Non-aqueous electrolyte secondary battery

Abstract

To provide a non-aqueous electrolyte secondary battery excellent in safety.SOLUTION: The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The separator includes a first surface facing the positive electrode and a second surface facing the negative electrode. Over the second surface or on both the first side and the second side, an adhesive layer is formed. The adhesive layer includes inorganic particles and an organic binder. The ratio of the peel strength between the separator and the adhesive layer to the peel strength between the negative electrode and the adhesive layer is greater than 0 and less than or equal to 4.0.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

Background Art

[0002] Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-146190) discloses a lithium-ion secondary battery including an adhesive layer between a separator and an electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the lithium-ion secondary battery as disclosed in Patent Document 1, the adhesiveness between the separator and the electrode is excellent due to the presence of the adhesive layer, but the heat shrinkage resistance is low. That is, when the temperature of the battery rises, when the separator shrinks, the adhesive layer may peel off from the electrode, and the positive electrode and the negative electrode may come into direct contact and short-circuit. Thus, there is room for improvement from the viewpoint of safety.

[0005] Therefore, an object of the present disclosure is to provide a non-aqueous electrolyte secondary battery excellent in safety.

Means for Solving the Problems

[0006] 〔1〕The present disclosure is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, the separator includes a first surface facing the positive electrode and a second surface facing the negative electrode, an adhesive layer is formed on the second surface or on both the first surface and the second surface, the adhesive layer includes inorganic particles and an organic binder, The ratio of the peel strength between the separator and the adhesive layer to the peel strength between the negative electrode and the adhesive layer is greater than 0 and less than or equal to 4.0.

[0007] The adhesive layer of the present disclosure contains inorganic particles and an organic binder. By including inorganic particles in the adhesive layer, the heat resistance of the separator is improved. In addition, the organic binder contained in the adhesive layer binds the inorganic particles to each other and also binds the separator substrate and the adhesive layer to each other. By providing an adhesive layer having such a configuration on the surface of the separator facing the negative electrode or on both surfaces of the separator, even when the separator shrinks due to an increase in battery temperature, a part of the adhesive layer remains on the surface of the negative electrode, and direct contact between the negative electrode and the positive electrode is suppressed. As a result, short circuit is prevented and safety is improved.

[0008] 〔2〕The peel strength between the negative electrode and the adhesive layer is preferably 8.0 N / m or less.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present disclosure will be described. However, the present disclosure is not limited to these.

[0011] <Non-aqueous electrolyte secondary battery> FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of an electrode body constituting a non-aqueous electrolyte secondary battery (hereinafter simply referred to as "battery") according to the present embodiment. The battery according to the present embodiment includes an exterior body (not shown), an electrode body 50, and a non-aqueous electrolyte (not shown). The exterior body may be, for example, a pouch made of an aluminum laminate film or the like. The electrode body 50 includes a positive electrode 10, a separator 30, and a negative electrode 20. The separator 30 includes a first surface facing the positive electrode 10 and a second surface facing the negative electrode 20. An adhesive layer 40 is formed on the second surface, or on both the first surface and the second surface.

[0012] The electrode body 50 is, for example, a laminated type. The electrode body 50 is formed by laminating the positive electrode 10, the separator 30, and the negative electrode 20. The electrode body 50 may have an arbitrary laminated structure as long as it includes one or more layers of the positive electrode 10, the separator 30, and the negative electrode 20 respectively. For example, the electrode body 50 may be formed by laminating the positive electrode 10, the separator 30, the negative electrode 20, the separator 30, and the positive electrode 10 in this order.

[0013] The electrode body 50 is, for example, a wound type. The electrode body 50 includes the positive electrode 10, the separator 30, and the negative electrode 20. The positive electrode 10, the separator 30, and the negative electrode 20 are all strip-shaped sheets. The electrode body 50 can be formed by laminating the positive electrode 10, the separator 30, and the negative electrode 20 and then winding them in a spiral shape. After winding, the electrode body 50 may be formed into a flat shape.

[0014] (Positive Electrode) The positive electrode 10 is connected to a positive electrode terminal (not shown). The positive electrode 10 includes a positive electrode current collector foil 11 and a positive electrode mixture 12. The positive electrode current collector foil 11 may be, for example, an aluminum (Al) foil or the like. The positive electrode current collector foil 11 may have a thickness of, for example, 10 μm or more and 30 μm or less.

