on a mass basis with respect to the total amount of the insulating layer.

The thickness of the insulating layer is not particularly limited as long as the effects of the present invention are exhibited, but it is preferably about 1 μm or more and 10 μm or less.

In the non-aqueous electrolyte secondary battery according to the present invention, for example, a laminate in which a non-woven fabric separator is arranged between a positive electrode and a negative electrode is prepared, and the electrode laminate is enclosed in an exterior body (housing) such as an aluminum laminate bag. It can be produced by injecting a non-aqueous electrolyte.

The non-aqueous electrolyte secondary battery according to the present invention has been described above, but the present invention is not limited thereto. The non-aqueous electrolyte secondary battery according to the present invention may have any other configuration or may be replaced with any configuration that exhibits the same function. Further, in addition to the lithium ion secondary battery, it can also be applied to a secondary battery such as a silver ion secondary battery.

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

[Example 1]
<Preparation of positive electrode>
A solid component containing 100 parts by mass of a positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, 5 parts by mass of polyvinylidene fluoride as a binder, and NMP as a solvent are mixed to obtain a solid content of 45%. A prepared slurry was obtained. This slurry was applied to an aluminum foil, pre-dried, and then vacuum dried at 120 ° C. The electrode was pressure-pressed at 4 kN and further punched to a 40 mm square electrode size to prepare a positive electrode. The prepared positive electrodes were used as the positive electrodes of Examples 1 to 3, Comparative Examples 1 to 3 and 5.
Lithium iron phosphate was used as the positive electrode active material and mixed in the following mass ratio.
Positive electrode active material: Binder (PVDF): Conductive aid = 94: 1: 5
The thickness of the positive electrode active material layer was 58.5 μm. The porosity was measured with a mercury polysimeter and found to be 41.6%. The peel strength measured under the following conditions was 3N / 10 mm.
The D50 of the positive electrode active material was 1.0 μm, and the density was 2.1 g / cc.
The peel strength of the positive electrode active material layer was measured by the following method.
First, a double-sided tape having a length of 25 mm and a width of 120 mm was prepared. The release paper on one side of the prepared double-sided tape was peeled off to expose the glue side. The double-sided tape was bent so that the glue surface and the glue surface adhered to each other at a portion about 10 cm from the end in the lateral direction (hereinafter referred to as "bent end").
Next, the positive electrode and the double-sided tape were attached so that the entire surface of the glue surface of the double-sided tape was in contact with the positive electrode to obtain a composite.
Next, the composite was cut out along the outer edge of the double-sided tape, and the crimping roller was reciprocated twice in the lateral direction of the cut out composite to crimp the double-sided tape constituting the composite and the positive electrode.
Next, the surface of the composite on the double-sided tape side was brought into contact with the stainless plate, and the end of the composite on the side different from the bent end was fixed to the stainless plate with mending tape. At this time, the composite is arranged so that the end of the composite on the side different from the bent end is located at a position of about 5 mm from the end of the stainless steel plate, and one end of the mending tape having a length of about 30 mm is composite. Stick it so that it is 5 mm from the above end of the body, weave another end of the mending tape (the remaining 20 mm) on the back side of the stainless steel plate (the side that is not in contact with the complex), stick it and fix it. bottom.
Next, the positive electrode is slowly peeled from the double-sided tape from the bent end side of the complex in parallel with the lateral direction of the double-sided tape, and the end of the positive electrode on the bent end side (hereinafter referred to as "peeled end") is a stainless steel plate. It was slowly peeled off until it protruded from the surface.
Next, a stainless steel plate to which the composite is fixed is installed in a tensile tester (EZ-LX, manufactured by Shimadzu Corporation), the bent end of the double-sided tape is fixed, and the peeled end of the positive electrode is in the direction opposite to the bent end ( The peel strength was measured by pulling at a tensile speed of 60 mm / min, a test force of 50,000 mN, and a stroke of 7 cm in the direction of 180 ° with respect to the bent end.
The average value of the peel strength at a stroke of 20 to 50 mm at this time was taken as the peel strength of the positive electrode active material.