[0015] The positive electrode composite material 12 may have a thickness of, for example, 10 μm or more and 200 μm or less. The positive electrode composite material 12 contains at least a positive electrode active material. The positive electrode composite material 12 may consist essentially of a positive electrode active material, for example. In addition to the positive electrode active material, the positive electrode composite material 12 may contain, for example, a conductive material and a binder. The positive electrode active material is, for example, lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt manganate, etc. (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 etc.), lithium nickel cobalt aluminate, and at least one selected from the group consisting of lithium iron phosphate. The positive electrode active material may be surface-treated. A buffer layer may be formed on the surface of the positive electrode active material by the surface treatment. The buffer layer may contain, for example, lithium niobate (LiNbO 3 ), etc. The conductive material may contain, for example, carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. The binder may contain, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), etc.

[0016] (Negative electrode) The negative electrode 20 is connected to a negative electrode terminal (not shown). The negative electrode 20 includes a negative electrode current collector foil 21 and a negative electrode composite material 22. The negative electrode current collector foil 21 may be, for example, a copper (Cu) foil, a nickel (Ni) foil, etc. The negative electrode current collector foil 21 may have a thickness of, for example, 5 μm or more and 30 μm or less.

[0017] The negative electrode composite material 22 may have a thickness of, for example, 10 μm or more and 200 μm or less. The negative electrode composite material 22 contains at least a negative electrode active material. The negative electrode composite material 22 may consist essentially of a negative electrode active material, for example. In addition to the negative electrode active material, the negative electrode composite material 22 may contain, for example, a conductive material and a binder. The negative electrode active material is, for example, graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, and lithium titanate (Li 4 Ti5 O 12 It may contain at least one selected from the group consisting of. The conductive material may contain, for example, carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. The binder may contain, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc.

[0018] (Separator) The separator 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator 30 spatially separates the positive electrode 10 and the negative electrode 20. The separator 30 blocks the electron conduction between the positive electrode 10 and the negative electrode 20. The separator 30 is porous. The separator 30 may be made of, for example, polyolefin. The separator 30 may have, for example, a single-layer structure. The separator 30 may consist of, for example, a polyethylene (PE) layer. The separator 30 may have, for example, a multilayer structure. The separator 30 may have, for example, a three-layer structure. The separator 30 may contain, for example, a polypropylene (PP) layer, a PE layer, and a PP layer. The PP layer, the PE layer, and the PP layer may be laminated in this order. The separator 30 may have, for example, a thickness of 5 μm or more and 40 μm or less. The separator 30 may have, for example, a porosity of 30% or more and 60% or less.

[0019] The separator 30 includes a first surface facing the positive electrode 10 and a second surface facing the negative electrode 20. The adhesive layer 40 is formed on the second surface, or on both the first surface and the second surface. The adhesive layer 40 only needs to be formed on at least the second surface, and it is preferably formed on both the first surface and the second surface. The adhesive layer 40 may have, for example, a thickness of 1 μm or more and 6 μm or less. The adhesive layer 40 contains inorganic particles and an organic binder.

[0020] [Inorganic particles] The inorganic particles are not particularly limited, but those having excellent heat resistance and electrochemical stability are preferred. Examples of the inorganic particles include aluminum compounds, magnesium compounds, and other compounds. Examples of the aluminum compounds include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum oxyhydroxide, sodium aluminate, aluminum sulfate, aluminum phosphate, hydrotalcite, and the like. Examples of the magnesium compounds include magnesium sulfate, magnesium hydroxide, and the like. Examples of the other compounds include oxide-based ceramics, nitride-based ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fiber, and the like. Examples of the oxide-based ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, and the like. Examples of the nitride-based ceramics include silicon nitride, titanium nitride, boron nitride, and the like. Examples of the clay minerals include talc, montmorillonite, sericite, mica, amesite, bentonite, and the like. One type of inorganic particle may be used alone, or two or more types of inorganic particles may be used in combination.

[0021] From the viewpoints of heat resistance and electrochemical stability, aluminum oxide, aluminum oxyhydroxide, and aluminum silicate are preferred as the inorganic particles. Examples of the aluminum oxide include alumina. Examples of the aluminum oxyhydroxide include boehmite. Examples of the aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite. Among these, aluminum oxyhydroxide is more preferred. This is because it can prevent internal short circuits caused by the generation of lithium dendrites, suppress thermal shrinkage at high temperatures, and has excellent heat resistance.

[0022] The inorganic particles may have, for example, a D50 of 0.2 μm or more and 3 μm or less. "D50" in this specification is defined as the particle diameter at which the cumulative frequency from the smaller particle diameters becomes 50% in the volume-based particle size distribution. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device.

[0023] The content of the inorganic particles contained in the adhesive layer 40 can be appropriately set from the viewpoints of heat resistance and electrochemical stability. The content of the inorganic particles contained in the adhesive layer 40 is 15% by mass or more, may be 30% by mass or more, may be 50% by mass or more, is 90% by mass or less, may be 85% by mass or less, and may be 75% by mass or less.

[0024] [Organic binder] The organic binder binds the inorganic particles to each other. Further, the organic binder binds the base material of the separator and the adhesive layer to each other.

[0025] The organic binder is not particularly limited, but those having excellent heat resistance and electrochemical stability are preferable. Examples of the organic binder include polyolefins, polyvinyl alcohol-based resins, fluorine-containing resins, etc. Examples of the polyolefin include polyethylene, polypropylene, and modified products thereof. Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol, polyvinyl acetate, etc. Examples of the fluorine-containing resin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, etc.

[0026] As the organic binder, from the viewpoints of heat resistance and electrochemical stability, polyvinylidene fluoride, a vinylidene fluoride-based resin, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer are preferable. Among these, vinylidene fluoride-hexafluoropropylene copolymer is more preferable.

[0027] The molecular weight of the organic binder is not particularly limited, but preferably has a mass average molecular weight of 130,000 or more and 500,000 or less. When the molecular weight of the organic binder is 130,000 or more and 500,000 or less, internal short circuits caused by the generation of lithium dendrites can be prevented, the retention of the non-aqueous electrolyte becomes high, and the cycle characteristics are improved.

[0028] The content of the organic binder contained in the adhesive layer 40 can be appropriately set from the viewpoints of heat resistance and electrochemical stability. The content of the organic binder contained in the adhesive layer 40 is 10% by mass or more, may be 20% by mass or more, may be 40% by mass or more, is 85% by mass or less, may be 80% by mass or less, and may be 70% by mass or less.

[0029] (Peeling strength) The ratio of the peeling strength (A) between the separator 30 and the adhesive layer 40 to the peeling strength (B) between the negative electrode 20 and the adhesive layer 40 (hereinafter, also simply referred to as "A / B ratio") is more than 0 and 4.0 or less. When the A / B ratio is 4.0 or less, even when the separator 30 shrinks due to an increase in the battery temperature, a part of the adhesive layer 40 remains on the surface of the negative electrode 20, and direct contact between the negative electrode 20 and the positive electrode 10 is suppressed, preventing short circuits. The A / B ratio is preferably 3.5 or less, and more preferably 3.0 or less. The A / B ratio only needs to exceed 0, and may be 0.5 or more, or 1 or more.

[0030] In the present disclosure, the peel strength refers to the peel strength (90-degree peel strength) when the separator 30 or the negative electrode 20 is peeled off in a direction perpendicular (90 degrees) to the adhesive layer 40. The peel strength can be measured by a peel strength measuring instrument.

[0031] The peel strength (A) is 30 N / m or less. When the peel strength (A) exceeds 30 N / m, the resistance of the separator 30 may increase, and there is a risk that the battery resistance, particularly the DC resistance, may increase.

[0032] The peel strength (B) is 15 N / m or less. When the peel strength (B) exceeds 15 N / m, there is a risk that the battery resistance may increase. The peel strength (B) is preferably 8.0 N / m or less.

[0033] (Non-aqueous electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and a supporting salt. For example, those obtained by containing a supporting salt in a non-aqueous solvent such as an organic solvent can be mentioned. The non-aqueous solvent may be, for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC), etc. One kind of solvent may be used alone, or two or more kinds of solvents may be used in combination.