<Manufacturing of negative electrode>
100 parts by mass of a solid component containing a negative electrode active material, 1.5 parts by mass of styrene-butadiene rubber as a binder, 1.5 parts by mass of carboxymethyl cellulose Na as a thickener, and water as a solvent are mixed and solid. A slurry adjusted to a minute of 50% was obtained. This slurry was applied to a copper foil and vacuum dried at 100 ° C. The electrode was pressure-pressed at 2 kN and further punched to a 42 mm square electrode size to prepare a negative electrode.
Graphite was used as the negative electrode active material and mixed at the following mass ratio.
Negative electrode active material: Binder (CMC): Binder (SBR) = 98: 1: 1
The thickness of the negative electrode active material layer was 39 μm. The porosity was measured with a mercury polysimeter and found to be 36.4%.

<Preparation of separator>
As the non-woven fabric separator, a cellulose non-woven fabric having a thickness of 15 μm was used.

<Manufacturing of non-aqueous electrolyte secondary battery>
As shown in FIG. 1, the two negative electrodes, one positive electrode, and two non-woven fabric separators described above were laminated in the order of negative electrode / separator / positive electrode / separator / negative electrode. At this time, the separator and the positive electrode were laminated in advance and thermocompression bonded at 90 ° C. for 1 Mpa for 2 minutes to bond the separator to the surface of the positive electrode active material layer. Next, the terminal tabs are electrically connected to each of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion, and the laminate is sandwiched between aluminum laminate films so that the terminal tabs project to the outside. The sides were sealed by laminating.
Subsequently, from one side left unsealed, a mixed solution containing 2% by weight of vinylene carbonate, 50% by weight of ethylmethyl carbonate, and 2% by weight of fluorinated ethylene carbonate was mixed with 1 mol / liter _{of LiPF 6 as an electrolyte.} A secondary battery (laminate cell) was manufactured by injecting a non-aqueous electrolyte solution dissolved in such a manner and vacuum-sealing.

[Example 2]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a cellulose non-woven fabric having a thickness of 12 μm was used as the non-woven fabric separator.

[Example 3]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a cellulose non-woven fabric having a thickness of 10 μm was used as the non-woven fabric separator.

[Comparative Example 1]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a polyethylene separator having a thickness of 12 μm was used instead of the non-woven fabric separator.

[Comparative Example 2]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the particle size D50 of the positive electrode active material was adjusted to 10.0 μm (peeling strength 4.7 N / 10 mm).

[Comparative Example 3]
A non-woven fabric having a thickness of 20 μm was used instead of the non-woven fabric separator, and the particle size D50 of the positive electrode active material was adjusted to 10.0 μm (peeling strength 4.7 N / 10 mm) in the same manner as in Example 1. An electrolyte secondary battery was manufactured.

[Comparative Example 4]
The binder resin content is adjusted to 0.3% by mass (peeling strength 0.4 N / 10 mm) with respect to the total mass of the positive electrode active material layer, and the positive electrode active material content is adjusted with respect to the total mass of the positive electrode active material layer. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the content was adjusted to 94.7% by mass.

[Comparative Example 5]
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that the density of the positive electrode active material layer was adjusted to 1.8 g / cc (peeling strength 1.6 N / 10 mm).

<Rate discharge test>
Each of the obtained non-aqueous electrolyte secondary batteries (cells) of Examples and Comparative Examples was subjected to a rate discharge test according to the following procedure.
When the non-aqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 5 were produced, the area of the laminate was adjusted to produce cells so that the rated capacity was 1 Ah.
First, the obtained cell is charged at a constant current of 0.2 C rate (that is, 200 mA) at a constant current of 3.6 V, and then at a constant voltage of 0.05 C rate (that is, 20 mA). ) Was charged.
Next, discharge for checking the capacity was performed at a rate of 0.2 C at a constant current and a final voltage of 2.5 V. The discharge capacity at this time was used as the reference capacity, and 5 times the reference capacity was used as the current value of the 3C rate (that is, assuming that the reference capacity of the cell of 1Ah was 1,000mAh, the current value of the 3C rate was set to 3, It was set to 000 mAh).
Subsequently, the cell is charged by the same operation as above to bring it into a fully charged state, and from this state, discharge is performed at a final voltage of 3.2 V at a 3C rate, and discharge from the start of discharge until the final voltage is reached. The time (seconds) was measured, and the rate discharge characteristics were evaluated based on this discharge time. The measurement results are as shown in Table 1 below.