[0034] The supporting salt is dissolved in the non-aqueous solvent. The supporting salt may be, for example, a lithium salt (LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 , SO 3 , etc.). One kind of supporting salt may be used alone, or two or more kinds of supporting salts may be used in combination. The supporting salt may have a molar concentration of, for example, 0.5 mol / L or more and 2 mol / L or less.

[0035] <Method for manufacturing a non-aqueous electrolyte secondary battery> The method for manufacturing a non-aqueous electrolyte secondary battery in the present embodiment includes "(A) preparation of a positive electrode", "(B) preparation of a negative electrode", "(C) preparation of a separator provided with an adhesive layer", and "(D) assembly and hot pressing".

[0036] 《(A) Preparation of a positive electrode》 This manufacturing method includes preparing a positive electrode 10 containing a positive electrode active material. For example, a positive electrode composite material 12 may be formed by applying a slurry containing a positive electrode active material onto the surface of a positive electrode current collector foil 11.

[0037] 《(B) Preparation of a negative electrode》 This manufacturing method includes preparing a negative electrode 20 containing a negative electrode active material. For example, a slurry containing a negative electrode active material is applied onto the surface of a negative electrode current collector foil 21 and a negative electrode composite material 22 may be formed.

[0038] 《(C) Preparation of a separator provided with an adhesive layer》 This manufacturing method includes preparing a separator 30 having an adhesive layer 40 on the second surface or on both the first and second surfaces. The method for forming the adhesive layer 40 on the separator 30 is not particularly limited, and examples include the following methods.

[0039] First, a solution in which an organic binder is dissolved in a good solvent is prepared. Next, inorganic particles are dissolved in the solution to prepare a slurry. Then, the slurry is applied to the second surface of the separator 30 or on both the first and second surfaces, and then immersed in a poor solvent and dried, whereby the adhesive layer 40 can be formed on the separator 30.

[0040] Here, a good solvent means a solvent that easily dissolves inorganic particles and an organic binder. For example, it refers to a solvent with a solubility of 1 mass% or more at room temperature with respect to the inorganic particles and the organic binder. Examples of good solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, and the like. A poor solvent means a solvent that hardly dissolves inorganic particles and an organic binder. For example, it refers to a solvent with a solubility of less than 1 mass% at room temperature with respect to the inorganic particles and the organic binder. Examples of poor solvents include water, tripropylene glycol, methanol, and the like. These solvents may be used alone or in combination of two or more.

[0041] Further, the coating method is not particularly limited, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, a screen printing method, and the like. When the adhesive layer 40 is formed on both sides of the separator 30, it may be formed one side at a time or on both sides simultaneously.

[0042] In addition, additives such as a dispersant, a thickener, and a pH adjuster may be added to the slurry within a range that does not inhibit the object of the present embodiment for the purpose of improving dispersion stability and coatability.

[0043] 《(D) Assembly and Thermal Pressing》 This manufacturing method includes assembling the battery including the positive electrode 10, the negative electrode 20, the separator 30 provided with the adhesive layer 40, and the non-aqueous electrolyte. For example, an electrode body 50 including the positive electrode 10, the separator 30 provided with the adhesive layer 40, and the negative electrode 20 may be formed.

[0044] The electrode body 50 is housed in an exterior body. The electrolyte is injected into the exterior body and sealed.

[0045] After sealing, the exterior body is thermally pressed. The temperature of the thermal pressing is preferably performed at 60°C or higher and 80°C or lower. By performing the thermal pressing at 60°C or higher and 80°C or lower, the adhesion between the electrode and the separator is improved.

[0046] The pressure of the hot press is not particularly limited, and for example, it may be carried out at a pressure of 0.5 MPa or more and 5 MPa or less. The holding time of the hot press is not particularly limited, and for example, it may be carried out for 1 minute or more and 10 minutes or less.

Example

[0047] Hereinafter, this embodiment will be described using examples, but this embodiment is not limited thereto.

[0048] <Preparation of separator> (Separator A) As separator A, PE having a thickness of 12 μm was prepared. The porosity of separator A is 40%, and it is cut into a shape with a length of 123.5 mm and a width of 103.5 mm.

[0049] (Separator B) The above-mentioned separator A and boehmite (D50 = 0.9 μm) as inorganic particles were prepared. Boehmite, water, and an aqueous solution of ammonium polycarboxylate as a dispersant were mixed to obtain a dispersion. To this dispersion, water, an aqueous solution of ammonium polycarboxylate, and acrylic latex as a resin binder were mixed and dispersed to obtain a slurry having the following composition (solid content ratio: 30% by mass).

[0050] [Composition] Inorganic particles: 95.0% by mass Resin binder: 4.0% by mass (in terms of solid content) Dispersant: 1.0% by mass (in terms of solid content) The above slurry was coated on one side (the second side) of separator A and dried at 60°C to obtain separator B having a coating layer. The coating layer was coated so as to have a thickness of 2 μm.

[0051] (Separator C) The above separator A, boehmite (D50 = 0.9 μm) as inorganic particles, and polyvinylidene fluoride-based resin (PVdF resin) (vinylidene fluoride: hexafluoropropylene = 95.5 mol%: 4.5 mol%, mass average molecular weight: about 400,000) as an organic binder were prepared. The PVdF resin and NMP were mixed to obtain a mixed solution. Boehmite was mixed into the mixed solution to obtain a slurry having the following composition (solid content ratio: 15% by mass).

[0052] [Composition] Inorganic particles: 85.0% by mass Organic binder: 15.0% by mass (in terms of solid content) After the above slurry was coated on both sides (the first side and the second side) of separator A, it was immersed in a coagulation liquid (water: N,N-dimethylacetamide: tripropylene glycol = 55% by mass: 30% by mass: 15% by mass) at 40°C. After immersion, it was pulled out and dried at 60°C to obtain separator C having an adhesive layer on both sides. The adhesive layer was coated so that the thickness of each side was 2 μm.

[0053] (Separator D) Separator D was obtained in the same manner as separator C, except that the composition of the slurry was changed to 30.0% by mass of inorganic particles and 70.0% by mass of organic binder.

[0054] (Separator E) Separator E was obtained in the same manner as separator C, except that the composition of the slurry was changed to 75.0% by mass of inorganic particles and 25.0% by mass of organic binder.

[0055] (Separator F) Separator F was obtained in the same manner as separator C, except that the composition of the slurry was changed to 55.0% by mass of inorganic particles and 45.0% by mass of organic binder.

[0056] (Separator G) Separator G was obtained in the same manner as separator C, except that the composition of the slurry was changed to 20.0% by mass of inorganic particles and 80.0% by mass of organic binder.

[0057] <Manufacture of Non-aqueous Electrolyte Secondary Battery> (Examples 1 to 11, Comparative Examples 1 to 17) As the positive electrode active material, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (94 mass %), CB (4 mass %) as the conductive material, PVdF (2 mass %) as the binder, and NMP as the dispersion medium were mixed and dispersed to obtain a slurry. The slurry was uniformly coated on an Al foil (thickness: 15 μm) which is a positive electrode current collector foil, and heated and dried to obtain a sheet for the positive electrode. After drying, the sheet was passed through a roll press and pressed to a predetermined density, and cut into a shape with a length of 120 mm and a width of 100 mm to produce a positive electrode sheet.

[0058] As the negative electrode active material, graphite (96 mass %), SBR (2.5 mass %) and CMC (1.5 mass %) as the binder, and water as the dispersion medium were mixed and dispersed to obtain a slurry. The slurry was uniformly coated on a Cu foil (thickness: 10 μm) which is a negative electrode current collector, and heated and dried to obtain a sheet for the negative electrode. After drying, the sheet was passed through a roll press and pressed to a predetermined density, and cut into a shape with a length of 122 mm and a width of 102 mm to produce a negative electrode sheet.

[0059] The positive electrode, each separator, and the negative electrode were laminated so that each separator shown in Tables 1 and 2 separated the positive electrode and the negative electrode. Thereby, a laminated electrode body was formed.