<Measurement of energy density>
For each of the obtained non-aqueous electrolyte secondary batteries (cells) of Examples and Comparative Examples, in the above rate discharge test, the product of the reference capacity (Ah) and the average operating voltage (V) of each cell is calculated as the cell volume. The value divided by (L) was taken as the energy density. The measurement results are as shown in Table 1 below. The cell volume (L) was measured by a change in the weight of the aqueous layer (so-called Archimedes method) when each cell was suspended and immersed in a water tank filled with water. The average operating voltage (V) changes depending on the combination of the constituent material of the positive electrode and the constituent material of the negative electrode.

<Short circuit test>
Each of the obtained non-aqueous electrolyte secondary batteries (cells) of Examples and Comparative Examples was subjected to a short-circuit test according to the following procedure.
First, the obtained cell is charged at a constant current of 0.2 C rate (that is, 200 mA) at a constant current of 3.6 V, and then at a constant voltage of 0.05 C rate (that is, 20 mA). ) Was charged.
Then, after the cell was fully charged, the cell was removed and the voltage in the open circuit state of the cell was measured.
The cell was then stored in a constant temperature bath at 0 ° C. for 1 week to avoid self-discharge and side reactions at high temperatures.
Subsequently, with respect to the cell voltage measured in the open circuit state described above, the voltage in the open circuit state is measured again after storage for one week, and if a voltage drop of 0.1 V or more is confirmed, the cell is short-circuited. It was judged that a current flowed between the positive and negative electrodes, energy was consumed by self-heating, and the voltage dropped. The results of the short circuit test are shown in Table 1 below.

1 Non-aqueous electrolyte secondary battery 10 Positive electrode 11 Positive electrode current collector 12 Positive electrode active material layer 13 Positive electrode current collector exposed part 20 Negative electrode 21 Negative electrode current collector 22 Negative electrode active material layer 23 Negative electrode current collector exposed part 30 Non-woven separator 40 Exterior Body 50 Double-sided tape 60 Positive electrode active material layer 70 Stainless steel plate 80 Tension tester

Claims (7)

A positive electrode having a positive electrode active material layer provided on at least one surface of the positive electrode current collector and the positive electrode current collector, and a negative electrode activity provided on at least one surface of the negative electrode current collector and the negative electrode current collector. A non-aqueous electrolyte secondary battery in which a negative electrode provided with a material layer is arranged such that the positive electrode active material layer and the negative electrode active material layer face each other via a non-woven separator.
In the particle size distribution of the positive electrode active material, D50 is 0.5 μm or more and 1.5 μm or less.
A non-aqueous electrolyte secondary battery characterized in that the peel strength of the positive electrode active material layer measured by the 180 ° method is 1.0 N / cm or more and 10.0 N / cm or less. The non-aqueous electrolyte secondary battery according to claim 1, wherein the peel strength of the positive electrode active material layer is 2.0 N / cm or more and 4.0 N / cm or less. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the positive electrode active material contains lithium iron phosphate. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the density of the positive electrode active material layer is 1.8 g / cc or more and 2.5 g / cc. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the non-woven fabric separator has a thickness of 8 μm or more and 30 μm or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material layer contains a binder resin. The non-aqueous electrolyte secondary battery according to claim 6, wherein the content of the binder resin is 0.5% by mass or more and 1.5% by mass with respect to the total mass of the positive electrode active material layer.

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