[0060] A pouch made of a laminate film was prepared as the exterior body. The electrode body was housed in the exterior body. As the non-aqueous electrolyte, a mixture of a mixed solvent (EC:DMC:EMC = 30 vol%:40 vol%:30 vol%) and a supporting salt (LiPF 6 ) dissolved at a concentration of 1.1 mol / L was used. The electrolyte was injected into the exterior body. After the injection of the electrolyte, the exterior body was sealed. After sealing, for Examples 1 to 11 and Comparative Examples 9 to 17, hot pressing was performed at each temperature shown in Tables 1 and 2 under a pressure of 1 MPa for 120 seconds. Thus, the test batteries of Examples 1 to 11 and Comparative Examples 1 to 17 were manufactured.

[0061] <Peeling Strength> (Separator) The obtained separators B to G were pasted using a tape (manufactured by 3M Japan Ltd., Scotch 600) with a length of 100 mm and a width of 20 mm, and the strength when peeling the separator from the adhesive layer at 90 degrees was defined as the peeling strength (A) between the separator and the adhesive layer. The peeling strength (A) was measured under the condition of a peeling speed of 50 mm / min using a 90-degree peeling strength measuring instrument (manufactured by IMADA Co., Ltd., IP-5N) in a temperature environment of 25 degrees. The arithmetic mean of the three results is shown in Tables 1 and 2. Regarding separator B, the strength when peeling the coating layer from the separator at 90 degrees was defined as the peeling strength (A).

[0062] (Negative Electrode) The obtained separators B to G were cut into a shape with a length of 80 mm and a width of 25 mm. Also, the obtained negative electrode was cut into a shape with a length of 70 mm and a width of 20 mm. Each separator and negative electrode were laminated to form a laminate composed of the separator and the negative electrode. Each laminate was housed in the above-described exterior body, the above-described non-aqueous electrolyte was injected, and sealed. After sealing, hot pressing was performed at each temperature shown in Tables 1 and 2 and a pressure of 1 MPa for 90 seconds. After hot pressing, the laminate was taken out from each exterior body. Then, it was installed with the negative electrode on the upper side, pasted using a tape (manufactured by 3M Japan Ltd., Scotch 600) with a length of 100 mm and a width of 30 mm, and the strength when peeling the negative electrode from the adhesive layer at 90 degrees was defined as the peeling strength (B) between the negative electrode and the adhesive layer. The measurement conditions were the same as those for the peeling strength (A). The arithmetic mean of the three results is shown in Tables 1 and 2.

[0063] <Evaluation> (Activation) In a temperature environment of 25°C, each test battery was sandwiched between aluminum plates, and in the stacking direction of the layers constituting the test battery, the applied pressure to the test battery was set at 1000 kPa for dimension constraint. Then, while under dimension constraint, each test battery was charged and discharged by a constant current-constant voltage (CC-CV) method. The conditions are shown below. Thereafter, as shown in Tables 1 and 2, the constraint conditions were changed to obtain each test battery for evaluation described later. In the tables, 1000 kPa means dimension constraint, and 15 kPa and 5 kPa mean constant pressure constraint, respectively. Note that "C" is a symbol representing the time rate of current. A current of 1C is defined such that the designed capacity of the test battery is discharged in 1 hour.

[0064] [Conditions] CC charge: Charge current = 0.1C, cut-off voltage = 4.25V CV charge: 3 hours CC discharge: Discharge current = 0.1C, cut-off voltage = 3.0V (Heating test) In a temperature environment of 25°C, each test battery was sandwiched between aluminum plates and charged to 3.3V with a charge capacity of 0.1C. After charging, a ribbon heater was wound from above the aluminum plate, and then a heat insulating material was wound around it. Thereafter, thermocouples were attached to each test battery near the tabs of the positive and negative electrodes. It was set so that each test battery would be heated at a rate of 5°C / min, and the temperature when the voltage dropped to 0.5V was measured. This temperature is shown in Tables 1 and 2 and Figure 2. The higher this temperature, the better the safety is considered to be. Note that the voltage of the test battery drops because the separator shrinks due to heating and the positive and negative electrodes come into contact.

[0065] (300-cycle test) In a temperature environment of 45°C, each test battery was subjected to 300 charge and discharge cycles by the CC method. One cycle represents one round of the following "charge → rest → discharge". The capacity retention rate was obtained by dividing the discharge capacity of the 300th cycle by the discharge capacity of the 1st cycle. The capacity retention rates are shown in Tables 1 and 2 below. The higher the capacity retention rate, the better the cycle durability is considered to be.

[0066] [Conditions] Charging: Charging current = 0.3C, Cut-off voltage = 4.2V Rest: 60 seconds Discharging: Discharging current = 0.3C, Cut-off voltage = 2.5V (100-cycle test) In a temperature environment of 45°C, the test batteries of Examples 1 to 11 were subjected to 100 charge-discharge cycles by the CC method. One cycle represents one round of the following "charging → rest → discharging". The capacity retention rate was obtained by dividing the discharge capacity at the 100th cycle by the discharge capacity at the first cycle. The capacity retention rates are shown in Tables 1 and 2. The higher the capacity retention rate, the better the cycle durability is considered to be.

[0067] [Conditions] Charging: Charging current = 1.0C, Cut-off voltage = 4.2V Rest: 60 seconds Discharging: Discharging current = 1.0C, Cut-off voltage = 2.5V

[0068]

Table 1

[0069]

Table 2

[0070] <Results> (Examples) Figure 2 is a graph showing the relationship between the battery temperature at the time of reaching 0.5V and the ratio of A / B in the heating test. When the ratio of A / B is 4.0 or less, the battery temperature at the time of reaching 0.5V rises significantly, and when the ratio of A / B becomes even smaller, the temperature also rises further. This is considered to be because even if the separator shrinks in the heating test, a part of the adhesive layer tends to remain on the negative electrode, resulting in a higher battery temperature at the time of reaching 0.5V. In addition, since the adhesive force between the negative electrode and the adhesive layer is strong, the capacity retention rate after the cycle test also increases, and it is considered that both battery characteristics and safety are achieved.

[0071] (Comparative Examples) In Comparative Examples 1 to 3, since there is no adhesive layer, when the restraint condition is set to a low pressure, the capacity retention rate decreases. Also, since there is no coating layer, the battery temperature at the time of reaching 0.5 V in the heating test is also low.

[0072] In Comparative Examples 4 to 6, since there is a coating layer, the battery temperature at the time of reaching 0.5 V in the heating test is high. On the other hand, since there is no adhesive layer, when the restraint condition is set to a low pressure, the capacity retention rate decreases.

[0073] In Comparative Examples 7 to 8, although there is an adhesive layer, since no hot pressing is performed, when the restraint condition is set to a low pressure, the capacity retention rate decreases. Similarly, the battery temperature at the time of reaching 0.5 V in the heating test is also low.

[0074] In Comparative Examples 9 to 10, since hot pressing is performed, although the capacity retention rate is increased compared to Comparative Example 8, it is not sufficient. Also, since the A / B ratio is high, the battery temperature at the time of reaching 0.5 V in the heating test is also low.

[0075] In Comparative Examples 11 to 17, since the adhesion force between the negative electrode and the adhesive layer is strong, the capacity retention rate after the cycle test is increased. On the other hand, since the A / B ratio is high, the battery temperature at the time of reaching 0.5 V in the heating test is low.

[0076] It should be considered that all aspects of the embodiments and examples disclosed this time are illustrative and not restrictive. The scope of the present disclosure is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Reference Numerals

[0077] 10 Positive electrode, 11 Positive electrode current collector foil, 12 Positive electrode composite material, 20 Negative electrode, 21 Negative electrode current collector foil, 22 Negative electrode composite material, 30 Separator, 40 Adhesive layer, 50 Electrode body.

Claims

1. A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator includes a first surface facing the positive electrode and a second surface facing the negative electrode, an adhesive layer is formed on the second surface or on both the first surface and the second surface, the adhesive layer includes inorganic particles and an organic binder, a ratio of the peel strength between the separator and the adhesive layer to the peel strength between the negative electrode and the adhesive layer is 2.3 or more and 4.0 or less, and the peel strength is a peel strength when the separator or the negative electrode is peeled off from the adhesive layer at 90 degrees. The non-aqueous electrolyte secondary battery.

2. The peel strength between the negative electrode and the adhesive layer is 8.0 N / m or less, The non-aqueous electrolyte secondary battery according to claim 1, wherein the peel strength between the separator and the adhesive layer is 30 N / m or less.

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